The Stovebolt Site Forums The Shop Area Engine Shop 85 S-15 power brake booster for 50 6400

Greetings, was wondering about upgradeing my brakes using a brake booster out of an 85 GMC S-15 blazer, is it big enough?? I think the brakes on a modern veh. like this would be better than anything made in 1950. Proportioning wise I was going to go without since they are drum front and rear. I would also use the residual pressure gadgets to help with reaction time and prevent backflow. My local welding shop is going to make the frame mounting bracket.

Yes, it is big enough.
I have one on my '67 3/4ton.
What are you planing on using for a master? The S-10 master has a third chamber, called a low pressure or Quick Takeup chamber. It is used with Low Drag Quick Takeup disc calipers.
I tried to use the S-10 master and booster when I put the '77 3/4 discs on my truck. I tried three masters before giving up and put the '77 master on the s-10 booster. I'm convinced that all three had a bad quick takeup valve, but didn't want to spend any more time on it.
Some masters will already have the residual valves in the outlets

Thanks Richard, I was planning on using the same master that was attached to the booster. I went back to double check and I can only see two res. after dumping the old fliud out. It also doesnt appear to have the residual valves. I do recall seeing them on systems before just cant remember were.

Not 100% sure what you mean by "two res." When I said three chambers, I was not refering to the reservoir or residual valves.
[img]http://www.babcox.com/editorial/bf/elements/60133a.gif[/img]
The items called out in fig.5 are added to a master used with low drag calipers. The shape of the caliper piston seal pulls the piston back away from the rotor. The low pressure chamber returns the fluid to the caliper in the first of a series of three steps before your foot can apply full pressure to both front and rear(reduced for disc/drum).
Everything I've read says that the low drag caliper will not work without this master. Using it the other way around?? I have not been able to find anything about using this master with standard calipers or even drums/front. I think, if the piston is already "out", the low pressure chamber should just vent its fluid out through the take-up valve to the reservoir.
Rebuild kits do not include a take-up valve and they are nearly impossible to remove without damage. I have to wonder if rebuilders replace or even test the valve.
I have to agree that for this master on drum/drum, you wouldn't want the combination valve and should use two 10LB residual valves.

Richard Sorry I didnt read your responce clearly, I do have the third chamber. In your opinion should I spend the money and use a diff. master cylinder off say a full size 1 ton chevy. Thank you for all your information, it has been very usefull.