Bad vibration in rear end, after doing a lot of work.
 

Ok guys I haven't posted in a while, but have an urgent issue as of now. Going to try to keep this short and give you guys a quick run down of what's going on. So on my 02 F250 7.3, back in June, what turned out to be an open differential blew up and put a hole in my diff cover. So that obviously had to be fixed. So I decided to a few other things since the axle, as I had some and really need the truck at the time. As with most things I do, it took much longer than expected and now about four months later.... :-roll its finally about done. Unfortunately I did not get to most of the work, other than doing some POR 15, since I just did not have the time with work. So my uncle and our mechanic at work did the work of putting it back together. Today I finally got the chance to test drive and it was not good. It has a very bad shake/vibration in the rear end. I mean it is a very violent shake and shakes the whole truck, to the point that it feels like something is going to break. We had plans to take it home, but after about 5 minutes of driving decided to turn around and take it back to the shop. It can be felt almost all the time, but is not too bad when accelerating or cruising on the highway, but is worse when decelerating in the 45-50mph range whether braking or not. And the to be clear the truck did not do anything this bad before I had all the work done.


So here's a quick run down of everything that I had done:


Had a Detroit TruTrac and a complete axle rebuild with new factory 3.73 gears installed by a local driveline shop that has a good reputation and has installed these in hundreds of other trucks. The owner has one in his personal truck and I talked to him personally, seemed reputable and definitely knew his stuff.


Painted the axle and rear springs as well as the rear part of the driveshaft with POR 15. Did 2 coats of silver POR 15 and 2 coats of their Gloss Black topcoat on the axle and springs. And did 3 coats of white topcoat on the driveshaft.


PMF flat 4" lift blocks, PMF u-bolts, PMF top plate, PMF stainless steel braided brake lines, Mag-Hytec rear diff cover, new backing plates, new rear parking brake cables, new parking brake shoes and a hardware kit, new hub seals. All new PowerStop front and rear brakes, including drilled and slotted rotors, powder-coated calipers and Extreme truck and tow pads. I also did 2 new Moog super strength grease-able u-joints in the rear part of the driveshaft after the carrier bearing. And also did a Mag-hytec deep trans pan and a John Wood valve body.


A couple things that are worth noting: My tires are very bald and need to be replaced before winter, the front aren't too bad but the rear tires are pretty bad. The rear ones have also been sitting off the truck for about 3-4 months or so. Not sure if just the tires could cause that much of a vibration or not though, but who knows.


Like I said I did paint the driveshaft. I'm not sure how sensitive those are, but maybe the coats of paint could have knocked the balance of the driveshaft off?


Also, which I was concerned about from the beginning, is that the new PMF blocks are flat, which from everything I read, is what a CC SB is supposed to have. But it turned out that for some reason the blocks that were on my truck, had a taper to them. They are about the same height as the new ones, but seemed to be two separate blocks that rusted together, at least that's how they look. So I'm not sure if that could have messed with the pinion angle in the driveshaft and maybe the carrier bearing needs to be re-shimmed? I plan to call PMF tomorrow to see what they think.


I know I changed a lot of things, but if you guys could give me a place to start looking for something wrong or what you guys think the problem might be, that would be great. I'm really not sure what is wrong, but would have to say something in the driveline, and would have to guess that it is driveshaft related. Thanks in advance! :-X22

I don't know if it's the cause, but I would for sure get the driveshaft re-balanced before doing anything else. Painting it with POR15 is sure to throw the balance off.

Hi guys new. Here what I found out is they don't balance the drive shaft at the carrier barring try a hose clamp by the carrier barring mount.It might be the front shaft or the back one try both.spin the clamp too balance .worked for me.

Very probably the rear pinion angle changed when you went from tapered to flat blocks. A change in angle could easily cause vibration. I went through this with a '95 F250 after installing a lift and ended up with slightly tapered blocks that got pinion angle to match transfer case output angle to get rid of vibration. A driveline shop should have a tool that can measure each angle and tell you what needs to get changed.

Since a lot of work was done, it is worth checking each driveline u-joint closely. As you mentioned, tires are a possibility. Swap front to rear to see if the vibration moves with the tires.

Lou Braun

Yep. I second the 4'' lift blocks throwing the driveline angles off.

