Brakes for a Fiat 131 rally car

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
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achy
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Re: RS 911 calipers for 131

Post by achy »

The most closer disk is the Delta HF turbo / Delta 4WD (not integrale) which is 257x20x52 mm .
The works disk have the following dimensions :
124 corsa disk #1
124 corsa disk #1
DSC00822_s.JPG (56.27 KiB) Viewed 19508 times
124 corsa disk #2
124 corsa disk #2
DSC00823_s.JPG (54.41 KiB) Viewed 19508 times
124 corsa disk #1
124 corsa disk #1
DSC00822_s.JPG (56.27 KiB) Viewed 19508 times
124 corsa disk #4
124 corsa disk #4
DSC00829_s.JPG (73.21 KiB) Viewed 19508 times
works label
works label
Picture 5.jpg (60.67 KiB) Viewed 19508 times
I hope it helps you a little bit
Achy
Attachments
124 corsa disk #3
124 corsa disk #3
DSC00826_s.JPG (90.25 KiB) Viewed 19508 times
124AbarthRallyeCorsa
131grp4
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Re: RS 911 calipers for 131

Post by 131grp4 »

What discs were used with the AP calipers, from what I can see from the 131 Abarth homologation papers they were 300mm x 20mm, if I'm correct that points towards the gravel caliper but according to AP both tarmac and gravel calipers can take a maximum of 267mm disc anyway?
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Re: RS 911 calipers for 131

Post by miro-1980 »

QUESTION: RE AP CALIPERS :

Building my replica I want to stay as close to the original.

Anybody knows the options open to me ?
Brakes modifications small .jpg
Brakes modifications small .jpg (96.7 KiB) Viewed 19141 times
BTW I am attaching a lict of 131abarth rally modifications I just did .

It looks like there were several versions:

Front: 300mm/275/275/274/ ranging from original 2 piston x 48 mm calipers to 4 piston x 38mm - introduced quite early on)
Rear (252mm disks with two piston x 38 mm calipers and 254mm disks with 4 piston calipers)

It is noteworthy that the most frequent modifications were to the handbrake. ( 2/4 piston calipers.caliper piston size 31/38, handle , corrector connections / mechanical / hydraulic/ hydro-mechanical / drum/disk/

You are referring to AP LOCKHEED calipers. Does anybody know the catalog number of the type used on 131 Abarth ???



MIRO
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131grp4
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Re: RS 911 calipers for 131

Post by 131grp4 »

The only caliper with bores of 38.1mm and to take a 20mm thick disc which correspond with the homologation papers are:

http://www.apracing.com/calipers/produc ... E_2701_656

The above calipers are apparently for gravel use, the tarmac calipers take a disc of 28mm, both calipers however only accept 267mm diameter disc.
miro-1980
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Re: RS 911 calipers for 131

Post by miro-1980 »

There seems to be four of the historic series available:

CP2361 - 38.1mm Bores
- suitable for 13" wheels.
- suits Ø267.0 to Ø248.0 x 20.7mm disc.CP2271

CP2271 - Ø38.1mm Bores
- suitable for 13" to 16" wheels.
- Suits Ø302.0 to 260.0 x 28.0mm disc.

CP2270 - Ø41.3mm Bores
- suitable for 13" to 16" wheels.
- Suits Ø302.0 to 260.0 x 28.0mm disc.

CP2279 - Ø44.5mm Bores
- suitable for 13" to 16" wheel
- Suits Ø330.0 to 260.0 x 28.0mm disc.

It looks like the only issues is to decide what size disks (from 248 to 330)

I personally find 4x 44,4 pot with x 330mm disk very appealing !!!

Miro
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131grp4
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Re: RS 911 calipers for 131

Post by 131grp4 »

it's only the CP2361 that accepts a 20mm thick disc though.
miro-1980
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Re: RS 911 calipers for 131

Post by miro-1980 »

131grp4 wrote:it's only the CP2361 that accepts a 20mm thick disc though.
What is the reason to limit the disc thickness to 20 mm ?

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miro-1980
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Re: RS 911 calipers for 131

Post by miro-1980 »

131grp4

Thanks for the tip. (I misssed this !!)

Incidentally what will be the limiting factor ultimately deciding which brakes I will use will be availability of mounting brackets for the calipers (of all things).

Anybody has knowledge of this area ?

Miro
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Abarthnorway - Remi L
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Re: RS 911 calipers for 131

Post by Abarthnorway - Remi L »

Hi Miro!

This discussion has so far mainly been about different possible fitments of brake discs sizes.

