'72 LWB with 700R4-Driveshaft ???

[fatfords]

I posted this in the "engines and drivetrain" forum, but thought I might get some useful input here, also.

I bought a ’72 LWB with a 350 and 700R4. I replaced the motor mounts this weekend, and noticed the carrier bearing was very loose. After a closer inspection, it looks like the transmission was installed without shortening either driveshaft, so it looks like that is my next project.

I searched the archives, but did not find any information on which driveshaft to shorten and how much to shorten it. The truck originally had a TH350 and is using the forward holes for the front motor mounts.

Based on this information, I plan to shorten the propeller shaft by approximately 3”, since that is the overall length difference between a TH350 and TH700R4. Anyone see anything wrong with the plan? Am I overlooking something?

Currently, the shafts are all shoved together and there is no “slip” at the end of the propeller shaft. It is so tight, that I can’t get the U-joint out of the rear end yoke. Is there an “ideal” amount of travel that should be allowed by the slip joint? Or a "minimum" length that the yoke should normally cover on the slip shaft?

Any help would be appreciated!
Thanks,
Kent

[sam's 72]

Kent,
How you doing? I have a 72' LWB with 700r4 in it. I had the tranny installed. What they did, was bolted the tranny up to the engine, unbolted the tranny cross member, slid it back, once the tranny was bolted to motor, they slid the cross member back into place and bolted up the tranny mounts to it, then redrilled the holes in the frame for the cross member, then bolted it in. They took my drive shaft, ( two piece shft) and seperated the two shafts, they shortened the front one. I do not know how much they shortened it?? I would have to get under there and measure it. As far as how much play should be in it, I would say 3/4" would be good. This will let the shaft travel a little when going over uneven ground. It should not be jamed up tight against the tranny, this could break the tail shaft houseing.
One piece of advice, you probabley already know this, but just want to say it, when you have the shaft cut and welded back together, have them balance it. Might as well replace all three u joints and carrier bearing while your doing this.
I hope I help you out some, if you need the measurement on the shaft, I can get it for you, but it will have to wait till tomorrow, I am out at work tonight.
Sam

[Longhorn Man]

If the tranny is 3 inches longer, have them chop 3 inches off the front shaft.
Keepin it like it is is bound to kill youyr tranny. The reason your Carrier Bearing is fragged is becouse it was taking the abuse that is being sent to your tranny. It is weaker so it is showing the abuse.

[fatfords]

Sam and Longhornmail,
Thanks for the reponses! It looks like they moved the trans x-member back, but then got lazy and just shoved all the shafts together and bolted it up. From the input I have recieved so far, it looks like I will shorten the propeller shaft about 3", as long as this will give me about 3/4" at the trans and have about 3" mated at the slip yoke, aft of the carrier bearing.

Sam, Thanks for the offer to measure. I am going to look at a truck with the same set-up tonight. If I can't get an accurate measurement or something is different, I will let you know.

Now that I see this, I guess I need to take it to the tranny shop and have the TV cable set. Who knows where they choose to cut corners!

Thanks,
Kent

[sam's 72]

YES! Get the TV cable set right as soon as possible, it could mean life or death to the trany. I will get the mearsurements today,
Sam

[sam's 72]

OK I got the measurement off of mine.
Front shaft from center line of front u joint to center line of middle u joint is 33 1/4" .
Back shaft center line of middle u joint to center line of rear u joint is 35" . 68 1/4" total, not counting the front yoke. I do not know how far mine is sticking inside of tranny. I would have to pull it for that, and I really don't want to do that right now. LOL!
But if you make it to were you have 3/4" to 1" of play, everything will be ok. But I would fix that and have the TV cable adjusted real soon.
LONGHORNMAN is right, with your shaft jamed up tight against your tranny, that is why your carrier bearing got tore up, you got lucky that it did not tear up the tail shaft houseing. Need any thing else, let us know.
Sam

[Longhorn Man]

And when you go to get the TV cable checked, see if they use oil pressure guages, or just adjust it my opening it to WOT and tightening up the slack.
If it is the latter, then find another shop. There is only one way to do it properly, and that is with guages. Some ppl get lucky doing it the way Chiltons says...others don't.

[fatfords]

Sam,
Thanks for the measurements. I rolled under the truck last night and came back with these measurements.
"Front shaft from center line of front u joint to center line of middle u joint is 33 1/4" -mine is 34" (+3/4")
"Back shaft center line of middle u joint to center line of rear u joint is 35"-mine is 34 3/4" (-1/4")

Longhornmail,
I'm not too far from Phoenix Transmission, so I'll get it over there as soon as I get the driveshaft issue resolved.

I will try to get some pics of the slip joints tonight. Also, the carrier bearing does not look like the drawing in the service manual, although I understand that several different set-ups were used. I'll get a pic of that, too.

[fatfords]

I got my driveshaft back from the shop yesterday with 3 new U-joints, a new carrier bearing, 1 1/4" shorter with a new end piece, all for $135. I put it in the truck last night and it fit perfectly. At normal (unloaded) height, there is almost 1" of travel remaining before the yoke is fully buried in the trans output.

Thanks Sam and Longhornmail for all your help and advice. Next stop-transmission shop for TV adjustment!

Kent

[sam's 72]

NO PROBLEM!
Sam