Differential specs wanted

[YoungCobra]

Hello ladies and gents, in my quest to hunt down the dreaded +80pmh vibe and wheel hop, I took the (red?) pill and ordered a bunch of IRS parts.

Namely Stage 5 half shafts, an Eaton posi with a diff rebuild kit, MM Lower and Upper CA Delrin Bushings, MM Aluminum diff bushings, Billetflow diff brace and IRS brace. I also ordered a MM 6 point cage just for fun.
I'm sticking with the stock 3.55 because I plan to go with a Whipple or KB over the winter.

I will be starting the job Monday, as soon as my cousin's Cuda is tuned and there's a spot in the garage for the Cobra.

I just wanted to make sure the diff specs are the same as other Mustangs. Backlash and all that. The diff is being sent out, but I just wanna make sure he uses the correct specs. Does anybody have them?

 

[ShelbyGuy]

you need a case spreader to do IRS housings. you'll destroy the housing if you just beat the shims in with a hammer like on a steel housing. the case spread spec is .030"

backlash is .008 to .012 with .010 preferred. preload is .014 total. so they're tighter than solid axles.

 

[YoungCobra]

Amazing dude, thanks for the info.

 

[RealBadDude]

i believe spec on the solid is for backlash to be set from .008 to .015 with .010 to .012 preferred as well.

the exact specs according to alldata are as follows for solid axles:

ring gear face runout: .004 max
max differential case runout .003
max axle shaft end play .030
ring gear backlash .008 to .015
***.012 to .015 prefered.

for the IRS again according to alldata:

max carrier spread: .030
max ring gear face runout .003
max differential case runout .003
Backlash between pinion and ring gear .008 to .013
preferred backlash .010
max backlash variation between teeth .004


pinion depth is set via gear marking compound with both solid and irs setups. i good measurement to take before disassembly is to measure your existing pinion depth.
when installing the pinion install the required shims to get you to this same measurement.
this will get you close. from there use gear marking compound.

Pinion depth is indicated by the position of the pattern between the face and flank of the ring gear teeth. Backlash must be kept within specifications, and will therefore only slightly affect the pattern between the heel and toe of the ring gear teeth. Housing alignment and pinion bearing bore alignment can also affect the pattern from heel to toe and can not be corrected without machine work. In some cases an ideal heel to toe pattern can not be achieved. If the backlash is within specifications, you may disregard the heel to toe pattern. A contact pattern that is centered from face to flank ALWAYS indicates correct pinion depth even if a pattern that is centered from heel to toe can not be obtained.

see here for an excellent write up on gear installation and acceptable contact patterns.

http://www.differentials.com/install.html

when i set my gears up the best i could get it was a little towards the toe on drive and a little towards the heal on coast. they were not in the center of the tooth toe vs heal, but they were perfect on root vs flank.

no noise what so ever.

in addition to the case spreader mentioned by shelbyguy you will also need a hydraulic shop press to remove and reinstall bearings on the pinion. they are pressed on. as well as the carrier. you will need a bearing splitter. you will need a dial indicator, you will need a torque wrench that measures from 0 to 5 INCH POUNDS! not foot pounds!!!

you will need a torque wrench to properly torque the carrier in. this one in foot pounds. you will need a big farkin pipe and a half inch driver to torque down that crush collar. believe me, i have air tools and it stopped my impact wrench cold in its tracks and it produces 450 ft/lbs in forward 650 in reverse mind you, just to give you an idea.
you are better off doing the preload by hand anyway because it is so easy to shoot past the proper setting. use your old pinion nut until you are with in 10 inch pounds of preload then finish with a new pinion nut. the pinion nuts from ford come with thread locking compound on the threads so loctite shouldn't be reqired, although some like to add some red loctite to the nut as well.

you will need a few crush collars, expect to ruin the first few if you haven’t done this before.

you will need a lot of patience. I took mine apart and put it back together 20 times my first gear setup before it was perfect. you get better with experience.

All new gear sets require a break-in period to prevent damage from overheating. After driving the first 15 or 20 miles you must let the differential cool for 30-40 minutes before proceeding. Drive 500 easy miles then change the oil and inspect for even wear in. recheck and reset backlash if needed.
i like to hit it up w/ the gear marking compound again to make sure it is will on a good pattern after the initial break in,.

 

[ShelbyGuy]

0-5? you cant properly do a gear install wtihout a dial torque wrench that reads up to 25 in-lb. breakaway preload on new pinion bearings is 20-24 in-lb.

my pinion flange holding tool has a hole cut to fit a 1/2" drive breaker bar so between that, and my 1/2" drive long-handled ratchet with a piece of pipe on the end, those are how I crush a crush sleeve.

for added durability, consider using a solid pinion spacer instead of a crush sleeve, and using the extra heavy duty pinion shims that go between the race and the housing instead of between the pinion head and the bearing. i'm working with ARP to get the stud length right. the stud kits for solid 8.8 axles dont work as the aluminum housing has a taller cap for the carrier bearings.

 

[RealBadDude]

sorry shelby guy i ment o to 50

 

[YoungCobra]

The Job is done, and on the first test drive everything was fine.

The next day, took the car out of the driveway, and a clunk started eminating from the back. Upon further inspection, we noticed the new DSS Stage 5 half shafts were moving freely inside the diff case. Push one, the other moves outward.

How do I correct this problem. Are the spacers off? Wrong parts? Does the diff need to come out?

 

[ShelbyGuy]

what do you mean by "moving freely inside the diff case?"

The inner stub shaft is held in the differential by a circlip on the shaft and a groove inside the spider gears. If you swapped differentials to one thats not IRS-compliant, then it won't have the groove and the half shafts wont stay in place.

 

[YoungCobra]

I mean there's play. It's a funny thing, what can I say. The Eaton is IRS compliant.

 

[RealBadDude]

like shelbyguy said, if that ring is in the groove them axles shouldn;t move at all, well maybe a hair, but thats it. if your axles slide in and out it can only be 1 of three things

1. the clips are missing (doubt it on new axles)
2. the diff isn't IRS specific or compliant. (most likely)
3. the axles arent pushed in far enough to engage the clip. (i doubt it)

what you described makes me thing of somethng else though.

most diffs have a "block" that installs in between the axle ends in the diff itself. this is more relivent on solid axle cars using c-clip axles, but it is important on all cars. the "block" holds the axles and prevents them from being pushed inwards, and the c-clip holds them against moving outwards. (in a nutshell). in most ford factory units it looks like a round long cylinder shaped peice of metal with a single small bolt holding it in place.

your problem almost sounds like yours is missing allowing excessive inward motion of the axle. However on an IRS car the snap ring little clippy thing should be all that is needed.

i don;t have any experience with the eaton specifically, but i would imagine it has something to that effect.

the fact that one axle slides out when the other slides in makes me think there is some kind of mechanical link between the two. so to be honest i suspect your diff being the issue. i think the snap ring is engaged and something in the diff actually is sliding back and forth.

if it were just the clips missing one axle would move but the other wouldn't.

honestly, drop the diff, and install the axles with the cover off. then move them around and see exactly what the hell is moving in there, and go from there.

something else to try: grab the axle near the housing and give a quick tug. if that clip is engaged it shouldn't move, if it does then the clip most definatly isn't engaged, or something is moving inside the differential.
eitherway it has to come out.

 

[YoungCobra]

OK now the question is, is it safe to limp it to a lift? Roughly 8 miles stop-n-go city driving.