Brake Light ON (New XJ Owner)

Hey folks,
Hopefully this isn't too much of a Noob question. I've just bought a old '95 Jeep Cherokee, 2.5L I4 w/ 5spd Man trans, 2WD. Its still sitting at the former owners house, while I await new tags.

The vehicle has the brake light on, the owner said it was on for the last 50k miles. I checked the brake reservour and it was bone dry, with lots of dirt and clumpy crud at the bottom of the reservour. The brakes work, but only work after you've pushed the pedal down 3/4 of the way.

Looks like to me, the brakes have air in them and/or Master Cylinder has a blown stage. So heres the question;

ON a '95 Cherokee (NON-ABS) what lights the Brake Light? Is it low brake fluid or is it pressure differential at the combination valve? It has a clear plastic Reservour on the Master Cylinder, like my newer Neon which the brake light goes on low fluid, but it is NOT the "X" stage arrangement like my Neon, its the front/rear stage arrangement like most older cars that uses the combination switch.

Rick Anderson said:

Hey folks,
Hopefully this isn't too much of a Noob question. I've just bought a old '95 Jeep Cherokee, 2.5L I4 w/ 5spd Man trans, 2WD. Its still sitting at the former owners house, while I await new tags.

The vehicle has the brake light on, the owner said it was on for the last 50k miles. I checked the brake reservour and it was bone dry, with lots of dirt and clumpy crud at the bottom of the reservour. The brakes work, but only work after you've pushed the pedal down 3/4 of the way.

Looks like to me, the brakes have air in them and/or Master Cylinder has a blown stage. So heres the question;

ON a '95 Cherokee (NON-ABS) what lights the Brake Light? Is it low brake fluid or is it pressure differential at the combination valve? It has a clear plastic Reservour on the Master Cylinder, like my newer Neon which the brake light goes on low fluid, but it is NOT the "X" stage arrangement like my Neon, its the front/rear stage arrangement like most older cars that uses the combination switch.

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I believe both will illuminate the brake lamp...and if you haven't blead the system yet thats probably why the brake lights work like they do, and by the way you can harm the master cylinder by pushing it too far down if it alraedy was'nt ruined

majic_tech said:

...and by the way you can harm the master cylinder by pushing it too far down if it alraedy was'nt ruined

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Are you talking about stroking the MC piston farther into the bore than it usually goes, messing up the seals on corrosion in cylinder?

The prevous owner says he's been using it like this for the last 50k miles, so I think the damage is already done.

Judging by the condition of the brakes I won't be surprised if I need to do a complete rebuild of the entire system. Something I've done before on other cars. I guess the thing to do is clean out that plastic reservour, fill with new fluid and completely flush the system with new fluid. If it cures the light, and a visual inspection shows nothing else to bad out, and the brakes feel good; then I can get it inspected for a new registration. I pretty much plan that a rebuild of all the brakes is in order, just on mileage, 201k miles. I guess its only a matter of doing before or after the inspection.

Whenever they manufacture brake master cylinders, sometime's the machining process doesn't bore down the whole way through the cylinder, leaving a rough finish inside the last portion of the tube. If there isn't enough fluid (i.e. pressure) to restrict the piston, then the possibility exists for the piston to be overextended. I've accidentally done this a few times on several vehicles with no apparent problems, but the thought has always lingered in the back of my mind.

With that said, I'd still probably replace the MC if it's as crusty as it appears -- remanufactured units are fairly cheap. You're probably aware of this, but don't forget to bleed the master cylinder if you replace it (or any time the fluid is completely drained from either resevoir). The easiest way that I've found to do it is to attach scrap metal lines to the output of the MC, press on some clear tubing, and pipe the lines back into the corresponding resevoir. Fill the fluid to the top and slowly cycle the brake pedal until you don't see air bubbles in the clear lines anymore. Works like a charm and will definitely get rid of that mushy pedal feel.

The brake light on the instrument panel can be activated by one of two things:

1. loss of pressure on one side of the brake system or the other. (You already know you have this problem, since you say the MC reservoir was dry.)
2. parking brake being on or partially on. This is controlled by a switch on the parking brake handle lever.

