I posted this problem earlier with a lot of replies, however after a bunch of troubleshooting and $, I still have the problem. So I thought I would clean this up and ask for new opinions. I am converting my 2wd into a 4wd and after i replaced the rear end I got this vibration. To make a long story sort, after the change my driveshaft wobbles at the rear end. The best way to describe it is that it looks like the pinion gear is bent, causing the driveshaft to wobble. I have put the ring and pinion out of my old rear end in, replaced the axles, pilot bearing, transmission, transfer case, driveshaft and pinion bearing, and pinion yoke and still have the problem. I have tried everything I can think of to fiqure this out with no luck. The only thing I can think of now is to replace the whole rear end again. However I thought I would try again for any ideas you guys might have to help me avoid this. Thanks in advance for any help and also for your replies in the previous post.

 

Does the u-joint fit correctly in the rear yoke? This has to be something simple your missing here. Have you had the drive shaft looked at yet by a shop? Maybe it got bent or something?

 

I know what you mean, this is driving me nuts. Since my last endever I have put in the new tranny and transfer case, so the driveshaft is totally differant. it is the one from a 4wd now. Therefore the problem has to be in the rear end. I have replaced the u-joint twice and there is a little side to side movement in the joint, it is fitting tightly and the movement is just in the u-joint itself. If I look at the plastic round thing that spins behind the pinion yoke I can see that it moves a little like it is out of round. I could just replace the rear end but even if that fixes the problem, it still would not tell me what caused it and I have to know what is causing it now because this has become personal between myself and this rear end. By the way, thanks RTM for all your help in the other post.

 

Since the problem happened after you replaced the rear end, it could be you have a mis aligned pinion angle on the axle, maybe from putting tapered spring blocks or shims in the wrong way? Also, did you check that the pinion nut is tight? Did you use new u-joints when you changed the driveshaft? If you are feeling play in the u-joint when the driveshaft is connected up, you shouldn't be able to feel any play there.

 

Maybe your driveshaft is bent or imbalanced. If you have the front 4wd working, take the rear driveshaft out and try driving it around as a fwd.

 

When I changed the rear end I just ground the spring mounting rivets off and changed the entire rear springs and all and bolted the rear from the 4wd on with grade 8 bolts like it says in the tech article section. I didn't mess with the blocks. I looked at a friends truck and everything that I can see as far as mounting looks the same therefore unless I'm missing something, pinion angle should be the same as a stock 4wd. As far as the u-joint, the caps bolt up good to the yokes on both the driveshaft and pinion yoke the u-joint itself just moves back and forth a little inside the caps. It did this with two differant new u-joints. I don't know if this is normal or not.

 

There should never be play in a u-joint. It souonds like you have a u-joint that may be to small for your set up.

 

Measure between the stops on the pinion yoke and then compress your ujoint caps together. The measurements should be the same. Are the splines on the pinion yoke worn. The previous owner may have drove it awhile with the pinion nut loose. Maybe your old pinion yoke will fit this pinion. Make sure the caps are the right size. Like I said in a previous post. Check pinion angle to transmission angle. Just because the rear end came out of another truck, doesn`t mean it was installed correctly in the donor truck you got it from. It may have done the same thing to the previous owner. You probably stated this in the other post but I can`t remember, what year and model is your truck and what year and model did the donor come from? Check the pinion yoke if you haven`t already done so. Good luck again. Bob

 

The u-joint fits tight in the yoke like it is suppose to. The play that I have is in the u-joint itself the u-joint slides between the u-joint caps a little bit one way. I swapped the yoke and also the ring and pinion gear from my old truck and it does the same thing. How do I go about checking the pinion angle? I don't know anything about it. Also my truck is an 89' f-150 that was a 2wd and the new rear end is from an 87' f-150 4wd. Both are 8.8 inch rear ends and look the same. I did swap the rear carrier (I think that's what it's called)(the thing that the ring gear bolts to) from my 2wd to the 4wd. It had the problem even if I completly took the carrier out and just ran it on jackstands with the pinion gear in. Also thanks Horton-racing for all your help in the previous post as well.

 

The u-joint is not supposed to slide at all! You have the wrong u-joint or something is broke.

 

I have had u-joints that do slide back and forth inside the caps approximately 1/64"-1/32". How much movement do you have on yours. You need a protractor to check pinion angle. Remove your driveshaft with your yoke pointing up and down. Put the protractor on the face of the yoke and read the angle. The bubble type are far more accurate but are far more expensive. Do the same for your tranny. The pinion should be pointing down approximately 2 to 4 degrees more than the tranny. This is my own opinion as to how much difference between the two and also on how to do it. I`m sure there are other ways of checking it and I am sure others will have their own opinions as to how much difference there should be. You do just have one u-joint at your tranny, right? If you had the double cardan joint or whatever it is called at the tranny, the pinion would need to be in line with the drive shaft. You may need closer to the 4 degrees to compensate for axle wrap with the lift blocks I think I remember you saying it had. You may have to get some pinion shims and just play with it until you get it to run the smoothest. It doesn`t make sense since when you ran it with just the pinion gear in it, you wouldn`t experience any axle wrap at that time. All I can figure is that the pinion angle must be way off. You have done swapped the trannies, driveshafts, carrier and have run it with only the pinion in the housing. To me that pretty much pinpoints the problem to the pinion angle area. Hope this helps. Bob

 

Thanks, I will try to check the pinion angle. As far as the lift blocks, they are just the stock blocks that come in all f-150 4wd's, they are more like a spacer with a strange thing pointing in toward the center of the truck. This is what I dont understand, I have a totally stock suspension. What could make the pinion angle be off if it is all stock.

 

When checking pinion angle it should match what the trans u-joint angle is. You may be able to get a close check with a sliding t-bevel. The angles being the same cancel each other out. My guess is the pinion angle will be fine.

 

RTM, Theoretically, you are right. The pinion angle should be the same as the tranny angle. But, torque being what it is, when you put power to your rear wheels to go forward, the rear end will actually try to rotate the pinion upward. For this reason, you need a couple of degrees more angle on the pinion than the tranny so that when the vehicle is traveling at high speeds, the pinion angle and tranny angle will be the same, thus, no vibration. The softer the springs and the more lift you have, the more you will need to compensate unless you have some sort of ladder bar setup to eliminate the axle wrap.

Duback, You are right, if it has the factory setup, it should be close. I would still check it anyway. I don`t know what else it could be since you have checked everything else. Does it have the right tranny mount in it? Are the frames built the same on the 2wd and the 4wd trucks? The holes for the spring hangers may be drilled in different spots on the 2wd frame than on the 4wd frame or the frame itself may be different. I am only guessing. That could cause your angles to be off. The strange looking arms are stops. The donor truck should also have the rubber buttons on bottom of the frame that the arms will hit against at full stuff. I bet you are about ready to shoot your truck, eh? Good luck.

 

I did a search on the web trying to understand this pinion angle thing and it seams pretty complicated. However on site says to use a magnetic torpido level and place on the pinion yoke and get the angle and do the same on the yoke on the tranny and they should be the opposite of each other (if I am understanding this right). What if I was to take my driveshaft off and put the level on my pinion yoke, get the angle, and then rotate it 180 degrees. Wouldn't this let me know if my yoke is causing the problem if the angles are differant? Just a thought since I am getting desperate.