Brake dancing

[silloyd]

I sometimes get sponginess in my brakes. I've tried bleeding them but they don't remain firm and there are no apparent fluid leaks.

If I pump the brakes then I get a good firm pressure and it will stay like that for a while but eventually goes soggy. If I apply gentle pressure on the pedal it will sink all the way to the floor.

Before I start pulling everything apart, can someone tell me if this is, as I suspect, a problem with the master cylinder please?

If that's the case then given that the M/C was overhauled two years ago is it more likely that the seal kit wasn't very good or that the M/C itself is past it and not worth refurbing?

[PSL184]

Seal kits rarely work in M/C as it is usual for the bore to be pitted and thus wreck any new seals immediately.

[bmcecosse]

Unless you have a silly servo (in which case suspect it first) then yes I would assume it's a master cylinder problem.

[silloyd]

No servo, just original drums.

Sounds like a new master cylinder is in order as I don't want to risk driving with dodgy brakes. 'Lockheed' versions appear to be the ones to go for and I guess all the suppliers are offering the same item, so it's down to price and availability.

Thanks gents.

[les]

If the linings are too far away from the drums, this can give the symptoms you describe. maybe worth checking before buying cylinder.

[bmcecosse]

Yes - it is indeed worth tightening up all the brakes and trying that.

[silloyd]

Thanks for the suggestion. I did adjust all the brake snail cams when bleeding, so I don't think that is the problem.

[bmcecosse]

And you don't think it just needs better bleeding?

[les]

Maybe now the linings have centalized the cams will take up more? Just another thought, as this proceedure solved a similar problem I had once, unfortunately I'd changed the cylinder unnecessarily first!

[silloyd]

I've tried bleeding in sequence (N/S/R, O/S/R, N/S/F, O/S/F) but still have this problem where the brakes go soft after a while and the pedal will go to the floor under gentle pressure. Could be my technique is not good I suppose.

[mike.perry]

The pedal sinking to the floor sounds like a M/C problem, if it was just pumping then it would be air or adjustment. Are you SURE that you have not got a leak somewhere? A loose connection or split pipe?

[fussyoldfart]

Since you are, in a sense, betting your life on it I would say that a new master cylinder is a pretty small investment.

Darrell

[kennatt]

take off the floor cover to expose the whole cylinder,usually when this happens the seals let the fluid passed and when the brake returns they draw fluid out of the cylinder and you can see it in the chassis leg or on the rear of the cylinder .If so definate new cylinder'

[Declan_Burns]

The new "Lockheed" master cylinders being sold are slightly wider than the originals and need to be dressed with a file. I have had two cases of this problem in the last two weeks.
Regards
Declan