Fixing a Rear End Clunk

Contributed by drbob

Ford suggests you can isolate you problems with a little trick. Clamp a straight bar to the rear companion flange, and the frame on the right side. Raise the car on one side and turn the wheel. If you can get a crayon stripe over an inch long at a point 12" from center, look at the differential. Less than 1" means it's someplace else.

Next step is to drop the driveshaft and do a few service things. Mark where everything lines up as you disassemble, including those companion flanges front and rear.

First to do is the front companion flange TSB. Pull the companion flange and inspect the splines. If they are OK, reinstall it, but tighten the nut to the top of the range, 200ft/lbs this time.

Cut one of the clamps that holds the boot on there in the middle. Slide the driveshaft apart, and inspect the splines. A hand wire brush will clean all the rust and powdery crud out of there. Apply a thin coating of waterproof grease to the splines and reassemble, maintaining the original alignment. Use a new clamp, or a heavy duty cable tie.

Replace the u-joints. You have them out on the floor, so now's the time. Mine didn't feel at all loose, but a high-speed vibration went away. U-joints are too cheap to not replace while all the parts are so easily accessible.

Most real mechanics will tell you to never put the driveshaft in a vise. The slightest dent will throw it out of balance and/or alignment, plaguing you with vibrations for the rest of your days.

So -- I sit in the floor with a Pepsi, a big C-clamp and a couple sockets. One socket has the same or smaller OD as the U-joint bearing, while the other will fit over the opposite bearing cap. Take the retainer clips out with pliers and a screwdriver, and use the C-clamp and sockets to push the u-joint far enough to one side to pull the cap off. You may be able to get the other cap off from in between the yokes, but I usually end up pushing the joint back through to the first side to get that cap off. It's a one-two bang-bang job. I wrap electrical tape around the exposed stuff when installing the new ones to protect the end of the cross if I drop the shaft.

BE SURE to make match and alignment marks so you can reassemble the slip yokes, shaft sections and companion flanges in the same positions as before.

With the two piece shaft pulled apart, each part is short enough to handle easily. No need for any heavy-duty supports other than your lap or the floor next to you. Once you do the first one, you'll just blow on through the second one in minutes.


Make sure you line up all your marks when you put things back together. Keeps the balance as delivered.

Not a bad idea to check the oil levels in the differential and transfer case while you are down there. Transfer case takes ATF, and should be changed when you do the trans service. Rear diff oil says 100k life from Ford.

If the differential oil is at all low, look for oil sprayed from the pinion seal. Mine never dripped, but instead threw a wide track of oil around in a stripe from side to side over the pinion flange. Noticed it while waxing the gas tank one day.

Anyway, these steps should easily eliminate that driveline lash.

Plan on an hour or two for this task, including the break for lunch.

A Relevant Question from Bob M.

I posted a few weeks ago regarding a strange clunking coming from the rear end of my 92 EB. I'm pretty sure it is not U-joints. But with some help from users here and research it sounds like the Slip Yoke on the rear driveshaft might be binding up then releasing. It seems most obvious when accelerating and then quickly letting off the gas, most noticeable in 1st gear where there is the most torque. It does not clunk usually when accelerating and not letting off the gas until I'm going a decent speed and its in 3rd or overdrive gear. I did try keeping the transmission in 1st and tested this out. There seems to be some noticeable slack while accelerating and then letting off, thunking sound almost. Is there any way to grease the slip yoke without dropping the driveshaft?

And a Relevant Answer from drbob

To effectively grease the splines, at least one end of the driveshaft needs to be unbolted. If you haven't done the front companion flange TSB service (assumes 4WD, otherwise you wouldn't have the sliding driveshaft) just drop the front end of the shaft and do both things at once. You'll need a 12mm 12pt socket and 65 ft/lbs on those bolts on the companion flange, and 200ft/lbs on the nut at the transfer case. Be sure to put match marks on the pieces as you take them apart.

And once again -- U-joints are relatively cheap, and you are 80% of the way towards replacing them with the driveshaft loose. Four more bolts and it's free, then a little work on the garage floor with the sockets and a 'c' clamp will take care of this.

Do all this stuff at once and you'll be sure the clunk won't be back for a long while.

Contributed by Roy D.

After reading your article about rear end clunk, I had to write to tell you that I found another cause. With Fords limited slip axle, clutches are used. As they wear, the end play between the axle and spider gear increases. Mine increased to the point of actually causing the brake shoes to split down the center lengthwise, and warped the drivers side drum. I obtained a new spring, clutch and steel pack from West Coast Differential for around $100.00. Everything can be changed with the carrier in the truck. The clutches increased from three to four per side. Traction is greatly improved, and the noise is gone.




Updated November 24, 2000

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