Master cylinder?

[max 02]

On my 77 I got a 2 wheel drive master cylinder that leaks...I want to change it for a 76 2 wheel 3/4 ton cylinder that I have.
Will that work?

The reason I ask is because the 3/4 ton one has got reservoirs that are the same size front and back,the 1/2 ton cylinder has got a bigger res for the front brakes and smaller one for the back. Does that matter at all?

The truck has got a 10bolt in the front and a 12 bolt in the rear.

 

[Fordum]

Odds are its going to give problems. Usually when you have different size reservoirs, its because you have disk on one axle and drums on the other.

I bet your truck has disk/drum, and the 3/4 has drum/drum. The different size of the reservoirs is not the main problem, although it is a problem.
The internals of the master are different for the drum brakes, and will screw up your disks.

 

[max 02]

The 76 cylinder that I want to use is out of a 2wheel drive crew cab...Disks on the front 14 bolt in the back.

 

[Fordum]

Well, if its the same type brakes as yours, and its free, might as well try it. Just expect trouble the first couple of times you stop.

In other words, have a plan if it don't stop. But, I do that everytime any brake work is done on any of my vehicles.

I suspect there will be some kind of an issue, but who knows? It might work better...

 

[dremu]

As long as the donor was vacuum boost, it'll at least mostly work. Mixing and matching masters from hydroboost and vacuum boost ... will bite you in the butt.

-- A

 

[76zimmer]

I think it will work Dean...the 14bolt probably has bigger wheel cylinders than your 12bolt, and the front calipers are probably bigger on the 3/4t too, I think it will work, although perhaps a bit less pedal travel.
Make sure your pushrod into the m/c is the correct length to fully push the piston into the m/c bore also.

 

[max 02]

Alright I'll try it...if I go crashing through the garage wall I'll take pics.

 

[diesel4me]

I think it will work Dean...the 14bolt probably has bigger wheel cylinders than your 12bolt, and the front calipers are probably bigger on the 3/4t too, I think it will work, although perhaps a bit less pedal travel.
Make sure your pushrod into the m/c is the correct length to fully push the piston into the m/c bore also.

I've put a Delco master cylinder with 2 equal sized fluid chambers in place of the original bendix one with two different sized fluid chambers on my '82 K2500 with hydroboost,as stated above,as long as it bolts up OK and the push rod seat in the piston is the same depth it will work--however the internal piston sizes in the master can vary between different GVW's and brake systems,they must "match" the wheel cylinder and caliper sizes to some degree,otherwise it could cause poor braking or be too "touchy" if a master with smaller or larger bore is swapped on--however,I have used 1/2 ton ones on 3/4 ton trucks and vice versa,and not noticed much difference...many 70's GM full sized cars used the same Delco master as the trucks too,BTW.....................................................................................................................................................................................................................on my truck I had to use adapter fitting to put the lines on the master with two equal sized chambers VS the bendix that had a small chamber and a larger one,in order to get them in the right ports...(the lines will fit if swapped,but DONT do it,I tried that and the rear brakes locked at the lightest touch,and the fronts felt weak,being hooked up "backwards!)......the brakes seem to work just as well now as before on my truck,maybe better--only bummer is the master cyl. I put on it leaks from the rear piston ,just like the first one did...it was a rebuilt I saved off my '77 K2500 with a vacuum booster,despite leaving it full of fluid I guess it didn't like sitting on a shelf 3 years before getting re-used..

 

[TheBeast_88K5]

It's larger because of the wheel cylinders.

 

[Cornfield creations]

It will work, the JB7 master will push more fluid through, so it may lock up the brakes. All you can do is try it if you don't want to spend any money and see how it turns out

 

[max 02]

I`ll do it when I got some time, we need running for a bit for some fall cleen up work.

I `m sure that after I start it`s going to need a bunch of little things fixed...this truck has not seen much love before I got it.

And I am building it on the cheep so usually if I got it at home it gets bolted to the Black truck.