Strange (but good) Brake Problem
  • Register
  • Help
Results 1 to 14 of 14
  1. #1
    Administrator
    mistareno's Avatar
    Join Date
    Nov 2002
    Location
    Melbourne
    Posts
    4,926

    Default Strange Brake Problem

    I drive my car reasonably hard, and have always felt that the brake pedal feel was just a touch to soft for my liking...until last weekend...

    I chucked a new set of rear springs (standard spring rate but lower) in the back of the Fuego and reset the proportioning valve to compensate for the reduced ride height...

    It felt pretty much the same but after a few hard high speed stops at DECA for some reason the pedal has come up noticebly and the pedal feel is fantastic...

    Advertisement


    There is no vibration or indication of brake binding and the car stops better than it ever has (and it has always stopped pretty well)

    I'm just a little concerned about why it has changed quite suddenly...

    The system has not been bled recently and the pedal felt no different after I adjusted the proportioning valve...

    Any Ideas?
    Last edited by mistareno; 17th November 2005 at 05:55 PM.

  2. #2
    Fellow Frogger!
    Join Date
    Aug 2005
    Location
    Athens, Greece
    Posts
    661

    Default

    Quote Originally Posted by mistareno
    I drive my car reasonably hard, and have always felt that the brake pedal feel was just a touch to soft for my liking...until last weekend...

    I chucked a new set of rear springs (standard spring rate but lower) in the back of the Fuego and reset the proportioning valve to compensate for the reduced ride height...

    It felt pretty much the same but after a few hard high speed stops at DECA for some reason the pedal has come up noticebly and the pedal feel is fantastic...

    There is no vibration or indication of brake binding and the car stops better than it ever has (and it has always stopped pretty well)

    I'm just a little concerned about why it has changed quite suddenly...

    The system has not been bled recently and the pedal felt no different after I adjusted the proportioning valve...

    Any Ideas?
    I have had the same thing happen to my 504 coupe after I lowered it and adjusted the brake proportioning valve. I took it on the hill to test the new supension and at the downhill portion the pedal feel improved significantly. The 504 sedan pedal felt low and spongy-then-stiff in comparison, even though it has the bigger STI pads so I took it to my brakes guy. He said that the servo mechanism has a fluid orifice that is quite narrow and it gets easily plugged. He cleaned it up and actually widened it a bit and now both 504's have great pedal feel. Both cars have Goodridge lines and you can actually FEEL the fluid pumping through. I think it is a bit puzzling that you experienced the same sequence of events, I do not understand WHY it happened and it may very well be coincidental, but it is a good thing to check if the brake pedal feels inconsistent. Sometimes it is hard to notiice because it is a gradual change and you only realize it after you drive another car without that problem.

    Thanos
    Last edited by Thanos; 17th November 2005 at 07:46 PM.

  3. #3
    1000+ Posts Haakon's Avatar
    Join Date
    May 2002
    Location
    canberra...
    Posts
    8,748

    Default

    Boiled the fluid from the hard stops? If the fluid is a bit old, it may have had moisture in it, but I cant think where it would go after heating the fluid. Very odd. Can only think that something was a bit blocked in the limiter valve that shaken loose from the hard use and the change in setting. I would imagine the little piston the valve would be sitting at a differnent point in the cylinder after adjustment. Maybe it is now sitting on a unworn part of the stroke and sealing better?
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

  4. #4
    Fellow Frogger!
    Join Date
    Oct 2003
    Location
    Hampton Park
    Posts
    523

    Default

    I had a 16 that had a cactus rear limiter and when it was replaced the brakes were firmer and felt completely different, it was amazing how much the rears do in stopping the vehicle.
    I think the car is doing a lot more braking on the rear wheels as the limiters are very conservative to prevent rear end lock up. the best way to adjust them is ease everything of until there is no liniting (and of course the back end locks up after hard braking) and then dial in small amounts of limit until there is just a hint of lock up under the most extreme stop.

