JoaoCaldeira
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 posted on 12/11/09 at 04:23 PM |
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Why are brakes braking?
Hi.
I have the following problem:
Sunday I went to a trackday. 3 x half an hour, separeted by 1,5 hours brake.
It was a more or less rainny day.
In the last run, after 4 or 5 laps, the car felted sluggish; it just didn't accelerate like it used.
I went to paddock and found front brakes smelling quite a lot, wheels' centre felt really hot, and bleed valves showed humidity around'em.
There were fumes exiting the callipers.
Reservoir was still full.
I went to the trailer, not before kicking quite hard 2 or 3 times the brakes. After that they felt loose again.
As it was raining, the brake into corners was quite gentle compared to the dry days, where I really hit the brakes in the last few meters.
My setup is
Remote double reservoir
Double master cylinders (front / rear) - Wilwood
Brake bias bar
MNR pedal box
Any comments on what could have happened?
Thanks in advance,
Joao
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Bluemoon
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| posted on 12/11/09 at 04:31 PM |
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Brake hoses gone soft? I believe they can breakdown and work like a one way valve (don't know if there is truth in this)??
Dan
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Steve G
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| posted on 12/11/09 at 04:41 PM |
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Was that one brake or all of them?? Sounds like they are binding for some reason - maybe the master cylinder isnt returning and allowing the calipers
to release properly.
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BenB
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| posted on 12/11/09 at 04:43 PM |
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Brakes overheated and boiled the fluid?!!?
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JoaoCaldeira
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| posted on 12/11/09 at 04:51 PM |
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quote:
Originally posted by Steve G
Was that one brake or all of them?? Sounds like they are binding for some reason - maybe the master cylinder isnt returning and allowing the calipers
to release properly.
Both front brakes were smelling and feeling / looking very hot.
Actually the reservoir was a bit above of "Full" mark, as I was thinking about bleeding the brakes on the track (though they were bled
twice already).
Why did it started returning, then?
I'll check master cylinders.
Thanks,
Joao
edited: reservoir was full, not master cylinder
[Edited on 09/11/12 by JoaoCaldeira]
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JoaoCaldeira
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| posted on 12/11/09 at 04:52 PM |
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quote:
Originally posted by BenB
Brakes overheated and boiled the fluid?!!?
I believe so, but what was the initial cause? They were running fine for a full session, and this happened after a few laps...
Thanks,
Joao
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Steve G
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| posted on 12/11/09 at 05:02 PM |
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Overfilling the master cylinder reservoir could well be the problem i guess. I'd try a quick pedal press on each caliper with a bleed hose on to
release any pressure and push the excess fluid through and see how they go.
It doesnt take much pressure there to cause them to start to overheat - and the warmer they get the more thermal expansion of the disk will make the
problem worse.
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Phil.J
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| posted on 12/11/09 at 05:15 PM |
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Possibly not enough free play in the pedal, I've seen this before, initially OK then start to bind.
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theconrodkid
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| posted on 12/11/09 at 05:37 PM |
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discs get hot and expand,fluid boils and expands?
give the pedal some more clearance and try racing brake fluid.
depending on what type of wheel bearings you have,you can slacken them off a little to allow the disc to push the pads back a bit more.
who cares who wins
pass the pork pies
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britishtrident
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| posted on 12/11/09 at 06:17 PM |
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Very simple --- I have covered this prpblem at least a dozen times.
Master cylinder piston is not coming fully back.
If the piston dosen't come fully back even by as little 0.5mm the port which allows the the master cylinder bore to vent to the resevoir is
covered by the piston and sealed off.
If the master cylinder bore is shut off from the resevoir when the brakes warm up the fluid expands and the excess fluid cannot vent back to the
resevoir as a result the hydraulic pressure increases forceing the pads on to the disc.
As a result more heated is generated the fluid expands more and the cycle continues untill the brakes jam solid.
The usual causes is either the master cylinder pushrods are too long (there is a lot of bad info on setting dual pedal boxes out on the web) or
washer under the wirclip at the end of the mastercylinder is fouling the the mushromm end of the pushrod.
[Edited on 12/11/09 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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BenB
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| posted on 12/11/09 at 08:37 PM |
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It could be a non-releasing MC. If the brakes got too hot the fluid would boil and expand, pressing the pads against the disc, thereby worsening the
problem etc etc etc. But it's a question of why (if this is what happened) the brakes got too hot in the first place... Were you doing heal+toe?
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JoaoCaldeira
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| posted on 12/11/09 at 08:41 PM |
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quote:
Originally posted by britishtrident
Very simple --- I have covered this prpblem at least a dozen times.
Very very interesting.
I'll have to digg a bit more on car's setup.
I've shortened the pushrods a bit to suit my pedal box's position, but even so I think they coiuld be shorter...
And I'll have to check that circlip...
Cheers,
Joao
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JoaoCaldeira
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| posted on 12/11/09 at 08:44 PM |
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quote:
Originally posted by BenB
It could be a non-releasing MC.
Humm... Actually, the pedal felt different during the time the brakes where locked... light... lighter... if one MC was stuck I would be feeling half
of the pressure... But then again... it was a bit in a rush, and in the middle of a trackday, where everything is felt differently...
quote:
Originally posted by BenB
Were you doing heal+toe?
Nope, and not even braking really hard (first rainny day event i got! )
Joao
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t16turbotone
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| posted on 13/11/09 at 07:42 AM |
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i had exactly the same proplem...turned out to be what british trident has already said....master cylinder wasnt returning far enough.
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britishtrident
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| posted on 15/11/09 at 06:47 PM |
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quote:
Originally posted by BenB
It could be a non-releasing MC. If the brakes got too hot the fluid would boil and expand, pressing the pads against the disc, thereby worsening the
problem etc etc etc. But it's a question of why (if this is what happened) the brakes got too hot in the first place... Were you doing heal+toe?
The brakes don't need to get too hot to cause the problem in normal use they will get warm and the fluid will expand enough to start the brakes
binding. When the brakes start to bind kinetic energy gets converted into heat and absorbed into the caliper. The resulting temperature rises
causes the fluid to expand more the pressue in the system increases and the system is stuck in a positive feed back loop.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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