M715 power brakes question

[Mikel2]

Hello all,
My 69 M715 needs some brake work and I figured this might be the time to upgrade to power brakes. What would be the easiest booster/master cylinder swap?
Thank you!
Mikel

[BIG BAD JON]

A brake booster and master cylinder from any FSJ should work. Remember, the M715 was based on the Gladiator's design.

[Mikel2]

Hello Big Bad Jon,
According to some info at the M715zone database, I have the pre-AMC steering column, so using the master cylinder from a AMC or later truck could be problematic. And old trucks like that are very very rare here in the rust belt. I wanted to use the double diaphragm brake booster and MC from a J20, but I'm not sure it will fit.
Thanks.
Mikel

[Sundowner]

when did you buy an M715?!?
buy a grinder, everything fits one way or another. :D

I hate to say it, but the most pragmatic thing for you to do may be to swap out the cab for a J series cab with all the civie stuff in it. Beachwood canvas wants as much for a new top as a clean cab will cost you.

[Mikel2]

Hello Sundowner,
I brought the thing home last saturday... From NJ :D :D :D :D

[talntar]

im almost sure i have the dual diaphram in mine if you want to tack some messurments.

[mdill]

There were some divorced boost units, don't know if anything currently
uses them, but with some research, you should be able to come up with one.
This might be the easiest.

[FSJeeper]

The J-20 dual diaphram MC will bolt up if you elongate the mounting holes. Simple and effective modification. Another tip is to use a MC from a Hummer. It is proportioned properly for the M715 4 wheel drum setup and bolts to the J-20 MC.

You can get your wheel cylinders sleeved with stainless steel and also have metallic brake linings added to your M715 brake shoes.

With the above mods, you will not believe the stopping power those massive M715 brakes will have.

[FSJeeper]

I meant power booster assembly when I said MC in the above post. Sorry.

[Mikel2]

Thank you all,
FSJeeper, I pulled my brakes apart yesterday and the shoes look very good. I could get them relined locally, do metallic linings really make a difference?
What would be the difference in performance from a J20 MC and one from a hummer? How much would the second cost??
Thank you all again,
Mikel

[Mikel2]

FSJeeper,
I was thinking about a J20 dual diaphragm booster/master cylinder too, but after going through the archives at the M715zone, I'm concerned that a disk brake MC might not flow as much fluid as an all-drum MC. Someone suggested getting a 75 J20 booster and a 74 J20 MC. What do you think?
Thanks.
Mikel

[krob725]

I am using a booster and MC from a 89 GW on my M725. it seems to work good. had to modify the the link that goes to the pedal. i replaced all of my wheel cyl's and shoes, hard lines, etc with off the shelf items.

krob725

[FSJeeper]

Use an 80's J-20 dual diaphram booster, and a Hummer master cylinder. You can find them in the military surplus places and ebay sometimes very cheap. The pressure the Hummer 4 wheel disk brake MC puts out is perfect for the M715 4 wheel drum setup. The Hummer MC bolts to the FSJ booster no mods.

This is the optimum setup for the M715 drum brake setup and you will not want any more brakes than that if you go the metallic brake linings too. Awsome brakes.

I speak from experience, not guessing. There are a lot of posts at the M715zone website that are not accurate. There are a group of us here in Texas that have been messing with M715's for years and have pretty much exhausted all the mods you can do to the M715.