Rear brake compensator

[philg]

I have finished my brakes on my gt turbo and now they feel ok. Im going to drive it for a bit the re bleed them.

While i jammed the compensator forwards to bleed the back i snapped the spring.

I have fitted 4 pots and im wanting to increase a bit more braking at the rear hopefully to stop the car locking up on the front.

I read a thread and for the life of me can not find it, it was where someone made a bolt and fitted it to the compensator to jam it open or shut all the time.

What is the best way to set this up for my needs guys?

[Brigsy]

You could fix the compensator solid to the chassis with threaded bar like the cup cars used to be.

As for setting it up it will be all trial and error, trip to the brake rollers at local mot station?

Id keep the bias somewhere near standard you dont want to be locking the rears up, easy to do with a stripped out light car..i had mine set wrong on my old gtt and it nearly all ended up in tears

[philg]

You could fix the compensator solid to the chassis with threaded bar like the cup cars used to be.

As for setting it up it will be all trial and error, trip to the brake rollers at local mot station?

Id keep the bias somewhere near standard you dont want to be locking the rears up, easy to do with a stripped out light car..i had mine set wrong on my old gtt and it nearly all ended up in tears

Just found a thread where ashy had replaced his and he basically set the nut to about half way on the rod, others were tightening there right up.

[Mart]

More bias towards the rear is defo not the way to go. Run like that on track & kiss your gtt goodbye.

[philg]

More bias towards the rear is defo not the way to go. Run like that on track & kiss your gtt goodbye.

Sorry mart can you explain better please

[philg]

Found the thread

It was a fixed rod on the compensator with a spring.

https://www.rtoc.org/boards/showthrea...ompensator+rod

[Brigsy]

The official renault way of setting the compensator was by using a gauge that screwed in where the bleed nipple fits in the rear caliper and checking the cutoff pressure (according to the coupe manual). I doubt anybody has the tool these days!

The book states cutoff pressure 17bar +0 -4, with full tank of juice and 1 person in car when on the ground.

Too much bias to the back and it will lock up for fun, imagine braking hard before entering a corner & sideways due to locked rears? happened to me in the wet at 70ish not good, proper brown pants moment

[Mart]

As Brigsy mentioned, the back end of a gtt is lighter than the front, and even more so if the interior is stripped out. The last thing you need is a more biased rear braking setup because it'll naturally unsettle the car during hard braking, and if you lock the rears with the slightest amount of steering also present, the back will step out/spin.

Always keep the majority of braking bias towards the front. Period.

[philg]

The official renault way of setting the compensator was by using a gauge that screwed in where the bleed nipple ifts in the rear caliper and checking the cutoff pressure (according to the coupe manual). I doubt anybody has the tool these days!

The book states cutoff pressure 17bar +0 -4, with full tank of juice and 1 person in car when on the ground.

Too much bias to the back and it will lock up for fun, imagine braking hard before entering a corner & sideways due to locked rears? happened to me in the wet at 70ish not good, proper brown pants moment

Is more bias to the back the nut tightened or slackened off on the spring bar brigs?

[Brigsy]

More bias to the rear brakes when the nut is tight on the bar, when the arm is toward the front of the car more. More flow like when its clamped in place to bleed the brakes

[philg]

As Brigsy mentioned, the back end of a gtt is lighter than the front, and even more so if the interior is stripped out. The last thing you need is a more biased rear braking setup because it'll naturally unsettle the car during hard braking, and if you lock the rears with the slightest amount of steering also present, the back will step out/spin.

Always keep the majority of braking bias towards the front. Period.

Ok mart, how do i get that?

The nut on mine was pretty central on the threaded part of the spring, but i do not know if the car was set like that or has never been moved.

I have also lowered the car another 15mm or so.

[philg]

More bias to the rear brakes when the nut is tight on the bar, when the arm is toward the front of the car more. More flow like when its clamped in place to bleed the brakes

Good man brigs, so if it was central like ashys set up on his car and my car was around the middle mark to, i would then slacken the nut of a little (towards the rear) after lowering it a little more?

[Mart]

If you're locking up the fronts, it sounds like the bias is already in the right direction

Either ease off the middle pedal, or refit the o.e gear

[philg]

If you're locking up the fronts, it sounds like the bias is already in the right direction

Either ease off the middle pedal, or refit the o.e gear

I have not driven the car yet just up and down the road, just from a bit searching it mentioned bigger brakes can cause locking up issues, therefore giving the back a bit more braking is recommended.

I will leave the nut where it is and have a good drive in it to test, is locking up the front mean is set about right?

[philg]

or refit the o.e gear

It was tempting

[Ian S]

Whether the front wheels lock up or not has little or nothing to do with the rear compensator setting and everything to do with how well the front braking is working or how poor the tyres grip is on the road.

I ran my rear compensator jammed fully forward for many years and the rears never locked up a single time. Not even in the wet.

So peoples experience varies.

But it's only logical that if the all the braking is working correctly then the fronts are improved with larger discs then the rears will be under braking.

A very high speed on a track with very grippy front tyres there is more weight transference to the front under hard braking, therefore the rears may well lock up. But not so much at normal road speeds perhaps with not so grippy and cold tyres.

If you want the car to stop as well as possible then you have to adjust it for the conditions under which you use it.

My car has 288mm front discs and naff green stuff pads all around. At anything up to 70mph the overall braking was noticeably better with the rear compensator jammed full on, ie, max pressure to the rears.

When I fitted the new over braided PTFE front brake lines the fronts were locking very quickly as the response was so much faster than with the squidgy old rubber hoses.

