I am having my TH400 on my 1976 Buick LeSabre rebuilt next week. The rebuilders States if my transmission has a variable pitch converter he cannot rebuild it. This is the first time I'm hearing about a variable pitch converter. The transmission in my car is the same transmission that was installed at factory.
The only difference between fixed pitch and switch pitch is the front pump, input shaft, converter and electrical wiring. If you can rebuild a fixed pitch, you can rebuild a switch pitch. I agree, find someone else to rebuild your transmission.
If it has one it it, then any converter shop can rebuild it.. In this scenario, he is taking in a running car, so it must have a good core in it. While this is not an issue for a 76, it is telling of his general knowledge of the 400.. I agree find someone who knows the product better.. JW
Less that 100,000 miles, just keep using the same converter. Huge engine, you might need a furnace brazed conv. Bruce Roe
Its got this real obvious chatter/shudder starting at about 65mph and higher. When you accelerate thru that range its real noticeable, and it gets worst when going up the grades of I80 thru Donner and thru the Carson Valley Pass from Reno to Carson/ Minden which have up to 8% grades. I dont remember it being there before I did a trans flush at my GM shop in Minneapolis. I have a feeling that its not happy with the Synthetic Dexron III that we used, but at same time I haven't done anything with the transmission either. So I'm just going to have it gone thru and see if we can use the regular non-synthetic Dexron.
Original, it is not a Variable Pitch. Shuddering could be converter, direct drum (clutch), or drive shaft (u-joints). (and also possible suspension/steering) Since it is happening at highway speed of MPH, and not at the same RPM in Low, or 2nd. I lean away from converter. Both direct and drive shaft are "common" at 65. You can get under the car and see if there is any slop in the u-joints, as the caps will be loose enough to see. Regardless, I would not drive it any more than necessary to get it to a good shop if you are unable to do the work yourself. If it is slipping clutch pack, the damage is already done, and no automatic ever got better driving it once a problem begins. It just rounds up to the next hundred dollars every mile you go. And you would need to service the pan/filter and do a flush with non-synthetic. Meaning running several gallons through the in/out cooling lines after filter change and cleaning the pan, to replace everything including the converter) and that is spendy if you still have the problem after. If it were me, I would rule out the drive shaft, then drop the pan and see if there is any clutch material and/or metal. After that, looking at tear down and fine eyed inspection of everything by a good shop.
Some transmission rebuilders insist on replacing the torque convertor every time a trans is rebuilt because stuff collects in them and can let loose and trash a rebuilt trans... I guess what he's saying is he can't source a switch pitch convertor. It's all academic since 67 (?) was the last year for the switch pitch.
The driveshaft was already rebuilt before the trip...had all ujoints replaced and then balanced. My gut feeling says transmission, and I will most difintely have him replace the torque converter as well as the starter since he is in there anyway.
