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Re: Fiat 124/Lada High performance Brake kit?

Posted: June 19th, 2013, 6:11 pm
by Urbancamo

Brilliant idea to use manufacturer's OE parts as a full bolt-on kit. I like bolt-on kit's like this when you don't need to invent a wheel again. This kit will work OK with stock brake master cylinder size?

I think one issue with these cars in civilian traffic is unsufficient brake booster. You really have to have plenty of force in your right leg in order to stop these cars. I'm not the weakest bloke around, but I still struggle to stop these cars in emergency situation. Feels like car could stop faster but I simply don't have enough power to push brake pedal. I think it needs something around 100 kg's to do full emergency braking with one leg.
My mate adapted bit bigger brake booster to his Lada with stock brakes and the end result is very light brake pedal, almost similar than 90's Western cars have. I think it needs at least 10-15 kg less pedal force than original setup. Significant modification to civilian driving.


Re: Fiat 124/Lada High performance Brake kit?

Posted: June 20th, 2013, 8:12 pm
by mark allison
the system works fine with the stock master cylinder. Pedal effort doesn't seem high to me, and the car stops in a much shorter distance

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 4th, 2013, 7:20 pm
by badlyworntoy
Another problem with Ladas and Fiat 124's is the lack of availability of a bias pedal box setup. After much scouring of the internet I quickly realised that the only solution was to manufacture my own. Now since I loathe working in the foot wells of cars I thought the easiest way to do it would be to build it on the bench using a old redundant standard pedal box, this way a "Bolt on" solution can be achieved, as I really didn't want to have to modify anything in situe.

I decided to buy a Combrake Universal pedal box and modify the dimensions of it to suit the original PCD of the Lada servo mounting points. Now as usual I have space constraints So I have tried to compact the whole unit by as much as 20mm. I have also used Wilwoods latest generation compact remote master cylinders. I have gone for 0.625 on the front and 0.75 on the rear, this is all guess work but perhaps someone can advise on that? I've not fitted this to the car yet as I need to find a suitable gap in the program for installation due to both me and the car having busy schedules.

Think its ok, anybody have any thoughts?


Re: Fiat 124/Lada High performance Brake kit?

Posted: August 5th, 2013, 12:25 pm
by Will01
Hi Nix, if you look online you should be able to find brake balance spreadsheets which will allow you to work out a basic bias setup for master cylinder sizes. I might have one somewhere but I will have to try and hunt it out.
Otherwise looks like a good job so far. Keep up the good work.

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 5th, 2013, 12:35 pm
by Guy Croft
so nice to see a balance beam setup at last!

I would have gone for 1/2" front 5/8" rear btw


Re: Fiat 124/Lada High performance Brake kit?

Posted: August 5th, 2013, 12:54 pm
by Will01
Another thing i forgot to mention was it may also be advisable to fit a separate proportioning valve for the rear brakes in the system. This will then allow not just split of braking front to rear (via bias box), but also fine tuning the amount of pressure applied to the rear cylinders.

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 5th, 2013, 7:59 pm
by badlyworntoy
Yes Will can you find me that? I've had a look but the only thing I can find I don't like the source it comes from.

I can't find anybody who makes a 0.5 master cylinder, the smallest that seems to be available is 0.0625 from both Wilwood and Girling?

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 5th, 2013, 9:13 pm
by Guy Croft
The AP Racing one is the only one worth buying.

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 7th, 2013, 3:24 pm
by Will01
Nix, I unfortunately cannot find the one I used to have.
Maybe if i can go through my university notes I will find the equations i wrote down a long time ago etc?
In the mean time I did a few searches on line and am working on producing a basic brake calculator, but it will be sometime before this is finished and tested.
If i come across anything in the meantime I will forward on.

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 7th, 2013, 8:25 pm
by TomLouwrier
hi guys,

Having both a balance bar and a reducer valve in the rear circuit seems like overkill to me. Whatever balance you set up between both master cylinders is influenced (read: disturbed) by the setting of the valve. You may however use it in place of the OEM load sensitive valve as you're likely to change the springs which would throw that valve's setting off. Your main knob to fiddle with should be the balance bar though.

