CJ7 Brakes

Brett Polwell

My Dad has a 1983 CJ7 with axles out of a 1975 CJ5 under it. On the front Axle we put the disc brakes out of a 1977 CJ7, but left the original master cylinder from the 83. Needless to say we had some spare parts laying around. Anyway this thing has never had good brakes. I was wondering if anybody knows if there was a difference in the size of master cylinders. Would the master cylinder off of a 77 work better. For some reason I am thinking the brakes were bigger on the older Jeeps and maybe had a mc that moved more fluid. It just seems to run out of pedal. All the brake parts are new and the lines have been bled several times.

tufcj

The 77 did have bigger brakes, But I don't know if the reservoir in the calipers are bigger. A 77 master may help. Check the little things first. Rotor runout, front wheel bearings, caliper slides clean, and rear brake adjustment are the usual causes of a spongy pedal. If it's just weak brakes, it could be the vacuum booster. What kind of vacuum does the engine pull? Does it have a bigger than stock cam? You might want to upgrade to the dual diaphram booster from somewhare like MPbrakes.com. If you're running 35s, you just aren't going to get the performance you had with factory tires (maybe 29s) without upgrading. Just a whole lot more mass and leverage to stop. Bob tufcj

Wrench Man

Brett Polwell wrote
It just seems to run out of pedal.

Is the pedal low?, does it pump up?

If you have a smaller master cylinder the pedal will travel farther but it WILL brake better, a larger master cylinder will have a higher/shorter travel pedal but it wont stop worth a crap.

donwag

In 83 the cj had front disc, so the 83 mc should work fine with front disk and rear drum. I just put all new brakes in my 84 cj and converted to power from manual at the same time. Manual brakes with 35" tires just did not cut it. If you are running out of pedal, it has to be in the fluid transfer somewhere. Did you bleed the mc? Also, make sure the rod from the pedal to the mc is the correct length. I purchased an adjustable rod to replace the stock one. Did you bleed the mc if you disconnected the lines to it?

jeepsr4ever

The first thing you should do is make sure you fully bled all the air out of the brakes. You should be stopping just fine but you may need to get your proportioning valve a tick.

Brett Polwell

It does feel better on the second pump but still doen't stop like it should. It has 35's on it but I had the same set up on an 84 CJ with those tires and had way better brakes. The only thing that hasn't been done in a long time is bleeding the mc. I did it when it was replaced several years ago. What got me thinking is that I have a YJ with bigger axles under it. When I did the E-350 MC swap I have better brakes than he could ever dream of having. I didn't know of the older MC moved more fluid. I will try to bleed the MC. After I get this problme fixed I have to work on the death wobble.