ecwieder

Looking for a one piece driveshaft for a TH400 to M21 conversion. Not exactly sure of the factory MT shaft length but based on where the old 55" TH400 shaft sits with the Muncie installed it looks like 55.5 to 55.75 would be about right. 56" would probably work but might not be easy to install without unhooking some trailing arms.
Here's the hole I'm trying to fill.



Thanks,
Eric

WTony

I have one thats 55.5 in NJ. Where are you in NE Pa?
Send me your email address, I'll get photo's to you.

442crzy

PM sent

ecwieder

I should have noted it's a 27 spline M21. Thanks for the replies!

2blu442

I'm under the impression the TH350 driveline is the same one as used on the 4 speed setup.

John

ecwieder

I was under the same impression, but all the TH350 shafts I looked at in junkyards have the two section tube with the rubber joint injection.
In the 70 parts manual there are only 3 parts #s for 112" wheelbase cars.
7804819 - this looks like the 4 speed and 3 speed shaft
7806237 - this looks like the TH350
7807106 - TH400
Can't find any more spec on these part# so my guess is there is one for TH400, one for MT and one for TH350 on the 112" cars.

joesw31

If you still have your current TH400 drive shaft, then, that can be used with a 4 speed 27 spline yoke. GM used several different yokes, and the base section of the yoke changed lengths to the center of the U-joint (type of U-joint used as well). Also, you need to make sure that there is no hole in the back of yoke. And the TH350 drive shaft is the correct length, however, they are generally two pieces. You need a one piece drive shaft. Good luck

ecwieder

I thought about that Joe, but someone must have taken this car off-roading before I got it in 1990. Or maybe it was one of my kids.

Gerald Nickels

Auto were sleeved and stick were solid one piece.

alain

Try the partplaceinc .com 4 spd cars are 56.5 in lenght
Alain

ecwieder

Alain, that's something I was going to post about. Based on the measurements on the car 56.5" wouldn't fit. It would be about 3/4" too long. 55.5 would leave about 5/8" of exposed slip yoke when installed.
I went to the trouble of moving the rear across the full extent of up and down travel while taking measurments. Never goes over 56.1"
Another gentlemen on these forums has a 55.5 for me from the identical application so that's resolved.

Given all that, I emailed and called Parts Place to ask why their 27 spline 1330 rear shaft was 56.5" The email response was "don't worry works great!" The guy on the phone was a little better but couldn't answer the question of how they measured.

I wonder if anyone on here has bought one from parts place for a 112" wheelbase car with M21 and type 'O' rear? Doesn't seem like it could work. If it does I'm missing something, and there is a non-zero chance of that.

Regards,
Eric

alain

Put one in my W 31 4 speed exact fit
Alain

ecwieder

That is very interesting. W31 is a 350 right? 350 is a little shorter than 455. Maybe that is the difference. Thanks for the input!
Eric

alain

W 30 and W 31 use the same driveshaft when 4 speed M 21
Alain

72455442RA

Hello

I have a nice, straight , stored inside for 30 years . 55.5 driveline solid 1 piece driveline ..
ran my hand all over it ... I feel no dents ... looks rusty but it doesnt have any deep pitting likesome do,,, the end loops are nice ... no signs of hammering or
damage ....

I also have a nice yoke if you need one ,,,, in the back of one of the muncies ...

Scott

2o6 465 9165

prompt fed ex shipping ..... pay a pal is good ........

ecwieder

I see in the manual that you're correct on the cars using the same shaft. So, I would like to know how Parts Place measures 56.5 since physics doesn't allow that on my car

ecwieder

Scott, I have found a driveshaft, thanks
Eric

alain

Usually center to center
Alain

ecwieder

Ok, to convince myself I'm getting the right used driveshaft I went through the Denny's Driveshafts FAQs on measuring.

1) put the rear yoke in a vertical position
2) make sure the rear is at normal operating vertical position
3) measure from the flat yoke center to the face of the transmission tailshaft
4) decide what slip yoke you need and get it's dimensions
5) take 3/4 inch off your total rear to trans face distance for slip travel
6) subtract slip yoke cap center to yoke face distance from distance measured in step 5
This is your driveshaft length center to center .
In my cars current state with M21 and type 'O' rear: 57.875 - 0.75 - 1.75 = 55.375. The 55.5" shaft I'm getting is withinn 1/8. When I run the rear through full vertical travel it is about perfect with between .75 and .875 " of exposed slip yoke