Brakes for a Fiat 131 rally car

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
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TomLouwrier
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Fri Mar 18, 2011 10:28 pm

Thanks Guy.

To be honest it was going through the catalogues page by page that took most time. The writing up itself is OK once I'm on a roll. My colleagues tend to call me Sir Speakalot with good reason...

Here's the links to the catalogues (I'm sure there are more to be found on the web):
Brembo aftermarket pdf:
http://www.bremboaftermarket.com/en/Car ... _List.aspx
Brembo aftermarket online database:
http://www.bremboaftermarket.com/En/Car ... earch.aspx

EBC pdf and xls formats:
http://www.ebcbrakes.com/catalogues.shtml

regards
Tom
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Sat Mar 19, 2011 8:20 pm

Tom,

Exceptional detail and work on your part.

Extremely useful . I thank you !

Re: Substance

Looking over all potential matches I have excluded every single one.

Key problem criteria :

1/ depth of the rotor (disk offset).

My hub is quite deep.( the 131 Abarth hub is a ca. 10 cm long cylinder). In fact use of the original hub will eliminate need for 45 mm thick distance plates to properly position the wheel under wheel arches.

2/ disk diameter ( I am not really very sure that 305 is a correct , can the disk be smaller? by how much?

3/ height of the rotor friction area
( none of the disk seems to accommodate am pad with 55 mm height)

I have stepped back and re-think and re-define the whole problem again.

What we are trying to do here is in fact design a new disk.The limitations are determined by the 3 key problem dimension criteria (hub dimensions, caliper and pad dimensions and their position relative to the required disk (determined by the mounting of the caliper to the hub).

As some of these dimensions must be measured in 3D it is not as straight forward as it sounds .

I therefore decided that my machinist will make a full scale model of the new disk from machinable plastic. We will install this model on the hub to make sure our measurements are correct and model fits the hub and the caliper. If this works we will put the wheel on and make sure this fits under the wheel. This will be the ultimate confirmation of disk dimensions we require, especially disk offset. This will also give us tolerances ( i.e. can the disk diameter be smaller than 305 and by mow much , can the friction area be smaller than 58 mm.

I read Brembo disk installation instructions and found for instance there must be 2 mm clearance between the disk top edge and the caliper and 1 mm on each side of the disk when put into the caliper. Without making a full scale model there is no way we can assure tolerances are kept and measurements we have taken will prove correct in real life.

So my final drawing and the hub with installed caliper goes to my machinist on Monday and he starts thinking what material to make the model from (probably a block or cylinder of hard plastic).

Once the model is made I will present detailed pictures as well as accuracy of our measurement taking.

Miro

PS : if we do not make a full scale model there is a very good chance the disk made to order will nit fit our requirements.

It took me quite some time to realize this , but as they say -better late than never....

M
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TomLouwrier
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Sun Mar 20, 2011 10:06 am

hi Miro,

I'm not sure why you think none of the found discs can be adapted.
- Total height is not a big problem as long as you can shim out the caliper and/or the disc.
- Disc outer diameter can be reduced as long as the inner rim diameter is small enough to accept 55m pads, for now that's 305-(2x55)=195mm
- Rim thickness anywhere between 20-24mm should work

Making a prototype from plastic is a good way of testing your dimensions, but a lot of work and money. Given the uncertainties you have at the moment, why don't you get yourself a used disk (or two) from a breakers' yard, drill the bolt holes and assemble. That will show quick enough what dimensions are off and by how much.
I would try the BMW ones (common on many 5-series (E60, E61) from 2003 >)
310x24x77; 24mm should work, needs 5mm shim, pretty good match
Brembo partno. 09.9173.10
Brembo partno. 09.9173.14
And maybe get the VW Tuareg one as well while you're at it. I believe this disc is common with some VW Transporter models and comes dirt cheap :-)
314x22x76; could be quite good
EBC partno. D1328

Guidelines as to how much space you need between disc and caliper have limited value; in the end it is the pads' position that determines where you need to have the rim.

