My 131 abarth (never ending) story - 2017 season updates

[miro-1980]

Re Brembo,

Once we actually get the front brakes finally installed and tested , the brembo and the mounting plate will be for sale,

Anyone interested.

Miro

PS: I will also make a new installation plate to fit the Abarth mounting holes with uniball-ended control arms.

M

[miro-1980]

Gr 4 fast steering

Background:

Original Gr 4 homologation (dated April 1, 1976) included a steering rack with a fast 2.85 ratio (2.85 turns lock to lock) with a steering shock absorber. Standard was 3.2

The 2.85 ratio proved to be very good and was never changed. The only other modification to the steering was six months later (1 October 1976) when reinforced steering rods were homologated.
This setup proved to work perfectly and required no more changes as long as 131 abarth was actively ralied in European Rally Championship (which preceded WRC).
The steering rack can be installed in 131 Sport (Racing) or a standard civilian 131. The racks are the same .
It is really a key part if one wants to race/ rally a 131.

Tried to get one for several years, to no avail. Last year I ad an opportunity to buy a German made replica but declined. It was priced at 1500 Euro. Now I have undertaken a small project with a friend from Finland , and a real expert in 131 abarth to build a short series of such fast steering racks by a professional gear making company. We have three orders now and need a total of five to launch the project . The cost will be 480 Euro. If anyone is interested , please send me a PM.

Important : This project is purely non profit (based on cost only).

Miro

[miro-1980]

URGENT HELP NEEDED !!!

Need to source a brake pump to fit instead of a standard 131 pump with 19.5 setup.

The pump should be either 21.6 or 22.2mm ( preferably the latter) !!!

The brakes we installed (original group 4) cannot be handled by what we have : 19.5 or 20.6 mm

Help please, as we are planning a start for September 5 , in a major rally and without it , we are dead in the water.

Miro

[miro-1980]

Re: URGENT HELP NEEDED re:21.6 or 22.2mm brake pump

Postby Walezy » Tue Aug 28, 2012 7:28 am

Fiat Croma 2.0 Turbo or any simmilar. it can be fitted with slight modification to Fiat 131 brake servo and it is 22.2mm. You need some kind of remote brake reservoirs as the pump does not have it.

[miro-1980]

Re: URGENT HELP NEEDED re:21.6 or 22.2mm brake pump

Postby Guy Croft » Tue Aug 28, 2012 8:48 pm

Are we talking Brake Master Cylinder?

I just don't get it Miro. Why are you not yet on an AP Racing dual master cylinder setup with balance bar? That is one of the first conversions you do on a rally car.

G
Guy Croft, owner

[miro-1980]

Re: URGENT HELP NEEDED re:21.6 or 22.2mm brake pump

Postby miro-1980 » Tue Aug 28, 2012 10:43 pm
Guy,

Yes we are talking Brake Master Cylinder!

It took us a long time to get the right setup for the calipers and disks . Finally we got lucky and got hold of a genuine gr 4 front disks.

Now the setup is this :

Front: 2 x 48 ATE calipers from RS 911 S and 300 vented two piece disks (original gr 4 )
Rear: 2 x 38 ATE ) (original gr. 4) disks 252

Handbrake : hydraulic - Brembo 2 x 31 with separate master cylinder (original gr 4)

The next stage is AP Racing dual master cylinder setup with balance bar, but I wanted to take a shortcut to take the car to a rally and we tried to use the servo with single pump . Obviously with two 2 x 48 ATE calipers in the front and two 2 x 38 ATE calipers in the rear the 19.5 master cylinder could not possibly handle this. Neither could a 20.64. Walezy suggested 22.2 from Fiat Croma Turbo, but it appears the even this might be too small( but we will try this as well), so we are shooting for a 25 mmm master cylinder - if it works we will take the car to a regularity rally, just to test the suspension and drivability. IF not we will continue working to complete the braking system to gr 4 specs.

