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8.8 IRS noise and diagnosis

rattle_snake

rattle_snake

Fuckwits
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Jun 23, 2020
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Chandler, AZ
Not 4WD related, but this is the only site I know of with actual diff/gear knowledge.... :flipoff2:
So 2004 Cobra 8.8 Trac-loc IRS started making clunk after some WOT shenanigans. Clunk is sync'd to pinion rotation. Disconnected driveshaft. Clunk is at a specific and repeatable location/index (example, random mark on flange at 4 o'clock) when rotating the tire on lift.

Rotating drive flange by hand, there is not excessive backlash in either direction. Can't feel any broken teeth or any change in rotation resistance. If rotated carefully, it has a 'dead spot' where pinion can be moved slightly more but axles don't anymore (with backlash preloaded). Once in this condition, can rock flange back and forth in dead spot. The rotational position of finding this dead spot is NOT consistent. This could be slop in the spider/clutches/cross pin.
If CV axle is rotated the dead spot is not there. Maybe due to opposite gear loading but if spider/clutches are fucked it should be noticeable. This leads me to believe maybe a pinion bearing.

You cannot remove the diff cover unless you pull the IRS apart and remove diff from vehicle. Trying to know what I'm after before blowing it apart.
 
The factory ford Trac-Loc are pretty bad, I want to say something in there blew up, but like you said, it's a pain in the ass to pull.
I'd just plan on an upgrade
 
welndmn said:
The factory ford Trac-Loc are pretty bad, I want to say something in there blew up, but like you said, it's a pain in the ass to pull.
I'd just plan on an upgrade
Click to expand...
They work well enough in a street car. They don't fail often even on 1000hp 9 second cars. Wheel hop will take out a half shaft.
 
Blew the IRS apart and yanked the diff. I did inspection and reseal when I bought it at 30k, and added a brace to survive the dragstrip. It has 66k now.
Vfeuvx3tvoiCCxa6Oiuw=w1271-h953-s-no-gm?authuser=0.jpg


And.... all appears well inside. No chipped teeth. No broken clutch fingers. There is some clutch goo so I probably should replace clutch packs, but it still performs like new. Going to pull the guts out and take a look.
HGnbZAXeUjPdWEQDCW_cw=w715-h953-s-no-gm?authuser=0.jpg


It has survived a lot of passes down the drag strip. 6500 RPM clutch drops with 700 torques on boost, nitrous & slicks.
 
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Good to see. I may be doing an 8.8 IRS in my 87 Conquest.
 
rattle_snake said:
They work well enough in a street car. They don't fail often even on 1000hp 9 second cars. Wheel hop will take out a half shaft.
Click to expand...
They don't work at all in street cars?
Maybe we hang around different group, everyone swaps to another brand limited slip out here, or better yet lockers and spools when you get serious.
 
They always look good with now psi on them. And "look" vs is good is down to the criticals.

Roll the gears and check back lashes
Clean the ring and paint n pattern the whole thing.

We used to have a viper pipion on the counter that yarred 2 teeth out of the pinion, but were still there. They broke loose down to the root and stretched the head, they were like loose teeth in a kids mouth.
 
welndmn said:
They don't work at all in street cars?
Maybe we hang around different group, everyone swaps to another brand limited slip out here, or better yet lockers and spools when you get serious.
Click to expand...
I am referring to their use in IRS. This way they have fuses on either side.

Also depends on definition of 'street car'. Abuse can break a lot of things.
 
Grendel said:
Maybe
Click to expand...
They're the same oddball center section as the Grand Cherokee, Nissan Frontier, Titan, etc, etc. Like bigger bearings and shit vs the old school 44 but no ring and pinion upgrade like later stuff got. They proved to be unreliable behind Nissan Titans but for what you're doing that shouldn't matter.

Nissan Armada had IRS so that's the application you punch in if you want one.
 
Measured backlash at 0.015". Spec is 8 to 12. Was like this when I bought it and went though diff for reseal. So nothing changed in 30k. There is one shim on each side.
Broke the diff and carrier down, don't see anything concerning. Clutches have some life left but plan to replace while apart. Pinion looks good and has rotational resistance I would expect, bearings still preloaded. Carrier bearings good. Half shaft bearings good.

Not much else to do but put it back together, check, and go from there. 3.55 is already a well matched ratio and t-lock does what I need it to do.
 
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Have you looked into the "cobra clunk" at all on SVTPerformance? Other than the oddities you describe with your diff, that is the only thing I can think of. My 03 had the "cobra clunk" and I even had full ladder style subframe bracing, delrin bushings in the rear and my diff cover braced so everything was pretty rigid. Mine made 460rwhp/468tq and I did race it for the few years I had it before I was forced to sell without any issues.
 
