TH400 transmission

[denise 20352]

   The transmission on my hearse has started taking a few seconds to go into gear when its cold.  When Im cruising with my foot off, I give it just a little bit of gas and it seems to slow down before it picks up speed, or maybe its my imagination.  It shifts and accelerates just fine.  Is the transmission going out?

   Will the transmission from a 78 Deville work in a 76 commercial?

   Has anyone tried transplanting a 700R4 into a car that had a TH400?

thanks

-densie

[Doug Houston]

The THM400 is a pretty tough transmission. Its probably the best one for a commercial chassis as yours is. You might want to have the trans. drained and put in new fluid.

And, no, dont EVER even THINK of putting a 700R4 in place of a THM400. If anything, do just the opposite.

[Michael Stamps 19507]

The 78 is going to have a short tail vs. the long on the 76.  You can swap that but it requires tearing down the entire trans.  Other option is to get a long driveshaft for the 78 trans.  But all that said they are pretty cheap and Ive heard easy to rebuild so Id just rebuild the 76 if it does end up going.

Stampie

[dale jackson 20895]

   Denise,

  I would stick the turbo 400. If look on ebay guys sale those for like 350 to 500 exchange for those things. There cheap and tough.

  The 700r overdrive I would not bother with swap since week trans and prone to go out. Unless spend 700 to 1500 for hi pro units. Those 700 overdrives are ok transmsions If bolted to thoses 454 chevy after the hipro rebuilt.

  On swaping those You need an trans adter to bolt an 700 to an cadillac engine. Try transadapt website or transtar transmsion parts etc.  I used all my stuff transstar. I may spelling wrong as always.

 Those cadillac engines used buick , olds, pointic , bell housing etc not like chevys engines etc.

  The cheap out is change fuild and filter and drive into goes out then buy an rebuilt exchange unit.

  Its not worth hasslie either of pulling that trans from 77 or 78 the tailshafht was short. It cost lots money cut and refab an drive shafht etc or relocate trans crossmebers etc

 Like said best idea is just buy rebuilt 400 turbo exchange unit becides all that. You maybe replace it yourself to save money. Let warn there heavy units .

  Dale

[Rhino 21150]

When my T-375 in my 76 Delta failed it gave warning by making a faint buzzing noise under the car when I first started the car, NOT moving. There would be a slight delay before either forward or reverse would engage. Tranny shops (3) said Its the front pump that does that. When that fails you may as well rebuild. Local shop rebuilt in two days, cost $650 and they removed/replaced. It has failed again, 55K later, but that probably had to do with pulling three thousand pounds every week. I got an owners manual and they recommend max three HUNDRED pounds.
Look for the really dirty shop with a Mercedes and a Dodge van in the lot.

[denise 20352]

  Ive always wanted to try overhauling a transmission.  Is it very difficult to find a spare for the commercial chassis, so that I could have one to work on?  Will any long tail work?

-d

[Michael Stamps 19507]

Yea any long tail will work.  68 to 76 RWD Cadillac.  Not sure of the BOP tail shaft lengths.

Stampie

[George Stipe]

The one she is looking for is listed as a 13 shaft,  and has a total length from bellhousing to output seal is 37-7/8 long.

[denise 20352]

  Thanks!  I will definitely save that information.