Another Pinion Seal thread
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Joined: Aug 1999
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From: Connecticut, USA
Another Pinion Seal thread
There have been several pinion seal threads recently and some of my old information from many years ago is still out there.
One thing people get caught up on is seating the seal in the bore. The old manual spec of 1/8" gap doesn't always hold true. The correct way to install them is to measure the yoke, seal, and bore. Doing that on the car can be a challenge so it probably won't be done. On a stand it is easier to check.
C3 diff's were not the best built differential on the market. There were issues with every year from 63-82. One of those was QC - or lack of it at times. The bores vary so that is why the seal has to be checked with the yoke used. The seal will tap down until it reaches the edge of the bore. At that time no more driving on it should be done since it will distort it. Sometimes the seal will seat on the edge of the housing, other times it may be up.
I just did one today and checked it. The gap was .155" +/- 003" If I tried to drive it deeper it would have distorted. This particular job didn't matter since the yoke used is a HD 1350 without a shield. If a stock pinion yoke with a shield was used, it might have hit the seal. This bore was shallow compared to most. If you find a shallow bore you can use a flangeless seal or carefully cut off the flange from a stock seal. In order to correct one like this the housing bore would have to be machined. That is not something done on the car and requires the diff to be disassembled. This is not common but isn't as rare as you might think.
Bottom line, it's up to you or your mechanic to correctly check and install the new seal. It was more of a problem with 12 bolt housings.
One thing people get caught up on is seating the seal in the bore. The old manual spec of 1/8" gap doesn't always hold true. The correct way to install them is to measure the yoke, seal, and bore. Doing that on the car can be a challenge so it probably won't be done. On a stand it is easier to check.
C3 diff's were not the best built differential on the market. There were issues with every year from 63-82. One of those was QC - or lack of it at times. The bores vary so that is why the seal has to be checked with the yoke used. The seal will tap down until it reaches the edge of the bore. At that time no more driving on it should be done since it will distort it. Sometimes the seal will seat on the edge of the housing, other times it may be up.
I just did one today and checked it. The gap was .155" +/- 003" If I tried to drive it deeper it would have distorted. This particular job didn't matter since the yoke used is a HD 1350 without a shield. If a stock pinion yoke with a shield was used, it might have hit the seal. This bore was shallow compared to most. If you find a shallow bore you can use a flangeless seal or carefully cut off the flange from a stock seal. In order to correct one like this the housing bore would have to be machined. That is not something done on the car and requires the diff to be disassembled. This is not common but isn't as rare as you might think.
Bottom line, it's up to you or your mechanic to correctly check and install the new seal. It was more of a problem with 12 bolt housings.
