The Stovebolt Site Forums The Shop Area Driveline Pinion Seal Leak, and Date Code ID

Hello, I had a friend ( a real mechanic)help me a year ago replace all the seals in the rear end of my 56 3100 because the Pinion seal leaked and also one of the axle seals. For the yoke & pinion, things didn't fit back the same and we had to make about a 1/8' spacer to fit between the crush sleeve and the yoke end so that the yoke didn't rub on seal flange. It has continued to leak and now I'm determined to fix it. I wish I had the original seal because I think it was different from what we got from Oreillys. Looking at one of the classic parts web sites they show two types of rear seals. The 1/2 ton has a Flange, and the 3/4 ton looks like a flush fit. I'm thinking I need the flush fit seal instead of the flange. That is about the 1/8" difference for the shim we had to make. So any history on seal type and variation would be apreciated. I'm not sure this is the original rearend because there are spots where they have had brackets cut off on the axel shaft. The numbers are 3707340, and D1 which from some other post here seems to be 1/2 ton. The date code is AF 1226, can someone decode that? I'm sure it is a 3.90 ratio. Would the 3/4 & 1/2 ton seals have the same Outside Diameter? Also do they make a sleeve to fix seal wear on my yoke? Thanks for any info or suggestions!

AF is the code for 3.90 ratio 1/2 ton rearedn, '55-'59. The date works out to December 26th. The 1/2 and 3/4 ton seals are diferent, 3/4 ton is the same as 1 ton.

The deflector on the yoke would be the only thing that would rub it seems like. They are tack welded to the yoke. Some times they come loose. Make sure it is back as far as it should be.

The deflector is rock solid so I'm sure thats not it. I packed up the yoke and old seal and headed to town to hit the parts stores. We have a couple of the computer parts stores, you know the ones where if its not in the computer, then to bad. After wasting about 30 minutes in one, I went to our real parts store that also has a machine shop. I showed them the yoke and seal, and asked about the sleeve to fix the seal wear. The guy didn't go to the computer, he grabbed a micromoter and started taking measurments. Went to a book cross reference and said he could have the sleeve and a new seal without flange tomorrow. So thanks for confirming this is the original 56 rearend, and now I know you can get a sleeve to fix the wear on the yoke. I'll just have to try the flush mount seal and see how that part works out.

I just wanted to update this thread that the new "Non Flange" pinion seal Car Quest #473448 ($11)worked great in my 56 3100. No need for a jury rigged spacer for the yoke, and the oil deflector fit perfect next to the case without rubbing on the seal flange. Also that the National "sleeve" #99170 ($38) solved the wear problem on the yoke. After topping off with gear lube, two test drives for a 20 mile total, and letting it sit for a few days, NO Leaks! So glad to get this fixed finally, and hope this info might help someone else. As others have noted in the forums here, make sure to use some permatex on the seal flange and the yoke splines as those are potetial leak areas as well.

Resurrecting this older (year 2010) thread; it's what I found today using the Stovebolt forum search function.

Can we confirm that a Car Quest (also Timkin) # 473448 rear pinion seal is what's required for my 1955 First Series 3100? 1/2 ton truck, 3.91 rear, open driveline.

Glad to hear the search function is alive and well and used! Never a bad thing to bring up an older thread. It'll help to "update" it as necessary. But we moved it to the Driveline section of the Shops since it's about the rear axle and not the engine itself.

Now to be the Stovebolt Brain-trust to help answer the question.

I am in the same spot. 1955.1 leaking rear pinion seal.(235, 3 speed, 3.9 open rear end) I have somehow ordered a seal, twice. Both seem to be the same seal. It appears that the 1955.1 are a little different, based upon this read.
Shop manual states, same as 3/4 open rear end. Is the flange less type the correct seal?
To repair/replace, isn't it just to remove drive shaft, then big bolt, remove u joint flange, pull out seal and replace??
I have been told to mark drive shaft along with marking position of u joint flange. Cant quite understand "marking U joint flange as it sets pinion to ring gear"??

Any help is appreciated. Thanking in advance to everyone.

That 6818 seal should be the right one. The GM PN from the attached catalog listing crosses over to Timken 6818.

As far as marking the u-joint flange, you need to reinstall the driveshaft in the same position as it came out to maintain the balance. Also the shop manual recommends marking the pinion flange so it's reinstalled in the same position on the pinion shaft. Mark both the pinion and the end of the pinion shaft. Check HERE for the complete procedure. (That's from the 55 second series manual, but the rear axle for the 55.1 is the same as the 55.2) That includes checking bearing preload before disassembly and rechecking while tightening the pinion nut so the preload on the pinion bearings is correct. You can't get that right by marking the position of the pinion nut before you remove it. It's important that the bearing preload is right, or you may get gear whine or early bearing failure.