How to diagnose a bad front diff?

[DeCaff2007]

I'll get right to it. Just bought an 05 KJ with 127K, pristine body, and runs perfectly. Problem is the front diff is probably shot.

I noticed that the front driveshaft was missing when purchased. Found a driveshaft at the yard, installed it, then took the Jeep for a test drive.

There was a noticeable grinding in the front after that. Especially when accelerating. The grinding seems to be just forward of the gas pedal.

Before I go tearing the front diff out, is there a way to test for sure if it's the front diff making that noise?

 

[derekj]

Get it up in the air, climb under it, and run it in 4wd - if it is the front diff making noise it will be pretty obvious

 

[DeCaff2007]

Get it up in the air, climb under it, and run it in 4wd - if it is the front diff making noise it will be pretty obvious

Will do, but here's a question: What if I'm hearing a noise in the front while in 2wd (not in the air lol).

What are the possibilities then?

 

[duderz7]

The dront diff turns weather you're in 2wd or 4wd with or without the front drivshaft. If it was quiet without the drivshaft it's likely that the drivshaft is the issue. The rear cv on the front drivshaft is known to go bad and make noise.

 

[DeCaff2007]

The dront diff turns weather you're in 2wd or 4wd with or without the front drivshaft. If it was quiet without the drivshaft it's likely that the drivshaft is the issue. The rear cv on the front drivshaft is known to go bad and make noise.

I get that, but that's with all 4 tires on the ground, correct?

 

[mrlavalamp]

I get that, but that's with all 4 tires on the ground, correct?

yes, whenever you drive the jeep, the front diff spins because there is nothing decoupling it from the tires.

In days of yore 4 wheel drives had locking hubs on the front wheels, but our jeeps do not have these so they are always engaged.

I would be looking into the driveshaft you added as your most likely source of noise. (driveshaftparts.com has great rebuild kits for it).
That or possibly something with the t-case's front output. Shouldn't be very much play there, but diagnosing that part any further involves tearing into the t-case.

 

[DeCaff2007]

Alright thanks for the info. Haven't had a chance to look at it yet, but when I do, I'll post pics/vid.

 

[DeCaff2007]

So, I'm sorry but I still have NOT had a damn minute to do that test that derekj suggested. I ended up having to put new struts, upper control arms, lower ball joints, and tie rod ends on both sides.

This is how it's going to be now, huh? Pristine body and runs excellent, but the whole suspension ends up being shot. Still going to need a rear control arm. Ended up replacing that TWICE on the last Jeep (we also had it for 12 years, lol).

Now, I did look at the wheel bearings in the front. They spin smooth by hand but I know that's not much of an indicator of anything. They are rusty crusty on the outside, but I don't think they are what's making the grinding noise up front. We gave the Jeep a much better test drive today after fixing the issues with the brakes. The grinding up front is constant. Turning either way matters not. Acceleration doesn't affect it at all, although it's SLIGHTLY more pronounced if decelerating WITHOUT hitting the brakes.... as in just let off the gas and let it coast to a stop. That's the only time the grinding is louder.

TOMORROW... I have a clear schedule for the most part and if the weather cooperates, this Jeep is going up on all 4 jack stands and I can listen real good.

I'll post back what I find.

 

[DeCaff2007]

Alright. Finally some results. I did exactly what derekj said. The Jeep was up on all 4 jackstands. The Wife started it up, foot on the brake, and put it in drive. As she took her foot off the brake, she cycled through everything. 2H, 4H, N, and 4L. NO grinding anywhere whatsoever. NONE. We turned the wheels both directions, gave it a little gas, did everything we could think of. No grinding anywhere. The good news is, all 4 wheels were spinning freely while in the air.

Aside from taking the junkyard driveshaft off again and retesting, I'm stumped!

P.S.: We have also figured out that the range selector does NOT like to switch from 4H to N to 4L, no matter if it's in park or drive.

Aren't there two different transfer cases? I seem to remember one is part time and one is "set and forget". Could someone refresh my memory?

 

[turblediesel]

The Selectrac transfer case allows "full time" four wheel drive and the Command-trac does not. Both have "part time" which needs a road surface like sand, ice, or snow that allows the tires to slip.

Jeep should be rolling less than 5 mph in neutral to get in and out of 4 low easier.

 

[DeCaff2007]

The Selectrac transfer case allows "full time" four wheel drive and the Command-trac does not. Both have "part time" which needs a road surface like sand, ice, or snow that allows the tires to slip.

Jeep should be rolling less than 5 mph in neutral to get in and out of 4 low easier.

Thanks for the info. How do I know which one we have on this heap?

 

[u2slow]

Thanks for the info. How do I know which one we have on this heap?

There a red button tag on the back of the tcase with the model #.

If the shift handle has a 'full-time' position, its the 242J select trac. Otherwise, its a command trac and most likely a 231J.

 

[DeCaff2007]

Ok I have more answers. First, there's no "full-time" position on the shift handle. That's actually irrelevant to my current problem, but it's an answer, nonetheless.

