Before I reinstall another TH400 transmission in My Scotsman I want to double check everything. One thought that occurred to me was that the cracked case took out the U joint instead of the reverse. I know the motor mounts both front and rear are very stiff compared to what I'm used to and wondered if I'm putting too much of a strain on the case supporting the weight of the Caddy at the factory tail shaft mount.
The factory Caddy mount was softer then the Chevy rear mount I'm using too.
John, You may have had a bad case to begin with. I used to have a GP that I did a little drag racing with. Poly motor mounts, no additional support and at least 400 ftlbs of torque, and the TH400 in it had at least 100,000 miles on it.
A softer mount would have allowed more movement but I've seen cars with busted mounts not do any damage to the trans, twisting the motor up a few inches and not hurting anything more than the radiator shroud. The Caddy mounts might have been softer to make the car feel smoother but I don't think a few durometers would cause your case to crack..
Have you pulled it out and really looked at it yet? Is it possible that the U joint pushed into the tailshaft and locked things up enough to put twist on the trans cracking it up front?
ErnieR
I was concerned about this too when I put the 400 in the CH but haven't had a problem yet. I did use a rubber mounted rear mount though. I have seen a few cracked cases at the strip when solid mounts were used.
Ted
No, the U joint stayed together and just threw the cap. Is it possible that the transmission is too tight against the floor ? (I have maybe 1/2-1 inch above it.) BTW, looks like Autozone will replace the transmission under warranty. I think the vibration of the joint letting go may have done the deed. At 70 MPH, there was a "bang" and the whole truck shook up and down.
I should have bought a Flight-O-Matic to Caddy adapter.
snipped-for-privacy@aol.com wrote:
After seeing the header, I think it's only a matter of time before OCF posts something!
Chip
I don't think you're using a front 'saddle' mount, but that 'Hurst' style mount with a THM tailshaft mount puts a tremendous strain on the trans case.
As suggested by another, if the engine was mounted via side mounts, as opposed to front mount, breakage of this type is unusual. Probably a bad TH400 case, which couldn't take the vibration, when the drive shaft went South.
Another text book example of "have it done by the professionals". Guaranteed cut and balanced drive shafts are cheap, when compared to the time and expense of cutting corners.
tempestan
I'm thinking it may have been a tranny issue, y'all know how that lowest bidder stuff works.
A transmission from AutoZone answers all questions of doubt to me...
JT
John Poulos wrote:
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