Brake help

[thescot]

Forgive me if this is the wrong place, but I dont see a home for brake related topics. Non the less...I recently picked up a 83 CJ7 . P/O said the brakes were worked on about 5K ago, rotors, pads,drums & shoes. Seems everything done by this shop who did the brakes was good, however the brakes are extremely weak to the point I have reservations about driving in on the road. Pads and shoes look good, rotors an drums are clean and un grooved, no leaks, no booster/ vacuum leaks. I used a mighty vac to bleed them a few days ago, fresh fluid, the pedal is firm but no way can you come close to a lock the up, more like it slows down, like I have no front brakes. The seller didnt mention anything either or appear to have issue with them. Last stop (no pun) the possibility of the incorrect master cylinder from a different year making insufficient internal pressure from to big of a bore? maybe a bad proportioning valve? Any thoughts?

 

[Jimbos76cj]

HAve you made sure the rears are adjusted properly? Id pul the wheels off.. draw a wide black line on both rear drums and both front callipers then take it around the block or make some good stops with it then remove the tires again and see if any ofthe marks aer worn off. Can you check the booster to kae sure its working right?

 

[chargermop]

I have the same problem on my 79 I guess I should really should pull the wheels and check all the breaks for myself. I guess you just get so excited with the new toy you forget to do the basics.

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[Jimbos76cj]

Also check your soft lines.. some times that will get soft and bulge causing the pedal to be soft.

 

[Barry2]

Do you have a power brake unit on it? If so is it getting vacuum to it?

 

[thescot]

Honestly that's a good question on the booster. The line if hooked up the the TB. Its a possibility the booster diaphram is shot and the line was plugged to avoid a vac leak. It also has braided lines front and rear. Looks like I may be tearing into the rear end after today so I'll check deeper into things but the shoes and disc pads are like new still wear wise.

 

[IOPort51]

two words, proportioning valve.

 

[jdarg]

Get the wheels in the air and see if you can lock the brakes enough to keep the wheels from turning if you try to turn them by hand as hard as you can.

If they don't lock enough to at least keep them locked in this scenario I'd lean towards one or both residual pressure valves missing or being bad. Usually when those aren't there you can't even get enough application at the wheels to pass this easy test because the piston has to move too far to get proper engagement. The RPV keeps the piston much closer to the point where the friction surface will start making contact vs. without one.