As You pointed out in Your last post it is a few other things to consider as well:

1) Correct caliper brackets to modify and correct distance and offset from hub.
2) You also have to seriously consider a way to center the brake discs relative to the hub - the wheel bolts will not do that alone in my opinion - at least not for a high performance application.
3) The size of the caliper piston relative to the size of the master cylinder.... a bigger caliper size means longer pedal travel if std master cylinder is used - not always taken into account.
4) Material quality of disc/caliper/brake pads is of the high importance

IMO brake mods are best left to the experts- Buy quality large discs and calipers from reputable sources or expect failure. Usually works out cheaper and safer than the alternatives, unless You posess serious macining and engineering skills.

Sorry that I am not able to offer a quick solution - but I have tried quite a few of the mentioned modifications - none good. Next step will be to shell out what is needed for an uprated quality brake kit.(Strada 130 front brakes) - Would have been better economy than the cost of my current and unsufficient mods. Have had my share of cracked, vibrating, warped and overheated discs.....

Safety and quality first.


Best regards

Remi Lovhoiden
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miro-1980
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Re: RS 911 calipers for 131

Post by miro-1980 »

Remi!

Very inter4estying and valid points you have made .

I need to think it through before I respond.

However : just of the top of my head :

1/ Correct caliper brackets - Caliper brackets seem to be the main mechanical limitation, at this stage
2/ "to center the brake discs relative to the hub" _ this is something which I am not sure of- never thought about it ...
3/ "The size of the caliper piston relative to the size of the master cylinder.... a bigger caliper size means longer pedal travel. Very valid point. the caliper piston capacity is something to look at ... I have changed from 227 to 240 disks and somewhat larger caliper pots. No effect you are referring to , but once I go for 4 pot calipers this may be an issue to look at...
4/ Material quality of disc/caliper/brake pads is of the high importance - I fully agree. I have actually so far been using F1 by Ferodo and found them to be top quality. Also the disk quality is of top importance. I would also add brake fluid type/quality and brake linkage. Typically all these should be designed and build for competition. Otherwise one is asking for trouble...

Now when I switch from 1 pot calipers with 227 disks to 4 pot calipers and 300 mm disks some of the elements you mention are bound to create a problem , and unless these issues are addressed beforehand (at the time of selecting the brake system) it could become a very ugly surprise ...

Miro

Does anybody have any experience with this ?

M
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miro-1980
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Re: RS 911 calipers for 131

Post by miro-1980 »

Gents,

I am re building a Fiat 131 Abarth and need help with rear calipers.

The rear abarth hub has two sets of mounting holes with distance of 145 mm (center to center) and 76 mm .

I need something to fit these mounting holes.

Currently I am planning to switch from Uno Turbo front calipers with 240 mm disks to RS 911 calipers ( two 48mm piston) with 250-285 mm disks. My current rear brakes setup ( 125p calipers with 227 disks) does not have sufficient braking power as compared to the front .

Can anyone suggest possible solution ?

Miro
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Guy Croft
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Re: RS 911 calipers for 131

Post by Guy Croft »

AP Racing and other names are all very well but I have no contacts at any of them, on the other hand we all have a friend in brakes and that is Jim Fierst in the USA who makes Whoa Brakes. Member Jon Logan is agent for them and I suggest you talk to him about your requirements rightaway.

G
TomLouwrier
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Re: RS 911 calipers for 131

Post by TomLouwrier »

Hi Miro,

It is vitally important to respect the balance between front and rear brakes when upgrading. Upset the brakes and you have a deadly accident in the making. Personally I will not even get into a car that has had a 'Big Brake' kit fitted to the front wheels only.

If I compare the OE setup on the 124 and the numbers you quoted for the '76 Abarth, then in both cases the balance is 67% front and 33% rear. This is typical for a front engine, rear wheel drive car. Neither Fiat nor Abarth engineers were stupid when they set it up like that.
124: front 1x48mm on 227mm disc / rear: 1x34mm on 227 disc
Abarth '76: 2x48mm on 300mm disc / rear: 2x38mm on 252mm disc
You're planning on fitting brakes with 200% more capacity at the front (2x48mm effective, compared to 1x48mm currently). Bigger disc diameter (260-280mm) will add another 30-35% to that (multiply, not add), giving a total increase of up to 275% at the front. This is a massive change!

Your new rear brakes should have a similar increase. That means a rear caliper piston of 48mm as well, or 2x38mm on a disc of at least 260 (257mm is a common Fiat size).
I do not know of existing cars with 2x38mm rear brakes, fronts maybe but that would be without handbrake.

Let's say you use 2x48mm pistions and 280mm discs, you will have about 255% capacity at the front.
1x48mm on a 257 disc gives you 220% at the back.
The balance will be 70% / 30%, near original with a bit more accent on the fronts. Not bad.

2x48mm on a 257 disc gives you 220% at the front.
1x48mm on a 257 disc gives you 220% at the back.
The balance will be 67% / 33%, identical to original Fiat and Abarth setup.