Another option to get more certainty about the sizes is to assemble the hub and caliper minus disc and bend a piece of steel wire to simulate the shape of the disc: around one bolt - across the hub - around another bolt- about 75mm down - out to where the pads are. A strip of sheet metal will do as well.
You can quickly bend/cut/mark the essential dimensions and measure up. Could even be done today... :-)

regards
Tom
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Sun Mar 20, 2011 2:18 pm

Tom: re shimming the caliper out :

This is exactly the problem ! The mounting lugs of the calipers go on the inner side of the hub mounting lugs , thus I can move the caliper only one way - in my case - the wrong way , making them more not closer ( as needed ) but more distant from the outer face of the hub.
WASHER ISSUE .jpg
WASHER ISSUE .jpg (40.25 KiB) Viewed 2237 times
Also note that in "314x22x76" the 76 is an external dimension. In my case this can easily be 80 or even 90. The dimension which is key to me is internal. 76 mm less the thickness of the bell's face must be 65. If it is larger I can shim it out (by moving the caliper towards the left (as on the picture above). If the distance is 4 mm or more I can put a distance pad under the hub.

I cannot get my hands on a drawing for the VW disk (please post it or send it tom me if you have it or can find it) , but looked at the Brembo (disk partno. 09.9173.10).
brembo match 1.jpg
brembo match 1.jpg (170.7 KiB) Viewed 2233 times
Having said that I will tell you that one of the cars I own is a VW transporter with these very disks and I should have a used disk somewhere in my one junk pile.

You are right that it can be done simpler than making a full size model....

Re: 5 mounting holes : Is re-drilling a 5 hole disk with additional 4 holes a safe procedure, will it not weaken the disk mounting ?

Will this not throw the disk off balance ? There is no way you can symmetrically place 4 holes on a 98 mm circle onto a surface with 5 holes on a 104 mm holes already made.
capture #264.jpg
capture #264.jpg (103.67 KiB) Viewed 2236 times
This must throw the disk off balance . Am I right ?

Miro

PS: I am confused as to the mounting hole measurements: 4 x 98 (I believe this means there are 4 holes with centers on a 98 mm center. Please look at the Brembo drawing : is the VW measurement 5 x 104 ( or is it 5 x 120 and the Fiat standard 4 x 98 should be interpreted that the edge of the holes is on a 98 mm circle?

M
Last edited by miro-1980 on Sun Mar 20, 2011 5:18 pm, edited 1 time in total.
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TomLouwrier
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Sun Mar 20, 2011 5:15 pm

Hi Miro,

We've been missing each others point a bit I believe. Let me repeat what we discussed so far.

The disc you have used for measuring up (250mm) is too shallow, so you need a disc with a deeper bell. Ideally that would be 72mm, as we think now. That is without any shims between the hub carrier and the caliper.
I am using total disc height because that is how most catalogues list them. Since most discs have a wall thinkness of 5-7mm in the bell, I took that for granted and used the 72mm size from your drawings as key dimension, which corresponds with about 66mm inner bell height in most discs. Close enough.

If we find a disc that is good in outer diameter and inner diameter but deeper than 72mm, like 77mm, you can use it and shim the caliper by 5mm.
This is why I have only searched for discs that are deeper than 69mm (69 if you could win 3mm by shaving caliper and carrier lugs). If you need even more total height there are discs that go up to 88mm. No worries, mate!
BTW: the original Abarth part in page 2 measures some 74mm on picture, so I would not be surprised at all when we find that is the total height you need. Certain dimensions are like surnames, they stay with a family for very long.

The beauty of the Brembo catalogue is that they give you good drawings and you can check inner bell height and rim inner diameter. Most other brands just list partnumbers after you type in the make, model and year of your car. That is useless for us now, we need the exact sizes, inner and outer.

You have found that on the BMW disc the inner diameter will do (190 < 195mm) so we can turn the outer diameter from 310 down to 305 and see what happens.
If you have an old VW disc as well, fine. That can be a second candidate.

