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Please Help - From standing the brakes are completely useless


SupraStar 3000
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I have a car thing planned this weekend, so need to get this sorted ASAP.

 

If the car is left for a few days without being used, I noticed the brakes are weak until I've pumped the pedal and traveled a few minutes down the road. They seem to start working pretty well after that.

This weekend after 5 days without being used, the brakes were nonexistent and I had to use the handbrake to stop the car rolling out of the garage. Scared the poo out of me.

A few minutes of pushing the peddle and the brakes started working again. I'd guess a cracked air pipe,.... but where to look?

No brake fluid on the garage floor and the brake reservoir bottle was full.

 

Any ideas chap'ets.

 

Thanks.

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Air in the sytem? whats the level like? id check the simple things first, look for leaks especially where the lines screw into the calliper and hardlines and if no leaks change the fluid. I use Motul RBF600, only need 2 litres for the system and you get a bit left over.

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Since this isn't in tech, you do realise it's the middle pedal, right?

 

Pedal???

This isn't a flint stone type car with pedals. It has a engine and everything,....

 

- - - Updated - - -

 

Sounds like the fluid isn't getting from the reservoir into the master cylinder.

 

A partially seized cylinder, or at least one where the piston isn't returning fully, is a likely culprit.

 

I hope it isn't that. Any way I can check for sure.? Thanks

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Air in the sytem? whats the level like? id check the simple things first, look for leaks especially where the lines screw into the calliper and hardlines and if no leaks change the fluid. I use Motul RBF600, only need 2 litres for the system and you get a bit left over.

 

Level is fine buddy. I have looked for leaks but can't see any dampness etc. Will look again though. Thanks.

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Sounds like a slow air leak from the booster or connecting pipework to me. Especially given you have light pedal feel and excessive travel after leaving the car standing.

 

If it were perished fluid I can't see this improving with use.

 

I'd check the pipes from the top on the intake plenum along the bulkhead and into the top of the booster. Failing that you would need to find a way to test the booster itself. If that's possible at all?

 

Edit - thinking about it more, the brake slave cylinder, as suggested, is probably a good guess too. That would account for the priming your having to do to improve response.

Edited by mwilkinson (see edit history)
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really appreciate your help guys. My gut feeling is a air leak somewhere. Maybe I knocked something when fitting the BOV.

Problem is, I don't know really where to look??

 

Just had a check this evening over the car.

No fluid from the nipples (giggle) or around the booster cylinder or around the reservoir bottle.

Bone dry. Level the same on the reservoir bottle and no puddles on the garage floor.

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I would start with the basics first Ed. If you don't know the last time you changed your fluid, or it's been a while, I would do a fluid change, bleed the system, and go from there. You could be chasing your tail if you don't rule out basic stuff first mate.

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I hope it isn't that. Any way I can check for sure.? Thanks

 

I guess a quick way would be to open a bleeder on a caliper enough to allow fluid to escape when the brake pedal is pressed.

 

If, after several pumps of the brakes, the fluid hasn't dropped in the reservoir then it could be fair to assume a problem with the master cylinder.

 

Note: If the fluid is bypassing the seals in the cylinder the above mentioned test probably won't net you much of a result as the fluid will be under less pressure due to the open bleeder and the master cylinder will probably perform as it would if the system was pressurised and the seals were good.

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I had a. Dry similar issue with mine, was dangerous to drive... I changed brake booster, no better, rebuilt the master cylinder, not really any significant improvement. I had Austec look into the problem and they couldn't find anything visibly wrong either.

 

I ended up changing the brake pads and low and behold it worked fine. Visibly the brake pads where fine, bought some Chris wilson ones and it cured the problem.

 

Maybe buy some cheap ones to rule this out.

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What will have happened is when fitting new pads you pushed the caliper pistons back into the bores. this forces fluid into the master cylinder, backwards. it will either have taken air back into the reservoir and it then floated out of the fluid, *OR* the fluid movement cleared a blockage in the return hole in the MC. I wish i could claim my pads were the secret, but that wouldn't have been the case.

 

 

To the OP. Do a slow, manual bleed, one nipple at a time. Open nipple, assistant SLOWLY presses brake pedal RIGHT to the floor. Close nipple. *SLOWLY* release pedal. Repeat at least ten times per nipple until no air is emitted with the fluid. MAKE SURE reservoir fluid level never drops much or it may draw air in on the upstroke.

 

 

this MIGHT clear things up.

 

 

Use cheap fluid in case it doesn't. DOT4 is DOT4, no need for anything exotic at this stage.

 

 

DO NOT use silicone based fluid, designated DOT5 The designations were crazily contrived. DOT5 is silicone based and will NOT mix with normal fluid and is NOT what should ever be used in 99% of cars. DOT 5.1 is glycol based like DOT 4 and is fine to use. EASY mistake to make....DOT5 can totally bugger up a perfectly healthy system as it can turn to jelly when mixed with glycol based fluids!!!

 

Have fun :)

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Fantastic

Excellent advice guys and really appreciate that detailed description Chris.

After taking the car for a quick drive this evening the brakes seem pretty good from the start,.. so I'm tempted to put off faffin about with them until after the weekend,... Then follow Chris's advice.

I have some new Dot 4 Halford special, so I'll use that. Thanks again guys.

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