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The mkiv Supra Owners Club

Strange brake issue


SteveL

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Dunno if anyone has had this or diagnosed it....

 

Pedal travel on first push is more than on all successive pushes.

No real difference in braking power, just pedal travels less.

If brakes are then used again the same happens.

Normal checks/changes have been done - fluid/bleed etc.

UK spec front and rear, front disks are apparently due for replacement soon - but not significantly worn.

Fluid is Motul HF600 and Porterfield Race pads with braided lines as well.

 

Any ideas anyone.

I'm considering Master cylinder refurb/replacement at the mo.

Is there any other part of the system that could need maintenance/replacement?

 

Cheers

 

Steve.

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You could try testing the brake booster by "pumping up" the pedal with the engine off, then with your foot on the brake (which by now should feel very firm) start the engine. The pedal should sink to the floor as the engine builds up the vacuum assist.

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Cheers guys :

 

IanC - pads are only about 1K miles old.

Chris - From what I remember, the brakes have been the same since new disks a nd pads were fitted - I just got used to them. It wasn't until someone else drove the car an commented on the brakes that I appeared to have an issue.

Digsy - Fooked as in replace whole MBC or just service?

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If it feels like you can pump up the cylinder by sucessive pedals pushes, but there's no leakage externally or air in the system then it sounds more like a fooked master cylinder to me.

 

I had exactly the same problem on my old Mondeo - turned out to be the master cylinder :) I needed a new one but it wasn't that expensive.

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If it feels like you can pump up the cylinder by sucessive pedals pushes, but there's no leakage externally or air in the system then it sounds more like a fooked master cylinder to me.

 

Aye, agree here. Seals on master cyl getting worn. First push allows a bit of fluid past the seals before they seal against the bore. Once sealed they retain a bit of pressure that allows them to keep the seal for a while... until it slowly leaks past. Eventually a master cyl recondition or new cyl will be required.

 

Easy test to do. After being left overnight start the engine and *very slowly* press brake pedal. If it sinks to the floor its the seals. Next day do the same thing but stamp on the brake pedal. If it goes hard (ooh err) quickly, that's the fault confirmed.

 

Seal kits are only about a tenner, and if the cylinder is worn it can be honed out (I have a brake hone) and a slightly oversize seal kit bought. I've done a few and its a piece of p*ss. PM me if you want to borrow the brake hone.

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