Redrilling the holes is not much of a problem, as long as there are not too many in there already. Some Audi and Lexus discs I saw have 10 holes or more, I would not like to add 4 extra to that. But adding 4 in an existing pattern of 5 is common practice in disc conversions. The disc will be clamped flat between the hub and the wheel so that helps in supporting the bell bottom.
The balance is not affected by the extra holes. As long as both patterns (5x and 4x) are concentric and equally spaced within themselves, they are unrelated from a balancing point of view. It looks strange to our human eyes, but that is all.

regards
Tom

PS: yes, 4x98 would mean 4 holes @90degrees, with their centres on a circle that is 98mm in diameter. Don't use outer diameter or the distance between 2 holes next to each other (some do in the US). Centre lines is what we must use.
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Sun Mar 20, 2011 5:26 pm

Tom,

I will reply in red entered into your latest case to make sure all is clear.
Hi Miro,

We've been missing each others point a bit I believe. Let me repeat what we discussed so far.

The disc you have used for measuring up (250mm) is too shallow, so you need a disc with a deeper bell. Ideally that would be 72mm, as we think now. That is without any shims between the hub carrier and the caliper. YES
I am using total disc height because that is how most catalogues list them. Since most discs have a wall thinkness of 5-7mm in the bell, I took that for granted and used the 72mm size from your drawings as key dimension, which corresponds with about 66mm inner bell height in most discs. Close enough. It is

If we find a disc that is good in outer diameter and inner diameter but deeper than 72mm, like 77mm, you can use it and shim the caliper by 5mm. Agreed !
This is why I have only searched for discs that are deeper than 69mm (69 if you could win 3mm by shaving caliper and carrier lugs). If you need even more total height there are discs that go up to 88mm. No worries, mate!
BTW: the original Abarth part in page 2 measures some 74mm on picture, so I would not be surprised at all when we find that is the total height you need. Certain dimensions are like surnames, they stay with a family for very long. I very strongly suspect you are right

The beauty of the Brembo catalogue is that they give you good drawings and you can check inner bell height and rim inner diameter. Most other brands just list partnumbers after you type in the make, model and year of your car. That is useless for us now, we need the exact sizes, inner and outer.

You have found that on the BMW disc the inner diameter will do (190 < 195mm) - this is fine - so we can turn the outer diameter from 310 down to 305 and see what happens.
If you have an old VW disc as well, fine. That can be a second candidate.

Redrilling the holes is not much of a problem, as long as there are not too many in there already. Some Audi and Lexus discs I saw have 10 holes or more, I would not like to add 4 extra to that. But adding 4 in an existing pattern of 5 is common practice in disc conversions. - Did not know that and this is very good news !- The disc will be clamped flat between the hub and the wheel so that helps in supporting the bell bottom.
The balance is not affected by the extra holes. As long as both patterns (5x and 4x) are concentric and equally spaced within themselves, they are unrelated from a balancing point of view. It looks strange to our human eyes, but that is all. I was afraid this will either weaken the disk face too much and will throw the disk off balance, but if not I will get this disk tomorrow from a junk yard and have it machined down to 305 to test fit

regards
Tom

PS: yes, 4x98 would mean 4 holes @90degrees, with their centres on a circle that is 98mm in diameter. Don't use outer diameter or the distance between 2 holes next to each other (some do in the US). Centre lines is what we must use.
I really appreciate your help.

Miro
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Mon Mar 21, 2011 10:17 pm

Tom,

I have looked into the Brembo catalog again and found the difference between Brembo part no. 09.9173.10
Brembo part no. 09.9173.14

Brembo part no. 09.9173.14 is for BMW 5 series and uses standard venting design. their minimum thickness is 22,4
Brembo part no. 09.9173.10 is for few Ferrari models and uses pivot venting technology ( COOLER DISKS !! ) and has a minimum disk thickness of 22 mm.

The Ferrari disk would probably be better as the minimum thickness of this disk is 22 ( just what we can match without much problem) , but Ferrari's are not common in Poland while BMW"s. I noted thought that these disks are for

I have found that a store just a few miles away from me has such ATE disks (part number Ate 24.0124-0181.1) (OEM BMW part number: 34 11 6 764 021) for BMW 5 series (E-60/E61 disks) same as Brembo 09.9173.14.

I will visit the store and see if I can match it to my hub and caliper. This will be quite quick and easy.

