Brake pedal travel

[phillpot]

Done a bit of a brake rebiuld recently, 278mm discs, Goodridge flexi's etc.

Brakes undoubtabley work but despite loads of bleeding (pedal won't "pump up")have more pedal travel than I would like !

My theory : bigger pistons in calipers require more fluid to move so more pedal movement ? Another theory I was offered was along the lines of bigger pad area requires more pressure hence more movement ? anyone had similar when upgrading brakes, agree with theory, have other ideas ? ?

[NorfolkSteve]

Yes, if you have fitted calipers with larger diameter pistons then more fluid will have to be moved to displace the pistons. If you have the same diameter master cylinder then you will have to move the pedal further. Also, you will need less effort at the pedal for the same force at the pistons.

[phillpot]

Thanks for confirming my thoughts !
Now have heard of XR2 servo's being fitted as replacements, is this complete with master cylinder or does Saab one go back on ( and are they different bores ) ?

Advice from anyone who's done this would be much appreciated

[mep12345]

The updated design for the S had the Ford Fiesta Servo (it is the same for all Mk 3 Fiesta models I believe) with the XR2i (22.2mm diameter bore) master cylinder (Other Fiesta models are 20.6mm bore). Therefore to change the saab servo I believe you need to upgrade to the later design with the Ford master cylinder as well one.

My S3 originally had the Ford fit and still does although I have upgraded to 260mm discs and also have a slightly longer pedal travel it is acceptable. I will shortkly be replacing the servo and MC with better uncorroded examples.

HTH

Mark

[phillpot]

Certainly does help, thanks Mark.

Am presuming that because reservoir is marked Saab, cylinder and servo are Saab !
Worded last response bit wrong, only looking to change servo if neccessary to fit Fiesta cyl. Servo seems fine so Fiesta master cyl. will fit onto Saab servo ?

One final question, presume would use complete with "attached" fluid reservoir and junk the remote one complete with pipes that run very close to exhaust !

Edited by phillpot on Wednesday 29th April 22:25

[Gerald-TVR]

Good 'ol Richard answered all your queries here

[phillpot]

Excellent Help and advise for anyone looking to replace faulty/worn components !

However doesn't realy sort my problem as both master cylinders,
if I'm getting this right, are 22.2 mm bore and to compensate for bigger caliper pistons I need a bigger one ?

Edited by phillpot on Thursday 30th April 07:58

[Barkychoc]

I am not so sure about the bigger master cylinder - on the V8S it has the same size 240mm front brakes as all other S's - it just has rear discs instead of drums which I think is the reason for the MC change.

I have also upgraded to 260mm discs - which have a 60mm piston front caliper (original 54mm I think) - I believe this is the same caliper piston size as the bigger front brakes - and I can't even tell the difference with the brake pedal movement.

What are you using to bleed the brakes?

I used an eezibleed kit and had to bleed my brakes from empty as I replaced all pipes, and didn't have a problem getting the air out.

I suspect if it is as worrying as you say that you may still have some air in there.

[phillpot]

Used an "easibleed" but maybe still little air in there somewhere ? Will try bleed again at weekend now everything settled in.
One "problem" with Goodridge hoses is don't think you can clamp them like rubber hoses to try and pin point which part of system may be holding air.

Bleeding again got to be easiest (and cheapest) first option

[Barkychoc]

Buy a large container of brake fluid and flush loads through to see if you can shift it.
Have you also bled the rear circuit?

[tozerman]

phillpot said:

Done a bit of a brake rebiuld recently, 278mm discs, Goodridge flexi's etc.

Brakes undoubtabley work but despite loads of bleeding (pedal won't "pump up")have more pedal travel than I would like !

My theory : bigger pistons in calipers require more fluid to move so more pedal movement ? Another theory I was offered was along the lines of bigger pad area requires more pressure hence more movement ? anyone had similar when upgrading brakes, agree with theory, have other ideas ? ?

Hi Mike, I recently upgraded my front brakes to 278mm discs and escort cosworth calipers, once I had fitted the kit I also found there was a lot of pedal travel. I bled the whole system twice to make sure there was no air in the system which didn't make any difference at all.
What I did was to adjust the rear brake shoes manually (overiding the auto adjusters) to take up as much slack as possible without causing any binding. That cured my problem, I now have a firm pedal and brakes that will stop a speeding train on a sixpence.
cheers.....Tony..

[phillpot]

Yeah, whole system bled (new flexi's and wheel cyls at rear)loads of fluid gone through, sure all old now gone,unless balance valve thingy causing some sort of problem ?
Rear adjusters cleaned up and "Copper slipped" but manually tweaking up a bit sounds good idea, will try at weekend or even this evening if rain ever stops !

Thanks guys

Edited by phillpot on Thursday 30th April 14:19

[z_chromozone]

tozerman said:

phillpot said:

Done a bit of a brake rebiuld recently, 278mm discs, Goodridge flexi's etc.

Brakes undoubtabley work but despite loads of bleeding (pedal won't "pump up")have more pedal travel than I would like !

My theory : bigger pistons in calipers require more fluid to move so more pedal movement ? Another theory I was offered was along the lines of bigger pad area requires more pressure hence more movement ? anyone had similar when upgrading brakes, agree with theory, have other ideas ? ?

Hi Mike, I recently upgraded my front brakes to 278mm discs and escort cosworth calipers, once I had fitted the kit I also found there was a lot of pedal travel. I bled the whole system twice to make sure there was no air in the system which didn't make any difference at all.
What I did was to adjust the rear brake shoes manually (overiding the auto adjusters) to take up as much slack as possible without causing any binding. That cured my problem, I now have a firm pedal and brakes that will stop a speeding train on a sixpence.
cheers.....Tony..

I have Cosworth brakes on the front of my v8s, with 278mm disks. The calipers were much larger, but the pedal is rock solid and the travel no more (in my experience), than before. It sounds like you have an air lock. To get rid of the air from mine I removed the calipers from the car and gave them a shake / rotated them to ensure any pesky bubbles had been removed. Prior to doing this the pedal was on the floor.

Z