Brake Booster/Master Q?

[ncgamedog]

I am working on my towrig and need a new booster (i'm pretty sure) so here's the deal: my truck is an 85' silverado k10 LWB, i swaped in some 3/4 tons (10b/sf14b) to get the 4:10's and bigger brakes. i know there were 2 brake opotions for the axles i have (83') 11" drum and 13" drum. i have the 13" "Big Brakes", i found this out when replacing the front calipers and rear shoes. now i called Advance Auto to price a booster/master combo. for the 1/2 ton there were two options JB5 and JD5 and on the 3/4t JB6 and JB7. i have no idea what i have stock and cant find any I.D. tags to tell me. i would like to run the 3/4 ton booster/master if it will work. the guy said the JB7 was for heavy duty braking, i would assume since i have the "Big Brakes" that would be the correct one. ok so question is: can anyone help me decipher these codes and will the 3/4t booster/master be a direct bolt on swap? all parts i checked on were for an 85' since thats what the truck is. thanks guys -justin

 

[Muddytazz]

Yes you can use the BIG BRAKE master/booster combo on your K10. The only thing you might have to do (as I can't remember cause its been so long ago when I did it) is you might have to adjust the plunger rod length that goes between the brake pedal and the booster/master.

 

[ncgamedog]

yeah i kind of figured on the rod adjustment. dont you need to do that when ever you swap a booster even if its stock to new stock? but cool, good deal on the swap. so its just a direct bolt up huh? should i expect great gains? or barley noticeable? my brakes stop almost too good now, but the pedal is low and gooshy. they lock up quick in the back it makes me uneasy sometimes under hard braking. i'm hoping this might change that too. have any idea on the codes?

 

[BGKYK5]

Your stock RPO brake code should be on a sticker in your glove box. Just look through all the codes 'till you see one of the ones you listed.

 

[dremu]

Assuming we're talking about a vacuum booster -- hydroboost is a whole other animal -- it's easy to test the booster.

First, with the engine running, if the pedal is really REALLY hard to push, like it is when the engine's off ... the booster isn't boosting, you don't have power brakes, replace it

Second, start the truck, let it run for a minute, turn it off WITHOUT touching the brake pedal. Come back fifteen minutes later, and pump the pedal. You should get two or three good pumps before it gets really REALLY hard to push. The idea being that the vacuum can stores the vacuum and has enough to give you a coupla boosts and then runs out.

If you don't get good pumps, then the booster is leaking -- check the hose to it and the check valve on it.

In my experience boosters rarely fail and often get replaced ... the master cylinder is more problematic and more likely to wear out, albeit more of a PITA to replace .. . but you sound like you know all this!

Also, the booster for the 1/2 and 3/4 may well be the same in those years ... I know that for my '74 there was a "single diaphragm" booster (like, I donno, 4" or so thick donut) but I've never actually seen one, they're all the heavier-duty "double diaphragm" which is the usual 6 or 8" thick donut.

HTH.

-- A