Vehicle vibration when shifting to 3rd

[mkoecher]

In my '76 F250 I am having troubles when I shift into third gear. Usually when driving up an incline as I am releasing the clutch the whole vehicle will start to shake violently. No matter how I vary the clutch or throttle it will shake like crazy. If drop it into second I can continue driving at higher RPM's until the road starts to level out more or I can go up to 4th and just have the vehicle lug up the hill until it gets to a speed it likes in 4th gear. Also, if I'm already on the incline in 3rd gear there are no issues.

A friend suggested that it could be bad motor mounts. But part of me thinks it is the clutch or flywheel slipping, but I am wonder why it only happens in third gear and on inclines? Is it the torque demand I'm putting on the flywheel in that scenario? Anyways, anybody have this issue?

Thanks

[sargentrs]

Check your motor mounts, tranny mount and crossmember bolts. The clutch on my F100 used to shudder badly. When I replaced the clutch it didn't look worn out. Had the flywheel resurfaced while I had it out. Problem went away. Don't know if it was the clutch or the flywheel but I'm leaning toward the flywheel since the old clutch still looked good and the flywheel had crazing and surface cracks.

[Manny]

2nd on sarge there. You either have clapped mounts or clutch is glazed. Oil leaks coating the clutch can cause it as well. Check and see if oil is drippign from your bellhousing. That's the old bronco with the 3 speed is bad it's down to needing and clutch for sure.

[Busboy]

Clutches don't stop slipping when you go to fourth. This is something else.

[lamogo33]

I've had a similar experience before. It happened to be a bad third gear in the gear box. It was missing a portion of one of the teeth. Not sure if it would have hurt it to keep driving like that or not but replaced the gearbox for an affordable used unit.

[Manny]

Clutches don't stop slipping when you go to fourth. This is something else.

Not slipping there going on chattering clutch due to hard spots and such. The trans could have a chipped tooth on third be he is stating on engagement which is whats got us thinking possibly hard spots on the clutch or oily disc causing chattering. Kinda tough to say without riding and driving in it..

[Busboy]

If there were teeth missing on any gear in a manual trans it would knock like hell.

[colnago]

If there were teeth missing on any gear in a manual trans it would knock like hell.

Is this because of a missing tooth/teeth, or because of material bouncing around inside the transmission?

Joseph

[Manny]

If there were teeth missing on any gear in a manual trans it would knock like hell.

Is this because of a missing tooth/teeth, or because of material bouncing around inside the transmission?

Joseph

The missing tooth gear set de meshing and re meshing