If I was in your shoes, I would replace the MC, flush and replace all the brake fluid, and posssibly even consider replacing the wheel cylinders and calipers, if they are OE. You have a 11 yr old vehicle whose brake system has been neglected. That, in my mind warrants a thorough overall of this very critical system.

Another vote for just replacing the m/c and doing a full bleed on the system. Replacing the front calipers isn't expensive and you're better than half way there if you're bleeding the lines anyway.

If nothing else, you *KNOW* there's a leak in the system somewhere. All that fluid just doesn't dry up and blow away.

Thanks for the replies guys. As far as buying a rebuilt MC or slaves at the different points. I'll rebuild them myself, I did that with my '91 Caravan and it worked great, its quite simple and the rebuild kits are only a fraction of the cost of buying a rebuilt replacement.

However, you all have a good point on the MC and corrosion. Upon dissambley, if the bore appears more corroded than a light honing to break the glaze will remove, then I'll have to put it back together and use it as a core for replacement rebuilt unit. I have a feeling that will be whats happens from the crud in the reservour.

ChiXJeff said:

If nothing else, you *KNOW* there's a leak in the system somewhere. All that fluid just doesn't dry up and blow away.

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D'oh, I can't believe I didn't diagnose that immediately. I "assumed" that it was because the pads/shoes were almost down to the backings, and the prevous owner never added fluid. That would explain a reservour very low on fluid, not a completely dry reservour, that's a leak.

The pedal does feel like one stage is completly dry, probably rears, judging from the stopping power during the test drives. The line running back to the rear is extremely rusted, any bets that its preforated somewhere along the bottom of the vehicle?

Still, $900 for an '95 XJ with good body, paint, interior and decent engine/drivetrain and tires (Believe it or not, the AC blows cold air). Even if the brakes are a total write off, I figured it is worth it. Its a 4 cyl, 2WD, which is actual what I wanted, less problems, less repairs, a little better mileage. This is a 3rd Family car, for the teenager to drive, the only other options I've found in my price range, were FWD econo-boxes that needed major work, like a new transmissions or major body repairs. Plus this has a little bit of size to it compared to the others, something that doesn't hurt with a new driver teenager.

I got the tags today, so I'll be picking it up from the prevous owner's home tonight, only I will drive it until the brakes are a 100%. A teenager and bad brakes are not a good combination, well, not good with anyone.

It will need the Maryland Safety Inspection within a Month, I've got a feeling I might be doing some tie-rods and ball-joints as well as brakes before then. The suspension feels fine, but with 200k miles, I'd be surprised if some of the front suspension joints don't need replacement.

SUCCESS

I could not find any leaks or evidence of leaks, the light must have been bad when I looked over the car during the purchase, because the lines are not rusted, they don't look in that bad of shape.

I picked up some speed bleeders during lunch, and put them on tonight. Bleed the entire system with Castrol GT LMA brake fluid. Boy was the old fluid black, and half of it was brand new fluid mixed in, I thoroughly flushed the brakes, easily pumping three times the volume at each point.

The Pedal height is up to Normal Brake Pedal, the brakes work great and the "BRAKE" light is out.

I'll keep an eye on the brake reservour level, because you can't rule out leak when the reservour is dry.

BTW, SPEED BLEEDERS, well worth the money IMHO. Less than $10 a pair, they make the brake bleeding job so much easier, faster and more effective. If you've never heard of them, there regular bleeder screws, except they have a one way check valve installed in them. So you just loosen the Speed Bleeder screw, attache a hose to a bucket and then pump away. I can bleed the entire brake system in 15 minutes all on my own.

I got them at my local auto franchise, they sell them in the "HELP" brand section, with the rest of the bleeder screws in that section. The "HELP" brand calls them "ONE MAN JOB, BLEEDER SCREWS". They only have them in the two most popular sizes, 3/8"X24X1.25" and 5/16"X24X1.00", which just happens to be the bleeder screw size for XJ, front and rear.