I had a shop switch out the Getrag to a new nv4500 w/ a conversion kit in my 92 cummins 3/4 ton 4x4 2 months ago. Since then I have busted the radiator 3 times due to the motor moving foward so far when I accel. The fan was ruined, the radiator ruined and the motor mounts ruined... 3 times. The transmission shop doesnt know what is wrong and nobody can tell me why this is happening. I cant drive it because I know it will happen again. I never had these problems before I installed the nv4500. Can anyone tell me why this is happening? :'(

P.S. The truck is lifted 6 inches and the motor is stock w/ stock settings.

 

Andrewhuey,
sir, I do not owen a 92 but if its like the rest of the newer ones its held in at 3 pts. (The eng and trany). The eng. itself is typical except the bolts that go thrue the frame are actually siting in vertical slots..you can jack the eng.up w.o. removing a bolt. so if yours are loose it may be wondering around in there. Check and see that they are dwn in the slots and tight.(also the 4 bolts to the eng. that go thrue the mounts.) Also the ruber is a huge bushing and could be broken.
the trany mnts. could be broken too, and check the cross brace that is tight!
ps what is the space between the fan and rad siting still??

 

I have checked all of the mounts and all of the bolts. The mounts are all new motor and tranny. The spacing from the radiator is about .75" on the bottom and 1.5" on top. When the fan hits it is hitting on the passenger side of the radiator not the top or the bottom.

 

Sounds like either the rear transmission mount is too far ahead or not stiff enough to hold the engine under full torque. The crossmember may not be far enough back for the new tranny either causing the engine to lurch forward.

The other thing may be that the driveline is too long still and under accelleration the rear axle will wrap or twist in the springs tilting the pumpkin forward. This pushes on the drive line and should be taken up by the slip yoke. Sounds like the slip yoke is all out of travel and the driveshafts are too long.

J-eh

 

I am not sure about that fan to rad #. mine is out so i can not go there to look...mabe someone else would be kind enough to go out and measure thir truck spacing.
how ever the above ans looks posable .If somthing is not right you have to suspect everything or run thre risk of continualy looking past it.
If your breaking mts.I suspect somthing is pushing on them real hard

 

Could the fan be flexing at higher RPMs and pulling itself into the rad?

 

I had a 68 roadrunner(souped up) that sometimes the axles would wind up and shove the motor into the radiator-twice! In my case it was the driveshaft was too long -it doesnt take much!! It had a 4-speed and lots of torque.

 

I have checked the driveshaft length and I have at least two inches left of travel in the yoke.

As for the tranny mount not being stiff enough, it is steel bar stock which was what came with the conversion kit.

It seems that there is a bind some where, The rearend is pushing everything forward but I cannot find where it is bound up.

Could I have the wrong pinion angle?

Maybe there is something in the conversion kit that needs to change since my truck is lifted?

 

When you check the length of travel on the slip joint, is the truck on the ground, on a hoist, etc. i am betting that in some configuration you do not have enough slip.
Just a guess

 

Your rear drive line slip joint should have 4" of free forward travel when the truck is setting unloaded at rest. If you only have 2", you are hammering the driveshaft into the rear of the transmission and pushing everything forward.

The quick way to test is to find someone with a big (100 horse or better) tractor with a bucket loader. Put a couple big blocks of wood in the bed, push down on the bed with the tractor while you watch the slip joint.

You will likely need to have the driveshaft shortened.

 

When checked the length I simply removed the driveshaft looked to see how much of the shaft was in the yoke and while on the ground there is 2 inches or maybe a bit more. One thing that I did try was holding the brake while pushing the accelrator so that we could see if the yoke was moving at all. There was no slip at all, it seemed to push everything foward. I didnt understand why this was happening ???

 

Is it possible, the angle of the driveshaft is causing the yoke to bind up and not slide. If it is that way, you will need to remove the driveshaft and apply some high pressure grease to the splines of the output shaft. I've seen splines machined so rough that binding is easy to imagine.

 

I would agree with the driveshaft being to long and I would like to add one more thing to the equation and that is with your lift kit if you used blocks under the springs on the rear to achieve your lift you may be experiencing spring wrap when getting on it which also adds to the problem.

You have alot of issues here to check out but go about it methodically and with a bit of patience you will get it figured out.


Good luck and dont drive it till you do find the problem as it sure as heck isn't going to go away by itself.


Jason

 

To look for axle wrap as a possible cause for the problem is not too hard. Put truck in lowest gear (engine off!) and pull it slowly backwards with a hand winch or the like. This will simulate the loads on your drivetrain while accelerating. If the axle moves forward you'll see the amount it pushes the engine etc.If the slip yoke seems to bind in this condition try to tap it with a hammer to see if it breaks lose and slips in- if it does it just lacks lube- if it doesn't it can be one of them buggers that have the splines protruding even though the shaft bottoms out in the pocket of the other half. Any binding on the driveshaft is extremely bad on the outrput side of the tranny and the input side of the axle. (and in your case onthe cooler)

HTH

AlpineRAM

 

Just to add another angle to this. Have you looked at the rubber bushings that hold the radiator in place? Could be the motor is not moving forward but the radiator is moving back. I had some on my 91 that had worn badly and where allowing the radiator to move quite a bit. Just a thought.