rebuild of brake booster

[bowen]

I rebuilt my early girling brake booster from a BT7, but it still did not work. I removed it again and have had in sleeved an I am ready to reassemble. The first time I rebuilt I had a kit from MOSS Motors which had a grease in it to grease the leather on the vacuum cylinder. All my original parts of the first rebuild are fine, I just don't have any grease anymore. What was that grease or what is recommended. Is there any way to check this thing before it is back on the car. Hard to take on and off.

 

[Legal Bill]

IIRC, the inside of the servo had a special coating that allowed the the leather to slide and not get hung up. I can't recall what it was or if it was brushed or sprayed on. I think it was sprayed on. I don't think grease does the trick.

 

[Patrick67BJ8]

IIRC, the inside of the servo had a special coating that allowed the the leather to slide and not get hung up. I can't recall what it was or if it was brushed or sprayed on. I think it was sprayed on. I don't think grease does the trick.

I believe the coating is the grease and you need to rub it into the cylinder bore much like you do when you wax a car. Be sure the leather is equally covered in the grease. I think the grease is the "rubber grease". It's been over 30 years since I rebuilt mine and I recall that when I did it there were some other Healey owners who provided the knowledge of the additional grease. The piston needs to slide freely inside the bore or it will "stick" and not move.
(recollection from "live" brain cells)...before Internet). There's also another part that is not included with the rebuild kit that you need to buy separately and a special tool you need to make with a coat-hangar.
Patrick

 

[Legal Bill]

Yes, they put grease in the rebuild kit, but it often fails. The original had some type of film. Someone found a modern replacement for it. I just did a quick search and found this reference to it. See the second response to the question. Dry film lubricant:

https://www.british-cars.org/austin-healey-3000-bbs/brake-servos-200302251738596419.htm

 

[Bob_Spidell]

Here's the page: https://www.sandstromproducts.com/airdrysfl.htm

I used their 27A product, which has been superseded by 28A. Looks like polylube# 420 would work, too. Recommend you call and discuss with them--they are specialists in coatings.

It seems to have worked well, but IIRC there's a minimum order of 2 spay cans--or the cost of the additional can is negligible--so I ordered 2, which would be enough for about 40 servos. There's also a significant hazmat fee, and it has a limited shelf life.

The stuff works, but I sometimes wonder if it was necessary; the original coating seemed to be holding up.

I wouldn't use any form of grease or oil.

 

[MikeP]

You should also check the rope type seal that goes behind the leather on the piston to push it against the cylinder. If you replaced it and the new one's too stiff it can cause the piston to hang up in the bore. It should be almost like soft foam rubber.

 

[MarkA]

Before you can use the Sandstrom product, you must ensure that the leather is completely free of any brake fluid. Any residue brake fluid dissolves the lubricant and turns it into a sticky mess.