RST With rear disc conversion pulls badly when braking hard

[Antti O]

Hi! I have sierra cosworth rear disc conversion completed wit all new parts. Only old part is std brake bias valves. Brake bias (front/rear) itself is spot on but car pulls right badly when i brake fast / hard, in slow and easy braking there is no problems. Ive got 290mm sierra cosworth front discs too and braided hoses. Car was in brake dyno and there brake balance in rear was also good and there was no any problems. I know car is very dangerous now. Do i have to change rear bias valves? My koni adjustables are now all set to same so the problem is not in shocks. Sorry my bad english.

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[jammerrs]

are they calipers not working on the left!?

[Antti O]

Originally Posted by jammerrs

are they calipers not working on the left!?

Calibers are new and all working fine

[orion_crazy_carl]

loose the standard bias valves, thats causing your problem!its unloading the the power from the back so the front is working harder so the back end goes light, u want more braking power to the rear wehn u have discs
IMO, loose the rear discs, there dangerous full stop!

[antony215]

Originally Posted by orion_crazy_carl

IMO, loose the rear discs, there dangerous full stop!

Id agree with that there such a pain in the arse for little difference imo the only upside to discs is they look pretty

Standard drums are just as good.

[Antti O]

Originally Posted by orion_crazy_carl

loose the standard bias valves, thats causing your problem!its unloading the the power from the back so the front is working harder so the back end goes light, u want more braking power to the rear wehn u have discs
IMO, loose the rear discs, there dangerous full stop!

I already sold std rear brakes..

But if i buy some proper rear bias valves and adjust them in same position? There is some valves in sale which have for example 7 different settings so i can adjust both sides in same.

[Karlos G]

If it's pulling badly to one side are you sure there is not a problem with one of the front brakes?
When my car did this it was because I had overfilled the gearbox with oil and it had come out the breather pipe all over my passenger side brake disc/caliper!!

[Antti O]

Originally Posted by Karlos G

If it's pulling badly to one side are you sure there is not a problem with one of the front brakes?
When my car did this it was because I had overfilled the gearbox with oil and it had come out the breather pipe all over my passenger side brake disc/caliper!!

wow, what a theory!

I have to check that

[JamboRS]

Originally Posted by orion_crazy_carl

loose the standard bias valves, thats causing your problem!its unloading the the power from the back so the front is working harder so the back end goes light, u want more braking power to the rear wehn u have discs
IMO, loose the rear discs, there dangerous full stop!

rear discs are dangerous???so why does every performance car come with rear discs and perform well??
its badly set up brakes that are dangerous,rear discs will out perform any brake drum set up if set up proper,that includes master cylinder which most people forget about

[Antti O]

Originally Posted by JamboRST

rear discs are dangerous???so why does every performance car come with rear discs and perform well??
its badly set up brakes that are dangerous,rear discs will out perform any brake drum set up if set up proper,that includes master cylinder which most people forget about

So whats problem with rs turbo master cylinder & disc brakes?

[orion_crazy_carl]

Originally Posted by JamboRST

rear discs are dangerous???so why does every performance car come with rear discs and perform well??
its badly set up brakes that are dangerous,rear discs will out perform any brake drum set up if set up proper,that includes master cylinder which most people forget about

from factory,yeah,abs set rear brakes,fine.
a rear light RST no abs,no, how can u set the rear discs up for every road type?
theres enuff storys on here of people crashing after converting to rear brakes, yeah, they might of needed setting up, but, it still happens!

[vroooom ptssssh]

Originally Posted by orion_crazy_carl

u want more braking power to the rear wehn u have discs

Actually, you want LESS power to the rear discs, think how much bias went to the original shoes, a lot to make them work....


mate, fit a bias valve, take some rear bias off and they will work fine

[Karlos G]

Or just fit some big fuck off brakes up front to ensure they lock up first!
Not forgetting that will make the back go light too though

[morph]

or jsut adjust the compensator valve so it gives less bias to the rear mate.

