Differential Input/Pinion Shaft Seal Leaking

[clawhamm3r]

I had my diff out 23k miles ago and at that time gave it a full seal service and new fluids. Now my front seal is leaking...did I screw up the install? The first seal went 92k miles before I changed it, and it wasn't even leaking. Seems like this should have lasted at lot longer, pretty annoyed right now. At least the others aren't also leaking (*knocks on wood*). I used all OE BMW seals too...

So what's your tips and advice on doing this seal? I don't want to have to do it every 6 years or 23k miles haha.

[bigjae46]

Did you install it at the same depth as the original? Is it in straight? If the seal is flush with the case it is in too far. It should be just a tad higher. If you press it in too far it will leak. I've done it twice but with the diff out of the car. I would imagine its a little harder to do in the car.

There is a spring on the inner lip of the seal...sometimes that fails.

[clawhamm3r]

I did it in the car on a buddy's car in my driveway like 5 years ago, it sucked but wasn't too bad to do. He sold the car a year later so no idea how it held up.

I want to say I matched it to the original. But maybe I made it flush, not sure, it was like 6 years ago. I guess I'll know when I go to fix this one, but not sure when I'll get to it at the moment. But good call out!
It was definitely in straight I wouldn't have done it any other way.

Is a leaking pinion seal a good excuse for 3.91 gears?

[eacmen]

I did it in the car on a buddy's car in my driveway like 5 years ago, it sucked but wasn't too bad to do. He sold the car a year later so no idea how it held up.

I want to say I matched it to the original. But maybe I made it flush, not sure, it was like 6 years ago. I guess I'll know when I go to fix this one, but not sure when I'll get to it at the moment. But good call out!
It was definitely in straight I wouldn't have done it any other way.

Is a leaking pinion seal a good excuse for 3.91 gears?

This is how a shop almost blew up our diff. They over tightened the pinion nut. You're supposed to mark it and count the turns needed to take it off.

The pinion seal is relatively simple job, unless you suspect that the nut was overtightened and the bearing is in races - no need to open it up for 3.91.


Sent from my iPhone using Tapatalk

[clawhamm3r]

This is how a shop almost blew up our diff. They over tightened the pinion nut. You're supposed to mark it and count the turns needed to take it off.

The pinion seal is relatively simple job, unless you suspect that the nut was overtightened and the bearing is in races - no need to open it up for 3.91.


Sent from my iPhone using Tapatalk

Haha nah I was joking about the 3.91s cause I need an excuse to pull the trigger. But yeah I did the whole mark it and count the turns thing for the preload.

What happened when they overtightened it? You said almost blew it up? haha

[eacmen]

Haha nah I was joking about the 3.91s cause I need an excuse to pull the trigger. But yeah I did the whole mark it and count the turns thing for the preload.

What happened when they overtightened it? You said almost blew it up? haha

Hard to tell on the car. but off the car the input shaft will be really hard to turn. The torque required to turn the input shaft with correct preload is measured in inch-lbs. When the diff was removed after the seal job (luckily just driven between two shops) took significant effort to turn the input shaft. I used to have one shop do all the mechanical and another do setup/alignment now the setup/alignment shop does *all* work on the car.

With it on the car you might also notice that when the car is on a small incline that if you clutch in the car won't roll. If that's happening then it could be over tightened.


Sent from my iPhone using Tapatalk

[clawhamm3r]

Hard to tell on the car. but off the car the input shaft will be really hard to turn. The torque required to turn the input shaft with correct preload is measured in inch-lbs. When the diff was removed after the seal job (luckily just driven between two shops) took significant effort to turn the input shaft. I used to have one shop do all the mechanical and another do setup/alignment now the setup/alignment shop does *all* work on the car.

With it on the car you might also notice that when the car is on a small incline that if you clutch in the car won't roll. If that's happening then it could be over tightened.


Sent from my iPhone using Tapatalk

That's pretty lucky you caught it haha. Have always heard/read the warnings about this but never heard what happens when it's torqued too much. Have heard of a lot of people being timid and going to soft and it backing off though.

[ATB88]

That's pretty lucky you caught it haha. Have always heard/read the warnings about this but never heard what happens when it's torqued too much. Have heard of a lot of people being timid and going to soft and it backing off though.

It will ruin your diff, eventually, but won't make it explode right away

I overcranked mine by almost a full turn when I did my pinion seal because I'm a moron and it was one of my first DIY jobs. Car felt great for the first little while, but at about 4k miles later, the diff started to develop a humming noise. Luckily, by then, I was doing a 6MT swap, so I dropped the diff out and had it rebuilt by a pro while I was doing the swap. The pinion bearings were obviously toast at that point, but the rest of the bearings and other diff components were apparently still in perfect shape. Who knows if I'd driven longer, though.

[clawhamm3r]

So I ordered Quick Jacks from the Costco sale a couple weeks ago and am waiting on them to come in before tackling this seal. I figured I still have 300ml of fluid leftover from the original job so I'd top it off. Raised the whole car up on blocks on level ground and oil started pouring out...not like popping an oil plug but more than a drip or stream...som steady flow.

So I thought okay, "level surface" must not account for rake lol. So I lifted the front from the center point enough that the side jack pads were equally off the ground. Then I put a level on the diff body and the diff is not level (I guess the body is angled). So I put the level on the rear chassis brace and it's level. Is this the level I want?

I popped the plug off again and it was still trickling for a second or two. Once a slow drip I capped it.

So...I have no idea what's going on. Did my diff have too much oil in it and that's also what caused the front seal to die so early?

I originally drained the fluid with the the diff out of the car so I was able to rock it over to get a full drain. On top of that I did the input and output seals. There's no way there was still fluid in there. Since I knew BMW called for 1.2L I filled it out of the car, just rocked it over and filled it with 1.2L exactly. Yet somehow it's pouring out when mounted.

Conventional wisdom says it's in the car, the car is level, and it's dripping out the fill so send it. See pic.
Any chance I win the lottery and it stops leaking? I can dream lol.

When I do the seal I'll drain and refill for good measure. But I'm stumped.

One more note: I will say it was hella dirty under there and looked like it's been flinging fluid around for 6 years/23k miles. Didn't look like that when I did my subframe job at the same time...wasn't leaking at all and very clean. Now looks it looks like it leaked since I put it back in and just now dripped enough where it was spilling off of the rear brace onto my garage floor. Pretty crazy if it's been leaking this whole time and was somehow overfilled. Also not ruling out aliens or diff that generates it's own fluid.



On diff body:


On brace: