I replaced my pinion seal last summer. When I put everything back together I used RTV black to lightly coat the splines of the pinion before putting the yoke back on it. I then put some more RTV at the top of the yoke where it meets the splines of the pinion before putting the nut back on and tightening it all up.

I did all this to try and prevent gear oil from walking up the splines and leaking. This is a trick mechanics I used to work with used.

Anyway, gear oil is still getting past the splines and the RTV I put in there. The seal I replaced is still tight with no leaks.

Should I have used something other than RTV black for what I did? Anyone have any other tricks to stop this leak?

 

I've never seen or heard of the type of leak you're describing, nor can I imagine that it's even possible. Are you sure it's not u-joint grease leaking out onto the yoke?

 

No. It's absolutely gear oil. I had this happen on my last truck too. A GMC Typhoon. But I hadn't tried to stop it with silicone on the last ruck.

When I took the nut off the pinion just now, gear oil came out from underneath it. It's definately coming up the splines. And it is starting to make a mess underneath the truck when it slings from the drive shaft spinning.

 

How is the vent on the rear differential?

 

I have never looked at it. I will when I get under there again.

 

I did a lot of searching and came across a youtube video of a guy chaning out a pinion seal. He used RTV gray on the splines of the yoke when he put it back together.

I went and found RTV gray to see what it was. I have only really used black and red. Gray is for "high torque applications". I guess that is what I am dealing with here. So I took the yoke off, coated the splines with the gray, and then put it back together.

I checked the vent on the rear also. I blew into the hose and was able to move a little air into the rear. When I stopped blowing the air started coming back at me through the hose. So I assume that means the vent is open and flowing.

No one else has ever had to deal with this?

 

Doesn't the gear oil have to get past the pinion seal in order to get to the splines?

How was the pinion shaft where it rides in the seal? Did it have a groove worn into the shaft from the old seal?

 

No. The pinion seal makes contact with the collar(I don't know what it is really called) of the flange/yoke. The splines of the pinion go through the center of the flange/yoke. So the pinion has no contact what so ever with the pinion seal.

It's a new seal and the collar on the flange/yoke are smooth.

The seal itself isn't leaking. I can clearly see the gear oil is coming from behind the large nut that goes onto the end of the pinion.

 

Oh, that's right. There is (should be) an oil slinger between the front pinion bearing and the pinion seal. Only thing I could imagine is that if the pinion flange splines don't fit tight on the pinion shaft splines, they might be able to leak along the splines.

Only other thing I could suggest is that you use something like brake clean to get all the oil film off the splines when you coat them with RTV. That synthetic gear oil will find any place where the RTV is not sealed.

Ford does have a specific tool to install the flange to be sure it is seated all the way on the splines.

What year vehicle and which rear diff does it have?

 

My seal leaks the same way. Ford rear, and 185,000 miles. I was wondering if the bearing was gone too.

 

My truck is an 01. I don't know which rear it is if there are different ones offered in the 01's. It is an open diff.

For my update, the rear has been leak free since my last posting. I have drivin it quite a few places around town and had it out on the highway for a 1 hour run each way. It is still dry.

So the RTV gray seems to have done the job.

 

my friends this is the best RTV. used it and works great 👍 recommended

ommended

 

Agreed. . .

 

+1 on the Permatex gasket maker.