So either way - the next stage is dual master cylinder with balance bar .

I have two options : try to get an original gr 4 or go for the ATE setup. I am sure the genuine will not be easy to find. So we will most likely go for current production.

If you can help suggesting specific solution I would greatly appreciate it.

Miro

[miro-1980]

NOTE : As you may have noticed I have copied replies of Walezy and GC to the topic of 22.2 master cylinder to this thread to keep it a part of the original subject.

Ad rem:

I have been proved wrong before , but with some experience now I should have expected that a 19.5 diameter master cylinder will not be able to operate a system upgrade from Uno trubo front and Polonez rear to gr 4. Stupid me!

We will deal with the temporary solution and if it works the 131 ( now with full 131abarth gr 4 suspension) will get tested on a rally leading us through 750 km of the best mountain rally stages in Poland , but with no time pressure. It is a regularity rally : 1st Poland Rally Historique. ( Note Poland Rally is the second oldest rally in the world - the oldest being RMC).

If not My 124 spider will have the pleasure of being a rally car for this event.

The issue again is this : you modify one element and when you believe it is a success you realize you musty modify several other elements for the system to work ... Again and again ... ( And I thought foolishly that we will finish the gr 4 suspension and brakes sage in just few weeks. No way Jose ! It is a never ending story after all ...)

No we face the issue of installing dual master cylinder system with balance bar .

I have seen some pictures and have a bit of data , but really I am not sure what it entails.

Here is a picture of a car prepared by a friend in Germany

dual pump gr 4 replica .jpg (63.1 KiB) Viewed 12537 times

DMC .jpg (34.62 KiB) Viewed 12537 times

I will need two master cylinders - balance bar but have no idea at this stage how to put this altogether to make it work.

So if anybody has any experience , pictures of the original , original parts as well as can assist - I will be very grateful.

Question one : do we need to modify the pedal box and if so how ?

Question two: How we can source the parts ( ATE ? )

Three : Any other issues we face ?

We have the next rally on October 20th and need to be finished with building the braking system as well as testing it !

I trust that friends from this forum will help !

Miro

[TomLouwrier]

hi Miro,

I don't get this.
Your setup is not that much bigger than original, hydraulically speaking. The front calipers are still 48mm, each piston travelling about half the distance that the original single piston does. OK, maybe a bit more, but very little really. Pad to disc clearance will be similar on both setups.
Your rear pistons are a bit larger, but only some 25% in area, with same travel.
You total demand from the master brake cylinder (MBC) will not be much more than +10%. This means a desired diameter increase of SQRT(110%) = 105%. No need for an increase in MBC diameter, just push the pedal down some mm's.

We never returned to the thread on these brakes where all the discussion and calculations are :-(
When I put in the numbers you just gave us above, I see no need to go up more than one step on a single MBC setup.
For a given pedal force (I used 2000N, depending on the size of your leg...):

A) Std 124, 131: MBC dia 19,1mm; MBC piston travel 9,5mm (100%); brake line pressure 70bar (100%)
Original setup for 124 and 131, taken as 100% value to compare with road car behaviour as set up by Fiat.

Alt B) F:UnoT(48mm)/R:125(38mm): MBC dia 19,1mm; MBC piston travel 10,3mm(109%); brake line pressure 70bar (100%)
Your setup for 2010 and 2011. Slight increase in travel because of bigger rear piston. Increased braking because of bigger rear piston and 240mm front disc. Main advantage is vented front disc.

Alt C) F:Ate Gp4 (48mm)/R: 125(38mm): MBC dia 19,1mm; MBC piston travel 10,3mm(109%); brake line pressure 70bar (100%)
Same as B), hydraulically speaking. Increased braking because of bigger rear piston and bigger Gp4 discs F and R. ATE fixed caliper may have better characteristics (hysteresis).

Alt D) F:Ate Gp4 (48mm)/R: 125(38mm): MBC dia 20,6mm; MBC piston travel 8,8mm(93%); brake line pressure 60bar (86%)
You'll have to kick this one harder or fit a larger servo to get the same line pressure. Pedal travel slightly shorter which may be good in competition. I do not know. Fixed ATE may help too.

Alt E) F:Ate Gp4 (48mm)/R: 125(38mm): MBC dia 22,2mm; MBC piston travel 7,6mm(80%); brake line pressure 52bar (74%)
Use two legs to brake or go to the gym very often in order to get enough line pressure.

The alloy ATE caliper is a pretty thing, lightweight, fits well and is historically correct. Purely form an engineering point of view I see more value in increasing the front caliper piston area (to 54mm or get more working pistons). You'll certainly need a 21,6, maybe 22.2mm MBC then. See the "124 BS1 Improved" I'm planning.
Remember the difference between a fixed caliper and a floating one! That is why the fixed ATE with 2x48mm pistons gives the same clamping force as the floating OEM 1x48mm.

Calc attached, it has become a pretty complex thing and it's more than a year ago since we touched it. It takes account of split MBC with balance bar and single MBC with pressure regulator as well. I think it's better to pick up this subject in the other thread.
On page 'discs calipers' note how close the Gp4 balance front/rear is to the std road car (66/34).
On page 'master cylinder' note I have no data on the Gp4 split setup, assuming 2x15,9mm. Please tell me if you know the value Abarth actually used.

regards
Tom

(edit 31/08/12: replaced the spreadsheet, I found a small error in the way the front/rear bias was calculated from the valve in the rear line)

[miro-1980]

Tom,

I really appreciate this and need to chew on it for few hours before I can say I understand .

Before that let me ask you one question:

The initial problem with 19.5 and 20.64 appeared was this: I needed to kick the pedal several tiles for it to go the the normal position ( you need to kick it several times to feel the pedal is actually executing some force in the system). After a while you had to do it all over again again.

Note with 20.64 it was just a bit better , but still not drivable.

I take it this is a diameter related (fluid volume required by larger brake cylinders.

Now we will test it with 22.2 and 25.0 mm BMC (25mm is likely to be an overkill as this will require a lot of leg/foot force to be applied - which brings up another issue - a bigger servo).

We are awaiting delivery of 22.2 and 25 mm BMC to test fluid volume issue. once this is resolved we will see if the servo we have is powerful enough) otherwise we will have top go for a bigger servo.

Note: Bigger servo another element in the equation !


Miro

[TomLouwrier]

hi Miro,

Having to pump the brakes several times is never good. This sounds more like too much disc-pad clearance to me. Look for excessive pad knockback.
Back to basics: are the discs all running true and not warped? Are the wheel bearings tight and without play?

Servos and boosters: later. Main thing is to start with the right line pressure. All else comes from that, both direction calipers (use pressure) and direction pedal (generate pressure).

regards
Tom

[Guy Croft]

You don't have to use balance bar to begin with.

You can have the rod from the pedal mounted so as to apply equal force to both cylinders. See sketch. The choice of cylinders is an iteration. You could for example start with a small front (the smallest from Girling) is 0.625" (15.875mm) and a larger rear (so as to induce bias to the front) a shown or equal cylinders with bias valve on the rear line. The smaller the cylinder the greater the pressure. In the sketch the actuating rod is fixed central betw cyls.

The balance bar assy would be fitted with equal cylinders and all it does is allow you to move the actuating rod left or right to bias the braking effort. The connecting beam tilts. AP racing sell them but you won't have time to do all that.

You can't run dual cylinders with servo so be prepared to press the pedal pretty hard. Tom's advice is peerless as usual and I guess if you can find a compatible cylinder to fix to your servo you might be in business...

Maybe Lancia Integrale?

G

[TomLouwrier]

Of course.
That, in fact, is exactly what Abarth homologated for 1976. (Unfortunately I can't post the document here as it was 'found' floating around on the web...).

regards
Tom

[miro-1980]

Guy and Tom,

As Snoopy would say " happiness ie being a member of this exclusive forum !"

