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MG MGA - Brake bleed nipples

I’m just in the process of renewing new brake fluid through the system using Easybleed. All well at the rears, came through easily, but the two fronts not wanting to bleed. Having a lousy memory these days I suspect I’ve been here before but can’t recall the conclusion. The front nipples are smaller diameter than the rears, taking a 3/8” AF spanner. Could it be that they have some sort of one way ball system inside and need greater pressure than the Easybleed 15/20 psi, (perhaps the good old foot pedal), to push fluid through?
I’m at a convenient pause position on the job so will wait to see if there is any guidance before proceeding.
Best
Bruce.
Bruce Mayo

PS. I should have said these are Twin Cam Dunlop disc brakes.
Bruce.
Bruce Mayo

Bruce
The original parts list (for the Mk 2) shows that the front and rear nipples are the same - it shows 4 x 3H2428. At least thats for the Mk2 with discs on the front, but as it has drums on rear with the same nipple, probably no different on a 1500 or Mk1?
Is it possible a previous owner has changed some over? Maybe just put a new one in (or switch a rear one for a front one quickly) and see if the nipple is the reason for the difference.
Graham V

Thanks Graham, and Colin on the Twin Cam email site, for info on this.
Just to conclude, I took one of the front bleed nipples out and plugged the hole and the picture shows what was there, and presumably the other side front too. No wonder the Easybleed 15psi can’t open the bleed path with that very strong little spring in its way! Much as I admire the no-return principle of those bleed nipples, I think I would prefer a simple open bleed nipple so have removed the spring, but retained the plunger with its very effective conical seating capability. Unless anyone perhaps would wish to advise me against such action, I will do both sides the same and finish the job of renewing the brake fluid.
Bruce.



Bruce Mayo

Bruce, I would not use the plunger type valve. You will still have to rely on fluid pressure to push the taper cone back but it could corrode or jam in place (as it did already) and stay shut with the valve backed off & open. The spring is meant to lightly close the valve once the pedal is lifted, before closing the valve with a spanner.

With a solid valve, the taper cone has to come back as you undo the valve.

Regards
Colin
Colin Manley

A further thought on this. Looking at the Brown & Gammon website for Twin Cam MGA, tending to find them more reliable than Moss, they show standard front bleed nipples to include a ball bearing which is presumably dropped into the the threaded hole to make the seating/seal. Is this the standard original arrangement? How would one ever get the ball out of the hole if ever required to do so? Anyone got any thoughts?
Bruce.
Bruce Mayo

Bruce

A sphere bearing on a conical seat would have only a single line of contact, where the radius touches the cone, and would be far less effective than a male cone bearing on a female seat. Always providing that the aftermarket nipple has the same cone dimensions as the original caliper female cone, so perhaps all bets are off.

I could not get the aftermarket (Moss) nipples to seal on the original caliper seats on my 1600. I tightened them as much as I dared, fearing they would shear off, and repeatedly loosened and tightened the nipples to try to improve the seal. In the end I made and annealed copper cones formed from 1mm sheet with a 2mm hole at the pointed end and used these as gaskets to make the seal. It worked.

Cheers
Dave
Bolney Coupe

Thanks Dave interesting! Hopefully not boring others here, but strangely now, having removed the mean little strong springs from the conical seatings in the picture above, the normally reliable nipples both weep! Damn, should have left well alone! I just didn’t like the amount of pressure required to overcome the spring when bleeding. Perhaps the presence of the spring was aligning the conical seating better than looser now. Having a think! Maybe put it back as it was? Or try different type?
Bruce.
Bruce Mayo

The nipples look like an early version of the Goodridge speed bleeder nipples
I got a later set for my elan, they look like an ordinary nipple but have a ball and spring inside
Just loosen the nipple about half a turn fit the bleed hose to the nipple and sit inside and slowly pump, best thing ever, the check valve stops any air getting back in when you lift the pedal, just pump away 'till you get fresh fluid, tighten the nipple and move to the next wheel----one person job and easy
I'd say the nipples you have there should work the same, just sit in there and slowly pump
willy
William Revit

The TC Service Parts List shows that the bleeder nipples are the same on the front and rear brakes. They are part number 7H8252.

Jim
JL Cheatham

This thread was discussed between 20/05/2022 and 29/05/2022

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