I believe it uses a double cardan shaft; there should be a double cardan joint with 2 U Joints in it at the transfer tailshaft / output yoke of the transmission or transfer case. If it has that, then you want the pinion yoke pointed directly at the tailshaft / output yoke. The Double cadan joint needs to do all of the work as the U Joints in it cancel each other out. Any angle on the single u joint at the pinion yoke will be felt.

I had thought about this, which is why I didn't want to put too many coats on. I only wanted to do 2 coats but ended up doing 3 because I didn't like how the second one came out, and I tried to keep it pretty even. But I didn't use POR 15 specifically on the driveshaft, but just POR 15's topcoat which is more like a heavy duty paint to go on top of the POR 15. I know it is still adding some weight, but was hoping just some paint wouldn't throw off the balance.


However my uncle and our mechanic did take out the driveshaft yesterday and sent it out to get balanced, so we'll see if that helps.



Not a bad idea, thanks for trying to help. But like I said I'm already having the driveshaft rebalanced.



I would have to agree with you guys. I had been worried about that from the start, once I realized the blocks that I had before were tapered, but my uncle and our mechanic didn't think that it would be an issue. So we'll see if rebalancing the driveshaft helps anything. And as far as I know before and after everything was put back together they checked everything over and made sure it was good. Almost everything is new or rebuilt in the rear end. If the rebalanced driveshaft doesn't work I think the next step would be to swap tires from front to rear and see if the vibration follows, at least before we start tearing anything else apart.


I ordered flat blocks because from everything that I had read, a crew cab short bed should have had flat blocks. Does anyone know what blocks a CC SB truck should have had from the factory? :-huh

The tapered blocks are absolutely what you want if it has a double cardan joint.

Can you grab a picture of the driveshaft? If it's getting balanced can we also get a picture of the way the pinion yoke looks in relation to the rest of the truck? IE - how is the rear end "clocked" ?

Edit: Here are some pictures.

The first picture is (what I believe) these trucks use. You want it set up like this. Older jeeps use the second one and are always having driveline vibration issues

http://www.4xshaft.com/images/cv_angle.gif

Second:


https://www.titantalk.com/forums/att...nangle3-3-.jpg

I can't get to the truck right now, but I'll see if I have any good pictures in my archives haha. I know I have some of the driveshaft and I took a few pictures before the test drive, so I'll see if any of these show what you're looking for. One thing, which not sure if the pictures your showing work for, is that I know my driveshaft is two-piece with a carrier bearing. So not sure if they are the same at the transmission or not.


Did some more reading and everyone seems to say that a CC SB, from the factory at least, is supposed to have flat blocks. I'll try to get some pictures up. And thanks for trying to help man.

Is a carrier bearing drop bracket/block installed? This reduces the angle.

Is it possible the driveshaft could have been installed out of phase?

I have not installed one, or changed the carrier bearing, since doing this work or since owning the truck. But the blocks that were in it before are pretty much the same height as the new ones and there was not a serious vibration like there is now. I'm not saying it was perfect, but nothing like it is now.



I'm sorry but I'm not sure what you're asking? `Just not understanding "installed out of phase".

if you replaced U-joints the yoke could have been put on 180 degrees out from where it was, further compounding the out of balance condition.

I have not installed one, or changed the carrier bearing, since doing this work or since owning the truck. But the blocks that were in it before are pretty much the same height as the new ones and there was not a serious vibration like there is now. I'm not saying it was perfect, but nothing like it is now.



Sounds like you just found your answer....If there was no carrier bearing drop block BEFORE and there was a small vibration...changing the angle even greater to the rear end is going to amplify that problem by not having the tapered blocks.
Get the correct blocks AND get the bearing dropped.
(IMO)

Hi Stan b here I'v had my driveshaft balanced 2 times they did not balance it at the carrier bearing so the hose clamp did the trick.I marked the driveshaft before removal and then the drive line shop installed it wrong I told them and they did not believe and then they looked again and found I was right.They put it back the right way and it still vibrated that's when I put the hose clamp at the carrier bearing it made it 98% better. The driveline shop should balance the drive shaft at the carrier bearing they just bolt the carrier bearing down and do not balance it at the carrier bearing .

The yokes on the driveshaft all need to be properly lined up when it's assembled. If you pull it apart at the slip yoke (or any splined section), it's possible to install the yoke at the wrong angle, which will cause vibration.

This explains it better than I can.