soft pedal after power disc swap

[skyjgmc]

Originally Posted by 61K10

on that master isn't the big reservoir for the disc's and small for the rear drums?

Originally Posted by Stocker

Calipers need a greater volume of fluid to operate than wheel cylinders (think large pistons in calipers vs small pistons in wheel cylinders).

With a disc/drum setup, the larger reservoir is for the front calipers -- the smaller reservoir is for the rear drum wheel cylinders.

Yes and yes. This is exactly how I have it setup. Just can't seem to figure out the soft pedal issue upon first braking then it's fine the rest of the trip.

[ERASER5]

1/2ton GM MC are backwards to the 3/4 ton MCs. It is more than just big reservoir/ small reservoir. The big ticket is the 10 psig residual valve needed for the drum brakes (usually in the MC) to work properly and no residual valve for the disc brakes.

[skyjgmc]

Originally Posted by ERASER5

1/2ton GM MC are backwards to the 3/4 ton MCs. It is more than just big reservoir/ small reservoir. The big ticket is the 10 psig residual valve needed for the drum brakes (usually in the MC) to work properly and no residual valve for the disc brakes.

I am not aware whether my MC has a built in rpv for the rear drums? I used a new/rebuilt MC unit for a 74 gmc 1/2 ton since they didn't have one for the earlier 72's in stock but from the looks and specs they seemed the same. Couldn't hurt to put an inline one in for the rear drums now? Im just tired of throwing new parts at it and not getting results. I'm not driving it much anymore that hunting season is over.

Not to derail this thread much but I've built a few rigs (jeeps) and while I don't claim to be an expert by any means, in my jeep that I built I swapped in a rear ford 8.8 with discs and used a e350 ford MC. It stopped good but my prop valve was still a disc/drum and I read on the forums to remove the ball out of the metering valve in the prop valve and wouldn't you know it stopped way better after that.

['63GENIII]

I too started out with manual drums, then power disc front and drum rear. I messed around with wilwood rpvs and probably went through a 55 gallon drum of brake fluid by the time I was done. The final working incarnation was running a 1973 K30 master and booster, the proportioning valve and no extra rpvs. It worked great if the rear brakes were adjusted. Im pretty sure they were self adjusting. I only adjusted them once. IIRC, the bore on the master was 1-1/4? It seems that I ran it that way for a few months before I went to rear discs and ditched the prop valve entirely and also found that I had swapped the lines to the reservoir. Yeah, the brakes will beat you down until you get them right. Just have to stick with it until they are the way you want them.

[skyjgmc]

Ok fellas I got another problem. last night I attempted to drive the truck to run an errand ( havent driven for a few weeks) I hopped in it and tested the brakes out in the driveway by jamming on them they locked up good , I proceeded to drive forward but the fronts didnt release so the rears just spun (been snowing and icy). I backed up they released and I continued forward and the brakes worked good (like they should) then I slowly applied them coming to stop at the bottom of the hill in my neighborhood and the rears locked up and I about lost control (icy roads). I immediately turned around and drove it home.
upon inspection at home I noticed brake fluid dripping from the bottom of the master, its obvious its leaking at the cap on top for the front reservoir. Is it possible that my prop valve is plugged for the front brakes and causing the fluid to choose the path of least resistance? and or causing the front calipers to lock up upon harder braking IE: jamming the brakes. it just seems awfully fishy that it could be my master since this is the second one Ive had on there because my first one was leaking out the top too and I replaced it thinking it was just because its old and wasnt sealing well. The calipers like the master are new rebuilt units from oreillys, so I have a warranty but dont want to replace them and go through the whole process of bleeding again if its not my problem.

[RedRoad]

Im in the same boat. Oreily booster and MC, just swapped out the MC for a new AC Delco and same issue.

http://67-72chevytrucks.com/vboard/s...d.php?t=687109

Let me know what you find. I hate anything in the brakes leaking

[skyjgmc]

Originally Posted by RedRoad

Im in the same boat. Oreily booster and MC, just swapped out the MC for a new AC Delco and same issue.

http://67-72chevytrucks.com/vboard/s...d.php?t=687109

Let me know what you find. I hate anything in the brakes leaking

man sounds like we got simliar problems. I'll check your thread too and see if we can come to a resolution to our problem.