Drivetrain grinding noise

I know there are a million threads about this but every one seems to be a little different.

I have this grinding noise (like two dry, rough pieces of metal rubbing together) coming from the tranny area under the following conditions:

1) clutch engaged (i.e. foot up)
2) in gear (all gears)
3) louder under load (i.e. quieter on jack stands, but still present)
4) goes away when coasting (i.e. when I let off the gas, that sweet spot where the engine is not pushing the tranny and the tranny is not pushing the engine)

In neutral, if i work the clutch in and out, there is no significant grinding or rattling noise in either position so I don't think it's the throwout bearing. It only happens in gear, under load.

I testing rolling forward downhill the other day with the engine off. With the tranny in gear, I get the grinding noise. In neutral, no noise.

The plan is to pull both the tranny and t-case and get rebuild kits from Herm, but if there is any way I could get away with just replacing a single bearing or two, that would save a lot of $$$. Any ideas, or should I just tear them down and be done with it?

 

Does it do it with the transfer case in neutral? If not then more likely a transmission issue.
Also, check your u-joints and u-joint angles. Bad joints or bad angles or joints out of phase can set up a vibration up through the transfer case and into the transmission that typically happens in those "float" conditions you describel.

 

I'll check it out tonight. I tried that with it up on jack stands but it was hard to recreate any of the noise without it under load of some kind.

 

FYI, I've changed the fluids in both the t-case and tranny. Both were full, anyway, and neither dropped a bunch of metal out the bottom as far as I could tell. The only disturbing thing I noticed was that the big gear in the bottom, rear of the tranny had a few chipped teeth (what is that gear called?). I'm guessing the chips disappeared via some fluid change by the PO in the past. I wasn't sure if that would cause the groaning/grinding sound.

 

is this the big gear in the transmission, or the transfer case?

 

Tranny.

So, I ran it in gear with the t-case in neutral and there's definitely some grinding. Not as loud, but it's not under load so that may be expected. Does that narrow it down any? Seems like it could still be either front or rear bearings in the tranny or input bearing on the t-case. What about the pilot or throw-out bearings for the tranny?

 

Pilot bushing has no effect with the clutch pedal up. The input shaft and flywheel are locked together, so no rotation on the pilot.

Throw out bearing should have no effect with the pedal up. It's just sitting on the bearing retainer.

The front bearing seems to wear out faster than the rear one ... from what I gather. If it were the rear bearing, the noise would change pitch in proportion to the gear you were in. If it is the front bearing, the pitch would depend only on the engine RPM, not the gear selection.

 

There's only one big gear in the bottom of the transmission. It's called the cluster gear.



The T-86 is basically the same transmission as the T-90. If you have a broken cluster gear, the best route would be to replace all the gears in the transmission with T-90 gears. They will fit as a group, but they cannot be exchanged individually.

I suggest you read the Novak pages about the T-90. That will tell you what's going on and what the parts are. http://www.novak-adapt.com/knowledge/t90_rebuild.htm

I would also suspect that your transfer case intermediate shaft bearings need replacing. This is a very very common problem for these Jeeps. Guys, does the intermediate shaft turn with the TC in neutral? I believe it does. Thus you'd hear it even with the TC in neutral.

 

Okay, good info. I think it's not the output bearing, then, as it seems to match engine RPM. And everything is quiet with the pedal down, so the pilot and throw-out bearings don't seem to be suspect.

Would a chipped tooth cause a grinding noise (assuming the "chunks" were not still in the case)? I guess my question is if I pull this thing to rebuild, can I get away with not buying any gears? It shifts fine and stays in gear.

 

Mmm. You place your bets and you take your chances.

Depends on the chips - where they are, how bad they are, and chance.

Note that the cluster gear is always connected to the input gear, and always meshes with the second gear, so both spin at engine speed.

 

I don't understand why people say the T90 is stronger than the T86. Other than all the gears being helically cut and the splines on the "slider" shaft being helical, as well, there isn't any difference, from what I understand. Being helically cut doesn't make either of those weaker, does it?

Where would I find a cluster gear for the T86 (or all the gears for a T90 if I was to swap them out)?

Edit: nevermind about finding them, I found several sources.

 

This is correct.

Beveled gears are weaker than straight cut gears. It changes the force vector on the gears from in-plane to out-of-plane, by the bevel angle. Beveled gears are also quieter than straight-cut gears. So all else being equal, the T-86 is somewhat weaker.

Look for a T-90 complete, I presume. Call Herm - he might be able to fix you up.

 

I had a '60 jeep pick-up years ago. It started grinding as you described. Ended up being the roller bearings under the cluster gear coming apart. I used to surf fish alot at Cape Hatteras (sp?)
had large sand tires on it and gave it a pretty good work out.

 

Thanks for all the input, guys. I think I'm going to just rebuild the D18 and T86 both. Herm's prices seem decent and I think I found a decent NOS T86 cluster gear. I don't drive my jeep too hard, just a little off-road at the farm for hunting, etc., so I think it will hold up fine for me and be the most cost-effective. Long-term, I'd like to swap to an SM420. I found one locally for $150 that is in pristine shape, but I don't think I'm ready to go down that road, yet, as I figured up the total cost to be around $1,200-1,500.

I'll update this thread with my progress. Going to get everything ordered first before yanking stuff out so I can still drive it for a while.

 

The intermediate shaft and gear will still turn with the transfer case in neutral. The way it works is the main shaft from the tranny has a gear that links to the intermediate gear. The intermediate gear is in the sape of and I. They link at the top left portion of the I. They don't shift. What does shift are the gears on the output shaft. When you shift the transfer case, it either links to the top right portion of the I or the bottom right portion of the I for low and high. It is in neutral in the center right of the I.

 

I've had the same desire to switch to the SM420 right up until you look at the cost of the adaptor and miscellaneous parts. The SM420's run $75 to $150 in this area and ends up being the the low cost item of the whole switch.

Sorry I can't help you on your noise issues.

 

I would be inclined to replace gears with chips outa them. But that is just me.

 

Here is a dumb question. Where should the twin sticks be set at on the d-18 while driving normally in two wheel drive? In/Out and Low High?