evolve991
Resident Problem Child
Can I swap my plastic MC out with a cast MC? Will it bolt to the booster or do I need to switch out the whole thing?
CK5
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Master Cylinder
- Thread starter evolve991
- Start date
Depending on what year & model your truck is--you might be able to bolt up either one to the booster,"most" have the same bolt spacing & mounting,on cast iron VS die cast masters--but there is a "deep" push rod hole for manual brakes VS power brakes,that only have a "dimple" for the push rod to seat in..
I believe there is also a difference between hydroboost master cylinders and vacuum assist but I haven't verified. I have an '83 diesel k5 with hydroboost and I swapped mine for a disc/disc master with aluminum reservoir for an '83 p30 step van with diesel engine and hydroboost and it bolted right up.
evolve991
Resident Problem Child
Thanks guys. Mine was a hydroboost but when we swapped in a 350 the guy who did the job also swapped the hydro out for a vacuum booster out of a K10 pickup,don't recall year or specs. I'd just like to ditch this plastic junk cylinder for a metal one,preferably a 3/4 ton or heavier duty MC.
My '82 GMC with hydroboost has the same master cylinder as many 70's GM full sized cars like Impala's and Caddilacs have on them...
The hydroboost ones are the same as vacuum power brakes at least in my truck...about the only things besides "will it bolt up" and having the correct push rod seat is the bore sizes of the master,and calipers & wheel cylinders..you have to match them to what your running for calipers and wheel cylinders,or you might end up with a very hard pedal or "too touchy" brakes...also whether or not it needs a check valve or not for drums VS discs..
The hydroboost ones are the same as vacuum power brakes at least in my truck...about the only things besides "will it bolt up" and having the correct push rod seat is the bore sizes of the master,and calipers & wheel cylinders..you have to match them to what your running for calipers and wheel cylinders,or you might end up with a very hard pedal or "too touchy" brakes...also whether or not it needs a check valve or not for drums VS discs..
evolve991
Resident Problem Child
Thanks Diesel. Mine is disc front and drum rear. The calipers should have been the big piston JB/JD7s but I suspect someone replaced those and the matching lines with JB/JD5s. I bought the 7s and had to return and trade them for 5s. The rear is now a 12 bolt from a 76 or 78 K10 Pickup ( it had 454/400 in it. nice 3.73s) and has bigger drums and shoes than my 85 corp 10 so I need more MC than that plastic one,at least my overkill obsession says so 
I plan on replacing the JB5s and hoses when I upgrade the MC/Booster too. And if I decide to find a wider AAM 14SF with drums later on it will be enough to power the even bigger drums.
I plan on replacing the JB5s and hoses when I upgrade the MC/Booster too. And if I decide to find a wider AAM 14SF with drums later on it will be enough to power the even bigger drums.
Crude rule of thumb is any master with more than a 1-1/8" bore has to be used with a power booster,smaller bore gives more pressure with less pedal effort ,but less volume,so excess pedal travel becomes an issue..most manual brake masters are 1" or smaller...
My '82 has a 14 bolt SF with 13" drum brakes and most of the 70's full sized cars only had 11" or 12" drums,yet the same master cylinder works OK on both--I'm not sure which calipers it has,I think JB7's...
I think the part # on my replacement master was a M1521 from Auto-zone,it was like 14 bucks exchanged for a rebuilt,but I think the one in the box was new,not a reman...one of those would probably be fine until you get crazy with bigger calipers ,etc..
My '82 has a 14 bolt SF with 13" drum brakes and most of the 70's full sized cars only had 11" or 12" drums,yet the same master cylinder works OK on both--I'm not sure which calipers it has,I think JB7's...
I think the part # on my replacement master was a M1521 from Auto-zone,it was like 14 bucks exchanged for a rebuilt,but I think the one in the box was new,not a reman...one of those would probably be fine until you get crazy with bigger calipers ,etc..
I'm running 3/4 ton calipers on my front 8 lug ten bolt and 1/2 ton calipers on my rear ff 14 bolt. The 1/2 ton calipers have a slightly smaller piston. I have a summit racing disc/disc prop valve and the '83 p30 disc/disc master which I believe has a 4mm larger piston than my factory hydroboost master. It stops awesome with a good stiff pedal, which is what I like, and plenty of breaking power. I just need to add an adjustable prop valve to the rear circuit to take away a little pressure. The rear locks a little before the front and it needs to be the other way around with the front coming on first.
evolve991
Resident Problem Child
Thanks guys.....Now..I hope you read this soon ...OK...I'm replacing the rotors ,they are the rotor only and I drove the studs out and split them. The driver side went back together snug with a solid punch and ball peen....the passenger side isn't being so nice, the rotor has play on the studs,which I did the same way as the drivers, I tried drawing it up tight but there is still play....before I got really torquing the lug nuts and maybe snap something IS there something I'm missing? I've done it this way before without a press and it worked fine. Rotor is identical to the other.
evolve991
Resident Problem Child
Oh well it's dark now anyway. Gonna take it back off tomorrow and clean the hub surface up real well and take my time. Shouldn't have been hurrying on brakes anyway right?
evolve991
Resident Problem Child
I've been wondering if my rear brakes aren't getting the pressure they need and suspected the fronts grabbing first might have been part of my death wobble problem but I've read the fronts are supposed to come in first a few times over the past few days so guess I'll know more when the new calipers and rotors ( and bearings) act like they should. Tired of gearing down and gritting my teeth every time I slow down.
evolve991
Resident Problem Child
UPDATE: I din't know what the hell my brain was off doing yesterday but I pulled the rotor back off, grabbed my trusty 'punch pin' (hardened steel rod from a rear) and smacked dat sh*t til the studs were flush and seated. In defense of my silliness I DID mention to you's guys before that I WILL be asking some beginners first day questions on here 
since my "buddies" always rigged stuff I paid them to do right and I've had to wing it or bug you guys about simple issues. Although I've owned dozens of GMs and a few lesser mechanical wonders this is my 1st and only ever 4WD and after 11 years owning it I'm still finding shortcuts and 'lowest price' nonsense in former repairs. I thank you guys for your advice,experience and speculations, that goes for everyone who's answered me in any post I've made. This Suburban is my Daily Beast and I'm too broke to have a muscle car ( Skylark) anymore so it's also the subject of my tinkering obsession 
since my "buddies" always rigged stuff I paid them to do right and I've had to wing it or bug you guys about simple issues. Although I've owned dozens of GMs and a few lesser mechanical wonders this is my 1st and only ever 4WD and after 11 years owning it I'm still finding shortcuts and 'lowest price' nonsense in former repairs. I thank you guys for your advice,experience and speculations, that goes for everyone who's answered me in any post I've made. This Suburban is my Daily Beast and I'm too broke to have a muscle car ( Skylark) anymore so it's also the subject of my tinkering obsession 