If you wish to retain the mechanical handbrake, there are several Citroen models that have handbrakes on the front wheels. The BX came with 48mm floating calipers, but used very thin discs (10-11mm). These calipers are of the Bendix BDA family, which have an alloy cylinder and cast iron bracket holding the pads. This means you can get parts from many French cars built in the 80's and 90's using the same calipers, in order to get pad carriers that go with thicker (13mm or 20mm ventilated) discs.


To push the bigger volume you need to increase the master cylinder as well, you would be looking at a 25.4mm at least (174% compared to the standard 19mm Fiat item) or near 27mm to be correct.

I have a spreadsheet that does all these calculations in a neat table, but it is completely in dutch. I will try to translate it and clean out my own mess this weekend and then post it here.

Note:
I know you're using this car for competition only, but if someone would like to upgrade his brakes here on continental Europe, it would be very difficult and expensive to use aftermarket components and keep it legal. Getting through the yearly test (MOT, TuV, APK, CT etc) would be one thing, but if ever in an accident the insurance company will immediately drop you like a brick for having a non-conform car.
Using parts from well known production cars, like from a later Fiat model, makes it much easier to get your modification homologated for street use.
This is why those aftermarket kits are not very popular over here.

regards
Tom
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Guy Croft
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Re: RS 911 calipers for 131

Post by Guy Croft »

Just want to add my two-pennyworth from exp with my 124CSA and new brakes/dual master cylinders.

You can use identical brake setups F&R. Disc and calliper. However you must have adjustable bias because the car must be capable of either equal F-R braking or more to the front. Too much at the rear wiill throw the car into a spin in a second. In wet conditions you need 50-50 F-R bias. In dry as much as you can get at the front, usuall 70-30 bias.

Selection of the master cylinders will dictate what happens in practice. The front will have a smaller cylinder to generate higher pressure. A balance bar setup is essential and Tilton and AP Racing sell them.

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Re: RS 911 calipers for 131

Post by miro-1980 »

Tom, and Guy.

This is what sets this GCRE forum world apart from any other in the world. Level of competence and technical details !

Thank you gentlemen !

I already have installed the Tilton bias regulator, which will hopefully give me capability to move from 70/30 to 50/50 on a fly.

Incidentally some time ago I have come across a very interesting article in Road and Track magazine (US) article by Sandro Munari in which he shared data on brake balance stup he used in 131 Abarth:

(front-to-rear )
tarmac :60/40
gravel : 50/50
mud : 40/60
snow : 30/70

I am not Sandro Munari and this is not really a GR 4 car. The chances I will be driving on snow or mud are remote. It does not have 240 hp but "only" 190hp , etc. So I do not necessarily need to replicate these numbers exactly but this is a good guidance. I am not sure I will be able to get such a wide range of adjustment with Tilton on a single Master cylinder (brake pump) with booster, but adjustment between 70/30 to 50/50 looks entirely possible, given proper calipers and disks. ( see next post )

Re calipers: Tom your information is priceless to me.
Here is the history of my brake modifications :

Evo 1/ Standard 131 civilian brake setup front 227 disk with single 41 mm (?) caliper.
Impression : unimpressive standard braking

Evo 2/ Front changed to Uno turbo caliper with piston ?? mm(??) and 240 mm disk with Ferrodo competition pads. Rear: retaining the original drums.
Impression : Very significant improvement in over all braking power !

Evo 3/ Rear: changed to standard 125p caliper single 41 mm cylinder ( no change to front - Uno turbo single ??? mm cylinder and 240 mm disk. Tilton brake bias adjuster installed.
Impression : The brakes seemed to be fine : improvement over Evo 2 ? uncertain? No real opportunity to test the effect of disk rear brakes and Tilton adjuster in action. Most of he time drove with the adjuster handle in position from half back to full back increase. In position "full front" the brakes seemed just a bit too weak on the rear.

Evo 4/(Under way) Front two 48 mm piston ATE calipers from RS 911 and 252 mm disk Rear : to be decided.

The front will have calipers twin 48 mm cylinders and (option one) 450 mm vented disks disks or (option two) 485 vented disks. These are the disks I have.

The key question is :

What caliper size (single or twin pot) to use in the rear to achieve the required brake balance with a front upgrade from Uno turbo to ATE 2x 48mm?

I intuitively recognized the problem which Tom explained in technical details. The basic unadjusted Front to Rear split should be ca 70/30 (or as Abarth had it 67/33) to make the car behave properly under general driving conditions.

Tom, I really appreciate your help, and can't wait to get my hands on the spreadsheet you mentioned.
Any further suggestions and comments will be greatly appreciated.

Related to rear brake caliper selection is a question of making the calipers fit onto the Abarth hub mounting holes.

I am also facing an issue of doing away with a mechanical hand brake and possible conversion to full hydraulic system with hydraulic rear brake.

Gents, I need all the help and support I can get!

Thanks

Miro
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