Okay so I've been having this problem since I got the truck and I think it may actually clutch chatter, was wondering if its possible to diagnose that without pulling the clutch. When accelerating I get a bad "knocking" now if I double clutch back into the same gear I can get it to go away sometimes. The problem is intermitant which makes it rough to diagnose. I have replaced all u-joints and they are torqued correctly, I just balanced my driveshafts and all my yokes are tight. The truck is a 76 f-250, np435, np 205, 390. Thanks a lot fellas.

 

check your rear end out if possible,,the tend to chatter, especially the limited slip if damaged(obviously).

 

Just was in the rear end before winter, had a detroit locker installed...Ring and pinion were good and it has all new bearings.

 

Clutch chatter can be the result of uneven friction around the circumference of the friction surfaces. This condition can be the result of oil leaks from the front of the transmission or the rear of the engine. The leaking oil spreads unevenly on portions of the friction surfaces creating an alternating slipping grabbing action that shows up as the clutch engages. Chatter can also be caused by mechanical wear or breakage of other clutch related parts which will cause the clutch to run out and give eccentric operation.

Worn input shaft splines or clutch disc hub splines, a heat-warped pressure plate or flywheel, or misalignment between the engine and transmission can all cause clutch chatter.

A similar situation results if one or more of the engine or transmission mounts are broken. As the clutch is engaged, engine torque causes the entire engine/transmission to move out of its normally mounted position. The result is a condition that resembles chatter but is accompanied by rocking or shuddering of the engine and transmission because of the broken mount.

Ok and 1 more thing long shot but ill still mention it.

You might want to consider the tune of the engine. Even if it idles fine, a engine with fuel system, ignition, compression problems may not be able to deliver torque smoothly under load and the result of that could also cause chatter.

 

This is most definitely not an engine problem, I considered the mounts. Motor mounts are fine but the tranny mount definitely looks like its seen better days, however it doesnt act as if its broken and there are no signs of movement there. The problem isn't when the clutch is engaging thats smooth, its just after the clutch is all the way engaged (pedal released) and acceleration. Thanks for the ideas, keep them coming lol. I do have a thought of my own and maybe you can help me on this...I'm thinking its possibly the input shaft of the transmission because if I put the tranny in neutral and let the clutch out, I get a little vibration and knock much like the one in gear only more quiet, thus I am thinking it could be that due to the fact there should be very little opposing friction on the clutch with the tranny in neutral.. what are your thoughts?

 

ok lets start with this...how old is the clutch?...or better yet miles on the clutch? im having a hard time thinking of knock in a clutch...is it like a clackity sound or is it more of a shudder? when you say knock I have the sound of a rod knock in my mind and Im not really sure what in a clutch would make that sound maybe other then a broken torsional spring...it just keeps popping in my mind that if its chattering that it would be a worn out clutch disc hub splines or input shaft so the clutch might not be rotating on true center...thats the only thing i can think of that would cause a chatter or knock.

what do you mean by opposing friction?

 

Clutch has less than 30k on it, when it was done it the flywheel was resurfaced and i believe a new pressure plate was installed. it was driven about 15k and then parked for 10 years, I have it now and have put about 15k on it. When I say knock I mean knock, sound of a rod knocking is not far off, I know it isn't a rod knock though, bottom end is nice and tight. I'm really thinking its the input shaft, is there a bearing or a bushing on it that could be worn out?

As far as what I said about opposing friction, when your in gear you have the inertia of the entire drivetrain as well as vehicle weight on the clutch, but when your in neutral you only have the inertia of the transmission shaft, and if I'm getting the vibration in neutral I wouldn't think it to be the clutch due to there being little to no opposing force on the clutch. However I think your on the right track with the input shaft off center, I am seriously thinkin the bearing on the input shaft is worn out so it is catching off center sometimes...

 

It may also possibly be the pilot bushing in the back of the crankshaft..sometimes people don't replace them even though one comes in the clutch kit...mine came with 6 different sizes. If for some reason they didn't bother to replace that the input shaft will wobble no if's ands or buts it will not stay on center. It's only purpose in life is to support the clutch/front of the transmission and to make sure the input shaft rotates on true center.

Another possibility is the bearing on the front of the trans that supports the other end of the input shaft. If thats bad maybe it intermittently lets somthing in your trans bind? possibly the countershaft? And thats where the knock comes from?

If it was me personally I would suspect the pilot bushing or the input shaft to start. Then if those both look good and there's no excessive play between the shaft splines and clutch hub splines and the disk looks good along with the pressure plate I would start thinking about something inside the trans itself.

Another question were the symptoms occurring before the clutch replacement or did this start after? If so possibly a reason they got rid of the truck?

BTW I hope this is helping...no wild goose chases intended on my part.

 

As far as symptoms go I can't say for sure, it was my fathers truck before mine. He changed the clutch and I'm fairly certain it started this maybe after it was parked for so long. He says it didn't do it when he drove it, and its been doing it ever since I purchased the truck (it was parked upwards of 10 years). This is probably a real dumb question, but can I pull the transmission without removing the bellhousing? I'm very curious about the input shaft like you say, as the transmission has never been rebuilt and I bet thats where my problem lies.

 

yeah you should be able to pull the trans without the bell housing but you'll have to take the shifter off and 4x4 linkage...cross member too..it looks like a B****. It can be done though. But at that rate you probably wont get a very good look at the clutch splines or the pilot bearing.

 

I might be way off here but have you checked the throwout bearing

 

its possible...how would that cause a chatter? its purpose is to give the fork something to ride on that rotates between the fork and pressure plate so when you engage the clutch the rotating pressure plate doesn't catch or bind on the static fork....I think your going to have to take it apart and look at parts. we could sit here and discuss and stuff all day but looking at the actual parts is going to be the best way to find the issue.

maybe this is all being over complicated...whats the most obvious answer?