About two years ago Miro and I had quite a long discussion going on about dimensioning the brake system on his 131. You may want to read that.
At the time I already had built a spreadsheet to estimate some upgrades on my own cars. I developed that quite a bit in order to help Miro (and because it was a lot of fun!) until it became somewhat of a complex model-thingy. Base of my thoughts was to compare the original setup on the car to be modified and some others with similar layout but different manufacturer and performance. This gives a good idea of absolute braking power and of F/R balance. If the numbers for Fiat, BMW, etc are in the same range you can bet your lunch they got them after a lot of testing. Since we don't have those facilities, I advise to follow the proven examples and scale up evenly. You'll have to take the effect of the original load sensing limiter valve into consideration of course, as stated above.
The model takes into account
- disc diameter
- caliper piston size, number and construction (floating or fixed)
- 1 master cylinder with limiter valve, or
- 2 master cylinders with balance bar
- master cylinder bore
- line pressure (80 bar is a good starting point)
- pedal force (can you stand on one leg? how much do you weigh? aha...)
- pad friction coefficient (about 0,5)
Final version of that spread sheet here: viewtopic.php?f=14&t=1901&hilit=brakes&start=90

I've found there are very distinct F/R ratios across many manufacturers and models, for
- north-south driveline, RWD: 65%F / 35%R
(Fiat 124 and 131, BMW, Merc, Volvo)
- mid engine, RWD: 55%F / 45%R
(Matras, Monte, X1/9, Stratos, Ferraris, etc)
- transverse engine, FWD: 75%F / 25%R
(nearly all hatches since the mid 80's)
All values plus/minus 5%. These are just the static values, load will shift tot the front under braking of course. Trust the boys at the factory to have tested that.
I did not do any analysis on tail draggers like Beetle, 911 etc. Don't like 'um, nuff said. :-)

If you have any questions I'll be happy to explain, but please accept that we're making 75+ hours a week here in order to stay alive. I may not be able to get back at you within a day.


Re: Fiat 124/Lada High performance Brake kit?

Posted: August 8th, 2013, 7:45 am
by Will01
Hi Tom
I have seen your workings and spreadsheet attached on the link you previously supplied.
I hope you are ok if i have a play myself and compare with what i have already calculated.
Very good to see and thanks for the work that you put into this, i am sure it will be a help to many.
Take it easy

Re: Fiat 124/Lada High performance Brake kit?

Posted: August 10th, 2013, 2:47 pm
by TomLouwrier
hi guys,

Since we're talking brakes again and people may be looking into modifying them, maybe even using my calculation model, I feel obliged to re-post the warning from 2 years ago (wow, time flies...)

!!! Note to anyone who is even just thinking of modifying the brakes of his or her car !!!

- I am not a brake expert.
I do not work for a company professionally involved with designing, fitting or modifying brake systems.
- I am a mechanics engineer who likes to do the math.
I do have over 40 years of love for most things that have wheels and go fast. BTW I turned 47 last March ;-)
- These calculations are my understanding of things.
I do my best to get it right, but there is really no warranty other than my professional honour. There may be grave errors or omissions in my work. Let me know when you find them so I can correct things.
- Many of my calculations are based on comparing existing, proven, mostly OEM solutions.
You and me do not have the time, the testing facilities or the correct data on the physical properties like pad friction coefficients and brake line pressures that would make reliable absolute calculations possible.
Also we can't do enough experiments to find out about dynamic behaviour (weight transfer, body and suspension movement under braking, cold, warm and hot brakes). Therefore I analyse a number of proven solutions and see where the common trends are. From there on I work out what things would be like if I scale them up or down. This approach helps me understand how the original designers came to their decisions. It gives me a a guideline on how to modify things by scaling them up in the right places, by the right amounts.
- This is what I use for my own brakes, and what I would do with my own car.
If I get it wrong, I may kill myself and hopefully just me. When you go changing the brakes on your car, the responsibility for safety -anyone's safety- is completely yours.
- To be street legal and properly insured, you will have to get your car tested by an official body.
They will want to see your calculations, your explanations for the changes you made (construction dossier) and inspect your car. Staying relatively close to a well known OEM specification, a related model and brand, will help you showing that it is in fact a well engineered solution.
- In traffic without official approval of your modified brakes you are a criminal and may become a murderer.

Think long and hard about this before you get the spanners out.

Have a good weekend all.