Spongy Brakes
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Thread: Spongy Brakes

  1. #1
    Tadpole
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    Default Spongy Brakes

    Need some expert advice on brakes, my mates 206 GTi suffers from spongy brakes, well actually his pedal goes right down to the carpet, but only in corners.
    He has had the system bled for air 3 times, changed the master cylinder, checked for leaks in the lines and hoses and cleaned up the ABS sensors on each wheel, with no luck!
    The only things he hasn't changed are the ABS pump and brake servo, he's even tried disconnecting the ABS, which by the way is a big NO NO, but still the same when cornering and braking the pedal goes to the ground.
    Any ideas?

    Cheers

    7

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  2. #2
    1000+ Posts Gamma's Avatar
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    A more detailed description is required.

    How hard do you have to press the pedal.
    Does the brake fail when cornering or does it just go spongy.
    What is the condition of the flexible lines and are they routed correctly.
    Does it pull to one side.
    Is it Ok in a straight line.
    Does the pedal assembly flex when cornering and is it bolted in place.

    Funky problem for the pros.
    Last edited by Gamma; 9th March 2005 at 03:25 PM. Reason: speelink
    /// 1986 SII 505 GTI
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  3. #3
    Gone Fishin' Ray Bell's Avatar
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    Sounds like pad knockback from a crook wheel bearing...

  4. #4
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    I agree with Ray Bell, Knock back happens with the disc moves within the capilar and opens up the pads, usally through a bad bearing, in older cars with diffs there are other causes too.
    You say the pedel travels to the floor, is this only on the first stroke then the pedel feels normal again??? if so thats your problem.
    It its spongey all the time i would suggest you have air in the lines, but you say you have bled the brakes.

  5. #5
    Gone Fishin' Ray Bell's Avatar
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    Nice to have someone agree with me for a change!

  6. #6
    Tadpole
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    He's had the front bearings changed a couple of days ago. But still the problem is there, it happens in corners and yes the first application goes to the floor then on the 2nd everything is fine.
    Cheers for the input anything else would be great! Got to find somthing wrong with it.
    He runs 180RC calipers and Tarox G88 discs with Ferodo DS2500, it only started a couple weeks ago.

    Cheers

    7

  7. #7
    Gone Fishin' Ray Bell's Avatar
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    Is there a chance the pads aren't sitting correctly in the calipers?

  8. #8
    Tadpole
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    I doubt it but everything is worth a try, he's that desperate.
    7

    Quote Originally Posted by Ray Bell
    Is there a chance the pads aren't sitting correctly in the calipers?

  9. #9
    Gone Fishin' Ray Bell's Avatar
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    I thought it was only one pump from bad to good?

    You should have driven some of the stuff I have over the years!

  10. #10
    1000+ Posts tekkie's Avatar
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    Quote Originally Posted by Seven
    He's had the front bearings changed a couple of days ago. But still the problem is there, it happens in corners and yes the first application goes to the floor then on the 2nd everything is fine.
    Cheers for the input anything else would be great! Got to find somthing wrong with it.
    He runs 180RC calipers and Tarox G88 discs with Ferodo DS2500, it only started a couple weeks ago.

    Cheers

    7
    Did this problem start when he changed the calipers?
    I would assume that the RC calipers have larger pistons (or more of them) therefore requiring larger volume of liquid to exert the same pressure. But the master cylinder I assume is still the same?
    Compare the MC from the RC and normal GTi for bore size and overall volume.

    another problem you may be facing (apart from those aleady discussed) is the case of poorly adjusted either handbrake or caliper guides which do not float freely. That way you have to push the pad much futher than normal on 1st application. Then after certain time unused, the pad will "wonder" away from the disc again.

    or its badly bled system. Has the same person bled the system each time?
    .
    1300cc's of jap buzzbox delivered the times below.

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  11. #11
    Tadpole
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    Hi everyone and I see Hot_Pug is there!

    I am the poor sod who has been experiencing this strange weird problem which is really annoying me.

    Just go over some of the main points incase Seven left something out so everything is laid out for all to consider.

    Car uses 307 calipers (direct bolt on with no custom made bridge or bolts), 283mm discs with correct offset and DS2500 pads. The 307 pads dont use springs but a thin blade that slots and sits neatly into the 307 calipers. Front pads have a good 9mm with rear on 2mm soon to be replaced. Calipers have been on the car for nearly a year now and discs has hardly worn down. Pads have worn down a tiny bit but why only after a corner is the repeated question in my mind.

    Brake hoses are braided from Goodridge, no protective outer cover but no signs of damage. Checked all hoses and wiped down with white tissue no marks whatever.

    Checked all steel lines from master cylinder to all four wheels. Nothing is damaged and all looks well, all paint is intact on all lines.

