rear differential: pinion gear shim?

[BerniniCaCO3]

Contemplating doing my rear diff: from 3.08 open, to 3.55 posi. OK, more than contemplating. Already bought my posi unit, gear set, new axle bearings and seals to do at the same time, etc, and planning for a friday night and saturday to do it over.

The biggest question I have is that i have no 8.8 ford pinion depth gauge tool, and to procure one, is $150 at a minimum.
Do I need it?
One fellow is telling me that I can just swap the shim from my 3.08, onto the 3.55 pinion gear: that the shim really is there to take up irregularities in the housing machining, not in the gears, so the original shim goes with the original rear end, and shouldn't need to be changed, changing gear ratios?

I also read on another thread just a few threads ago on this subforum, that there should have been some number on the pinion gear indicating the shim thickness to use with it? I've got my gear set, and a posi carrier, and I see no such number. Was it to have been painted on? Or will it be stamped in fine lettering, and I'm just overlooking it?

thanks!
-bernard

[Mercracer]

I can tell you that I went from 2.73 to 4.10 and didn't have to change my pinion shim(s).

[86VickyLX]

use the existing one from your differential case. So take the one from the 3.08, and put it in on the 3.55 pinion. 9 times out of 10 you should be fine just like that. You'll have to play around with contact patterns for the gears and whatnot. Gotta figure out how much to shim the new carrier. And where

[BerniniCaCO3]

Regarding shimming the carrier... ford dealership told me that they have dozens of sizes, none in stock and all on say a 2 hour order from the warehouse, and that I need to know *exactly* what to get.
Is there any chance my original shims might work?
It sounds like I won't be able to do this on a friday night; I'll need to measure it, and order the right shims, before I can finish.... and that there won't really be an opportunity for trial and error, seeing as that would involve a half dozen special orders and subsequent drives to the nearest dealer to pick up the next shim size!

Well, I'll try my original shims, and see. If it's loose, I'll use the dial indicator and try to find read what larger size would work instead.
Unless I can get a shim kit that has multiple thinner shims to modify one of the thicker sorts? E.g., ford sells $25 a pop thick metal plates: a .241" shim, and a .243, .245, etc. Could I just get a .241, and then a .010, and .005, and .001, rings of foil, and add them up to get what works?

[Mercracer]

Is there any chance my original shims might work?
It sounds like I won't be able to do this on a friday night; I'll need to measure it, and order the right shims, before I can finish.... and that there won't really be an opportunity for trial and error, seeing as that would involve a half dozen special orders and subsequent drives to the nearest dealer to pick up the next shim size!

Well, I'll try my original shims, and see. If it's loose, I'll use the dial indicator and try to find read what larger size would work instead.
Unless I can get a shim kit that has multiple thinner shims to modify one of the thicker sorts? E.g., ford sells $25 a pop thick metal plates: a .241" shim, and a .243, .245, etc. Could I just get a .241, and then a .010, and .005, and .001, rings of foil, and add them up to get what works?

There is zero chance that your original shims will work. Carrier shims are somewhat trial and error. Also, you must maintain your carrier bearing preload. What ever you take from one side you must add to the other. I have found gear installation kits lacking in enough shims but they get you close. It is better to end up with extra shims than to be stuck without what you need.
Do you have a a bearing puller and/or a press to use? Don't do this on a Friday night with your dealer closed.

[BerniniCaCO3]

whelp, did this on friday night with my dealer closed!
Ran into two issues.

1) I thought, and i had been informed by several, that 8.8=8.8=8.8. Turns out, a 2001 8.8 (28 spline, of course) differential has side gears that do not allow my stock axles to come in all the way.
Any chance my local ford dealer might be able to get side gears for me?? ...or take a die grinder to the ones I've got.

2) LR axle looked great. RR axle, at 123,000 miles, has a groove worn in where the bearings rode. A few thousandths, I should think, though I did remember to measure. You can catch your fingernail in it no problem.
Need a new RR axle? Does the RR=LR, so if I go to a junkyard, I ought to be able to use the less-worn LR axle? Or can I use my stock axle for a while longer, grooves notwithstanding?

3) Here's the wear pattern I've got. It very closely matches the first column, second row, and is "acceptable." can you make out any thing from the photos I've taken below, does it seem that I've got it right? Backlash is .011"

[BerniniCaCO3]

err, and since a 2001 28 spline mustang posi does not work with my axles (unless I take the side bearings to a machinist), which posi units will? When did the side gears change? The axles are about 1/4" too far out, the splines in the side gears are too wide and need to be cut back.

[Mercracer]

8.8 does = 8.8. Are you hitting your ABS sensors? You are missing something....

[BerniniCaCO3]

ah, turns out in 2000, mustangs went to a slightly different diff. The only diff-erence is that the side gears do indeed accomodate an axle with longer splines.
I have a unit from 2001.
Grand marquis, on the other hand, had the same posi unit from 1980 through 2005.
Called the dealer for my answers...
Now just gotta drive to PA for the right diff!

[BerniniCaCO3]

is auto parts unlimited/ APU a good quality brand?
Looking at this aftermarket axle:

http://www.ebay.com/itm/Ford-Crown-Victoria-Grand-Marquis-Towncar-Axle-Shaft-90-/360300329383?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item53e392b9a7#ht_658wt_1163

Why does the RR wear so much worse than the LR?

Also... gear wear pattern as per the yellow grease, looks good?

[BerniniCaCO3]

I figured out the gear problem, took care of this week.
Everything goes together now. I know I did this over a week ago, but I'm going to try to wrap it up tomorrow night, now that I FINALLY have all the parts.

Took a much better photo of the wear pattern.
The pinion is just ever so slightly too deep. I've got a couple very experienced guys saying that it's probably OK, and just run it and see. I've got a couple guys saying it's off.
What's your experience?
And if it does make noise, how far might you try backing off the pinion? (i.e., this pattern is caused by the pinion being too close to the ring gear, so I need a thinner pinion shim in there. What i used, was just the stock).
Backlash is good at .011".

[sly]

if backlash is good... run it.

[Mercracer]

I figured out the gear problem, took care of this week.
Everything goes together now. ..

What happened with your axles apparently not going in far enough??

[BerniniCaCO3]

It was a late model differential, from the year 2001, from a mustang, that I was installing.
The side gears accommodated an improvement: 1.17" splines. My stock axles have 1" splines. The change was in 2000 for a mustang, 2005 for a grand marquis. I only found that out after the fact, when I was talking with a ford parts guy at the local dealership to figure out what had gone wrong.
So when I slid my axles in, they bottomed out, 0.17" too far out, and I couldn't get the c clips on
I took my gears to a machinist, and he turned them into 1" splines for $75.

I was worried whether that was all that was off. I guess I'll find out for sure tomorrow night! But I believe so. Even though the side gears are different in width as well as spline length, they're thicker and beefier, the carrier's internal width is correspondingly wider also, so that the ends of the gears where the axles come through are in precisely the same spot. I checked this all with telescoping bore gauges and a micrometer.

Sadly, ironically, the brand new axle I ordered (link below), has the longer splines that would have worked with my gears!! I would have saved $20 (machining was $75+ $30 in gasoline for two round trips), AND had upgraded wider splines, and for less stress and headache. But hind sight is 20/20. I dropped my gears off at the machinist on Monday, and only got my axle on Tuesday, and more importantly only opened it on Thursday. I had simply no reason to guess that an axle made for a 1990 grand marquis would have late-model wider splines. I guess to fit more models; makes it cheaper for the aftermarket.
Here's the axle I bought, no complaints at all: http://www.ebay.com/itm/Ford-Crown-V...#ht_658wt_1163
I only bought one. The LR looked in fine shape, and wasn't going to fix what wasn't broken.