[rst in breaking]

when i had my escort on the road with my 6 pots and cossie rear discs i tested the brakes at around 130mph (emergancy stop) to see how good they were) mine stopped perfect with them with no skidding, admittedly the rear did start to get light eventually but braking hard at that speed id expect it lol

[NUTS RuS]

Do you have the rear load valves still on ?

[JamboRS]

Originally Posted by Antti O

So whats problem with rs turbo master cylinder & disc brakes?

nothing as std,its when its being asked to shift more fluid with 4 pots and rear discs that they cant cope

Originally Posted by orion_crazy_carl

from factory,yeah,abs set rear brakes,fine.
a rear light RST no abs,no, how can u set the rear discs up for every road type?
theres enuff storys on here of people crashing after converting to rear brakes, yeah, they might of needed setting up, but, it still happens!

the fact u cant even talk proper leads me to dismiss anythin u say,rear discs are not dangerous,FACT,numnuts that put rear discs then dont get them set up,either using bias valve or compensators are dangerous,im included in this as i done the slame,so through my mistake i learnt,thgats called experience in my book,u can set a bias valve up for wet and dry conditions or as most do compromise in between,but thats not proper set up as ur not gettin the most out them in wet/dry conditions

check this thread a while back,more to setting up brakes than what u think

http://passionford.com/forum/ford-es...al-set-up.html

Originally Posted by vroooom ptssssh

Actually, you want LESS power to the rear discs, think how much bias went to the original shoes, a lot to make them work....


mate, fit a bias valve, take some rear bias off and they will work fine

[vroooom ptssssh]

Which reminds me, before I start using my car, I NEED to REMEMBER and set up the bias valve

[NUTS RuS]

And remember a bias valve wont ever adjust bias.

All it does is increase or reduce pressure.

To shift bias you need a bias pedal box.

[makaveli96]

Hi, I’m looking to do a rear brake disc conversion soon I’ve almost bought everything needed but my question is will my rear brake compensator valves which were fitted last year so are near enough brand new be ok to adjust the rears?

[orion_crazy_carl]

Originally Posted by JamboRST

nothing as std,its when its being asked to shift more fluid with 4 pots and rear discs that they cant cope



the fact u cant even talk proper leads me to dismiss anythin u say,rear discs are not dangerous,FACT,numnuts that put rear discs then dont get them set up,either using bias valve or compensators are dangerous,im included in this as i done the slame,so through my mistake i learnt,thgats called experience in my book,u can set a bias valve up for wet and dry conditions or as most do compromise in between,but thats not proper set up as ur not gettin the most out them in wet/dry conditions

check this thread a while back,more to setting up brakes than what u think

http://passionford.com/forum/ford-es...al-set-up.html

talk proper guv init
numb nuts is 2 words!its compensator's
anything has a G on the end, dont should be spelt like don't , so dont say i cant write proper dude

[Antti O]

So i have to rebuilt brake lines because those are original diagonal. So i will buy one brake bias adjuster and set of new brake lines.

I comment when i have done that.

[JamboRS]

Originally Posted by orion_crazy_carl

talk proper guv init
numb nuts is 2 words!its compensator's
anything has a G on the end, dont should be spelt like don't , so dont say i cant write proper dude

least u understood mine
did i say write???i says talk
so no follow up to the dribble u wrote,thats ur best,carry on

[xr2wishy]

personally i'd just buy new adjustable bias valves and adjust till you've got it right.

[orion_crazy_carl]

Originally Posted by JamboRST

least u understood mine
did i say write???i says talk
so no follow up to the dribble u wrote,thats ur best,carry on

only just

what master cylinder can you use then?there's no direct replacement is there?

[morph]

Originally Posted by orion_crazy_carl

only just

what master cylinder can you use then?there's no direct replacement is there?

I cant see why you would need to go down the route of changing master cylinders to get the braking on the back right? that just doesn't make sense, when there are other easier methods!

[JamboRS]

Originally Posted by orion_crazy_carl

only just

what master cylinder can you use then?there's no direct replacement is there?