  5. #5
    1000+ Posts alan moore's Avatar
    Join Date
    Oct 2001
    Location
    Ipswich, Queensland.
    Posts
    1,895

    Default

    I would put to you that at the circuit you pressed the brakes harder than you usually do, and amazingly (for a Fuego) the self adjusters have actually worked, and moved the shoes closer to the drum. Adjusting the rear brakes always brings the pedal up.
    '56 Renault 750 (16TS Power)
    '62 Renault Dauphine Gordini
    '89 Renault Alpine GTA V6 Turbo
    '08 Renault Megane sedan

  6. #6
    Administrator
    mistareno's Avatar
    Join Date
    Nov 2002
    Location
    Melbourne
    Posts
    4,926

    Default

    Quote Originally Posted by alan moore
    I would put to you that at the circuit you pressed the brakes harder than you usually do, and amazingly (for a Fuego) the self adjusters have actually worked, and moved the shoes closer to the drum. Adjusting the rear brakes always brings the pedal up.
    I generally brake pretty hard if I'm driving 'enthusiastically'...

    I know the feel of the brakes when the rears are adjusted very tightly and this is different. The handbrake appears to have the same amount of travel as before which would indicate that the static adjustment on the rear shoes hasn't changed...

    It almost feels like the pads are just biting earlier?

    Hmmm... As I typed that, I just remembered something...

    When I removed the pads for inspection, I noticed that they had a thin layer of rubbery stuff on the backing plate (anti rattle perhaps?)

    It looked a bit soft and I was worried that the high temps might make it melt so I scraped it all off...

    I wonder if it has lost that slight layer of 'compressibility' and now has a more positive mechanical connection between pedal and pad?

    Hmmm... I might throw in an old set of pads I've got and see if they feel the same...

  7. #7
    Fellow Frogger!
    Join Date
    Aug 2005
    Location
    Athens, Greece
    Posts
    661

    Default

    Quote Originally Posted by mistareno
    I generally brake pretty hard if I'm driving 'enthusiastically'...

    I know the feel of the brakes when the rears are adjusted very tightly and this is different. The handbrake appears to have the same amount of travel as before which would indicate that the static adjustment on the rear shoes hasn't changed...

    It almost feels like the pads are just biting earlier?

    Hmmm... As I typed that, I just remembered something...

    When I removed the pads for inspection, I noticed that they had a thin layer of rubbery stuff on the backing plate (anti rattle perhaps?)

    It looked a bit soft and I was worried that the high temps might make it melt so I scraped it all off...

    I wonder if it has lost that slight layer of 'compressibility' and now has a more positive mechanical connection between pedal and pad?

    Hmmm... I might throw in an old set of pads I've got and see if they feel the same...
    Okay, but how would this make the pedal higher? And I agree with you, if you drive enthusiastically there is no difference between braking in the street and braking in the track. There is something else at play, i am sure you have enough miles under your belt to tell if it was just adjustment. It has to be something less obvious.

    As for compressibility, it is more due to heated gases than softer pad backing material. At the braking pressures involvrd, the elasticity of the backing material gets absorbed in fractions of a second, too quick to feel.

    Thanos

  8. #8
    Administrator
    mistareno's Avatar
    Join Date
    Nov 2002
    Location
    Melbourne
    Posts
    4,926

    Default

    Quote Originally Posted by Thanos
    Okay, but how would this make the pedal higher?

    As for compressibility, it is more due to heated gases than softer pad backing material. At the braking pressures involvrd, the elasticity of the backing material gets absorbed in fractions of a second, too quick to feel.

    Thanos
    Think about it...The brake pad material is very hard and not very compressible (the compression force goes through the pad into the disc to slow the car down)

    Even 1 mm of freeplay can cause the pedal to drop very low (Think of how many pumps of the brakes is required to move the caliper a few mm after a brake pad change for example) it wouldn't take all that much to add an extra 10mm to pedal travel...

    If the first 10 mm of pedal travel was mainly just compressing the rubbery backing material then removal of the material would bring the effective pedal height up 10mm. It would also expain the slightly spongy pedal feel...

    I'll try an old set of pads on the weekend (hopefully they have the becking material)

  9. #9
    1000+ Posts dogboy's Avatar
    Join Date
    Sep 2001
    Location
    melbourne,victoria,australia
    Posts
    1,332

    Default 504 brake proportioning valve..brakes binding

    problem with a 504 brake proportioning valve that was rebuilt 3 years ago..it seems the brakes are binding a little.... Is there a cure? any ideas what would cause this?
    Thanks brains trust....
    Rev. Dogboy


    1969 DS21 Pallas BVH with leather
    1970 Renault 16TS
    1967 Honda S800 cabrio
    Citroen 1970 DS21 Cabrio replica
    Citroen 1966 ID Safari (with 23 running gear)
    Citroen 1975 DS23 Safari
    1975 VW Kombi poptop
    1987 2CV
    Porsche Boxster S manual
    1988 Vespa PX200E

  10. #10
    1000+ Posts jo proffi's Avatar
    Join Date
    May 2003
    Location
    sydney
    Posts
    8,396

    Default

    Hmm. Interesting.
    I'd forgotten that you have disks on the back.

