70 C3 Brake Booster Question

[Travis Williamson]

[Chuck S.]

Re: 70 C3 Brake Booster Question

We are looking at the front of the booster shell where the MC bolts on, so the corrosion area is under the MC to shell seal, correct?

The outside of the shell looks pretty rough in this picture...Bubba must have left the hood off when he parked your car last. The best way to remove that rust is by bead-blasting, and even then you probably won't get it all. Sanding or wire brushing is only going to burnish the rusty surface IMO. Small bead-blast cabinets can be had pretty cheap these days, and they have a lot of uses...you might want to check one out.

If you can thoroughly seal all the openings, you can probably bead-blast the shell to near white metal, and that corrosion in most of the MC seal area can be completely removed. After that, I would appply PPG black epoxy primer (1-2 coats), then top coat it with a black enamel flattened to semi-gloss. Spray can semi-gloss black will work if you don't want to mix paint, but you still need a good primer under it IMO.

If you end up with heavy texturing on the booster surface after the rust has been removed, multiple coats of primer-sufacer, and block sanding between coats, will help smooth it to perfection. Of course, at some point, a replacement booster will be cheaper and easier...paint is expensive and sanding is WORK.

As for the seal, it's hard to tell anything about the depth of corrosion from a photo, particularly before all the loose scale has been removed. You really won't know until you try it, but my opinion is it will seal OK; instead of RTV, I believe I would apply a thin coat of dielectric grease (ordinary grease should work just as well), being a little more generous in the corrosion area.

I suspect RTV could work contrary to your purposes; it's pretty thick so it doesn't flow out well, and begins to set up and stiffen as soon as it's exposed to air...you don't want any "lumps under your mattress"; the seal has to conform to the both the MC and shell to work, and the grease is there to fill the voids. Unless you install the MC when the RTV has just been applied, "lumpy" RTV may prevent the seal from conforming as it should.

[Travis Williamson]

Re: 70 C3 Brake Booster Question

Thanks Chuck.

Yes, its the front of the booster where the mc matres to the booster.

You know how it goes, its a lot of work to restore it but if its the original (which Im trying to find out) its worth the extra work.

Im still thinking I may just get a replacement and hold onto the old one. Id rather have a replacment than to have the original with unreliable braking...

Travis