Uprated Front Brakes, Mastercylinders,

[ricdat 0]

That´s what I meant.

 

You are right about the friction area, of course.

 

When jonah said "piston size", I took it to mean how big it was - in square mm - ie the area. Obviously we are all in agreement then.

 

Anyway I've played with jonah's spreadsheet - what a beauty! Now I just have to decide whether I have fixed compensator/s and accept the compromise between slippery and grippy surfaces (like car manufacturers do) or adjustable ones to optimise. I'm tending toward the latter as adjustment will be needed in the first place to get it right anyway after upping the front braking. I'll be experimenting with the spreadsheet a bit more first.

 

Cheers,

Rick

[whizzer71 0]

And the effect of the extra weight over the front caused by fitting the later cast block engines,Gti6 into 205 for example ?,This extra weight must bear some relevance....besides the increase in understeer.

 

Tris

Edited January 7, 2007 by whizzer71

[Grez4 2]

It would be intresting to see how pads of the same cof but different in surface area would cope with the generated heat, and how this effect braking efficiency?.

[fangio 1]

This is the 2nd time I have read through this topic.

 

On the 1st reading I ditched the idea of GTi-6 brakes due to the 'logic' given.

 

However having experienced the braking effect of GTi-6 brakes with std rear 1.9 discs and compensators I am in no doubt as to the substantial increase in stopping ability. It was absolutely in a different class altogether.

 

I have currently got the standard 1.9 set-up with Ferodo ds2000 pads all round with new compensators and the pads are well worn in. I am very impressed with this set-up, but there is no comparison to the stopping power of the GTi-6 front brakes. I would agree as Anthony states that removal of the compensators is beneficial to level the braking force between front and rear with this set-up.

 

I agree that ultimately there is tyre rubber against road surface and that CoF would be the same for the same car and yes I can lock my wheels on the std set-up.

 

I think there is another factor that comes into play though; that of the initial bite in the first second or so of braking effort that the bigger brakes will provide, rubbing off much more speed than the smaller brakes could manage. Also toward the end of braking from higher speeds where the smaller disc and pad would suffer from a higher degree of fade.

 

This I believe is the deciding difference between the two set-ups.

 

I much prefer proven science to mere conjecture but the proof is always in the pudding.

[jackherer 543]

I would have agreed with that until I tried some proper pads on standard calipers. I think what you are describing is the 'feel' of big brakes rather than the performance and even that can be replicated with decent pads.

 

DS2000 aren't good enough IMO, I run Mintex M1166 now and with standard discs and calipers they are at least as good as any big brake setup I've tried, even on track and with a 16v engine. Given the (unsprung) weight of big brakes I avoid them now, with the exception of my mates wilwood 4 pots on 285mm discs which weigh nothing compared to standard calipers but they are ridiculously over the top in reality, in terms of price and performance.

[kenp 3]

Just to add my twopenny worth....

 

Never mind brake upgrades, I've always been of the opinion that (1.9) Gtis are overbraked on the front (well perhaps more correctly, underbraked on the rear) for my driving style.

 

Before I get jumped on by the circuit racing boys I'll qualify this by mentioning that my sport of choice is road rallying which includes a whole mixture of surface changes - wet, dry and/or muddy tarmac, gravel, mud tracks etc.

 

So with that in mind, I prefer to have a "slight" rear brake bias as it reduces the chance of locking up the fronts and allows me to setup the back much better for the next corner with the tree on the outside that's frantically trying to be friends with me

 

I have junked the rear compensators, converted the lines to a conventional front / rear split and fitted a bias valve neatly under the dash accessed via the driver side cubby hole. Pedal is so much firmer and I can now adjust the bias the suit the conditions. Car feels much more confident under braking than it ever did before and pulls up very nicely. A less techy than the full twin reservoir bias setup un my Escort but does the job nicely nevertheless

 

 

Poncy health and safety disclaimer : Playing about with your brake bias is not recommended unless you know what you are doing. Failure to get it right could result in physical, mental and/or financial damage.

Edited May 1, 2007 by kenp

[Rob Thomson 6]

I absolutely agree with Kenp, more rear bias is great; not only does it reduce stopping distances but it also gives you loads of extra control, especially in a car that you steer from the rear like a 205.

 

Going back to Fangio's point, I really don't agree. I had all kinds of brake set-ups on my old 309 (including GTI-6) and by far my favourite was the standard without compensators. The GTi-6 brakes basically buggered the pedal feel (even with the 406 MC) and brake balance without helping stopping distances at all.

 

My 106 Rallye (in my avatar) has standard front brakes. Everyone always comments about how bad they are, and how I should upgrade. But it's funny how it'll out-brake anything, including me...

 

My standard 1.6 GTi also stops very well, though it isn't very stable cos the suspension's f***ed. But if I ignore the instability and jump on the pedal it scrubs off speed very well indeed and also has great feel, progression and modulation.