    Some background questions.

    Did you stick a gauge on the rear brakes and measure the proportioning valve cuttoff pressure at each wheel???

    or

    Did you manage to get both rears to lock then wind it back so both rears didn't??


    Considering the bottom valve has a propensity to jam (manifest in the rear left locking up) I wonder if you can rule out that possibility?

    IF it was jamming open, and the high pressure with possibly fast attack seen on the track has freed it up, then maybe what pressure was going to the back left is now not doing so as the valve functions properly.

    My undrstanding of how the valve works is that if you hit the pedal hard and fast, it wont matter if the end of the pipe was open to free air with no brakes attached(or had squishy backing material on the pad), it will still slam shut at whatever threshold you have set and the remaining pressure/pedal travel will be put into the front brakes.

    I think if you realy want to know whats happening down there, you need to get a pressure gauge in place of the bleed nipple.

    Jo

  11. #11
    1000+ Posts dogboy's Avatar
    Join Date
    Sep 2001
    Location
    melbourne,victoria,australia
    Posts
    1,332

    Default

    Quote Originally Posted by jo proffi View Post
    Hmm. Interesting.
    I'd forgotten that you have disks on the back.

    Some background questions.

    Did you stick a gauge on the rear brakes and measure the proportioning valve cuttoff pressure at each wheel???

    or

    Did you manage to get both rears to lock then wind it back so both rears didn't??


    Considering the bottom valve has a propensity to jam (manifest in the rear left locking up) I wonder if you can rule out that possibility?

    IF it was jamming open, and the high pressure with possibly fast attack seen on the track has freed it up, then maybe what pressure was going to the back left is now not doing so as the valve functions properly.

    My undrstanding of how the valve works is that if you hit the pedal hard and fast, it wont matter if the end of the pipe was open to free air with no brakes attached(or had squishy backing material on the pad), it will still slam shut at whatever threshold you have set and the remaining pressure/pedal travel will be put into the front brakes.

    I think if you realy want to know whats happening down there, you need to get a pressure gauge in place of the bleed nipple.

    Jo
    Problem might be solved
    took all wheels off and brake dust not escaping and building up causing calipers to stick !!
    Rev. Dogboy


    1969 DS21 Pallas BVH with leather
    1970 Renault 16TS
    1967 Honda S800 cabrio
    Citroen 1970 DS21 Cabrio replica
    Citroen 1966 ID Safari (with 23 running gear)
    Citroen 1975 DS23 Safari
    1975 VW Kombi poptop
    1987 2CV
    Porsche Boxster S manual
    1988 Vespa PX200E

  12. #12
    1000+ Posts jo proffi's Avatar
    Join Date
    May 2003
    Location
    sydney
    Posts
    8,396

    Default

    Ah Derr.....I just realised how old this thread was.



    Jo

  13. #13
    1000+ Posts jo proffi's Avatar
    Join Date
    May 2003
    Location
    sydney
    Posts
    8,396

    Default

    Quote Originally Posted by dogboy View Post
    Problem might be solved
    took all wheels off and brake dust not escaping and building up causing calipers to stick !!

    I was actually replying to mistareno's original thread.


    Tempted to delete my reply, but someone will surely have fuego proportioning valve issues in future so might gain some insight from it.
    As you were.

    Jo

  14. #14
    Fellow Frogger! Uffee's Avatar
    Join Date
    Oct 2004
    Location
    Adelaide
    Posts
    651

    Default

    Quote Originally Posted by Thanos View Post
    The 504 sedan pedal felt low and spongy-then-stiff in comparison
    I've had exactly the same thing, the brake pedal on my coupe had always been spongy. I just put it down to the single master cylinder as it was the first of it's type I'd used. The car sat for a bit and the rear proportioning valve and both of the rear calipers were seized (fun to diagnose) and once all were free the pedal is now nice and stiff.
    504 GL Coupe '73 Silver
    504 GTDT Pickup Mini-Motorhome '83 Coral Red
    407 HDi Sedan '05

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •