Lowering rear/driveshaft question. Help

[StepinNJ]

I had my 2.5 inch drop spindles and 4 inch rear hanger/shackle combo installed today. My mechanic told me the driveshaft is too tight now and suggested I cut it 1 inch to loosen it up. Has anyone had to do this? He says there is no give. It rides fine but he thinks it may break or something. Any suggestions? So far you guys have been right on the money about everything.
Dave
1979 GMC 2wd step side 6 cyl auto if that matters.

[AirMale]

Yoke Needs To Slip 1/2 - 3/4 Inch Out Of The Tailshaft Of The Trans. For Suspesion Travel.

[bigblock73]

I did a 4" rear drop on mine a while back, didn't have to modify the driveshaft and had no problems whatsoever.

Did your mechanic unbolt the driveshaft and slide it in/out of the trans to inform you of this? How did he know or find out?

[Rc 415]

We will answer your question if you show us pics of ur truck after lowering

[Ivan D.]

Originally Posted by Rc 415

We will answer your question if you show us pics of ur truck after lowering

Yep, and through in a pic of the tranny tailshaft housing and the front yoke of driveshaft while you're at it

[Slonaker]

I didn't change my driveshaft after dropping ther rear 4 inches with drop leaves. Oddly enough, when i bought a new yoke shortly before I lowered it, the guys at the driveshaft place said, based on the wear on the yoke, that my driveshaft was too long or too short (I don't remember which). I told them I was about to lower it, and they said that would correct it.

Wierd...

Slonaker

[StepinNJ]

Did your mechanic unbolt the driveshaft and slide it in/out of the trans to inform you of this? How did he know or find out?[/QUOTE]

He disconnected it from the rear. There is no play or movement in it now. It is slammed up against the rear.

[StepinNJ]

Could this be why the driveshaft is so tight after the lowering kit was installed? The truck was originally a 3 speed trans but it was converted to a turbo 350 auto sometime ago. Could they have used the same driveshaft at that time and maybe the tightness was only noticed now?Is there a difference in auto vs stick driveshaft lengths?
Dave

[bigblock73]

Originally Posted by StepinNJ

Could this be why the driveshaft is so tight after the lowering kit was installed? The truck was originally a 3 speed trans but it was converted to a turbo 350 auto sometime ago. Could they have used the same driveshaft at that time and maybe the tightness was only noticed now?Is there a difference in auto vs stick driveshaft lengths?
Dave

That would be my guess. One way to tell would be getting the trans dimensions.

[benoit454]

Well guys the stock 3 speed saginaw trans. in our 76 was the exact same length as a car saginaw 4 speed, and that's the exact same length as my th350 short tail transmission.

So I say that's not the problem. If it's short tail and was 3 speed stock they are the same length driveshafts or should be anyways.

[bigblock73]

What if his is a long tail shaft th350? How can one tell the difference...other than measuring od course.

[benoit454]

If he has a long tailshaft 350 then I'd bet the DS was swapped from a donor truck that had a long tail 350 because it's about 3 or 4 inches I'd guess shorter then a factory 3 speed or short tail truck.

All you'd have to do would be measure or look at it, if you've seen a short tail 350 and a long tail it's easy, or you might find pics online or the 2 and compare. if you measure from the 4 tailshaft bolts to the end of the tailshaft a short tail is 6 inches I think, and then there's a 9 inch and 12 inch I think.


As I said I know the stock 3 speed in our 76 was the exact same length and we used the stock DS when we ut in a 1974 camaro 4 speed saginaw transmission. Then when I pulled it from the truck and put it in my monte carlo, which the previous owner said was a th350 short tail when he had it, the saginaw 4 speed bolted right up to my crossmember and used the factory monte carlo th350 short tail driveshaft. I changed the saginaw 4 speed out for a th350 short tail and it went right in place of it.

[piecesparts]

I had to trim my driveshaft about 1" when I dropped mine. It happens, some do and some don't.

[Slonaker]

This will give you the different lengths:



Slonaker