 

But most people couldn't give a f*** about useful attributes like those, they just want brakes that make the car stand on its nose if you blow on the pedal. Bollocks to that.

[taffycrook 2]

Just my 2p worth.

My track car on std brakes, without compensators and a bias valve, can't work the rear brakes enough the bias is fully rewards and the guy who drives it most thinks it will benifit from more rear brakes.

Now this has made me think, fit the 283mm discs and gti6 calipers but find bigger rear calipers too. Increase the area of the rear pistons more than the fronts and then i may get the balance right.

Lower pressures will reduce driver fatigue on test days resulting in more laps and track time.

 

So what car has the correct sized rear calipers?

[Guest Le JC]

Just my 2p worth.

My track car on std brakes, without compensators and a bias valve, can't work the rear brakes enough the bias is fully rewards and the guy who drives it most thinks it will benifit from more rear brakes.

Now this has made me think, fit the 283mm discs and gti6 calipers but find bigger rear calipers too. Increase the area of the rear pistons more than the fronts and then i may get the balance right.

Lower pressures will reduce driver fatigue on test days resulting in more laps and track time.

 

So what car has the correct sized rear calipers?

 

The rear Bendix calipers are sized 30mm (like these on Renault 5 GT turbo), It's possible to find the same in 32mm (ZX Volcane if my memory is good) and someone told me they also exist in 34mm (fitted for ???)

 

However, it is possible to find bigger : Citroën BX forward in 50mm with the handbrake lever. The fact that they are designed for mineral oil (LHM) is not a problem and they are easy to convert without fixing modification.

I also have a Lotus seven replica home made (by myself) with these in the rear. I try putting the seals in mineral oil for 2 weeks and the seals remain OK (13 years ago ! and my braking système is still operative)

 

I have chosen 50mm in the rear for my seven because of the propulsion (30mm Bendix were too small)

 

Infortunately, many years later, I discovered that these calipers where fitted on the rear of ex-works Alpine A310 (50mm) and I suppose Renault can provide the good synthetic seals. Great minds think alike.

 

 

 

For my 2p worth / 205 Gti brakes front upgrade :

 

I have dismantled the pressure valve on my 205 Gti XU9JAZ to see how they are into. My idea is to remove them (make a clone piece without system in it)

 

My question(s) is :

 

In France, the technical check is awkward and we have to stick the better we can to standard specification (in fact, not too far...)

 

I would like to know if there is a good compounding for the front brakes with confines :

 

-not too big (266mm discs seems to be the best, like I read in this forum)

-not too heavy (20,5 thickness rather than 22mm if possible and rather than 283mm discs visually too big)

-sufficient efficiency (the bigger caliper's diametre : 57mm rather than 54mm if possible) to use without rear pressure valves.

-the good offset (no modification).

 

The 206 2.0i 16V / 2.0 Hdi year 2000 / peugeot 405 discs are 266x20,5mm but how about the 27mm Offset ???

Can we find 57mm Girling calipers for 266mm discs like these fitted for Peugeot 306 2.0 XU10J4RS (283mm discs)

 

And.... sorry for my bad English

 

[matt.f 16]

Can anyone help with whats the best to do with mine then please,road rally car build?

I have a 1.6(modified 1.9 engine approx 155bhp)set up and have bought some 1.9 calipers and mintex 1155 pads and im running the brake lines inside.Is it just a case of swapping the front calipers over and leaving the rest or do i need to start removing compensators etc?If a bias valve needs fitting then i will get one as everything else has been done properly and im not cutting corners here.

Cheers Matt

[Rob Thomson 6]

If you're not cutting corners then the best bet is to fit a bias valve to replace the standard compensator. You probably want a bit more rear bias than standard, but I've done road rallies in very s*itty conditions where you might want to be a little more circumspect. It's best to have the option to change the bias.

 

Otherwise I believe the 1.9 calipers bolt straight on.

[matt.f 16]

Thanks,tbh ive not really had chance to look at the brake set up yet as ive been buisy with building the rest of the car so any info off you guys is much appreciated.

[DRTDVL 4 1 Cars]

I've gone overboard on my brakes no doubt, but they didn't cost me much as i had all the parts laying about. I've removed all limiters/factory bias valves and installed a wilwood adjustable one in the cabin.

 

With the upgraded master (406) and the larger 307 front brakes, i couldn't get the rears to lock at all even with the bias valve opened for full rear brake or with the hydro handbrake.

 

I for the fun of it, through the 1.6 gti front brake pad carrier onto the rear brake mounting bracket to increase the rear piston size. The rear brakes now lock with ease and the hydro handbrake is a dream to use unlike before.

 

I'll eventually look at a new brake setup that will lighten up everything and be better suited to the car, but for now it's got the car running properly. The only thing was i needed to get new lines made with banjo fittings as the previous ones would foul against the body work.

