Frame Swap Problem

[Quietman]

After an accident, i am replacing the frame of my 87 GN with a frame from an 83 Cutlass. I am nearly ready to set the body back on the frame, but the drive shaft appears to be one-fourth to one-half inch too long.

Even when forcing the driveshaft fully into the transmission, the rear u joint will not go into the yoke on the differential. Since the body is not on the frame, the rear shock are fully extended.

Any thoughts on what may have caused this, or a possible remedy other than shortening the drive shaft?

 

[Topjimmy]

Engine mounted too far back on the frame crossmember? If so, the firewall-to-engine clearance may be an issue also. How does the transmission support line up with the trans mount/frame? You might need to drill new holes in the crossmember to move the motor pads forward.

Good Luck - Jimmy

 

[Quietman]

Thanks Jimmy,

The transmission lines up fine because the transmission crossmember has a slotted hole for the transmission mount. I have pretty well decided i will need to move the engine mounts forward by a quarter inch or so by elongating the frame crossmember holes. The only thing I have changed in addition to the frame are new motor mounts. Its possible these contribute to the misalignment as well. With parts made in China and India and elsewhere, it pays to check everything.

 

[ts87ttype]

Make sure the trans yoke has no twist in it, that will not allow the trans output shaft to sink all the way into it, also full extension of the shocks may not necessarily be the furthest the rearend is from the trans.

 

[Quietman]

The yoke does go all of the way into the transmission. You are right, i need to try to insert it at different spring heights to see if it will go. Once in, i need to check for binding at all spring heights.

Thanks

 

[Topjimmy]

Sounds like you're on the right track. Could the new motor mounts be installed on the wrong sides? Could be something simple....

-Jimmy

 

[ttaowner]

7.5 & 8.5 rear driveshafts differ in length by about 1" are you sure you have the correct driveshaft? did it get swapped with the frame?

 

[BILL HAINES]

Frame difference

On the lt side frame rail,there is an extra brace welded to the frame for the trans crossmember. I just changed & frame and ran into this issue only.. I just cut the brace of one frame,added it to the replacement frame,, i had no issue with driveshaft or engine mounting...

 

[Quietman]

I will double check on the driveshaft, but i am fairly sure this is the correct one. Thanks

 

[Quietman]

Thanks everyone for your help. By removing the springs, and shocks, and then lowering the frame, the yoke will fit. Once the yoke is bolted in, and the the shocks are fully extended, there is 1/4" of clearance at the transmission. One simply must have the weight of the of body on the frame to compress the springs enough to allow the yoke to slip into the differential. Guess i learned how to check for correct driveshaft length with no binding!

 

[Topjimmy]

Glad it was something simple. Good info for the future too.