Question about transmission sag

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
Posts: 234
Joined: Tue Jan 22, 2019 8:16 am
First Name: Richard
Last Name: Gould
Location: Folsom, CA

Question about transmission sag

Post by rgould1910 » Wed Aug 28, 2019 1:58 pm

The engine transmission assembly is in the pan and I am fitting the 4th main. I have a 26 27 so I can adjust the 4th main up and down. The engine is sitting horizontal. I'm wondering if I should attempt to account for transmission sag and place the 4th main so it holds the tail shaft up a tiny bit. I dont know if the gyroscopic effect of the flywheel when the car is running eliminates the sag. If not I 'll go for a perfect slip fit as the engine tramsmission sits. Any enlightenment ?

Posts: 322
Joined: Tue Jan 08, 2019 6:01 pm
First Name: R.V.
Last Name: Anderson
Location: Kennedy, NY

Re: Question about transmission sag

Post by R.V.Anderson » Wed Aug 28, 2019 2:41 pm

An issue worth considering but I don't think you'd get quite the benefits you are looking for. It would be difficult to hold such a minute adjustment for long, what with the front of the rear axle putting added downward pressure to the area. As long as the engine and tranny have both been balanced as a unit, your pan is straight, and that fourth main is poured with top quality babbitt before being accurately bored and fitted, just set it on its nose and proceed.

Les Schubert
Posts: 520
Joined: Thu Jan 10, 2019 5:47 pm
First Name: Les
Last Name: Schubert
Location: Calgary

Re: Question about transmission sag

Post by Les Schubert » Wed Aug 28, 2019 3:06 pm

I ALWAYS install the 4th main with the engine vertically on its nose. Prior to the installation I put a dial indicator on the shaft and rotate the engine just to be sure there is as close to no runout as I can reasonably achieve.
After putting on the bearing I then drill a couple of small holes through the cap into the pan flange and install a couple of roll pins to maintain the alignment even if I have to pull the hogshead or the rear axle.
For additional assurances consider using a floating transmission shaft. This doesn’t negate the benefit of what I’ve mentioned above

Posts: 16
Joined: Wed Aug 07, 2019 10:47 pm
First Name: CHARLES
Location: Margate fl
MTFCA Number: 50722
Board Member Since: 2015

Re: Question about transmission sag

Post by Yatcwhit » Wed Aug 28, 2019 9:26 pm

I just replaced my 16 T crankshaft. I put the engine on a stand on and. Installed 4th main with ultra gray TV and bolts. Let dry and removed bolts to install u joint. Fit no.4 main using original with large socket installed with tape shim. Socket drive adapter and battery drill spun with lapping fine compound. Fit snug.greased and pulled the T around the block 3 times to get it to start.fired up .fist attempt. Old crank broke at flange. Suspect improperly installed 4 main. Removed to seal an oil leak. Leak stopped but so did crankshaft.

Post Reply Previous topicNext topic