I've been searching on this for a while now, so forgive me if this is obvious... it is still eluding me.

Here are the symptoms:

- I'll put my front wheels in to a curb, keeping the truck from moving forward.
- Slip the clutch and let it out while giving gas, like I'm getting started up a big hill.
- While the clutch is grabbing, the truck will jump a little. It feels like the truck is driving over a bump (but we're still not moving).

I'm thinking something is slipping or shifting in the drivetrain. It does this in 2WD. I can feel this slip/bump thing while taking off from a stop in normal driving. Sometimes it's very strong.


Signs:

I've had a small leak around the pinion flange of my rear diff for a while. Now, I have quite a serious leak... there's plenty of fresh gear oil after work today.



My guess so far:

I think the pinion nut must have come loose. Does that make any sense? I got under it and checked for play in the drive shaft. There isn't any, so I don't think it's pinion bearings. (I hope it isn't, I'd rather not have to pay to get this third member set up with new bearings.)


I'm going to quit driving it until I can drop the drive shaft and check the pinion nut. Does anyone have any other thoughts? Am I missing something obvious?

 

The pinion nut in itself would not cause the problem since the drive pinion is splined. You would have to have stripped splines as well.

Did you say it only does it in 2WD? Did you try it in 4WD?

Do you hear any metallic clunking noises when this happens?

 

If it does it in 4WD it's much more subtle... I've tried to replicated it in 4WD and I think it's doing it, but it's hard to tell. It's not as pronounced.

There's no noise that goes a long with it.

 

Let's see, leaking around the pinion shaft and showing signs of teeth slipping between the ring and pinion gears. Sure sounds like a bearing problem to me. I wouldn't drive it another foot until i pulled the third member and looked at what's going on in there. Otherwise you run the risk of damaging some really expensive parts, if you haven't already.

 

during normal driving....are you getting vibrations and clunks when going between decelerating and accelerating? any vibrations at constant speed?

 

I don't remember any vibrations. Couldn't feel any clunks between acceleration and decelerating... it seemed to have only happened at a certain point during acceleration, once per load.

I've parked it until I can figure this out. I dropped the drive shaft today, and the pinion nut hasn't moved (even with the splines, I still wanted to check it to see if it had come loose and introduced any play in and out). There's no lateral play in the pinion flange, but there seems to be some notchiness to it when I try to rotate it, so maybe it IS bearings. I've stil got the wheels on the ground so the ring gear isn't moving.

Driveway space is at a bit of a premium, and the truck is in a one-car garage, so I don't have side room to pull the rear axles out to drop the third member right now. I don't want to hang the rear axles out of the housing since that may damage the outer seals.

Thanks for the feedback, everyone. I was hoping someone would say, "Oh yeah, that's a common sign of xxxxxxx!" but oh well. I'll post updates as I make progress.

 

If you can't pull the axles all the way out, another way to protect the seals is to stack up some old 2x4's, bricks, concrete blocks, whatever and make a support for the brake drum that's just the right height to keep the axle shaft centered in the seal opening and the pressure off the seal. I've done it that way several times w/o causing any seal problems. It saves having to disassemble the rear brakes in order to disconnect the parking brake cables, which is required if you want to pull the axles all the way out.

 

Thanks for the tip. Seems worth it just to avoid disconnecting the brake lines. Maybe I'll pick up a couple more jack stands. There's not much spare lumber around my house.

 

i'm thinking bad clutch

 

Have a buddy, from a safe distance in case anything lets loose or the truck jumps forward, watch your driveshaft as you try your curb trick. If it spins, but the wheels don't, you have a problem in your rear diff. If the driveshaft doesn't spin, it's likely in the trans or tcase or... the clutch. I would be quite surprised if it's anything other than the clutch since there would be bad grindy noises.

If it does the same in 4Hi, it's either the tcase or the clutch. Again, $$ on the clutch.

Many years ago, I had a 68 el Camino that did the same thing after an Autozone clutch install. That clutch was junk. My $$ is on a bad clutch.

 

if you have a cell phone, start recording and put your cell phone on the ground underneath the truck and video the drive shaft.

 

Good ideas everyone. Swapping the clutch would be relatively straightforward... I'll see if I can get a friend to watch under the truck while I put load on it. The clutch seems pretty smooth and strong, but I've never felt one go bad, so I'm not sure what to feel for.

 

I'm betting u-joints. If the truck is in gear, and theres any tension on the driveline, shaking the drive shaft wont do anything. Jack up the rear end, place on jack stands, then check for play in the drive shaft. Im willing to bet my left nut its a bad u-joint...

 

I haven't had a friend over to look at the driveshaft's motion while replicating the problem yet.

Tonight I dropped the rear driveshaft. The u-joints seem smooth and tight with no binding. They've also made absolutely no noise. I've heard very loud failing u-joints, but I'm not ruling it out.

So with the rear driveshaft out I put the truck in 4-hi and tried to replicate the jump/slip. I put wheel chalks infront of the rear wheels with only the front wheels driving and slipped the clutch while I loaded the engine. I couldn't get it to do the jump. I DID, however, toast my clutch quite a bit... smoke and stink and all, so maybe I'll be replacing that after all.

For now my plan is to drop the rear diff and have a look at everything. I need to replace the rear pinion seal anyway (ordered one tonight). If everything seems fine there, I guess I'll try swapping out the u-joints.


Thanks again for the brainstorming, everyone.

 

Sounds like you're closing in on the rear end. That's easier to get into than the clutch, anyway. Not necessarily cheaper to fix, though, depending on what you find.

Good luck!

 

clutch. still calling it. i highly doubt its the rear end or a u joint. its the clutch

 

Well I guess I gotta give up my left nut then huh?

If it was the clutch, I'd expect it do the same with the rear shaft removed. So rear diff seems plausible.
But... How exactly did u check the u-joints? I always keep the shaft on the vehile, and raise the rear, the spin the shaft while trying to wiggle it... any movement and they need replaced. You may not notice the play as easily just moving them around with the shaft out...

 

You haven't lift your truck recently, have you? it could be binding in the joints.

ok, I see on your other thread that you changed the trans. mount. Is the new one is higher or lower than the old one?
If that's the case then your d-shaft might be binding at the transfer case side of the d-shaft.

 

test the clutch...get going on the road and when you get in third gear, put it to the floor and see if your RPMs go up more than normal, usually a failing clutch will slip in third gear under a lot of torque.id bet clutch.

 

I yanked the driveshaft around pretty hard while it was on the truck and couldn't sense any play in the u-joints.

I agree that it seems like I'd be able to replicate a clutch problem when the rear driveshaft is out. I'll drive it a bit more with only the front shaft in to double check.

I don't think the clutch is slipping. I had a full day of hard wheeling with plenty of steep climbs and never felt it slipping. 4lo up a steep climb has to put a ton of force on the clutch.

I'm hoping to drop the rear third this weekend. At this point, I see no reason not to. If things look good I'll order a Spartan locker and get it installed while it's apart, you know, so the work won't go to waste.

Thanks again for the feedback, everyone.