Also, when I went from 6 1/2 inch wide 15 inch wheels to 7 inch wide, then front locking up stopped. Same tyres, swapped them over. Then I fitted the braided lines.

[philg]

Whether the front wheels lock up or not has little or nothing to do with the rear compensator setting and everything to do with how well the front braking is working or how poor the tyres grip is on the road.

I ran my rear compensator jammed fully forward for many years and the rears never locked up a single time. Not even in the wet.

So peoples experience varies.

But it's only logical that if the all the braking is working correctly then the fronts are improved with larger discs then the rears will be under braking.

A very high speed on a track with very grippy front tyres there is more weight transference to the front under hard braking, therefore the rears may well lock up. But not so much at normal road speeds perhaps with not so grippy and cold tyres.

If you want the car to stop as well as possible then you have to adjust it for the conditions under which you use it.

My car has 288mm front discs and naff green stuff pads all around. At anything up to 70mph the overall braking was noticeably better with the rear compensator jammed full on, ie, max pressure to the rears.

When I fitted the new over braided PTFE front brake lines the fronts were locking very quickly as the response was so much faster than with the squidgy old rubber hoses.

Also, when I went from 6 1/2 inch wide 15 inch wheels to 7 inch wide, then front locking up stopped. Same tyres, swapped them over. Then I fitted the braided lines.

Thanks ian

I will leave it where is is and maybe do a bit testing with it, once the new set up is worn in a bit.

If you have not seen my posts i have fitted wilwood 4 pots, 285 brembo disks and feredo 2500 pads front and back.

I have some williams alloys not sure if they are 6.5 or 7" wide, but may be changing them for some team dynamic pro race.

The 888 tyres are giving me a real head ache to with the larger 50 profile, i might just end up buying some proxys in a 45

[Trevhib]

Great insight Ian

[Ian S]

Wilwood 4 pots, 285 brembo disks and feredo 2500 pads front and back.

I had a further thought after reading that you've lowered it a lot.

Doing that increases the -ve camber a bit and so the tyres are more on their inner edges so the foot print on the road is a bit less so they are more likely to lock up under braking. Also to spin on applying the power.

If they're the gold colour Williams Clio alloys they 7" wide.

Did you fit the larger master cylinder to go with the four pots? I forget the part number, etc. It may be in one of the articles somewhere.

[raider_gtt]

anyone thought of phoneing hi spec at dartford kent and asked then as they have good ideas on setup as they make the kits for the renault 5 gt turbo up to a 325mm with 4 pots or take the car there for them to setup brakeing

[Ian S]

Why?

Fit better fronts and you must fit better rears of have less rear braking. What is there to not understand or be confused about?

With other cars people just fit bigger discs all around. Everyone knows it outside of this club.

As far as Hispec goes, although it was 10 years ago and maybe Hi-Spec have improved, but CTM bought some Hi Spec kits for the 5GTT and a Sierra Cossie.

Quality was poor. A lot of vibration on the Sierra. They had to manufacture their own hub adaptor to fix the problem. I forget the details now but they were surprised at how wrong it was.

I've never thought much of Hi-Spec after that.

But like I said, maybe they improved.

[Ian S]

It's the tyres that stop the car, not the size of the brake discs.

I don't know what the normal front to rear proportion of braking is on the 5GTT, but maybe it's 5 at the front to 1 at the rear. But it might be 5 to 2 or 40% at the rear.

So if you increase the front discs braking by 100% you need to increase the rear by 100% to maintain the same balance of 100% effort of the front tyres to 20% effort on the rear tyres.

Change the proportion and you get locking fronts or locking rears.

For a given set of conditions.

Racing drivers are changing the brake balance from corner to corner as they go around each lap because the conditions are different for different corners.

Road car users would ideally change the balance for wet or dry, high speed or low. But that's too much to ask of them, so the manufacturer just sets it to a worst case to ensure the rears don't lock. At least some cars have a rear weight sensing valve.

[philg]

Thanks for the info ian.

Im will keep the thread updated.

One thing i did notice when up and down the street was how different the pedal feel was, The old system needed a good hard push and brakes came on more gradual, with the 4 pots the pedal will travel a bit further down but they lock up alot quicker.

Only time out on the road will find how the tyres cope.

[philg]

I got under the car today, tried messing on with compensator.

I have a little problem im not sure if its normal, when i jam the lever forward, ie bleeding brakes direction, if the nipples are not open i get a bit of a weep from the seal on the compensator, i can basically open it 3/4 of the way with no problems its just the last 1/4 to jam it when it starts to weep.

What do you think guys is a new one needed?

[Alex]

I can't imagine that's normal - mine certainly didn't do it when I last bled them

[philg]

I can't imagine that's normal - mine certainly didn't do it when I last bled them

It does not do it when bleeding, as the fluid is not under so much pressure when the nipples are open. Only when they are closed and i jam the compensator forwards, i suppose its just looking for the easiest place to escape.

[Alex]

Even prior to opening the nipples - just pusing the lever forwards there shouldn't be any leak I'd imagine

[philg]

Even prior to opening the nipples - just pusing the lever forwards there shouldn't be any leak I'd imagine

I agree, just wanted to check, probably a new one needed

[markey b]

I agree, just wanted to check, probably a new one needed

mine does the same

[philg]

mine does the same

I got one for about £70 markey so not to bad and it did improve the braking the pedal did not travel as far before they started to bite.

[Matt Cole]

Phil,

Any leaking of fluid form the braking system is a no go. Glad you fitted the new one.