Brake problems in 88 XJ.

[XJPioneer88]

So, I have a 88' Pioneer I6, 4x4, 5 speed manual, with no ABS on it.

Lately, I've been noticing my brake light on my idiot cluster coming on...Usually it means no brake pressure? At least thats what happened in my old 93 Sport I had when a brake line pop like a zit.

So, In the 88 pioneer, the brakes had been just replaced the month I got it. (I've had it for 4 months.) The resistance has been great, they haven't given me problems...This whole problem has been going on for the last 2 weeks or so.

Just tonight, When I stopped to turn onto the main drag...Thats when it happened. The light came on. I tested the brakes on the road and they seemed fine, Till' I got home, I came to a complete stop (45mph) to zero. The brake light turned off. No change in pedal resistance.

So, basically what I'm thinking, is that it might be an air bubble in the lines...If you guys can confirm it is, great.

Because as far as I'm concerned, I'm stumped.

 

[magimerlin]

The light can come on from two different switches.
First is the one on the combo valve, if you get a leak it moves the check ball to that side to block the leaking side(front or back) and will throw the light on.
The second one that will put the light on is the e-brake switch. I know it sounds funny but make sure your e-brake lever is all the way down, If it is even just one click up it can pivot on the switch and trigger it.

 

[Lifted87chevy]

Have you checked the fluid lately? For the check ball to move to one side there has to be no fluid first. I had to bypass my Switch when i swaped in a brake booster form a 2001 grand chero.

 

[XJPioneer88]

The light can come on from two different switches.
First is the one on the combo valve, if you get a leak it moves the check ball to that side to block the leaking side(front or back) and will throw the light on.
The second one that will put the light on is the e-brake switch. I know it sounds funny but make sure your e-brake lever is all the way down, If it is even just one click up it can pivot on the switch and trigger it.

The parking brake is all the way down...no problems there.

I don't have leaky brakes. Like I said, all the lines were replaced. It could be the wheel cylinder. Ill take a look at it real good...once it decides to stop friggin' raining.

Thanks for your input you guys.

Anyone else wanna tackle this savage of a problem?

 

[cherokee chuck]

I had a similar problem with my 87, I replaced the calipers but eventually I stepped on the brakes & they weren't there. Pretty scary. They pumped up & worked ok but I replaced the m/c ASAP & that cured the problem. I wish I'd Known about the dual diaphram swap before I'd gone through the whole system. Our early XJs have notoriously crappy brakes.

 

[XJPioneer88]

What is it, like $300 for a m/c with labor these days? I mean, I can live with this, for now...I mean, the resistance hasn't gotten worse to be honest (I usually just pump it and it works fine the rest of the drive like you said.) But it does not mean that I'm going to ignore it when it worsens.

Blech, I hate spending money.

 

[cherokee chuck]

$300? That's a $65 m/c NEW, not rebuilt. It should be 1hr shop time[just a guess, sorry, I don't have a flat rate book any more] plus fluid. That should be more in the line of $125/$150. If you did the previously mentioned work yourself you can swap the m/c. Just bench bleed it before you install it. Don't put this off too long. You'll drop a load in your drawers when the pedal hits the floor.

 

[XJPioneer88]

So, it's been a few days and here is what I uncovered...

Opened up the brake fluid reservoir, to find that the smaller section (Rear brakes?) was pretty much bone dry. Checked thoroughly for leaks and can't seem to find any, which is to imply that it's probably internal. A lot of research later, it seems that many signs are pointing to the master cylinder?

I'd figure if I kept driving it I might lose my brakes altogether... :smsoap:

I'm just in need of come conformation from you guys!...

 

[cherokee chuck]

:cheers:If you are losing fluid with no visible leaks it's the m/c. When you wreck your Jeep because the brakes fail, that will confirm it. Your booster can be damaged by the fluid that leaks from the m/c. Remember, the fluid's going somewhere, probably into your booster. Once again, now is the time to upgrade to a dual diaphram setup.

 

[Rick Anderson]

magimerlin explained what lights the brake light. Just to add, modern brakes are a dual system, having 2 pistons in the MC (in line in the same bore) that each supply pressure to half the brakes, usually Front/Rear (recently some cars have switched to an "X" pattern). The combination valve senses a difference in pressure between front/rear, that check valve moves if pressure difference is too great between the two and throws the switch to light the light. The pressure difference can be a leak, or one of the 2 pistons in the MC blows out, or anything that will cause pressure to drop in one of the two brake hydraulic circuits.

My Jeep had the same problem as yours, just after I got it from the Previous Owner. Turned out, I had leaky rear slave cylinders, the drum cylinders. The leaking fluid is hidden in the drums, there was enough dust and dirt in the drums that the leaking fluid mixed with it to form goop and absorb it all before it could drip out. Didn't spot it till I pulled the drums.

Of course, it could be a leak at the MC, but the fluid has to go somewhere, and often a leak at the MC means its going into the Brake Booster that will damage the booster eventually. As well, its NOT uncommon for a MC to go bad shortly after doing brake work. Bleeding the brakes stroke the MC into parts of the bore that hasn't been used before, that can be corroded and that corrosion can cut, mess up the seals on the pistons. Or pushing slave cylinder back in their bores, for new pads, can force dirt/contaminates in the fluid back up into the MC and mess it up.

Pull your rear drums first and inspect, that costs nothing, see if you can see brake fluid leaking from the slave cylinders in there. If the rear drums check out perfectly, then I'd look at the MC.

 

[XJPioneer88]

My Jeep had the same problem as yours, just after I got it from the Previous Owner. Turned out, I had leaky rear slave cylinders, the drum cylinders. The leaking fluid is hidden in the drums, there was enough dust and dirt in the drums that the leaking fluid mixed with it to form goop and absorb it all before it could drip out. Didn't spot it till I pulled the drums.

Hm, never thought of that...It would be a less expensive fix too as opposed to a mc, huh?