BB and BC transmission differences

Houtan

Houtan

Member
I`m in middle restoration my 1974 century gran sport 455 stage 1, now I found out previous owner had changed the transmission and installed a BC-69 th400 on the car (from a 430 Wildcat or Electra), I know BB-70 are unique and different with other BBs but want to know what is differences between BC-69 and BB-74 th400s and can I made some changes on my BC-96 and reach BB-74 specs or maybe BB-70 specs? or I must search for BB transmossions because finding exact BB th400 any year will be a hard and maybe impossible task in our country. If anyone have some map, blueprint, manual or pictures that shows internal parts of those two type th400 it will be very helpful.
 
The 1974 Buick Chassis manual has a page that shows the differences between the calibrations. It's on page 7D-150. It's a few valves/springs in the valve body. It isn't as simple as swapping them out. Can't tell you much about the 1969 transmission as I don't have a 1969 Buick chassis manual.

This is an article about switch pitch transmissions, but it explains what made the 70 BB transmissions different. It's a good read.


If you don't have a 1974 Buick Chassis manual, you should get one immediately. They are cheap on Ebay, and it is the most important book to own for your car.

www.ebay.com

1974 buick chassis manual for sale | eBay

Get the best deals for 1974 buick chassis manual at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!
www.ebay.com
 
To add on to LARRY70GS's comments, the '69, '70, and '74 shop manuals show another major difference in the BC vs. the BB. The BC has the long-tail case which is several inches longer than the short-tail BB. The long-tail case uses a longer output shaft and rear case extension than the short-tail.

The '71 shop manual is posted on this site in the reference section. From that you can get an idea of the TH400 info available there. The number of clutch plates vary by year and transmission model as well.

It would be interesting to see how others installed the BC in your car. Either short-tail parts were used from another transmission or a shortened driveshaft was installed.

Here is a thread from another forum indicating one TH400 rebuilder's preference for the '68-71 models. He indicates the direct drum construction is better on these than later models.

Best year core for TH400?

Is there a specific year TH400 core that is desired more than another? I know I'm looking for a BOP bolt pattern and short tailshaft, but aside from that... what?? Thanks, -Banning.
turbobuick.com turbobuick.com

It is possible to go through the Buick Master Parts books line by line and determine the differences (if any) in each year and model of TH400. The Buick Master parts books ('72 edition) are available on line at:


Would probably be easier to find a transmission rebuilder who has done a lot of these to consult.

You may have a very good transmission in your car already that may not need much improvement.
 
Last edited:
You must log in or register to reply here.
Back
Top