Hi Guys,

Another problem from over the pond that I hope some of you XJ experts might be able to advise me on.

I have a 1994 Cherokee XJ with ABS. It has recently failed our MOT road worthy test for the first time since I bought her in ’97 on a rear brake issue.

Mr Tester has failed it on ‘unequal brake pressure across the rear axle’ with the left rear reading low on the rolling road brake test (right rear is OK).

I took the drum off and found nothing wrong other than the adjuster was backed right off and seized. I replaced the adjuster and adjusted the brakes both sides and deglazed the drum with emery cloth. I fitted new shoes about three years ago since when the car has done less than two thousand miles and the shoes are hardly worn. Took the car back for a retest and it failed again on the same issue and same pressure reading. I then fitted new wheel cylinders (Bosch) and put in for another test. Plenty of brake fluid was bleeding out under pedal pressure when we bled the brakes.

Again, failed the retest, same issue.

From underneath the car I can see the rear metal brake pipe that goes front to rear along the chassis rail to the rubber brake hose which connects to a ‘’T’ block bolted onto the rear axle. From the ‘T’ block run the two metal pipes across the rear axle to each wheel cylinder. The metal brake pipes appear to be undamaged and are protected by what looks like a metal conduit.

Does the ABS work across the rear axle and effect each wheel?

Any ideas guys where I am going wrong?

Cheers Jim

 

If there's just one brake line to the rear axle, and it splits at that junction fitting, there's no way for the ABS to control each rear wheel independently. This may be a stupid question, but are your brake shoes installed correctly? The shorter shoe should be toward the front on both ends of the axle.

 

Hi IJ,

Thanks for the reply. Yes shoes fitted correctly and my Jeep has passed three previous tests since fitting them.

 

Thankfully I have no personal experience with the MOT brake test but found it on the internet. Given how the rear brakes are plumbed, assuming you have bled and adjusted them correctly (the self adjusters are useless) and given how little the thing is driven my guess is that the shoes/drum on that side is contaminated with something... brake fluid/hypoid lube/ greasy fingers.
I suspect that ultimately you will be really degreasing the drum ,replacing the shoes, driving it around some while litely applying the parking brake to seat the shoes, adjusting them again and praying.
(Having spent a lot of years around chassis dynos I did wonder if the tire on that side could be slipping on the rolls but the thing I looked at seemed to show the brake testing rolls have a texture)

 

So it's a chassis dyno test measuring the braking force at the wheel, not the pressure itself? If so, something as simple as tire pressure or wear will affect the results.

 

JimWatch and weep
If there was inspection like that here there would be no xj's. I can imagine the rusty criteria

 

You can make your own "dyno" test rig. Securely chock the front wheels. Jack up the back at the diff so the wheels clear ground by 2-3 inches put jackstands under the axles. The farther out the better. Keep the jack just barely touching the diff, as a backup. In N do both wheels freely turn? Set the parking brake...are both wheels locked? Start the jeep in 2wd and let idle, shift into D. Are both wheels not moving? Do the same check while stepping on brake pedal. It sounds like you are just out of adjustment .Was your truck running when they did this brake test? Do not attempt to shift into P until engine is off.

 

Hi guys, thanks for your suggestions, much appreciated.

OK there's no contamination of the shoes and everything inside the brake drum is working as it should.

Exasemech, thanks for the video clip, I've not seen that before and had a chuckle re the comment about no XJs in the US if you had a similar test regime.

Jim you mentioned something that had not occurred to me regarding tyres. I run with General GRABBER HTS 225 70 R15 tyres over here. Earlier this year I had the left rear (the 'problem' corner) replaced after I picked up a nail through the sidewall. The tyre fitters could not get an HTS and have fitted a same size AT which has a chunkier tread pattern. Being on the rear I didn't care much and it was legal. I'm now wondering if that might be the problem, but I can't believe our test procedures wouldn't take that into account but then this is the UK!!!!. I'm having to admit defeat on this problem and putting the Jeep into a workshop next Monday for them to look at and will mention your comments. I'll keep you guys posted.

Cheers

Jim

 

You had not mentioned the tire before. That may well be the problem, either different tread or different rolling diameter.

 

does the vehicle have a "spare tyre" ?

put that on, and compare circumferences while you are at it

 

Hi Guys

Well, here is my feedback re my rear brake issue. Over here the greater majority of our MOT testing stations are garages that carry out repairs, servicing etc. I have avoided these stations because there are so many stories about unscrupulous testers telling the car owner as they suck in through their teeth "sorry but its failed because a brake light isn't working - but we can fix it for you for £20" for example. I'm sure you've all had similar stories your side of the pond. But we also have a few Council run stations that do not carry out repairs or are affiliated with garages. It's one of those that I prefer to go to. Up until this year I knew the tester on first name terms and he was very honest and fair. If for example it was a brake bulb issue he would say to me "I'll give you ten minutes to replace it while I carry on checking something else". This year he's gone and it's a new tester that failed my XJ. To cut a long story short I bit the bullet and put it into my local garage yesterday for them to have a look at the brake problem because it had beaten me. The result was they couldn't find anything wrong with the brakes, did another MOT and have issued me with a 'pass certificate' for another twelve months'! I'm not sure if there is a moral here but thanks for your suggestions and no doubt I'll be back with something else before too long.

Cheers

Jim

 

1) doesn't surprise me. Crooks are everywhere. It's also possible the test equipment was screwed up.

​​​​​​2) Thanks for the follow up. Too many folks post questions on here, people provide well intended advice, and you never hear the resolution.
3) I would try to figure out if the one tire that's different than the other 3 has the same rolling diameter as the others. If not it could cause problems on either end of the vehicle.

 

Somewhat related... Where I work we have a number of mountain top communications sites. Typically there are several other sites on the same mountain and an "association". We have yearly inspections of the sites through the association. If there is a new head of the association he will fail every single site on some made up factor that has passed inspection for the last 20 years and can't be backed up by relevant law or bylaw. After two or three years of that he will calm down. Happened with several sites with different associations.

The moral of the story is you need to recognize and bow down to his authority. You'll have to bow pretty low to not tower over such a tiny man.

I'm glad to hear you got past your LMS patient.

 

Seizing? Use an infared thermometer to check