Differental slop ? - FFCars.com : Factory Five Racing Discussion Forum
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post #1 of 8 (permalink) Old 10-11-2019, 07:59 PM Thread Starter
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Differental slop ?

Hi guys, Since starting to drive the Coupe I've noticed some drive line slack i.e. when letting off the throttle there's a clunking and also when applying throttle-clunk. once its engaged its noise free-ish this car is LOUD! Gordon Levy supposedly re built this Diff cause he charged me for parts and labor, the driveshaft is from Denny's and has no slop. Since I'm replacing my clutch fork and T.O. Bearing (see my other post in roadsters) should I have this looked at? this is a quick video I did:
Thanks!


Coupe #641 started 6/19/14. Levy stage 4 347, Super Alloy T5, FAST EFI, IRS, Willwoods, Fast Freddie's EHPS, Custom Carbon dash. More mods to come I'm sure.
MK 3.1 Roadster #4759 completed 2005, 4.6 sohc,Bullits, Willwoods, ABS, Hydroboost, A dream to drive and auto cross !
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post #2 of 8 (permalink) Old 10-11-2019, 08:58 PM
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See page 17 of the Ford instructions for the 8.8 rear. (link below). Spec is .008" to .012" measured at the ring gear. You will have to remove the rear cover to measure the actual backlash but looking at the pinion backlash I would say that there is a pretty good chance that the ring gear backlash is excessive.

https://performanceparts.ford.com/do...htM-4209-8.pdf

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post #3 of 8 (permalink) Old 10-11-2019, 11:11 PM
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Didn't get what you paid for on that one.
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post #4 of 8 (permalink) Old 10-12-2019, 01:44 PM
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Before you start tearing it down, see if you have any in and out play in the pinion flange. I watched your video and could not detect any.
There should be ZERO movement. In the event you can detect any, you can remedy it by tightening the pinion flange nut. This also sets the pinion bearings preload, so you are not tightening it for a bottom out feeling. Just get the slack out. Good luck,
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post #5 of 8 (permalink) Old 10-14-2019, 07:02 AM Thread Starter
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Railroad, no movement there, I think I’ll put everything back together and drive it till it breaks or I get pissed enough to take it out and have someone make it right. I’m pretty sure that it wasn’t rebuilt since the axle seals were filthy! I also checked my mk 3 roadster with a 8.8 solid axle and it moves about half as much FWIW.

Coupe #641 started 6/19/14. Levy stage 4 347, Super Alloy T5, FAST EFI, IRS, Willwoods, Fast Freddie's EHPS, Custom Carbon dash. More mods to come I'm sure.
MK 3.1 Roadster #4759 completed 2005, 4.6 sohc,Bullits, Willwoods, ABS, Hydroboost, A dream to drive and auto cross !

Last edited by MauiKarl; 10-14-2019 at 07:15 AM.
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post #6 of 8 (permalink) Old 10-14-2019, 03:06 PM
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Just me, but if your trac lok design is compatible, I would put 90w-140 non syn in it. It probably has 70w-90 in it. It will not fix anything, but can soften the sound to some degree.
good luck,
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post #7 of 8 (permalink) Old 10-14-2019, 04:22 PM
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Same Problem Here...

Interesting timing on your post. Because I have had the same issue since I first got my MK 3.1 on the road. I have just started the removal process for my IRS differential. Going to have it rebuilt and I am going to replace the front and rear solid mounts with poly mounts. The front mounts are no problem, because the kit came with them, but the rear mount on the 3.1 IRS is solid and I am going to have to come up with some sort of fix. I want the poly mounts to better isolate the diff from the frame.
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post #8 of 8 (permalink) Old 10-14-2019, 05:59 PM
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Run it. Mine has had about 1/2 inch as you show it for many years. If you add up all the places on an IRS which can have a little play that does not look too bad. at least assuming the ring and pinion are ok.
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