Secondly, I tore the front driveshaft off and the grinding noise is still 100% there when driving. Mkay, so it's gotta be either the front diff, the wheel hubs, or the CV axles in the front diff. Well, after doing that test on jack stands, the ABS came on and stayed on. I'm thinking that was a side effect of that test. I have a scanner that can read ABS lights and it told me that the Right Front sensor has no signal. Yes, I triple checked that it's plugged in lol.

I had also noticed that during that test on jack stands, the passenger front wheel was spinning just a little slower than the drivers side (and in reverse! So these are open differentials, eh?)

Dunno... can a wheel bearing make THAT much of a grinding noise that it's heard and felt in the whole front end?

The front driveshaft, btw, wasn't too bad, but it wasn't great, either. I tore BOTH CV joints apart. The front joint wasn't terrible, but it had very obvious signs of wear. The rear joint was actually pretty decent, but it took a BEATING to get that joint off of the splines on the drive shaft. The splines themselves looked to have micro-pitting (is that even a word?) and the part of the shaft that the boot slides up and down on was pretty worn.

MEH. Junkyard junk lol. I'm going to order both CV rebuild kits. The cost of the drive shaft from the yard and the two CV rebuild kits is still considerably cheaper than a brand new drive shaft.

 

[DeCaff2007]

So, let me ask the next question here. With the front driveshaft off, is there a way to test, without a doubt, what is making the grinding noise?

 

[DeCaff2007]

Lol so everyone is stumped, including me, or did I miss a reply somewhere?

 

[u2slow]

Are you supporting the front of the jeep under the suspension? (Loaded) Or is the suspension at full droop? This can make a difference on cv and bearing noises.

I have pulled the whole front diff out before and drove the jeep for several months while i slowly worked on the front diff. The outer bearings where the CVs plug-in are known to wear out. So does the spline coupling on the passenger side.

The dead ABS signal may be a sign of a failing wheel bearing; can't say for sure - ours doesn't have ABS.

 

[DeCaff2007]

Are you supporting the front of the jeep under the suspension? (Loaded) Or is the suspension at full droop? This can make a difference on cv and bearing noises.

I have pulled the whole front diff out before and drove the jeep for several months while i slowly worked on the front diff. The outer bearings where the CVs plug-in are known to wear out. So does the spline coupling on the passenger side.

The dead ABS signal may be a sign of a failing wheel bearing; can't say for sure - ours doesn't have ABS.

Suspension was at full droop.

I'd LOVE to just replace both front wheel bearings. Can't swing the $ for that right now as they are $150 each from Rock Auto. They can be had cheaper, however, I'm a FIRM believer in you get what you pay for.

I don't get it. The grinding sounds a whole lot like the front diff is going. But I did that test and heard nothing.

Oh, and also, what's to say I pull a diff from a yard it's not just as bad or worse?

 

[u2slow]

I would reposition the jackstands under the control arms to better simulate road conditions.

Are you able to move the inner CV joints up and down in the diff housing with a prybar? Thats usually a sign those outer bearings are shot.

I guess i got lucky when i snagged Timken wheel bearings from rockauto for $40 each. You could try a cheap non-ABS bearing for trial & error testing.

 

[Ksat]

Just so I'm understanding, when you started, there was no driveshaft and no noise, then you installed a driveshaft and it started making noise, then you removed driveshaft and it continued to make noise?

Bad wheel bearings typically make more (or less) noise when the car leans into corners. If the noise is the same regardless of how much you toss the wheel, it may not be that. Having no noise when you had had all 4 wheels up and spinning could point to bearings again. The ABS sensor code could also be another indication there's a bearing issue on that side. You may want to lift the front end up again and test for any play in the bearings, if you haven't done that already.

You may want to invest in a ChassisEAR tool. It'll help you narrow down on the source of the noise when the car is running on the road, I have one and I find it invaluable.

 

[DeCaff2007]

Just so I'm understanding, when you started, there was no driveshaft and no noise, then you installed a driveshaft and it started making noise, then you removed driveshaft and it continued to make noise?

Bad wheel bearings typically make more (or less) noise when the car leans into corners. If the noise is the same regardless of how much you toss the wheel, it may not be that. Having no noise when you had had all 4 wheels up and spinning could point to bearings again. The ABS sensor code could also be another indication there's a bearing issue on that side. You may want to lift the front end up again and test for any play in the bearings, if you haven't done that already.

You may want to invest in a ChassisEAR tool. It'll help you narrow down on the source of the noise when the car is running on the road, I have one and I find it invaluable.

Ah, well, you're close. When we started, there was no driveshaft AND noise (but we didn't know this just yet). We couldn't really take it for an extended test drive upon purchase because, well, it had ZERO gas in the tank and it was such a tightly packed area in the city that there was really nowhere to go. We were able to run it up and down the sellers very small driveway, but that was about it.

After fixing the brakes (it needed a driver side caliper and a thorough bleeding) and AFTER installing a driveshaft, we were able to do a much, much better test drive here at home. That's when we noticed the grinding. Then, we removed the driveshaft and the grinding continued.

The jack stand test was performed WITH the drive shaft installed and yet we heard ZERO grinding. I've had several people tell me that it would be obvious where it's coming from. LoL well it can't be obvious if it's not there.

Also, I did check into that Chassis Ear tool. $280 - uh, NO!