Okay this is kind of a long story, so bear with me. Pickup is a 1998 F150 4.6. Awhile back, my ring and pinion took a dump on me, so I bought an 3.55 8.8 axle out of the junk yard. While I was in there, I did new shoes, drums, hardware, parking brake hardware. On the test drive, I noticed, especially at speed, a horrible shake from the rear end while braking. Felt like warped drums. I came back, and sure enough, the brakes were hotter than hell. Discolored, etc. So I turned my old drums, set the drums once again, and went for a drive. Same shaking issue, but the drums didnt lock up this time, so thats good. I must of adjusted them too far out the first time. Next thing I do is swap backing plates for the shoes, since junk yards are not necessarily nice to the axles, I figured they might be tweaked. No avail. Still the shake. Next I put a dial indicator on the axles to rest for a bent axle shaft. The drivers side was very bent. I replaced the bent axle with a new one from Yukon. While I was in there I put in a limited slip differential. Might as well. ZERO change. Finally, at my wits end, I brought it into a shop. They said its a mix of my drums, and the parking brake cables are very sticky. Understandable. So yesterday, I put brand new drums, and parking brake cables on. Parking brake now works like brand new. BUT...still have the exact same issue. It still shakes like a mad man at speed, and when coming to a stop, you can feel it pulsing.

So, to list what I have replaced:
Shoes (x2)
Drums (2 new sets, and the old ones turned)
Brake hardware
Parking brake hardware
L and R wheel cylinders
Parking Brake cables
Drivers Side axle
Backing plates swapped from my old axle

I am absolutely at my wits end here. The only think I can think of next is maybe the axle housing itself is bent where the backing plate bolts to it? I have no clue how to check that though. Any advice is greatly appreciated! I love this pickup, but it is really making me lose hope right now.

 

If you've never replaced the flexible brake hoses, I suggest you do so.

Take it to an alignment shop and see if the rear is out of alignment. Something else to check is to make sure the pinion angle is the same as the angle the driveshaft makes with the transmission. If the angle at both ends of the driveshaft is not the same it will vibrate because of the way u-joints work.

 

I'll check those things. I would think the pinion angle would be the same, as it is an axle out of a 98 F150. Flexible lines never crossed my mind. I thought bad flexible lines caused the brakes to stick, not pulse like this.

 

I'm wondering how that axle got bent? Overloading the truck? Wreck? The axle housing may be bent also. An alignment check should find out.

 

Im calling to get an alignment check today. It must of been in a wreck. Thats all i can think of

 

Little late for this, but why didn't you just rebuild your original axle?

 

No reason other than it was going to be cheaper and easier to swap a complete axle. Nobody would forsee this happening. Ive replaced entire axle assemblys im the past with no issues

 

Have you checked for mud cakes in wheel, or maybe a tire that has a broken belt? I wasn't real clear from the posts if this was a shake only while braking or all the time after the axle change. Does braking make shake worse?

 

The shake is directly related to braking. The only time it shook without brake pressure was when I adjusted the shoes too far out and they were dragging. Now it is only upon application of the brakes. I did notice today, although at this point I am very hypersensitive. But it seems as if the rears lock up rather easy as well, not with tiny brake pressure, but if in a situation where moderate braking is required, they would lock and ABS would kick in.

 

If the axle aint bent, the tube is.

 

Very, very strongly agree!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Have you double checked you installation? If something was left loose?

 

I'm leaning more and more to the tube. If the drivers side axle WAS bent as bad as it was, it only makes sense that the tube would bend as well. I have had the rear end apart so many times now, I cannot imagine I still missed something. There really isn't much at all back there.

 

Check your tires, I had a similar issue and my tires were the culprit......

 

Could you explain this? It only occurs under braking, and I also never had this issue before I did the axle swap.