brake issues

Recently My brake light came on and I have a spongy peddle and diminished braking on my 89 xj non-abs.Usually when something like this has happened in the past there would be a leak somewhere and the master cylinder would be out of fluid but I've looked and can't find a leak and the master cylinder fluid level has never dropped and is full.How can my brakes be acting like this without a visible leak or drop in fluid level?

One last thing.What makes the brake light activate...I mean how does it sense when the brakes are not right?I always thought that it comes on when there is a drop in fluid?

The master cylinder could be failed internally, like a blown seal. You may not experience any fluid loss, but thier can be problems. The light comes on when the sensor on the prop. valve detects no pressure.

12GaugeXJ said:

The master cylinder could be failed internally, like a blown seal. You may not experience any fluid loss, but thier can be problems. The light comes on when the sensor on the prop. valve detects no pressure.

Click to expand...

Thanks...

I had the same problem for over a year. Originally, my master cylinder cover came off and the brake fluid leaked out while I was driving. I bled the complete system, including bench bleeding, and nothing worked. Replaced the master cylinder and the light went out, and brakes work much better.

There have been similar threads on here and it was usually a rear brake cylinder that was going out. They are cheap to replace. The last ones I bought were about $16 each. You may want to look at those, too.

If you have been leaking in the past you might have air in the lines also I would try bleeding the breaks first its the cheapest route to begin with

12GaugeXJ said:

The master cylinder could be failed internally, like a blown seal. You may not experience any fluid loss, but thier can be problems. The light comes on when the sensor on the prop. valve detects no pressure.

Click to expand...

Minor nitpik. The light is triggered when the prop valve sees a significant pressure difference between the front and rear circuits.

wheel cylinders are new.On a side note if it is the master cylinder it's only going to be 20.00 for a reman from napa!!I thought it was going to be around 60-70....

lawsoncl said:

Minor nitpik. The light is triggered when the prop valve sees a significant pressure difference between the front and rear circuits.

Click to expand...

Theres a Piston in the Proportioning Valve, really called the Combination Valve because it also contains this safety item. The piston has one brake circuit on one side, and the other circuit on the other side, before the pressure reducer. When you press the brake pedal and make pressure with the Master Cylinder (MC), both pistons in the MC should make equal pressure, and equal pressure for both circuits and thus the piston gets equal pressure on each side and does NOT move.

When there is a signficant difference in pressure on one circuit compared to the other, there is more pressure on one side of the little piston and it moved by the unequal pressure. The piston is connected to a little switch that lights the Brake Light if the piston is moved by the unequal pressure.

http://auto.howstuffworks.com/master-brake.htm


Obviously a leak in one of the brake circuits would cause a pressure drop and that would cause the difference in pressure that moves the piston in the combination valve and light the light. BUT, as mentioned, a blown seal in the Master Cylinder, could cause one of the two pistons to NOT make much pressure and give you the same symptoms and light, BUT NOT lose any fluid out of the system.

A lot of air in system could cause the same, but air usually doesn't get into the system unless you suffer a leak, open the lines or run the reservour dry; so you should have had the light immediately after one of those events. Air just doesn't get into a properly working brake system all on its own, something has to go wrong or someone has to have been working on the brakes to get it in there.

Wow...you took me to school with that illustration!!Thanks for the info.I took my pass side drum off today and as mentioned above the rear brakes were out of adjustment and the front shoe was down to the rivets on the top half only(the bottom half looks fine)??The back shoe looks fine....what would cause the front shoe to wear out on the top portion only?Got new shoes today but I don't want them to wear out in 500 miles like these shoes did!!!

I just put these shoes on 500 miles ago.What would make them wear so fast?Even though I have 34" swampers and ran through deep mud about 5 times since I did the brake job,I can't see that causing my rear brakes to wear like this??The front brakes are wearing good and were done the same time as the rear.....

Could it be an out of round drum??Or a weak spring?

Thanks

jeepdeepfreak said:

Wow...you took me to school with that illustration!!Thanks for the info.I took my pass side drum off today and as mentioned above the rear brakes were out of adjustment and the front shoe was down to the rivets on the top half only(the bottom half looks fine)??The back shoe looks fine....what would cause the front shoe to wear out on the top portion only?Got new shoes today but I don't want them to wear out in 500 miles like these shoes did!!!

I just put these shoes on 500 miles ago.What would make them wear so fast?Even though I have 34" swampers and ran through deep mud about 5 times since I did the brake job,I can't see that causing my rear brakes to wear like this??The front brakes are wearing good and were done the same time as the rear.....

Could it be an out of round drum??Or a weak spring?

Thanks

Click to expand...

500 miles is a pretty short time. I would guess that something was seriously wrong. Assuming the brakes were assembled properly, possibilities include a weak spring or an adjuster was way too loose and never adjusted. Also check for a damaged or dislodged mounting nail and holddown spring. One possibility, easily done, is to accidentally swap right and left adjusters so they loosen instead of tightening.

When you put the brakes together, make sure you operate them a few times, and then manually adjust them. Do this a couple of cycles, to insure that the shoes have oriented themselves properly.

I recently had a problem with my brakes (someone else's repair) and found that the adjuster cable guides were not properly installed. Everything looked good, but the guides were not all the way into their holes in the shoes. The cable was too slack for the pawl to hit the adjuster teeth. The guides just set into the hole, and are retained by the spring. They will be retained by the spring even if they are not centered in the hole, and it is not readily visible unless you check for it.

The whole kit of new brake hardware is pretty cheap (adjuster and cable are separate, but all the springs are there). I would strongly recommend that you get new hardware before putting it back together, and that will insure that you get good springs.

yep it was only 5 bucks so I got it but I'm sidelined once again by this damn Ohio rain(no garage).Any one have a good pic of how everything should look when assembled properly,just for my reference.
I did one side at a time so I could use the other side as reference during assembly,but who knows if they were put on right by the previous owner....

I can take a picture later tonight, I'll be striping my drums down to the backing plates to put them on new axles rebuilt.

Ok I have a problem...when I ordered the shoes autozone asked my what size drums I had so I took one in and they measured it.They said they were 10x 1 3/4" and the other sizes were 10x 2 1/2" and 11x 2" why are there three different sizes??What Were the axle options available in 1989??Do some dana 35's use different size drums???

I'm starting to think that the previous owner had the wrong drums and or shoes on there to begin with.These shoes don't sit right....the front shoe won't contact the round pin at the top and it looks like they are making the wheel cylinders push rods sit crooked.Something is not right.How do I tell what size brakes my jeep came with stock?This is a 1989 cherokee 4.0 5 speed with d-35 rear...I hate dumping money in this boat anchor but I need to drive untill I get the cash for a d-44

Thanks in advance.

you need to measure the drum. Measure the mating surface inside the drum and it's diameter. I thnk that only the d44's got the 2.5" drums. I didn't get to take a picture of my rear brakes tonight for you, I got hung up on my fronts.

Ok I feel stupid but I got it figured out and my brakes are back to normal and the light is off.
The damn e-brake cables were seized up!!!Which made the shoes not seat fully.Freaking stupid little problems!!!!

anyhow,thanks to everyone....