78 transmission mounting problem
Thread Starter
2nd Gear
Joined: May 2021
Posts: 2
Likes: 0
From: Orlando,FL
78 transmission mounting problem
I just bought a 78 base model. It didn't come with a motor, but did have a TH350. I picked up a 350/700R4 combo. I installed the TH350 and upon dropping in the motor, there is a gap of about 3 inches between the bellhousing and the engine block. I've never seen or heard of this. The crossmember and mount bracket look to be original, and I'm pretty sure the 78's came with 350/350 for the small block autos. After crawling under the car, I also noticed the output shaft yoke is contacting the parking brake pulley. The transmission has the short tail on it. Again, with the motor bolted in and the transmission bolted to the crossmember there is about 3 inches of space between the bellhousing and the block.
What is going on here? Any help would be great.
What is going on here? Any help would be great.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Yep. That's the one I bought.
You also will have 'issues' with the various mounting brackets on the trans oil pan rail. Since the bolt pattern on those two transmissions are different, the geometry of the shift cable bracket and the steering column locking cable bracket will be wrong, if you try to use those from the THM-350. You will need to purchase brackets for that conversion or physically modify them to be correct for the change.
You also will have 'issues' with the various mounting brackets on the trans oil pan rail. Since the bolt pattern on those two transmissions are different, the geometry of the shift cable bracket and the steering column locking cable bracket will be wrong, if you try to use those from the THM-350. You will need to purchase brackets for that conversion or physically modify them to be correct for the change.
Last edited by 7T1vette; May 19, 2021 at 03:35 PM.
Thread Starter
2nd Gear
Joined: May 2021
Posts: 2
Likes: 0
From: Orlando,FL
Melting Slicks
Joined: Jul 2010
Posts: 3,176
Likes: 633
From: perth western australia
Is there 2 elongated holes in the middle of the cross-member ? Is that where you have bolted the transmission to ?
There's supposed to be a bracket that bolts to the cross-member and faces forward , which would bring the mount area forward by about 3 inches .
There's supposed to be a bracket that bolts to the cross-member and faces forward , which would bring the mount area forward by about 3 inches .
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
they probably did that to go from the th400 they were using to the smaller th350 and still use the already manufactured th400 crossmembers.
but since you are doing trans from scratch, try the 700r and see how it fits the crossmember... what, if anything, do you have for a driveshaft?
but since you are doing trans from scratch, try the 700r and see how it fits the crossmember... what, if anything, do you have for a driveshaft?
Last edited by derekderek; May 20, 2021 at 03:27 AM.