Thansk Tom, this would not be possible without you.

Hope it works for me !

Will report tomorrow !

Miro
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Mon Mar 21, 2011 11:45 pm

Got the disk in my hands. Not dirt cheap 100 quid plus machining , but still, the cheapest solution (if it works).

The thickness can be managed , so can the diameter.

The problem will be the 5 holes ( plus a giant positioning hole) among which I have to drill additional 4 holes one mm from the .

The margins will be very minimal ...
ATE BMW DISK 1.jpg
ATE BMW DISK 1.jpg (54.38 KiB) Viewed 2208 times
Jut but over a millimeter to cut through 2 of the 5 holes and the edge .... on all 4 of the new holes - very close indeed.

The giant front hole will also leave only a small edge .. some simple technical issues to be resolve.

First attempt at positioning the 4 holes:
hole positioning first try  .jpg
hole positioning first try .jpg (72.89 KiB) Viewed 2208 times
Tomorrow the disk goes to to be machined ...

Miro
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TomLouwrier
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Tue Mar 22, 2011 10:25 pm

Hi Miro,

That's some aligning of holes you're doing there. I did see the 79mm centre hole, no big problem there. But the positioning hole is a bit awkward indeed.
Surprising you found one of the numbers pointing to a Ferrari disc instead of a BMW. Must be an error in one of the catalogues, or I was getting cross-eyed from all the part numbers.

I'm very curious now to see what the turned down disc will look like when it's mounted on the hub and with the caliper on.

regards
Tom
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Tue Mar 22, 2011 11:45 pm

Tom,

The calipers, disks and hubs are at my machinist workshop.

The owners are a very experienced mechanical engineer Jan ( in his 70's ) and his grandson Michal (in his 30's). Jan was a chief design engineer at a tools factory in Warsaw called VIS. Truly a jewel among experts in mechanical engineering. The machines they use are simple old style Soviet made lathes, milling machines, etc. of 1960 and 1970 - vintage. The machines look pretty primitive but in the skillful hands of their employees : Joe , George and Leon (all in their late 60's) these machines produce elements with extreme accuracy.

Look at this picture of Joe shaving off the top of the original Abarth gr 4 rear shock to fit it into the spherical bearing mounted in the rear shock top mount designed by Jan.
Joe at work .jpg
Joe at work .jpg (59.43 KiB) Viewed 2185 times


The engineering ingenuity and technical imagination of all these is absolutely amazing. What they make are almost "one of" items , they make replicas of broken parts for both auto fans like me and my friends as well as save production of most modern industrial plants in Warsaw area. (They often serve as last resort to keep the production going short of shutting the whole industrial operation for weeks. In such cases they make the broken part overnight at a quarter of the cost to order a new part from the manufacturer). I have never heard of a failure of any part they made.

This is just a small tribute to these guys who represent a dying species. The parts they make for local hospital to keep their medical equipment (like a Cat-Scan) operating is done at cost ( no profit). Real technical aristocrats of the old kind !

Jan looked at it took some old style measuring devices and drew a technical sketch of a plate that will go between the hub and the disk. It role of the plate will be to position the disk relative to hub to match the caliper's relative position and strengthen the assembly weakened by the re-drilling of the disk. The pad will have 6 "tabs" sticking out in positions to fill the 5 mounting holes and the positioning hole. It will also have a 79 mm central tub to fill the front center hole and position the disk centrally. This will be drilled with 4 Fiat style ( 4x98 ) mounting holes (so the wheel can be bolted to this assembly). The plate will also be bolted to the hub making it a very, very solid assembly.

Simple but very thoughtful solution. Incidentally he inspected the calipers and decided the caliper can be easily adapted to accept the disk without decreasing its 24 mm thickness.

I will take the pictures and post key of them here to document it and share with others how a problem of this kind can be resolved.

Miro
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Re: Brakes for a Fiat 131 rally car

Post by WhizzMan » Wed Mar 23, 2011 7:05 am

I would refrain from shimming discs and calipers if at all possible. You will create additional shear points on the threads/bolts you are using by doing so.