Originally Posted by morph

I cant see why you would need to go down the route of changing master cylinders to get the braking on the back right? that just doesn't make sense, when there are other easier methods!

there was 2 parts to that,highlighted below

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv vvvvvv

Originally Posted by Antti O
So whats problem with rs turbo master cylinder & disc brakes?
nothing as std,its when its being asked to shift more fluid with 4 pots and rear discs that they cant cope

the std master cylinder is shit with 4pots AND rear discs

out of interest what master cylinder does a 2wd cossie have in comparison to an rst ?????

[NUTS RuS]

Originally Posted by JamboRST

out of interest what master cylinder does a 2wd cossie have in comparison to an rst ?????

22.2mm bore master on the cossie
23.8mm bore master on the RST

The larger bore will shift more fluid than the smaller bore

The smaller bore will give you a stiffer pedal, but wont actually brake any better.

HTH

[JesseT]

Originally Posted by NUTS RuS

The smaller bore will give you a stiffer pedal, but wont actually brake any better.

HTH

You probably meant lighter.

[NUTS RuS]

No I meant what I typed

[morph]

Originally Posted by JamboRST

So whats problem with rs turbo master cylinder & disc brakes?
nothing as std,its when its being asked to shift more fluid with 4 pots and rear discs that they cant cope

the std master cylinder is shit with 4pots AND rear discs

out of interest what master cylinder does a 2wd cossie have in comparison to an rst ?????

I have 4pots with cossie rear discs and the setup is able to stop my car just like i want to and i can't see how the master cylinder is shit with them?
so what are you advising everyone to run?

[S2Dan]

The plan for mine was, if this will help, was to fit cossie stuff front and back. Losing the ABS and the rear compensators. And then to control and balance of the flow to the rears, use a bias valve on the rears, so effectively just having a permanent fixed pressure to the rears, rather then using weight varying compensators.

The secret to good braking with the rear disc conversion is balance. In my opinion the best way of achieving the balance on the rears is by means of a bias valve. As it’s a quick solution, although would recommend improved breaks up the front.

I think initial problems occur with the rear disk conversation if no attention is made to the fronts. As just fitting rears dicks without improving the fronts, will instantly increase the breaking percentage more then required before you’ve even started.

As for your problem of it pulling when breaking, check the calipers, just to make sure one aint sticking or some thing.

Good luck mate, and don’t be put off by the haters, they fear what they don’t understand.

Cheers

[JamboRS]

Originally Posted by morph

I have 4pots with cossie rear discs and the setup is able to stop my car just like i want to and i can't see how the master cylinder is shit with them?
so what are you advising everyone to run?

im not advising anything,im merely stating that a master cyl designed to run single pots fronts and rear drums is shit when running 4 pots and discs,a completely new braking system which the std master cyl was made for

[Rick]

Not if the 4 pot capacity doesn't differ greatly from the single pot on there now.

[Antti O]

Problem sorted now, just had to reduce rear braking power.

[Rick]

and how did you do that?

[Antti O]

Adjusted original bias valves in rear axle. Last night i drive it lot and it is fine&safe now but there is no so much braking power as earlier so i may next spring buy proper bias valve and make new brake lines to correct that.

[JesseT]

Originally Posted by NUTS RuS

No I meant what I typed

Could you please explain the reason, as this is on my mind completely against physics.

[Rick]

Well first you need to define stiffer!Does it mean you have to press the pedal harder/with more force to stop the car, or does it mean that the pedal requires more force to move it a certain travel?!

[Antti O]

Another year and same problem. I wish i never got into rear discs.
Now i have one brake circuit for fronts and one for rears and in the rear circuit there is wilwood valve with 59% max reducing going.
I have been thinking to replace stock rs turbo front cylinders with sierra cosworth 4 pot if that can help. I know those calibers are not cheap and not so easy to find.. but that rear brakes overpower drives me crazy and car is dangerous.

Now i have couple of questions:

1) Where i can get some cad pictures about those front brackets or who sells brackets?
2) Or is it better option to reduce rear brake disc size 273mm-> 253mm

ps.

If you read this and still plan to do rear disc conversion instead of working drums, DONT DO THAT.