Grendel said:
Cheap, too:

2019 Nissan Armada Rear Axle Carrier (2.94 ratio), rear (OE Used) | $115.00, 440-50529, D354757276K, Birmingham, Alabama (FAST Shipping)

automotix.net automotix.net
Click to expand...
You want 04-15 because it has a normal flange on the front. Pricing is comparable.

04-06 is listed seperatly from 07-15 so I assume there's a mounting difference in there somewhere.

s-l16002.jpg


You can tell I haven't looked at those since before 2015 because I didn't even know they changed them up until you posted that. :laughing:

Edit: Looks like a bunch of years of Pathfinder use the 44 as well.
Screen Shot 2024-01-18 at 2.47.55 PM.png
 
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Toy4rnr said:
Have you looked into the "cobra clunk" at all on SVTPerformance? Other than the oddities you describe with your diff, that is the only thing I can think of. My 03 had the "cobra clunk" and I even had full ladder style subframe bracing, delrin bushings in the rear and my diff cover braced so everything was pretty rigid. Mine made 460rwhp/468tq and I did race it for the few years I had it before I was forced to sell without any issues.
Click to expand...
Yes the 'cobra clunk' was the wrong size bolts in forward subframe. I replace them with proper size and that slop went away. Car has SFC, cover brace, Full Tilt Boogie Delrin IRS subframe bushing & solid aluminum diff bushing. So the diff is more or less solid to chassis. 315 drag radials for the street.

I see the Cobra 8.8 came with carbon fiber clutches. M-4700-C.
 
Trac Locs work better when they have an extra half bottle of the ford additive. The Wife's S550 just started chirping and squeaking with 25 K on the diff fluid change. Fresh fluid change and the extra fluid took care of it till i can buy a GT500 rear suspension with the brakes.

Torsen is the best option.
 
Cleaned the stinky black goo off of everything and put new clutches in carrier.
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Popped carrier in and re-checked backlash, same as before. The one thing I didn't do before disassembly was try to replicate noise on the bench. I popped cover off and did visual instead.
UW3m2USnwO7b3PJP3R_vQ=w715-h953-s-no-gm?authuser=0.jpg


So next step was to spin assembly carefully, pre-loaded to see if I could find the 'spot' before doing pattern check. Well I found it. I could feel that 3 teeth that made contact differently. Popped carrier back out and found cracks at the root of many teeth
YNk7Swi0WOIm2giCCegg=w1271-h953-s-no-gm?authuser=0.jpg


Given the damage I can't imagine the one last drive had too much to do with it. It has taken a beating for many years. Guess I get to buy more tools and a R&P set. I've done 9" gears but avoided doing setup on this type. At least I can do the job on the bench.
S8cgz8uq9wcxJh-vjOMw=w1271-h953-s-no-gm?authuser=0.jpg
 
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Damn good find. I'm impressed the wear pattern on the teeth doesn't look any sort of torn up. You found it at just the right time to keep from having to clean metal glitter out of the diff later hah
 
Yes I was 2 miles from home. Teeth has just come loose. With pinion bearing off all teeth are cracked all the way in.

Went to a 3.73 ratio, Ford gearset. Put in all new bearings. Final pattern with 0.008-9 backlash. Reused pinion shim and only had to do 3 iterations on carrier shims.


How does it look?
ref: 0.036 pinion shim.
9ZpmsrHPt5t3dI05dCDrQ=w715-h953-s-no-gm?authuser=0.jpg


3k_xcH9k-ARVtbNv6C_iw=w715-h953-s-no-gm?authuser=0.jpg
 
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You're deep. The flat line at the base of the teeth is your indicator. I'd suggest pulling 0.005" out and re-run a pattern.
 
0.004 out of pinion shim to 0.0032. No change to carrier shims. Backlash is 10 (spec is 8-12).
C0nmGrOI-HrqN77_4QOPQ=w715-h953-s-no-gm?authuser=0.jpg


Coast side looks like it needs thinner pinion shim still.
zOzqsoVqCF2Duoe_wyQdA=w715-h953-s-no-gm?authuser=0.jpg
 
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Another -0.005, 0.027 PS.

My read on this is drive looks ok, but toe side
xLxv8veZSgcq5NHf1J2pQ=w708-h944-s-no-gm?authuser=0.jpg


but coast side contact is on heel. My read is drive/toe and coast/heal indicates too deep still?
e_5QyRz_f3X6mM1p0XTsA=w708-h944-s-no-gm?authuser=0.jpg
 
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