    Suspension has been replaced with Bilstein B6 sport. Top bearing mounts along with rubber tops have been replaced. All caliper and suspension mounting bolts have been replaced with new OE parts.

    Front LHS wheel bearing was found to be worn. Thus changed the whole arm with wheel bearing and hub for a small fortune. Rear bearing on arm was found worn and replaced both with new seal.

    Four new tires which have been run in nicely, currently run A048 on 195/50R15 on 28psi.

    Now the problem only started about a month ago when my mate asked me if I had this issue with the brakes. I said no but after another week started to notice his problem so thank u for that! It wasnít as bad before but the deep pedal travel is more noticeable after fast driving with small bends or hard cornering. Apply brakes and the pedal goes to the CARPET which is very worrying. If I quickly reapply the brakes once the bite is there again and stops about 2/3 down on travel. Iíve tried the car without ABS but removing the fuses the problem remains. The brake fluid has been flushed twice once by air suction other manually by TWO diff shops. Brakes felt great but the fact is the brake pedal is spongy and not normal. My third shop bleed the master cylinder and said AIR was still in the system so something is leaking in air? No loose of brake fluid from what I can see. Use ATE TYP200 dot 4. With the engine started and me pumping the brakes I can hear a metal noise from the rear brakes. Asked the shop what that was n they commented its normal n from the cable. Maybe the rear pads n cable r causing the problem?

    Iíve been to FOUR garages and none can tell me what the problem is. My mate had both front bearings changed to no avail. He did comment that after changing his braided brake hoses for OE ones the problem was not so apparent but still present. His problem finally went away when he totaled his car so no more for him but thatís not an option for me. I thought the problem would be the brake servo but if that went pedal would be rock hard. I will test the servo by sucking n blowing into the vacuum line to see if its leaking air inside. Iíve checked the housing for the brake pedal and everything is secure with nothing loose.

    I note that some say it could be pad knock back. If so could such cause that much of an increase in pedal travel? I know that by jacking up the car I could check the bearings but not the force that is caused by cornering hard. Any other way I could check the wheel bearings for wear? My car is driven daily and its fast road mostly which has covered 96,000milesÖyes 96,000miles in just under 5yrs! I would sell the car but would prefer to keep it as a roundabout if n when I get another car.

    Thanks for the input guys! I really need all possible causes as changing part after part to no avail is making me very poor!

    Update:

    Sorrie I am brainstorming and editing this post like mad. Just a thought here. Could I put the car on on a lift take off both front wheels and then drive car as normal. Take a pretend corner then brake to see if no road contact would still cause the same deep pedal? If so, I could narrow it down to maybe the braided hoses as there is not side movement for any fluid or air to travel around right???

    James
    p.s.
    Sorrie for the LONG boring post but I need help asap.
    Last edited by jc_333; 9th March 2005 at 06:10 PM.

  12. #12
    Gone Fishin' Ray Bell's Avatar
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    Yes, definitely, pad knockback can cause that much travel...

    Think about it... your master cylinder diameter is probably around 20mm... each piston on the calipers is probably 40mm, and there are how many of them? If I read this right, there might be 4 or 8.

    Calculate the area of a 20mm circle, then compare it to a 40mm circle's area... then multiply the latter by the number of pistons... you'll see how it works out. 1mm pad knockback on each side would be fatal, methinks.

  13. #13
    Tadpole
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    Hi Ray

    Thanks for reading my long boring post.

    I shall look into this pad knockback but first might get the car on the lift and try to duplicate the problem. If it doesnt give the deep travel then it could very well be the pad knock back so I need three new wheel bearings to replace...pricey!

    Its strange as I've spoken to three mates whos cars are nearer the 100,000mile mark...maybe wear n tear on the bearings.

    Thanks

    J

    Quote Originally Posted by Ray Bell
    Yes, definitely, pad knockback can cause that much travel...

    Think about it... your master cylinder diameter is probably around 20mm... each piston on the calipers is probably 40mm, and there are how many of them? If I read this right, there might be 4 or 8.

    Calculate the area of a 20mm circle, then compare it to a 40mm circle's area... then multiply the latter by the number of pistons... you'll see how it works out. 1mm pad knockback on each side would be fatal, methinks.

  14. #14
    1000+ Posts tekkie's Avatar
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    Quote Originally Posted by Ray Bell
    Yes, definitely, pad knockback can cause that much travel...
    are you describing the thing I mentioned about t he pad "wondering" away from rotor? (if so - I never knew the proper name for it)
    .
    1300cc's of jap buzzbox delivered the times below.

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  15. #15
    Gone Fishin' Ray Bell's Avatar
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    Ya gotta hang around in some pretty evil circles to know these things...

  16. #16
    Tadpole
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    Cheers Ray!
    The brakes are on hold for JC at the moment, he has other problems such as a uprated fuel pump which is more content in flooding petrol at the tank seal
    7

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