8.8 Pinion Nut Leak

O

OX1

Active Member

Apr 16, 2014

50

74

29

Jan 3, 2026

#1

• Jan 3, 2026

• #1

Looked like pinion seal leak, but no oil just outside seal itself.
Appears to be getting by pinion nut.

Pretty sure I used Motorcraft nut when I put it together,
but did not use any sealer or RTV (since Ford nut had
generous amount of "loktite").

Luckily, I set up my 8.8's with crush sleeve eliminator,
just in case this ever happened (and I hate crush sleeves in general).

You'all using anything specific on pinion nut/flange at all?




Pulled seal anyway and picked up new Ford seal. Figured while I was in there.
Seal surface does not look too bad.
One bearing looks good, so guess I set pinion bearing "eliminator" preload, OK.

 

Reactions: General karthief

2Blue2

will be trying this sex one when I can find it

Mod Dude

Mar 5, 2019

4,430

2,893

163

Oahu

Jan 3, 2026

#2

• Jan 3, 2026

• #2

giantpune said:

smear the splines

Click to expand...

+1

 

O

OX1

Active Member

Apr 16, 2014

50

74

29

Jan 4, 2026

#3

• Jan 4, 2026

• #3

Thanks guys, will glob up the splines.......

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#4

• Jan 4, 2026

• #4

Wait... You're putting RTV on the splines?

If the pinion seal is good, the splines will never see oil.

Measure the yoke for wear. If it's a bit worn there are "Speedi-Sleeves" (SP) for pinion yokes.

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#5

• Jan 4, 2026

• #5

Aha! I thought I had seen one in recent travels:

https://lmr.com/item/LRS-4851RK/88-Rearend-Pinion-Seal-Repair-Sleeve-Mustang-86-04?utm_source=chatgpt.com

 

AeroCoupe

lube between the nut and the face. I know my lubes

Founding Member

Oct 28, 2001

5,846

3,975

183

Claremore, OK

Jan 4, 2026

#6

• Jan 4, 2026

• #6

The driveshaft flange rides on the pinion seal so fluid can travel the splines that the driveshaft flange slides down.

I had to go and look for a pinion gear to remember what all was going on.



I watched a few of this guys videos (Eric the Car Guy) and he had one tearing down an 8.8.

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#7

• Jan 4, 2026

• #7

One other though: Check the vent and make sure it's not blocked.

 

nickyb

I gotta say i never painted my nuts, Never Ever

15 Year Member

Apr 3, 2009

2,979

1,626

153

nevada

Jan 4, 2026

#8

• Jan 4, 2026

• #8

Just don't put paint on the nut.

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#9

• Jan 4, 2026

• #9

giantpune said:

I'm not following your logic here. The pinion seal is for the outside of the pinion flange. Oil can still seep out through the inside edge of the pinion flange, where the splines are. Its a straight shot from inside where you've got all the oil, between the pinion and flange (along the splines), then popping up behind the nut, or wicking through the threads and coming out the front of the nut.

Click to expand...

The pinion seal is leaking (pinched/torn/worn)
AND/OR
The yoke sealing surface is worn or grooved
AND/OR
The vent isn’t doing its job and pressurizing the housing

The pinion seal seals against the smooth pinion yoke (flange, whatever you want to call it). If oil is slipping past the pinion seal then it usually appears in the threads (inside the flange).

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#10

• Jan 4, 2026

• #10

That seal has two sealing surfaces. One around the shaft and the one where it mates with the yoke or flange.

The yoke land should be smooth. The pinion seal lips rides on this surface. If the oil level is correct and the diff is not pressurizing then the only oil it sees is what makes it's way past the oil slinger.

Lateral movement in the shaft can cause leaks here too (wrong spacer/worn crush sleeve).

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#11

• Jan 4, 2026

• #11

I don't know what else to tell ya man.

I have no RTV on my splines nor do I have instructions for putting RTV on the splines an It is as dry as a bone.

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#12

• Jan 4, 2026

• #12

I resealed mine in the real world too.

Per the shop manual.

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#13

• Jan 4, 2026

• #13

giantpune said:

And just because yours isn't leaking (yet?) doesn't mean than nobody else's leaks there. Not sure why you feel like that warrants a goofy emoji. If your car doesn't get a rear main seal leak, but mine does, are we all making silly emojis about it?

There is a potential for diffs to leak between the splines. OP's is leaking there. Now he has a fix for it. And you learned something too.

Click to expand...

What is it that you want to argue about exactly? You said you didn't follow. I explained it.

Is there something else you want?

 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Admin Dude

Jan 4, 1985

43,009

21,193

234

Box behind Walmart

Jan 4, 2026

#14

• Jan 4, 2026

• #14

Nobody said you have to like the emjoys or use them.

I do not GAF.

What I did do is offer an alternative to putting RTV on the splines including repair kits specifically for those repairs when something may be worn or not perfect.


If you can't find a way to have a conversation without resorting to lighting your hair on fire then you may be happier somewhere else like bookface.

 

nickyb

I gotta say i never painted my nuts, Never Ever

15 Year Member

Apr 3, 2009

2,979

1,626

153

nevada

Jan 4, 2026

#15

• Jan 4, 2026

• #15

Whatever you do,don't paint your nuts.

 

Reactions: General karthief

O

OX1

Active Member

Apr 16, 2014

50

74

29

Jan 5, 2026

#16

• Jan 5, 2026

• #16

nickyb said:

Whatever you do,don't paint your nuts.

Click to expand...

Especially with POR-15

I don't recall ever having a pinion flange spline/nut leak before, so this is a new one on me.

But if you don't put this seal in an old 205 TC (flange), it will 100% leak by the splines/nut.
(maybe those splines on old TC's, were not cut as "tight", even new).

NP203/205 Yoke Nut & Seal-Broncograveyard.com

Spline Sealbr Yoke flange Nutbr br This is a one time use nut, once it is torqued to 150 FT. LBS. and removed it must be replaced.

shop.broncograveyard.com