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Last week, I've changed a stock 22.5 mm master cylinder to 25mm Master Cyliner (E32,750iL). I took the car(85 GTV6) to local Brake sepecialist and they did it for me.

when I pick up the car that afternoon, I've realised that they took out proportioning valve and did't refit it. they said I don't need a propotioning valve and it does not do anything.

Generally happy with feel of brake pedal and distance it traveled but I could not able to lock up the wheels and I have to press a brake pedal harder to stop.

Is it because I don't have a proportioning valve any more? Should I refit it?

Any comment will be appreciated.

Nope,ita because you have probably reduced brake force by fitting the 25mm master...
Give me some data on your conversion,what discs,calipers??
Once you can get enough brake force to lock up either front or rear,the p/valve comes into the picture

Finally,

Thanks barry

My brake system is original 85 GTV6(except steel braided hose) so far. I thought first step for brake upgrade is bigger master cylinder then bigger brake conversion later.

I re-bleeded all calipers last saturday and manage to lock front brake only. I have to press a pedal harder but I can lock the brake with much less distance travel of brake pedal. Before this modification, I have to press a brake pedal all the way to the floor to lock the brake.

Do you think I still better to have a proportioning valve?

J,I think you might have a problem here,The 25mm master on std setup is moving in the wrong way-UNLESS,as you say,you are fitting larger DISPLACEMENT capacity calipers,ie: bigger 4 pots,6 pots etc..
Alot has been said on this topic right here.Go back and check out what the guys are ,or have done..Mike Harris(he of mmwec fame...)and myself have posted loads on the subject.

Getting back to the problem I mentioned,It is imperitive that when you bleed the system,your handbrake is fully released..
The two rear calipers have handbrake levers,one on each.
These MUST be in the neutral position with the handbrake cable adjusted correctly.The levers must be against thier stops.
A lot of guys adjust the cable such that the levers are floating off the stops.This takes up piston displacement and your rear setup will never work as designed..
Bleed the rear calipers from the insides out.First the inner on one caliper,then the outer.Then move to the other cal.
Forget about feeler gauges to set up the clearance on the pads,use feel by turning the wheel while adjusting the pads...I have posted this elsewhere...
Im assuming that a moron worked on your car,NOT you.....ok?Are the bleed nipples on the front cal`s` facing upwards??Dont laugh,Ive had it many times ,even on professional race teams!!
Dont bang down on the brake pedal when bleeding the system,this causes the press.limmiter to lock solid and no fluid flows to the rear al`s..
Go back to your original master for the std system...Go bigger once you have fitted those f40 calipers you have in the garage..
Is your original master assembled correcty,seals facing the correct way..etc...

Let us know what you find and keep updating,ok?

Barry wrote:The two rear calipers have handbrake levers,one on each.
These MUST be in the neutral position with the handbrake cable adjusted correctly.The levers must be against thier stops.
Do you mean they should touch the'r stopers on the calipers ?
Bleed the rear calipers from the insides out.First the inner on one caliper,then the outer.Then move to the other cal.

When bleeding the hole system, should I start with right side rear caliper, then left rear, right front, and finaly left front ?

the bleed nipples on the front cal`s` facing upwards??Dont laugh,Ive had it many times ,even on professional race teams!!

Can you explain what you mean by that ? and in any position they are from factory, why should they turn around if not taking them out ?

Dont bang down on the brake pedal when bleeding the system,this causes the press.limmiter to lock solid and no fluid flows to the rear al`s.

should be gentle pressing the pedal slower ?

Dear Barry and jisop! sorry for taking advantage of this to my own questions and bad english understanding

Yes,definatly..If they are not touching the stoppers,it means the pistons have already moved,taking up displacement..must be against the stoppers...

Does not matter which ide,but you must start with the rear-the first section in the master to start working is for the rear brakes..

You are dead right,the only way the nipples can turn aroundis when the caliprs have been fitted wrongly-left to right and right to left-As I said,we have had top race teams doing this and wondering why they could not get brakes....ok,a single team once...

Yes,nice slow even pressure strokes-come on,you know what Im talking about here.................................................................................................................!



J,fit the valve again..it does work -I personally have fitted a Berlina valve,modifid to adjust it.The best though is to use a Tlton,A.P or simmilar valve...

Appriciate you Help

BTW - can you tell me what size of MC should I use with front Brembo 4 pot calipers with size 0f 40 and 45 mm Pistons ?(calipers from a TVR )

Brake Rotors size will be 284 mm from 4 cylinders fiat coupe and rear brakes will be originals with SZ rotors.

Yes,Now you use your 25mm master...its what im using with Brembo 4 pots,same piston size..

Let me know how it goes..

Barry wrote:Yes,Now you use your 25mm master...its what im using with Brembo 4 pots,same piston size..

Let me know how it goes..

Will a 23.6 mm ATE MC works ?

From wich car Should I take the 25mm's ? is it perfect fit ?

Thanks Barry.

I will take my car to local brake specialist tomorrow to refit a Proportional valve. But I will keep 25mm MC and start look for 4 pots calipers on ebay.

I've read about so many brake upgrade in this forum. which upgrade is the most bolt on upgrade which required less modification?

Maybe Volvo 240 series Caliper????

Hey Jisop the volvo 240 girling calipers will bolt on your gtv(6) spindle fine and they are a very economical caliper i got mine for $50 for the pair from the wreckers and they've been fine so far but..............
even tho' these calipers bolt on ok with the stock gtv6 vented discs the brake pad will sit a few mm above the disc i believe an SZ disc (same thickness but greater diameter) will fit perfectly with these calipers(prob very expensive to get in australia)
These calipers weigh heaps too
guess it all depends on how much you want to spend$$$$$$$$ This is a low cost option but not perfect

I went thru the excercise of differing masters-started with 23mm,24mm..finally ended up using 25mm..check out topic,i explained all there.
My current master is of an Isuzu pickup,modified to fit..Also got a Japanese Tokico 1" master that worked very well..

Barry,

Is my brake caliper on wrong side?

No,they all look good...Bleed nipple is up top...
I would suggest pulling them off and reconditioning them,from the looks of them,new kits and a clean can go a long way..

Bleed nipples look good all right.

For gods sake, put in some brake pads!! They look totally worn out. A sure way to f.ck up the brakes.