Re: 3 on the tree
 

[QUOTE=raycow;49507]If you get an SM420 transmission (used 67 and earlier) it will bolt to your present bellhousing with no modifications needed. You will need to replace the driveshaft, and, of course, cut a hole for the shift tower.

If you get an SM465 (used 68-up), you will also need to have the bellhousing center hole bored out to approximately 5.125" to accept the front bearing retainer. This is a job any machine shop should be able to do.

Ray

Do I need a new clutch or tailshaft? Are the splines the same?

Re: 3 on the tree
 

You won't need to do anything to your stock clutch. The input shaft length, splines, and pilot are the same as on the 3 speed.

Not sure what you mean by tailshaft. If you are talking about the transmission output shaft, you won't need to do anything to that. It should have a flange or yoke on it that the front U-joint bolts to. You WILL need to replace the driveshaft, though. The 3 speed and 4 speed driveshafts are entirely different.

Ray

Re: 3 on the tree
 

Since the transmission is -shorter- wouldn't he have to lengthen the driveshaft?

Re: 3 on the tree
 

Valuable?

Would you cringe if I told you it spent at least a year, maybe two, just sitting out in the yard... coupled to the motor... but in the weeds. I only brought it into the cover after I gave the motor to a scrapper.

I refused to part with the transmission.

Re: 3 on the tree
 

Since it has already been relocated to the floor, I *assume* a hole has been cut for that. You might try scrounging the wrecking yards to see if there is an unmolested 4 speed floor cover (ie. one with a factory hole in it).

I know that on my first truck, the butcher job done to move the three-speed to the floor would have remained a nasty hole if I hadn't replaced the cover.

Re: 3 on the tree
 

I could have written that better. What I meant to say was that if he had a short SM318 on the truck now, he would have to shorten his present driveshaft in order to use it with the O/D transmission, because all of the overdrives are long.

Ray

Re: 3 on the tree
 

I have already cringed. As soon as I saw your pics, I KNEW it had been sitting out in the weather.

When I said valuable, I meant scarce. You might have to look for a long time before you find another T-85/T-89 with overdrive. If you do intend to use it, you might want to start looking now for a GM pattern case. That won't be easy to find either.

Ray

Re: 3 on the tree
 

Hey guys, one of those overdrives on ebay is gone already, and I can hear the clock ticking on the other one. Going, going.......

http://www.ebay.com/itm/Manual-3-spe...34daec&vxp=mtr

Ray

Re: 3 on the tree
 

If I happen to find NSM 420 in a junkyard how would I identify it?

Re: 3 on the tree
 

You might want to print some of the pics on this page and take them with you.
http://www.6066gmcguy.org/SM420.htm

Lacking the pics, a quick and dirty way to tell the SM465 and SM420 apart is that the 465 has two PTO covers and the 420 has only one, on the left side. The 420 also has a very significant "bulge" on the right side of the case.

Ray