I thank you both for most insightful and competent advice.

We have found a 22, from Alfa GVT and an unknown 25 recommended by a friend who prepares cars for competition drift.

We will see bu s[ecial attention will be placed on pad free play . We will try to bleed the system by "populating" it with fluid from the bottom , not the top to begin with. This is to make sure there is no air bubble anywhere in the system .

Will let you know how it goes early next week.

Thanks

Miro

[Rallyroller]

Hi Miro

I understand your problems. On my old Rally Spider, I had brake balance bar , 0.625” ( 15.9) BMC and single piston standard FRONT callipers on the front and rear. As the car was a stage rally car, the balance was to the rear, but the balance bar was not central- (due to the equal calliper piston sizes front and rear. ) It seemd to work. The other thing was it had twin remote servos, (one in each line) and the hydraulic handbrake was in line with the rear callipers. The set up was mainly for forest stages, it was a bit to rear biased for tarmac. The only problem was that there was pad knock off that seemed to only affect the hand brake function. It meant that a slight application of the foot brake was required to bring the handbrake to 100% performance. (only really an issue in auto tests though as in a rally you have usually applied the brakes before you apply the handbrake)

I then swapped the MBC set up to my 124 ST. This had the same system except the rear callipers were the standard smaller ones. The set up worked but the balance bar was in a different position.

The balance bar was mounted onto a modified standard brake pedal. The cylinders were mounted on a plate that bolted to the holes in the bulkhead where the original servo fitted.

The one issue with this system was the bleeding due to the twin remote servos and the twin cylinders. Also the cars were of a low power so the standard size callipers sort of worked.

On my new car, I have converted it to right hand drive. One reason for this is the brake system. ( my original Spider ran the same set up in left hand drive and in right hand drive form). For the new system I am retaining the standard servo, and putting the brake master cylinders + balance beam on the servo ( a number of companies offer kits for this). This removes the problem of the servo. Bleeding twin systems is still difficult. I add a "bleed screw" in a fitting just after each BMC . This means when you bleed the brakes (lets say the front) you can slacken the bleed screw next to the BMC of the rear brakes, and feed this with a pipe into the bleed bottle. This means you get full pedal travel when you bleed the brakes (if you see what I mean).

The advantage of Right hand drive is that there are no carbs in the way. ( Shielding from the exhaust is another matter though) . If you find your pedal too hard then remote servos may be the answer. Am I right in thinking that some Lancia Montecarlos had a servo in front brakes only? could also be worth a try.

However Miro, as you quite rightly say- you change one thing and it has an effect on 5 other things.

Regarding the hand brake, in the UK you have to have a mechanical hand brake due to the law. On my new rally Spider there will be a hydraulic handbrake again in line with the main rear callipers. The mechanical handbrake will be on a separate calliper.

On my new Spider I will be using 42mm Front callipers and 34mm rear callipers. ( Porsche 911) These are on 257 discs ( vented front- solid rear ). I am not sure what size BMC to start with but may try a 19.2 to start with .

I will watch your progress with interest.

[TomLouwrier]

On my new Spider I will be using 42mm Front callipers and 34mm rear callipers. ( Porsche 911) These are on 257 discs ( vented front- solid rear ). I am not sure what size BMC to start with but may try a 19.2 to start with .

Smaller front calipers, std rears. 257mm discs all round.
Expect your brake capacity in theory to be 97% of the original setup, but with a 60/40 front to rear balance (balance bar in neutral position). That will tend to lock up the rears prematurely, limiting the overall braking effort.
To drive these calipers you would be looking at a 17,8mm single MBC or a set of 12,7mm twins. Smaller calipers, smaller MBC.

Have you plowed through our thread over here yet?
viewtopic.php?f=14&t=1901

regards
Tom