Old 1981 Allegro motorhome with AT545 well maintained I purchased to horse camp in. Drove 45miles to camp early last summer, stopped on the rode to survey camp, and vehicle lurched and jumped and shuttered even in neutral. Tried to move it ahead and it lurched and stalled the engine (3208 Cat) several times. Called and talked to my mechanic buddy and he asked what it did in reverse when i shifted it to reverse it snapped the pinion shaft in two. I found another diff. and installed it with the same results. lurched jumped and stalled in forward gear and (should have never done this) broke the pinion shaft in the diff. when shifted to reverse. These diffs are $800 from the bone yard. Is this a locked up torque converter? Any transmission tests that can be done on the AT545. Could the trans itself bust the pinion shaft? Any help would be appreciated.

 

The 545 doesnt have a lockup converter. Being behind a 3208, it's right at the upper limits of capabilities. Only thing I can think of would be the idle speed is way too high. It'll slam in and out of gear if it's much above factory spec.

 

thanks for the reply neverenuf and i have a follow up questions after the update. i have been cruising these forums off and on since may after the disappointing destruction of a replacement diff ($800)last fall. i have not had time to remove the trans.. this weekend i did and to make a long story short there are nothing but crumbs in the torque converter, so now i can't simply replace the tc and trans and drive away. i have to go through(or pay to have someone go through) the tranny. I still need help on finding cheaper diffs. a where used for Rockwell D140 .433 differentials, and any tips or tricks for getting inside this AT545. and neverenufhp...i'm i reading correctly that the job i have given this setup (3208CAT and AT545) towing itself and the horse trailer is too much? I can't tell if this trans. is original but the machine has in excess of 150,000mi , couldn't it have just been used up? In your opinion, if refreshed, could i get 3500mi/yr out this set-up? i am probably towing 6500-7500 loaded.

 

My suggestion would be to swap the axle and the transmission. The axle can be swapped to a Rockwell F106 fairly easily. Plentiful, so pricing should be decent. Plus, a good step up in strength. The one you have is aging, and being close to max input torque causes metal fatigue.
The trans, I suggest an MT643. It may make it ok on the current setup, but it's at the point of breaking again. The 3208 makes a bunch of torque, which the 545 can take for a while. It's literally, at the max rating for the 545. If you do keep the 545, keep the rpm up, since there's a lot less available torque up there.