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Thomas A
09-17-2010, 08:28 PM
I have had the worst luck with rear-end's in my MN12's and FN10's. I've had 5-8 different gear setups in different cars built by different people, and they have all whined on deceleration. I've had places pull them back apart, say everything is perfectly fine, and they still made all sorts of noise.

I am getting ready to have the rear-end rebuilt in my Mark VIII, again, just becuase I can't stand the gear whine. Does anyone have the "perfect" specs to setup an IRS 8.8 that I can provide to a reputable shop?

Thomas

Douglas Walker
09-17-2010, 09:13 PM
Are you buying new ring / pinion?

Dirtyd0g
09-17-2010, 09:52 PM
Are you using new or used gears? OEM or aftermarket.
The only setup I have ever done silently( I have done it several times) is Brand new OEM gears. The pinion shim must be configured using a rotunda pinion depth guage and backlash need to be .008-.010 on a cast iron case or .010-.012 on a aluminum case. The aluminum case must be done with a case spreader. If you want to bring the rearend down before the day before the shootout I will gladly help you do it here.
Alan

frdlvr30
09-17-2010, 10:05 PM
Alan is correct. OEM gears and aftermarket gears are two different worlds. I have installed just about all of them. Even the difference between Ford gear sets and Motrocraft Gear sets are no where near the same in quality. Can you install aftermarket gear sets up for quiet operation? Absolutely. Will they stay that way? That depends on the gear. Using used gears if you are going for noise free operation is a No No. Best starting point I have found is a .029-.030 pinion depth shim beneath the pinion bearing, plus anything stamped on the pinion itself(For pinion depth) and .008 backlash. Set depth first....always. Then the backlash. Run 75W-140 Motorcraft fluid as well....

Thomas A
09-17-2010, 10:45 PM
Thanks for the suggestions! This is what I have purchased, but I might change it up.

Used Mark VIII Aluminum Housing
New FRPP 4.10 Gears
New FRPP Master Rebuild with Timken Bearings
New Auburn Pro Differential

Any good sources for OEM gears other than the Ford Dealership? What came from the factory with 8.8 4.10 gears??

Thomas

DLF
09-18-2010, 12:11 AM
Thanks for the suggestions! This is what I have purchased, but I might change it up.

Used Mark VIII Aluminum Housing
New FRPP 4.10 Gears
New FRPP Master Rebuild with Timken Bearings
New Auburn Pro Differential

Any good sources for OEM gears other than the Ford Dealership? What came from the factory with 8.8 4.10 gears??

Thomas

You'll also need the IRS side bearings and seals - FRPP M-4413-A

I'd also use ARP ring gears bolts and main cap studs, cheap insurance.

Which FRPP 4.10's did you get? There are two part numbers. M-4209-G410A and M-4209-G410M. The "M" gears are made by Motive and are a little harder to setup. The "A" gears are like Ford OEM gears.

Pinion depth and backlash are critical. And the contact patch always needs to be double-checked.

If you were closer, I'd help out, none of the diffs I've setup make any noise.

I even made my own case spreader. :D

Thomas A
09-18-2010, 09:49 AM
This is the kit I got. It appears to have the side bearings but not the side seals, so I'll have to pick up a pair of those yet.

The gears are M-4209-G410A so hopefully they will be a bit better. Yeah, NJ is a bit of a drive :( If you were going to the Shootout, I could send parts along and have you ship it back.

Thomas

Dirtyd0g
09-18-2010, 10:02 AM
Do the FRPP gears you bought have the M in the part number? Those are motives, without the M they are OEM. I just put OEM 4.10's in a 06 mustang and you cannot hear them at all even listening. 2 days before that I had a set of aftermarket gears apart 45 times trying to produce a good pattern and never did get happy. I ended up settling for a pattern the chart said was ok and they whine on decel. I made my own case spreader as well. For the aluminum cases I get studs and nuts from Mcmaster.com
Alan

DLF
09-18-2010, 11:07 AM
This is the kit I got. It appears to have the side bearings but not the side seals, so I'll have to pick up a pair of those yet.

The gears are M-4209-G410A so hopefully they will be a bit better. Yeah, NJ is a bit of a drive :( If you were going to the Shootout, I could send parts along and have you ship it back.

Thomas

I'm not talking about the diff side bearings. Sorry for not being clearer, I'm talking about the half-shaft bearings and seals.

Dirtyd0g
09-18-2010, 11:13 AM
I have a set or 2 of those in stock, I buy all my diff rebuild kits from SCP and keep them in stock so when I do a mustang I have bearings and seals left.
Alan

Thomas A
09-18-2010, 11:18 AM
Thanks Doug. I forgot about the smaller half-shaft bearings towards the outside of the case.

Thomas