Lotus Elan

Brake Master Cylinder Leak

PostPost by: Cinbearcat83 » Mon May 20, 2024 8:30 pm

I was bench bleeding my rebuilt brake master cylinder (Girling 6467617) and the bleeding was straightforward...until I noticed the dripping. (The master cylinder was rebuilt by a brake specialist using an RD Enterprise kit). There is weeping between the reservoir (Girling 64476296) and the master cylinder under the front reservoir chamber. The two screws were already tight but I tried to tighten them a little more. No difference. Any thoughts? One option is to replace the reservoir (RD Enterprises).Thanks for any ideas - Kevin
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PostPost by: nmauduit » Mon May 20, 2024 9:40 pm

have you had a good look at the reservoir (nylon can be brittle after all these year and not cope with the briskness of some specialists)? then if no cracks are apparents you may want to double check with the specialist if the seal has been changed (supplied with the kit? fitting with the proper residual pressure?), or if fitting a new seal should be attempted before proceeding further... if need be making one in a material resisting fluid in the long run (nitrile ? ....)

I had a similar problem though coming from the tin part, the seeping was minimal but irritating over time, it took me a while to solve the issue (also a more tricky one at the front where the reservoir is locked in with a wire ring, had to use 2 o'rings to replace the NLA seal there)... I once made the mistake of trusting my master cylinder to a "specialist" and after some hasty butchering it and swearing some his comment was to find a new one: since then I do service it myself (you can do it, too).

good luck !
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PostPost by: Cinbearcat83 » Tue May 21, 2024 1:55 pm

Thanks for your thoughts. The O ring/seal is new and is in good shape. One observation: there isn't much of the seal that extends above the flat surface of the master cylinder - there is not much to compress when the reservoir screws are tightened. Is this normal? By a very rough measurement, it extends ~ 1/64" or .39mm - thanks, Kevin
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PostPost by: nmauduit » Thu May 23, 2024 9:35 pm

it's been a while since I've done mine so take all this with a grain of salt and use your better judgment in priority: I would think that 0.4mm of (relatively stiff) rubber (nitrile ?) would be adequate, provided that the mating surfaces are clean of debris or rust spots/flakes (I assume this is the case), then would come the possibility of a deformed (from too much previous stress?) or scratched flange on the nylon side... This last point you can assess by checking manually the pressure required to get the opposite flanges to compress the seal, and the effort required to screw the 2 holding fasteners without and with the seal. Since this is not a pressurised sealing surface, you may want to try an other, thicker seal (e.g. an O-ring of the proper material with respect to your brake fluid, which may compress more initially and better cope with some variations in the sealing surfaces depending on the small diameter).

Again, my (numerous) problems were on other areas but not on this one...

good luck !
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PostPost by: 2cams70 » Sat May 25, 2024 12:41 am

Whatever you do make sure you get the wife to take that tube of silicone sealant away from you.
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PostPost by: Cinbearcat83 » Tue Jun 04, 2024 8:10 pm

Problem solved - I replaced the old tank with a new one and no leaks!
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