Hey group, I have my 1983 BJ42 master cylinder leaking in which I rebuilt about 6 months ago. behind the master cylinder i had a gasket but it is leaking where the master and booster meet. the master cylinder shouldnt leak should it? just wondering why a gasket there then? was goin to dry it up and use gasket sealer/ maker?? any thoughts? or should I try and find an aftermarket master cylinder? I used a a new late model master cylinder rebuild kit when I rebuilt for they dont show one for BJ42? the cylinders look to be exact? any idea for an aftermarket source?
hello, the leak is caused by a bad bore seal in your MC. causes can be pitting-normal brake fluid absorbs water and causes pitting, especially in vehicles that sit a lot. remove the seal and if you have three sided hones to hone out the bore and then replace the seal you'll be good to go. i would recommend using silicon fluid going forward. it doesn't absorb water and it also doesn't act as a pseudo paint remover...
a silcone brake fluid? never heard of it but I like the idea of it not eating my new paint. so I need to take the master apart and bore out cylinder? never heard of a 3 sided honer? where can i get or do i need to take to someone to do?
... behind the master cylinder i had a gasket but it is leaking where the master and booster meet. ...was goin to dry it up and use gasket sealer/ maker?? any thoughts? ....thanks...Rob
Whatever you do - don't try making a complete "seal" with this gasket Rob.
The gasket itself doesn't really serve much purpose and you'll notice a "drain groove" indented into the mating face of the booster anyway (that is there to allow any fluid from that area to escape into the engine bay).
In fact - I ran mine with no gasket at all there for many years with no ill-effects. (Now I have one cut from black plastic.) .......Obviously the thickness of the gasket (or abscence thereof) affects the desired pushrod length.
Unfortunately - much of any leaking fluid (from the master) often gets sucked into the booster via the little seal on the "booster output pushrod" (even with the drain groove there). .... I'm just mentioning this for "information purposes" because, without going to alot of trouble dismantling your booster, there isn't an easy way to get this fluid back out (if this has indeed happened to you).
If you were to seal that gasket - the booster would definitely try to suck all the brake fluid from your master (via the pushrod seal that will always leak to some extent).........which is NOT good!!!
Personally I wouldn't change to silcone brake fluid despite the fact it is more friendly to paint. Harley Davidson motorbikes use this fluid but not many other "vehicles" do. (When it was invented quite a few years ago it was supposed to take over the market completely! But it has had few takers! ) - And it can cause some seals to swell (and thus maybe seize wheel cylinders up etc) depending on what type of rubber they're made of.
I think the advice to obtain a replacement master is good because they are really easy to source and not too expensive.
