Transmission or rear end?

JasonNC

Took the 49 out for a test drive after making a few changes to the engine.  The car ran well except for when I either accelerated rapidly or let off the gas quickly, at which point it the car would lurch and make a loud bumping sound.  I can't tell if the "bump" sound is coming from the rear end or the transmission.  I wonder if the driveshaft is engaging the rear end too hard or if the clutch is slipping.  When decelerating quickly, when the hard thump sound occurred, the car would sway slightly.  Any ideas? 

boothguy

I would check the trans mount and the carrier bearing mount first

Glowplug

Did you look under the car?   The outcome of what you see may point to the problem quickest.  GUESS from afar....the center bearing has has come loose from the mounting insulators, one or both?   

JasonNC

Thanks guys, I'll check it out Monday and let you know....

JasonNC

Ok guys I have checked the center bearing and the mounting insulators and they are ok.  Ken I really can’t see if the front eye bushings are bad because the cover blocks my view, but my guess is they need to be replaced.   I assume by isolators you are referring to what Wildrick Rubber lists as spring mount bushings #103.  Correct me if I am wrong . Thanks.

Geoff

Check U-bolts holding the diff to the springs, universal joint nuts,  axle end nuts. 

Jon B

I don't know your level of mechanical expertise, so please don't take offense if you've already checked this, but have you rotated the drive shaft to see how much play there is back at the rear axle?  I am not sure what the acceptable play is, but I would think that if it's too much, you'd get a "thunk" back there when accelerating or decelerating .

JasonNC

Jon B said:

I don't know your level of mechanical expertise, so please don't take offense if you've already checked this, but have you rotated the drive shaft to see how much play there is back at the rear axle?  I am not sure what the acceptable play is, but I would think that if it's too much, you'd get a "thunk" back there when accelerating or decelerating .

I have done this and there is quite a bit of play back there.  Is that going to be a problem down the road.  As far a mechanical expertise is concerned, I'm a lawyer by trade and a wanna be shade tree mechanic by night...

JasonNC

Geoff said:

Check U-bolts holding the diff to the springs, universal joint nuts,  axle end nuts. 

Thanks Geoff.  I had tightened the U-bolts with an air wrench months ago and thought that they were tightened to the max.  Turns out that when I started to tighten by hand, they were a lot looser than I wanted them to be.  I will see if that cures the problem once I get the car off the jack stands and back on the road.  

bob ward

Are your back axle U bolts double nutted? 

JasonNC

bob ward said:

Are your back axle U bolts double nutted? 

Yes they are.  I took the second nut off.  Tightened the inner nut an then put.the second nut back on. 

JasonNC

Good one Ken.  I had to Google that word to see what it meant.....

barrysweet52

Some times the second nut is not close to the first. In this situation its called, One Hung Low.