You can get great discs with machinable aluminum hats from several vendors. Wilwood is well known in the racing business but there are other brands that can help you here. The advantage of this setup is that you can get the hight, thickness and diameter of disc you want and you can bolt on the hat that you have machined to exact fit for your application. Added benefits are better heat dissipation, less unsprung weight and less chance on disc warping.

305/304 mm is 12", that may make it a bit more clear why they chose this exact measurement. Another something to keep in mind is that you don't want any balancing weights knocking off when they hit your caliper. My daily driver has uprated brakes and I have to use roof leading strips with double sided tape to balance those.
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Wed Mar 23, 2011 9:10 am

hi Miro, guys,

@Miro
Nice to see that true craftmanship. Nothing wrong with those old machines, I learned the trade on some exactly like it. Nothing wrong with the old men either :-)
An adaptor between hub and disc can very well work, if this plate is thick enough. I was counting on no more than a couple of mm's at most, also to keep your wheel geometry correct.

@Whizzman
"You will create additional shear points on the threads/bolts you are using by doing so."
Sorry, don't agree with you on this one. The disc is held in place by the clamping forces of the bolts and the friction that creates. If not, then you're using the wrong bolts and/or preload and your setup is in danger. Same goes for the caliper bolts.
There may be a non-threaded part on the wheel studs with a larger diameter than the thread, but that is for location only. Using threads for that is plain wrong.


regards
Tom
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Wed Mar 23, 2011 10:17 pm

Tom,

Re: " An adaptor between hub and disc can very well work, if this plate is thick enough. I was counting on no more than a couple of mm's at most, also to keep your wheel geometry correct"

Currently the adaptor hub-to-disk adaptor plate is estimated at 10 mm and diameter of ca. 160mm. On the hub side the hub face a ( 12 x 117 disk ) will go into the adaptor plate by some 8-10 mm. This will keep the disk in position on the hub side. On the wheel side it will also have a 79 mm tab sticking out to hold it in position on the disk side and smaller tabs sticking out to fill all the 6 holes 5 mounting ones and one positioning hole. This will make a very tight assembly with no friction between any of these elements. The assembly will make sure the the disk sits on the hub very, very tightly tightly. Actually the 79 mm "tab" will stick out all the way to the wheel keeping the wheel in position to the whole assembly.

Up to now we had an adaptor plate over the disk which was 41 mm thick and there was absolutely no problem with the geometry of the wheels or stability of the whole assembly. Because the Abarth hub stick out much more than the standard hub the 41 mm adaptor plate will be done away with entirely. ( all distance matters will be compensated by the adaptor under the hub).

See pictures below.
distamce plate 1.jpg
This is my old steel adaptor plate , current ones are made of high grade aluminum.
distamce plate 1.jpg (70.13 KiB) Viewed 2051 times
distamce plate 2.jpg
Even with this thick adaptor plates there was no problem with geometry and / or wear of the mounting bolts.
distamce plate 2.jpg (45.22 KiB) Viewed 2051 times
Eenzo distamce plate 1.jpg
This is an adaptor plate used by my friend Enzo on his 131 Abarth replica on standard 131 suspension. He also did not report any problems.
Eenzo distamce plate 1.jpg (46.99 KiB) Viewed 2051 times
RE : Whizzman' s position on the shimming discs and calipers. Your view is appreciated and I agree with it in principle. However , an adaptor plate under the disk ( between hub and disk) has exactly the same affect as an adaptor plate over the disk ( between the disk and the wheel). I have made some 30 K of which probably 1000 on rally stages /track events and have not seen any signs of wear or damage to the bolts and or their thread. The Bolts do not come into physical contact with any other parts but the wheel and the hub. ( They do not touch the brake disk or the adaptor) and - as Tom correctly put it - the only force acting on the bolts is a pulling force (balanced by the clamping force). The bolts we had before were quite long ( well over 100 mm ) and showed no signs of wear at all. The bolts are highest grade steel available commercially.

When we finish the conversion the bolts will be less than just about half this length which will make an even stronger connection. Note that the force affecting the hub , disk and the wheel will be only the clamping force. The wheel , the disk and hub will be held in "central" position " by the adaptor plate and any other forces affecting these elements will be perpendicular to the clamping force. All the bolts do will do is to compress the assembly together. I have no problem with this solution at all.
(Shimming the caliper is only theoretical option as I do not believe we will have to do this. But even if we did I have no problem with it.)

