I'm back on the road but with a reacurring problem...

Well, I finnally got my jeep back on the road after three weeks of replacing the entire brake system (10 inch) and then rebuilding the carb (I filled the holes in the mount, still don't know why there there) Well, The engine runs better than ever and stopping is greatly improved , However, my rear tires still lock up before my front ones. I tried tighting up the front but that didn't work (even way to tight), so I'm not sure whats going on. Does anyone know why this might be happening. Everything is new from the master cylinder to the drums themselves. How do I fix this? :?

 

Do you have smaller cylinders on the rear wheels? Most of the stopping force is applied by front wheels, so the fronts should be larger (i.e. 1-1/8" v. 7/8" or something like that).

 

It is possible to install an adjustable proportioning valve, which allows the driver to increase or decrease the relative power of the rear and front brake lines.

Used for trucks when loaded versus unloaded, etc. I don't have experience with these however, not sure if they are still available.

First I would be certain there is not some other problem. Do you have a dual master cylinder - are the output lines reversed, maybe?

Pete

 

where did you get your master cylinder? I had the same problem and it turned out that the ports on the new MC were reversed. try reversing the lines and see what happens. $.02

 

Make sure there are no kinks in your lines too.

 

Looks like yall pretty much have it covered. Either master cylinder or brake cylinders, one or the other. You could put a proportioning valve on it but I would try the other things that have been mentioned first. Just my .02

 

Hey guys,
Well, as for the wheel cylinders, 1 inch bore is on the front and 3/4 is on the back, which is correct, so thats not the problem. I've made sure there were no kinks in the lines many times. Don't think I would have missed them. I got the MC from pepboys, and I did what the think had molded into it. front brakes are the rear MC and back brakes are the front MC. Which makes since because they bore a one inch hole then continue with the 3/4 bore when they are making the MC. $ sink- did you switch it from this or to this?

I was talking with my dad today, but this CJ has 33'' by 12.5'' supper swampers, fairly massive tires, and all the wight of the cj is in the front... So if there's more wight in the front means the tires are going to get better traction, which would keep them from locking up. But on the rear, there is very little weight so it has a tendency to lock up first. does this seem like sound thinking, or am I off base?

 

This could be the problem if you can't find something else. If it turns out that the weight is a factor, then you need to get an aftermarket proportioning valve so you can adjust them to your liking.

 

reverse those lines and you should have the problem solved. it seems, to me, that the lines were cast in wrong. it's been a while, but i believe the resevoir closer to the pedal always goes to the front cylinders.

 

Alot of cars trucks etc will lock the rears first.
Weight transfer at work. .
Besides if one set had to lock up I'd much rather it be the rear instead of the fronts. A skidding tire wont steer.

 

Good point. the back only lock up when I slam on the brakes now. Perhaps I'll just leave it alone until it becomes a problem.

Yeah, the one closest to the pedal is what I called the rear of the MC. so it goes to the front.

 

Sounds normal, With a lifted short wheelbase vehicle the weight transfer is significant.

 

Did you replace the hard lines also? Most people just change the MC, wheel cylinders, and hoses, and forget to either change the hard lines or clean them (roto-root them) out. The same crap in the system (dirt, debris, rust) that made you replace the majority of the system is probably still in the hard lines. Rust, dirt, etc. in the hard lines can cause pressure irregularities (somewhat like a proportioning valve would do), which can most definitely lead to premature wheel lockup. In sum, if you have not changed or thoroughly scrubbed the inside of your hard lines, you might want to do so. CJ

 

if they lock up when you're standing on them then i really don't see a problem. mine do that when i slam down on 'em... the front nose dives and the rears lift up a bit and lock up. nothing i can, or want to do about that.

 

Cee Jay - yep, I replaced the hard lines too. The only things left of my old brake system is the pedal and the pressure switches, which I cleaned diligently.

I guess I shouldn't worry about it then, Its just everything I've read here says the front should lock up first, so I thought there might be a problem. Thanks Guys

 

I think you should follow up on this. You do not want the rear brakes locking before the front - it's just too big of a risk. The vehicle will tend to spin. You would not notice this much on dry pavement but it would become real clear real fast on ice.
The fronts must lock up first. This is a safety issue & I just don't think you can leave it.

Now, how to fix? Because you've replaced just about everything some of the usual suspects are out. How about:
-kink in a hard line?
-wrong hookup on the MC
-wrong wheel cylinders
I agree that none of these seems very likely. If nothing else get an adjustable proportioning valve & install it on the line to the rear, it could mount right on the frame. I ran the hard lines inside the firewall on mine but it was not worth the effort as I don't need to fiddle with it often.
HTH

 

My old Topaz would lock the rears first, the first few times it happened it scared the crap out of me. After that I just got used to it.

 

I'll look into a porportioning valve. Again, wheel cyclinders are correct, I asked around before I put them in. big up front. MC is correct because it would be a little hard to put a bigger bore behind a small one. so the one closest to the petal has to be the one's to the front. I know the lines are not kinked because when I bleed them it came out strong enough to splatter brake fluid all over my safety glasses.

Lucky I won't have to deal with ice for quite a while. The jeep is going to southern MS while I'm in Brazil, So I've got a while to find out whats wrong.

 

X2 On the road. Climbing up a hill that you end up not making it to the top of is another story though.

 

He stated that it only happens when he slams on the brakes though.
Going up a hill more wieght is on the back end.