id say caliper seals or pistons,, put a new kit thru them and maybe see if the calipers have had it.

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1974 Moke - 998cc
76 Clubman B16a2 Vtec AWD Turbo 12.9@105mph
https://www.youtube.com/watch?v=V9PW49e1hYs

Id say they might need a kit through them then. The seals might have perished in that time, or perhaps were never lubed from the begininng.

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[Maverick] 1971 Mini K

With new seals in, they will pull the pistons & pads back clear of the discs.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ok............... checked the seals and pistons in the calipers etc - all lubed and still fine, could not make out any perishing. Pumped the pedal and checked the nipple at the Master Cylinder end............. pedal dropped so no problems there. Same with both brakes, pumped up, cracked the nipple and the pedal dropped on both occasions.

Now i'm totally lost.................

Could it be a problem with the booster at all (in relation to corroded pistons internally)??????. I also have a missing split pin on the wheel hub nut - could that even be an issue???? (clutching at straws now )

Getting very bewildered right about now

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I got nuthin......................

I would check that the wheel hub nut is still tight I ran mine for a liitle test drive with out split pins and the nut came undone it scoured the rotor but it could have been disasterous.
If this happens there is only the calipers holding the wheel on

But because the rotor normally was locked in place by that nut the rotor as I slowed down slopped sideways which pushed one of the calipers back which if I remeber rightly made the pedal go soft. It might be an outside chance the same thing is happening to you. It also felt like the brakes were dragging (I think).

Definately get the split pins ASAP or stick some heavy wire through it anything.
It appears they will come undone

Maybe if you suspect the booster can you still bypass it and see how it goes

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

G'Day SG,
I once had an air leak in the brake booster diaphram, OK until the brakes were applied then they would not let go again until I turned the engine off. Got home by removing vacuum hose from booster, but you have to seal the end of the hose to keep the manifold vacuum and carbys' sucking.
Just last week I had disk on one side grabbing, when jacked up was hard to spin the front wheels, pedal very firm, no air in lines. Nearly burned my hand when I "Tested" which wheel hub was getting warm. Had replaced hoses a few months previously, so I replaced pistons and both inner and outer seals. Problem cured.
The pistons and calipers were still shiny on the inside, but I figured since I got 31 years out of them (last time I re-did them) a new set would be a treat.
Dino

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Over 1,000,000Km, but now my retirement restoration project

Holy crap - 31 years.................... Circus_Maximus if i can get 3.1 years i will be happy as a pig in mud

Thanks for the info, i will check all of the things you mentioned

Steve

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I got nuthin......................

If you think it's the booster, get a standard short Mini brake line from MC to the bulkhead tee, bypass the booster to test.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

SG,
I forgot to mention when the problem happened, on initial application of the brakes, they were not very effective. I had to push the pedal much harder then they would suddenly grab and only slowly let go again when I let the pedal go. The inner rubber rings were hard as... pistons were stiff in both directions.
In all honesty I would not leave mine go for that long again, even though they did not leak or weep. The difference in brake response and effectiveness was chalk and cheese, and as an added bonus they are much quieter, especially in the M2 tunnel. They no longer squeal or shriek.
For lubrication of brake parts I use glycerine, slippery as hell sticks like, well you know, to a blanket, will not affect rubber or contaminate brake fluid.
For filling those "conveniently" located master cylinders, without soaking the engine and firewall I use one of those garden drip irrigation riser tubes, the one with the piercing screw tip, and just screw it in to the lid of the brake fluid bottle. Fluid tight and you don't have to calculate wind velocity while pouring.
Dino

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Over 1,000,000Km, but now my retirement restoration project