75 GMC motirhome TH400 rebuild ?

[CampaS75]

I have a '75 GMC motorhome and the transmission slips so bad n lost 3rd gear so took it out.
Bought a rebuilt TH400 from an '87 Chev truck but splines are 27 and my original is 32 spline.
Is it possible to swap shafts(rear) ?
How tricky is it ?

[kwmech]

How did a 27 spline output end up in a 1987 trans? Anyways, it can be done, but both transmissions will have to come completely apart. The output shaft is held into the rear planetary drum with a snap ring. I'm thinking the trans you are looking at is a 700 not a 400

[CampaS75]

Oh boy. Should run some numbers I guess, not muchto go on.
I'd love to run a 700 in this thing but time n money is an issue.
There's alot to convert and I'm not a transmission rebuilder so replacing one just like original seems good if I can find one.

[mongocanfly]

pan I'd

[mongocanfly]

keep in mind ..as it was pointed out in your other post on this ..that most likely in a motorhome its actually a turbo 475.. (or 3l80hd)

[WyattTX]

Resell the transmission you just bought, and use the money to rebuild the one you were having problems with.

[homemade87]

All th400 came with a 32 spline . There is several trany company's making a 27 spline for the 400 . It was so you could adapt the the 27 spline transfer cases to the 400 for a stronger trans ( my guess the 87 was a 4wd , could be a 2wd w/proper tail housing) . This was popular for mud trucks . This trans you have has been modified with the 27 spline or it is not a th400 . It has been apart at some point and possibly with some upgrades for the truck it was used in .

If you are planning to use it one option you have if you know indeed it is a good trans is to change the driveshaft yoke and tail housing ( If needed , depends if they use it on a 4wd ) if the trans shaft is the same length . This may get you by for a while until you have the time to build the original . Yokes are less than a $100 .

[CampaS75]

I have looked at the pans - first thing I did, and they are both 400. The shaft lengths are different (I wanted to find a yoke for it)
The fellows I bought the rebuild from were off road truck builders and also said they were initially going to use the rebuild in a hot rod but went with something else.

I am listing the rebuild for sale on Kijiji.

[CampaS75]

Thanks to all for input and advice !
I am picking up another used that will be nearly identical.
I'll hope the rebuild sells soon.

[57NAPCO]

Originally Posted by mongocanfly

keep in mind ..as it was pointed out in your other post on this ..that most likely in a motorhome its actually a turbo 475.. (or 3l80hd)

This...

[wahl4m]

sometimes the motorhome units had a parking brake on the tail housing??& yes most motor home trannys were thebigger 400 turbos?

[donw1986]

I have 86 c10 that came with a 700r4, however those trannys sucked when they first came out mine went out 3 times then i found a kit that you could put a turbo 400 in instead kit had a smaller output shaft to install in the 400 and a shorter tailhousing, so you could just bolt it to your motor and use the factory yoke and driveshaft, you vould have some kind of kit like that in it

[sweetk30]

there is a th375 model factory with 27 spline shaft . . . not near as common to find .

as others said rebuild the one from your motor home for the best results in the end .

a th475 the motor home spec one there is a few major things in there that make them beefy for there heavy duty use .