68 Chrysler Newport with 3.55 sure-grip, small pinion (741) rear end.

Decided to swap out the 3.55's for a used non sure-grip 2.94 complete carrier/case assy for highway cruising.

It all works ok, except on deceleration (especially at relatively low speeds), I hear a rapid 'clunking' sound as the car is slowing down. If I 'feather' the throttle or accelerate even just a little bit, the noise stops....until it starts slowing down again.

The shop that did the work insists there's nothing wrong...even "pretends" not to hear the noise either.....says they will have to charge me to take it apart again and find nothing wrong (with their work).

As best as I can tell, it is NOT the u-joint, and when I inspected the 2.94 ring/pinion and spider gears before installation, there was no indications of any chipped/broken teeth.

Not being knowledgeable with this sort of thing, I am at the mercy of the "experts" in these kinds of shops.

Anyone here have some idea as to just what might be causing this noise, and if it is something I should be concerned about, or should I just live with it...as it's not really all that loud, but I can certainly hear it.

Finally, IF push comes to shove and this rear end needs to be pulled out again....it is feasible and cost efficient to simply have the 2.94 ring and pinion installed in place of the 3.55, so I still have the benefit of the sure-grip?

All suggestions/opinions welcome..thanks in advance

Sounds like the clearance between the pinion and ring gear "backlash" IIRC isn't set correctly. If that is the case it would need to be pulled out and correctly adjusted. If the two center sections are the same case style (both 741), you should be able to remove the sure grip carrier and bearings currently on the 3.55, bolt on the 2.94 ring gear and install in the new case with the matching 2.94 pinion already installed.

Shops suck, if it is a big name place consider calling their regional office etc. Had a similar experience with AAMCO Transmissions. Good luck, hopefully they will do the right thing and make it right.

I do a fair amount of work on my car and engine but don't mess with rears. There are some special tools and tricks involved. You may be able to send the complete rear to a shop for service/correction. Some suggestions are Dr Diff (this board), Moser and Randy's Ring and Pinion. Its worth calling these folks.

In general, setting up a rear with used gears is hard. There shouldn't be any clunking but getting it as quiet as original is difficult.

if you supplied the parts, the shop installed them. if its the parts fault it has nothing to do with the shop installing your faulty parts...the problem is the part not the install. You can slam the installer all you want but ultimately if they swapped out the chunk most likely its nothing they did!

now as for your clunking, id check to make sure the pinion isnt loose...grab the yolk and see if there is any movement, up down in out etc...there should benone. feel the backlash you should be able to feel the pinion contact the ring gear and the spiders contact the axle shaft...if there is alot then its internal.

as far as changing the carrier from one chunk to another...its not to hard you have to remove the carrier and ring gear swap the gears to the carrier you want to use...torque the bolts, reinstall, set your backlash, run a contact pattern and interperate that to see what your contact is. some times you need to move the pinion to achieve ideal contact.

but in my experience it sounds tome like the pinion is loose...did you have the shop change the yolk? i would think a newport would have the big yolk and a 741 case would be a small yolk...if thats the case the pinion may not be tightened correctly.

do you still have the 3.55 chuck ? if it's a clutch type sure grip look in the axle holes and see if the thrust buttons are still in it , if they aren't and the shop didn't give them to you GUESS where they are .

when i bought my 69 bee it had had the rear housing swapped in at some point I was told from a 68 GTX , when i pulled the axles to pull out the 4.30 chuck I found a groove ground in the axle in 2 places on one side . I looked in the axle tube and there was a hunk of metal , looked like a bolt , later I figured out it was a thrust button from the clutch type rear, the other button was wedged between the sure grip and the ring gear of the 4.30 setup.

If the buttons are missing I would point that out to the shop and ask to be present when they yank the chuck so they do not try to COVER UP their screw up and charge you.

Also do the checks pnypwr suggests above, the chuck you gave them could have issues .

Did they set the wheel bearing endplay to specs?

Rick