Help Me Identify The Leaking Part Of My Master Cylinder

[mattmanic]

Hello,

I've got a leak on the brake master cylinder in my '98 GS300 and I'm wondering if it's repairable.

This image show the area that's corroded and is letting fluid past. I'm not sure what this is called or whether it'd be included in the master cylinder rebuild kit (Lexus PN: 04493-30280) Is it just a stopper? If so, I may be able to machine a new one up. Exploded diagrams in the workshop manual don't seem to show it as a part.

If anyone can shed any light on this it'd be appreciated :)

[Mihanicos]

A leak is developed when the bore of the brake master cylinder is scratched, scored or not having a perfect smooth mirror surface.

The brake fluid is hygroscopic and absorbs water moisture from the air every time you brake.

This in turn causes corrosion which damages the seals of the piston thereby allowing brake fluid to be drawn into the brake servo operated by the vacuum of the inlet manifold.

Examine the bore of the brake master cylinder and polish it with very fine wet sand paper like P 5000 or finer. A lapping compound will give the mirror surface.

The corrosion I can see is not within the operating range of the piston seals and you should have no problem. Remove the corrosion in the photo and polish the surface as above.

Be very careful as you slide in the piston with the new seals not to damage or scratch them. Use brake fluid to lubricate the bore of the brake master cylinder and the seals. Push them in the bore with a smooth instrument.

If you need further help, do not hesitate to contact me.

Kindest regards,

Chris.

PS

The best thing to do is to get a good used brake master cylinder if you can and replace the seals. Bleeding the whole system is a lot of trouble and work to risk for a poor repair.