I see physical no force that would in any way adverse way effect the stability and strength of this assembly. If we start "over the crest" jumping and manage to get the car high enough over the ground to make 10 meter jumps I think the car - including the hub/adaptor/ brake/wheel assembly should hold well enough, but (to put it mildly) I would be mildly concerned that the chassis would just disintegrate. This car was not build and will not be used for such extreme driving. Under all other conditions I have full trust in this adaptor connection. By the way we will do a computer simulation of forces that would brake this connection on the Warsaw Technical University with participation of vehicle and steel material experts. I am sure this assembly they will well exceed the auto industry standards.

Miro

PS : all elements : the adaptor and the disk will be balanced , and when we put the wheel on this it will be balanced as one single unit ! ( without taking the wheel off !).
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Re: Brakes for a Fiat 131 rally car

Post by miro-1980 » Wed Mar 30, 2011 7:07 pm

Progress update :

The flowers in my back yard tell me the spring is here :
SPRING  2011.jpg
SPRING 2011.jpg (89.08 KiB) Viewed 1997 times
It is time to make sure progress is made !

So here it is ...

The ATE RS 911caliper opening in is 24 mm. The disk used by Porsche were 290 x 20 front. This means that the caliper opening must be 2 mm wider than the disk.
ATE DO 131.JPG
ATE DO 131.JPG (49.28 KiB) Viewed 1997 times
The caliper opening were widened to 26 mm.
ate wider 1.jpg
ate wider 1.jpg (30.81 KiB) Viewed 1997 times
ate wider 2.jpg
ate wider 2.jpg (31.98 KiB) Viewed 1997 times
We will test if this is wide enough for a 24 mm disk . If not we will machine the disk by up to 1 mm on each side of the disk
disk fit 2 .jpg
disk fit 2 .jpg (38.9 KiB) Viewed 1995 times

The whole assembly is still,too big for the 15 " CD 68 wheels. We plan to shave off 2,5 mm of the disk making the diameter 305 (from 310. I hope this will do the trick and the disk will fit properly into the caliper and the whole assembly will fit into the wheel. If not we will place a 10 mm distance plate between the disk and the wheel mowing the wheel out thus increasing the clearance between the caliper and the wheel.
wheel fit 4.jpg
wheel fit 4.jpg (48.53 KiB) Viewed 1995 times
wheel fit 2.jpg
wheel fit 2.jpg (39.94 KiB) Viewed 1995 times
wheel fit 3.jpg
wheel fit 3.jpg (37.44 KiB) Viewed 1995 times

After the disk fitting is completed we will make the distance plate - see drawing below.
distance plate draw 1 .jpg
distance plate draw 1 .jpg (33.62 KiB) Viewed 1995 times
The distance plate will:

1/ position hub face plate centrally in the hub

2/ position the disk properly to fit the hub caliper assembly - so that the disk axis is exactly in line with caliper axis.

3/ hold the disk on the hub

4/ position the hub caliper disk assembly in the wheel

With some luck , this should resolve the issue and be ready to be tested in real life.

Miro
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Re: Brakes for a Fiat 131 rally car

Post by TomLouwrier » Thu Mar 31, 2011 1:06 pm

Hi Miro,

Good to see you make progress here! It's sure a tight fit in those rims, hopefully bringing the discs to 305mm will do the trick.
Now that you're mounting the disc and the caliper both onto the hub, what do you see when you put your pads in? The position of the friction material dictates where your disc outer diameter should be. More than 1mm extra is not needed.

Something puzzling: I can only see 1 piston per side of the caliper. Since this is a fixed type and not floating, I count that as 1 effective piston in my earlier calculations. We've been discussing this setup as upgrading from 1x48mm ('fist'-type floating caliper)to 2x48mm (fixed caliper, so 4 pistons in total).
What's the correct number and working diameter of the pistons in the caliper we see here?

Enjoy spring, enjoy life!

regards
Tom
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