 

*waits to be told i'm doing it all wrong...*

[matt.f 16]

I absolutely agree with Kenp, more rear bias is great; not only does it reduce stopping distances but it also gives you loads of extra control, especially in a car that you steer from the rear like a 205.

 

Going back to Fangio's point, I really don't agree. I had all kinds of brake set-ups on my old 309 (including GTI-6) and by far my favourite was the standard without compensators. The GTi-6 brakes basically buggered the pedal feel (even with the 406 MC) and brake balance without helping stopping distances at all.

 

My 106 Rallye (in my avatar) has standard front brakes. Everyone always comments about how bad they are, and how I should upgrade. But it's funny how it'll out-brake anything, including me...

 

My standard 1.6 GTi also stops very well, though it isn't very stable cos the suspension's f***ed. But if I ignore the instability and jump on the pedal it scrubs off speed very well indeed and also has great feel, progression and modulation.

 

But most people couldn't give a f*** about useful attributes like those, they just want brakes that make the car stand on its nose if you blow on the pedal. Bollocks to that.

Know what you mean,my dads 106 rallye brakes are really good,and there just braided hoses(caliper-master cyl),5.1 fluid and mintex 1155's.

[RossD 44]

(Taken from post above)

 

So with the picture of the dismantled 1.9 compensator above, does anybody want to hazard a guess as to how they work?

Do they:

 

1) Slow down the pressure rise to the rear calipers (i.e rear calipers will see full master cylinder pressure but the pressure rises slowly)

2) Limit the pressure to the rear calipers to a pre-defined value

3) Limit the pressure to the rear calipers as a ratio to that of the fronts

 

I think this would answer a lot of questions flying around this forum regarding 1.9 rear compensators!

 

From the look of it, the strength of the spring effects the pressure the rear caliper will see. (I.e Stronger spring = more pressure) That, or it the controls the rate of change in pressure. There looks to be a piston\plunger type affair in there too which the spring acts on (Note the small O-ring on the end of it).

 

To me, it looks as if this valve slows down the rate of pressure change, i.e if you jab the brakes the valve closes to prevent a big pressure change to the rears. There must be a very small drilling through somewhere that the pressure can slowly bleed through (This would also assist in bleeding the rears as air can get through it) In my eyes, this compensator meets option 1) on my list above.

 

 

 

Anyone have any other input?

Edited July 5, 2010 by RossD

[Jamal 2]

The rear Bendix calipers are sized 30mm (like these on Renault 5 GT turbo), It's possible to find the same in 32mm (ZX Volcane if my memory is good)

 

Also all the Citroen Xsara's has got 32 mm calipers too.

[ftoomsh 5 1 Cars]

this is exactly the set up I have on my 206 mi16 rallycar.

 

the only issue I have is too long a pedal and am looking to change the mc to a non abs 4 port edition (24mm diam mc) which I believe can be found on some 406's, boxers and experts (please correct me if I am wrong)

[welshpug 1,657]

ALL 406's use 23.8mm.

 

Doubt a boxer unit will fit.

 

Why do you want 4 port on a rally car? Two will suffice, single line to tee piece and front brakes, single line to rear via bias valve, handbrake tee pieve and rear brakes

Edited February 11, 2014 by welshpug

[ftoomsh 5 1 Cars]

so the 2 port abs mc's work then?? I was under the impression they didn't??

[dobboy 231 2 Cars]

Can someone tell me what I need to do to fit my reservoir bottle to my new MC?

 

Does it just push in?

 

The new MC has a small pin in the box, where does that get fitted? If at all.

 

The new MC also has a hole through the side of it, what's that for?

 

Thanks

[dobboy 231 2 Cars]

To answer my post above, it looks like the 306 has a screw that holds the reservoir bottle on to the MC.... so my 205 one should just push in only. Still not sure what the pin is for though.

 

 

But, another question...... and after reading the big break conversion guide, are longer break flexi's required for the bigger calipers?

 

The guide doesn't mention it, but i've seen it mentioned elsewhere.

 

TIA

[Anthony 1,003]

You need longer flexis for 283mm setups (eg 306 GTi-6) as the standard ones pull tight on full lock.

 

The standard flexis are OK for most 266mm setups (eg 306 S16 and HDi).

[welshpug 1,657]

standard flexis on standard calipers will kink on excessively low cars.

 

the pin is to secure the MC.

[dobboy 231 2 Cars]

Thanks Anthony/WP

 

I'll be lowered 30mm and have 283mm set up.... so looks like i'll need to get another set of flexi's.

[dobboy 231 2 Cars]

On the MC there are four connections, and it looks like two compartments on the reservoir bottle.

 

Is it usual to put the back two lines on to the MC so they are served by the same compartment? (And put them back nearest the bulkhead)