I installed my 14bolt disc brake conversion with the typical GM 3/4 ton front calipers on my 72 blazer. My question is what is the best master cylinder and combination/proportioning valve to get. I'm trying to find one that is designed for front/rear disc brakes. I’ve searched but the more I read the more confused I get. Is there a specific year and model master cylinder and combination/proportioning valve I can get that will install without a ton of fab? Part numbers?
CK5
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Disc brake conversion master cylinder ?
- Thread starter jerden
- Start date
cegusman
3/4 ton status
Im running the stock master cylinder. but swaped in a 4 wheel disk prop valve from inlinetube.com. Was about $100
You'll find a lot of opinions on this. In your case there's a twist as your first-gen truck is a little different than the 73+ models.
I've done disc convos on two trucks. My K5 has the stock vacuum booster and master, 3/4 front calipers and Caddy rears. She stops like a sportscar and can hold the truck even with the Doubler in 4:1 low (at least unless I goose her
)
The sixpack has a stock style hydroboost system, no combo valve, residual valves on both circuits and an adjustable prop valve on the rear. It took me months to get the thing dialled in and even now I suspect I'd have been better off with the stock plumbing.
I *strongly* recommend not fiddling with the master cylinder, i.e. using a stock replacement type. I think a lot of folks who say their brakes improved after switching to some other type were replacing an old and worn unit, so they would have had improvement with a (new) stock type as well
At the very least, be wary of masters made for vacuum boosters vs. hydroboost, as they do not interchange well. (They can be physically compatible, but the booster output travel is different and bad things happen when you push the master too far or not enough.
)
If it were me, I would keep your current master if you have replaced it recently and know it's good.
Otherwise I'd replace it with an appropriate stock unit, i.e. the one for disc front brakes (IIRC, some 67-72 trucks had drum fronts.)
I forget the details, but the combo valve is up by the master on your truck, yeah?
I would leave the valve and plumbing as is, and try the truck out. Brake changes like this are all about bleeding properly, so if you have problems, bleed, bleed, and bleed again. Read up on the garden sprayer pressure bleeders as IMO they are the ONLY way to go.
IF after a LOT of bleeding you find you have brake issues, then -- and only then -- consider changing the valving. You might just use an adjustable valve inline with the rear circuit.
But do the change in pieces, rather than all at once. No sense in "fixing" something that isn't broken.
Just my .02 from being there, doing that, and soaking myself in brake fluid for days on end.
-- A
I've done disc convos on two trucks. My K5 has the stock vacuum booster and master, 3/4 front calipers and Caddy rears. She stops like a sportscar and can hold the truck even with the Doubler in 4:1 low (at least unless I goose her
)The sixpack has a stock style hydroboost system, no combo valve, residual valves on both circuits and an adjustable prop valve on the rear. It took me months to get the thing dialled in and even now I suspect I'd have been better off with the stock plumbing.
I *strongly* recommend not fiddling with the master cylinder, i.e. using a stock replacement type. I think a lot of folks who say their brakes improved after switching to some other type were replacing an old and worn unit, so they would have had improvement with a (new) stock type as well
At the very least, be wary of masters made for vacuum boosters vs. hydroboost, as they do not interchange well. (They can be physically compatible, but the booster output travel is different and bad things happen when you push the master too far or not enough.
)If it were me, I would keep your current master if you have replaced it recently and know it's good.
Otherwise I'd replace it with an appropriate stock unit, i.e. the one for disc front brakes (IIRC, some 67-72 trucks had drum fronts.)
I forget the details, but the combo valve is up by the master on your truck, yeah?
I would leave the valve and plumbing as is, and try the truck out. Brake changes like this are all about bleeding properly, so if you have problems, bleed, bleed, and bleed again. Read up on the garden sprayer pressure bleeders as IMO they are the ONLY way to go.
IF after a LOT of bleeding you find you have brake issues, then -- and only then -- consider changing the valving. You might just use an adjustable valve inline with the rear circuit.
But do the change in pieces, rather than all at once. No sense in "fixing" something that isn't broken.
Just my .02 from being there, doing that, and soaking myself in brake fluid for days on end.
-- A
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lots of posts on this, search the first gen forum for 4 wheel disc.
I used a one ton booster and master from a 72 chevy, bought new from the parts store. You will need to get the shorter mounting brackets if your truck didn't come with front disc (I had 4 wheel drum).
If you had front disc then just buy a master for a 1 ton. Both fluid reserviors are the same size. Then I used an adjustable proportioning valve from wilwood and a residual pressure valve from Summit, both were plumbed into the fluid line for the rear brakes. I don't use any of the stock proportioning valve but then I didn't have front disc to start with. My adjustable valve is close to closed so I could get the rears to lock up at the same time as the fronts. Took a lot of skid testing to get it right. Works great now.
Mine has 14 bolt FF rear with chevy calipers and 3/4 ton 10 bolt front with stock type calipers. It stops very well for being 6200 lbs on 37" Krawlers.
I used a one ton booster and master from a 72 chevy, bought new from the parts store. You will need to get the shorter mounting brackets if your truck didn't come with front disc (I had 4 wheel drum).
If you had front disc then just buy a master for a 1 ton. Both fluid reserviors are the same size. Then I used an adjustable proportioning valve from wilwood and a residual pressure valve from Summit, both were plumbed into the fluid line for the rear brakes. I don't use any of the stock proportioning valve but then I didn't have front disc to start with. My adjustable valve is close to closed so I could get the rears to lock up at the same time as the fronts. Took a lot of skid testing to get it right. Works great now.
Mine has 14 bolt FF rear with chevy calipers and 3/4 ton 10 bolt front with stock type calipers. It stops very well for being 6200 lbs on 37" Krawlers.
chulisohombre
1/2 ton status
i have a 72 and i didnt change anything in my truck.i just gutted the proportioning valve for the rear output.there is a holding valve in there that keeps 10 to 20 psi to the rear.mine would hold the rear brakes a lil bit that i could feel.so i gutted it.other than that the rest of the system is stock master and booster.it works good as is.just try it out after the install and bleeding and see how it works.you might get lucky and it works fine in stock form.
This is exactly the info I needed guys thanks. From what was said I think I'm going to leave it as is for now and see how it performs. Then if there's problems get a 1 ton master and a combination/proportioning valve from SSBC.
I'll let you know how it goes.
I'll let you know how it goes.
I’m bumping this. It feels like some of the folks with positive things to say after doing the rear discs where doing this with a 3/4 ton set up. Meaning non-60 fronts.
Getting to why I’m bumping this.
I found out, after a drive, that my MC is bleeding down while stopped. I haven’t confirmed yet if it’s an external leak, but I didn’t notice anything. Sitting at a stop she starts to creep, apply more pedal and it creep again after 20-30 seconds.
I have a 60/14. Stock front calipers and 1/2 ton rears. 1 ton booster and MC. I can’t remember all the previous MC I’ve tried, maybe 5 total. Brakes have always sucked but won’t get into that.
I need to replace the MC. Just get another K30?
Getting to why I’m bumping this.
I found out, after a drive, that my MC is bleeding down while stopped. I haven’t confirmed yet if it’s an external leak, but I didn’t notice anything. Sitting at a stop she starts to creep, apply more pedal and it creep again after 20-30 seconds.
I have a 60/14. Stock front calipers and 1/2 ton rears. 1 ton booster and MC. I can’t remember all the previous MC I’ve tried, maybe 5 total. Brakes have always sucked but won’t get into that.
I need to replace the MC. Just get another K30?
