The Stovebolt Site Forums The Shop Area Engine Shop Pinion Oil Seal

Need some advice, the pinion oil seal on my 1 ton seems to be leaking, I have a motors truck manual, and it seems to cover this but it's not real clear, does anyone have any recommendations on what and how to do it? Maybe a step by step description.

Hi, USN

I'm shooting from the hip and going with a general proceedure on a typical seal replacement. Should be correct. Take the "U" joint bolts out and push the drive shaft foreword enough to drop the end of the drive shaft down and out of the way. Take some masking or electrical tape and go around all the "u" joint cups to keep the two that are not in the shaft from falling off. Remove the large nut on end of the pinion shaft and remove the yoke. Most of the time, the yoke will knock off with a small hammer, but sometimes you need a puller. Tale a pry bar and pry the seal from the housing. Sometimes you have to drive a screwdriver in the edge to pry it out. Best to take the old seal out and have it ready at the parts store to match up. Use non-hardening sealer on the outside edge and tap seal into the housing. Use wood block to tap seal into place if possible. Replace nut and torque to specs. Refer to a service manual or maybe someone on the forum knows the right torque for your make/model. Then hook up your "U" joint (now is the time to check it out and replace the joint if it is bad) and you're done. Grease it and the other joints if they have fittings.

Truck Tinker

Before you do anything, try to determine WHY the seal is leaking. Sometimes they just fail due to old age, but more likely, the bearing behind the seal has gotten loose. This allows the seal surface to flop around, and the lip of the seal can't keep up. If you just change the seal, and not the bearing, the fix will only be temporary. Before loosening the pinion nut, check for up-and-down, or front-to-back movement of the pinion flange. Either one indicates enough wear to require replacement of the pinion bearings, probably both of them. No slack, OK, now you need to measure bearing preload. Remove at least one axle, or the cross pin and spider gears, to prevent excessive drag from messing up the measurement. Adapt an inch-pound torque wrench to the pinion nut, and see how much torque is required to keep the pinion flange turning. It's generally somewhere in the 10-to-20 in/lb range. Write this value down, you'll need it later.

Remove the pinion nut, with a 3/4" drive socket and a long breaker bar, and probably a big pipe wrench to hold the pinion flange. You'll probably need a long handle, and lots of elbow grease, these things are TIGHT! Remove the pinion flange, being careful not to damage the bearings by hammering on the flange. I like a 2-jaw puller for this operation. Remove the seal, and inspect it for unusual wear or damage caused by the dust shield or foreign matter wrapped around the shaft. I've seen weeds, hay baler string, etc., get between the flange and the seal, and cut one to pieces in a short time.

Reassemble the flange with a new seal, being sure to lube the seal lip liberally with rear end grease. Never install any seal dry. Retighten the pinion nut until the preload drag is the same as it was before disassembly. If it had no preload, try for about 12-15 inch pounds, tightening the pinion nut a little at a time until it measures correctly. Be careful! A small change goers a long way, when you're close to the correct preload! Install the driveshaft, check the lube level, and drive on!
Jerry

HotRod,
I have been trying to find out information on this for a while. The photos in the manual seem to show a seal that is mounted on the inside of the front cover, for the 1 Ton.

These 1-tons are different than the smaller ones.
After removeing the drive shaft remove the cotter
pin & pinion nut.Pull the yoke. There are 5-6
7/16 bolts around a flange. Remove these & the
flange. Than you can remove the seal from the
flange. There is a thick cork gasket that goes
under the flange. Tighten pinion nut securly &
tighten it farther to line up cotter pin holes.
There is no crush sleeve so preload is not
nessesary.

Thankyou, thankyou! I have been tring to get this information for a while. I have a replacement pumpkin with a better ratio and I wanted to put a new seal in before installing it.

Two more things.

Usually when the seal hardens, it cuts a groove into the mating surface on the trunnion. If this isn't taken care of, the new seal will leak. Get a Redi-sleeve to go over the trunnion, cost is $35-40.

Also, be sure your differential vent is clear. Location varies with the rear axle housing, on the 3/4 ton driver's side on top of the housing. It's probably under a glob of gunk. It unscrews and is easier to clean off the truck. If the vent is plugged, pressure from the heated gear lube will blow out the weakest seal, causing another replacement.