Driveline position fitment issues

Original 79 frame junked and replaced with an 80. Verified dimensions and length, same as original frame. My current issue is with the drive shafts, the front is almost too long to install, and the rear is too short. I kept my original engine, transmission, transfer case and crossmember. 258 / T-150 / D-20. Not sure what engine the donor frame had, it didn't have mounts installed when I purchased it. I do know Jeep switched to the 4 speed and D-300 in the 80s.

Lengths are off by about 1 1/4". Coincidentally, the transmission is about 1 1/4" too far forward to bolt up to the torque arm / mount. If you look at the pics below, you'll see my current engine mount bracket locations. The drivers side mount can be moved back one setting (1 1/4" between holes, hmm coincidence?) but would require drilling one hole to match the mount pattern. Passenger side would need 2 holes drilled to match. Does anyone know for sure if Jeep changed these frame holes from year to year? My main concern about setting the engine back another inch is running the back of the valve cover / engine into the firewall.

drivers side


passenger side

 

1980 was the first year for Dana 300 and SR-4/T-4,T-5 transmissions. I'd be willing to bet that is what you are fighting. The bolt holes in the crossmember/skid plate were different to accommodate this as well
Do you have your '79 frame you can take engine mount measurements from?

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Frame is long gone, went to the scrapyard. Regardless of my pan alignment, I don't understand why my same drivetrain, is 1 1/4" forward of the correct position. I made an adapter plate for the crossmember which works decent enough, but the big problem is my drive shafts don't fit. The front I can get in, it is slightly more forgiving but the rear is simply too short. It almost reaches the yoke but of course there would be no slack left for compression / travel. I'm willing to bet at this point it is these frame holes causing me grief.

The only other thing I can think of is maybe the rear spring hangers were set slightly farther back, which would explain why I'm over an inch short on the rear. I've googled cj5 late model frame dimensions but everything measures up, a bit over 46" from the end of the frame to spring hanger. I checked my axle too, thinking maybe I have a 3 hole spring perch and possibly set my axle further back than I should have. Perch has a single center hole on it and axle is perfectly centered on leaf springs.

 

Frames are the same. The bolt holes for the tcase xmember are probably drilled in a diff location because the 80,s frames used a different trans and tcase than the 79 which would make the dshafts different lengths. Just guessing here, but seems to make scents.

 

Crossmeber position makes do difference on the assembled length of my drivetrain. Even if my crossmember aligned correctly, my driveshaft lengths are still wrong and the engine is still over an inch too far forward. I tried loosening all my brackets and nuts last night, thinking maybe I'd tighten a bit of slack but there was none. At this point I'm going to have a buddy come over and help me lower the tub back on and see how much room I have to work with. Assuming I don't hit the valve cover, I'm going to re-drill holes for the engine brackets back 1 1/4".

The frames have to be different in some way, I re-used all my original parts from my 79 except for the frame. Same axles, suspension, drivetrain, engine brackets, mounts, etc...so frustrating.mehh Another think I noticed, my original photos show the Dana 20 drain plug positioned very low and close to the cut-out on the crossmember. The rear driveshaft also had a smaller angle in relation to the output yoke of the transfer case. Looking at my assembly now, the transfer case seems to be sitting quite a bit higher, and the rear shaft has more angle to it. By re-drilling new holes, I'd have to move down slightly along the frame channel which would lower my assembly by about 3/4".

 

I got the tub back on, no room to move the engine further back. At this point I'm just going to have my front shaft shortened. I also have another driveshaft that is too long which I can have shortened to fit the rear.

 

Do you have the driveshafts swapped front to rear?


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I wish that was the case, would have been a simple resolution. No way really to mix them up, rear shaft falls quite short of front position, and front shaft is too long to even attempt to install in rear. Since my firewall prevents me from setting the drivetrain any further back, probably safe to say the frame holes for the engine mounts are correct. Maybe the rear driveshaft I have isn't factory and was replaced at one point and the only reason it fit before was due too many worn suspension components, engine mounts, etc....My other frame wasn't square or straight for that matter either.

 

Do you maybe have the springs themselves reversed?

 

Springs are installed correctly. I checked my driveshaft length against a replacement, factory shipped 18.25" collapsed for this combo. At this point I'm at a complete loss how this happened.

 

it would be interesting if you had the drvietrain on the hoist and positioned it to fit the drive shafts...
see what’s out of whack then..

 

It shouldn't matter, but then again who knows at this point. I used a hoist to lower the engine onto the motor mounts, no misalignment there. Installed the clutch, bellhousing, transmission and then transfer case. I do know for a fact Jeep moved the lower skid plate mounting holes, who knows what other minor differences there are.