dremelts

I know how hard it is to diagnose a problem just from a verbal description so I'll try to provide as many clues as possible.

This past winter, quite suddenly, it became almost impossible to shift into 1st gear at a stop light. (In the winter I carry about 700lb of weight in the back to help provide traction, so I start in 1st). I managed to get it home and noticed that the clutch reservoir was low so I filled it. It didn't help right away, but after a couple of days it seemed to clear up. I've kept an eye on the reservoir and it has not gone down any since then.

Then a couple of months ago I started having a problem downshifting into 3rd gear - it would really grind if I tried to force it. So I really babied it: shifting into neutral and double clutching whenever I had to downshift. At about the same time that I had this downshifting problem I also would occasionally hear a loud grinding when I would back up and then put the clutch in and stop hard. It was as if something "shifted" inside the transmission (I know - that's what transmissions do) and it was trying to engage some other gear while reverse was still engaged (although the clutch was disengaged). Anyway, quickly shifting into neutral would stop the grinding.

We were about to leave on a camping trip, pulling the trailer, and I didn't have time to mess with it before we left. Since we returned, about 3 weeks ago, these symptoms have completely disappeared!!!

One more clue: in the mornings, the first time or two when I start out in 2nd it will chatter. After everything gets warmed up it doesn't chatter anymore.

I've had the truck for about 75,000 miles and I think the clutch was changed some time before I bought it. I have ordered a LUK Pro Gold clutch just because I figure it's probably about time to replace it anyway and the chattering and problem shifting into 1st kind of point to a clutch and/or pilot bearing problem. But, I don't know if the clutch has anything to do with the downshifting into 3rd problem and am worried that it could be a bad synchro. While I have the tranny out for the clutch I will replace the fluid in the tranny (I last changed it about 50,000 miles ago).

Sorry for such a long post, but I'm kind of baffled and am trying to figure out if I'm dealing with multiple root causes or if they are all somehow related. I find it somewhat strange that two problems have appeared and then gone away - that's just not natural. Am I sitting on a time-bomb?

Clayten

Changing the oil in the transmission might take care of the problem make sure you use the right oil I think it has to be a gl4. I was haveing shifting problems a while back and changed the oil to Amsoil and it smothed right out.

gmctd

Most probably the pilot bearing in the crankshaft is deteriorating - time to check before it destroys the end of the trans input shaft.

Common

Can you clarify "chatter"?

dremelts

It doesn't engage smoothly, it's jerky and it kind of stutters as it starts moving.

Common

Mine does that, let me know what you find out...

gmctd

Can also be burned spots in the flywheel surface - need to pull the trans and clutch housing to check it all out - have the flywheel resurfaced to cure.

dremelts

Well, I got a Luk Pro Gold clutch, I ordered a gallon of Syntorq from Standard Transmission and I'm going to pick up a rear main seal at Cummins this afternoon. Now I just have to find some time to pull it apart.

I'll let you know how it all turns out.

shrtmntdiesel

Mine had the same symptoms. With the exception that it would not downshift into 3rd, 2nd, or 1st, plus the shutter-chatter kind of grinding noise when engaging the clutch. The pilot bearing on the clutch plate was shot, so we replaced the clutch with a south bend and replaced all syncro's. All is well now . Hope this helps.

dremelts

The pilot bearing was completely shot. I'm sure that is what was causing the shuddering when starting out. It is probably also what caused my shifting problems last winter.

Just an F.Y.I. When I ordered my LUK ProGold clutch I asked if I could get a bushing instead of the needle bearing for the pilot. I was told that it came with both so I thought that was cool. Well, it came with the needle bearing and two different bushings - one straight and the other with a flange. Neither bushing fit the bore of the flywheel - they were too small, so I had to put the needle bearing in. If I had actually measured the bushings before taking everything apart I would have realized that the bushings were not correct for my application and I could have found the correct bushing.

gmctd

Replacement SB flywheels have a sealed ball bearing, similar to what GMC and Pontiac used, years ago.

It's nice, because it doesn't ruin the input shaft nose when it goes - but still the same problem with any dynamic bearing, as opposed to a bushing - when it fails, it fails, usually trying to lock the input shaft to the crankshaft.