For anyone who has opened and rebuilt our 3:45 on the bench please read this.

[55Designs]

My Diff was clunking bad out of the blue yesterday it got really bad and I thought the gears broke teeth it was that loud. Been 3 weeks since we drove the car. We drove 1 mile up to 30mph then brought it back in the shop. I was afraid to even drive more so we ripped the car apart today. My car still vibrated from the rear at very high speeds prior and since new kinda like something inside the diff was causing it. We stuffed one of the techs in the trunk with a vibration metering device over the diff housing and the internals were resonating beyond a normal scale.We never cracked it open until today.

There were several things that we found and since I never opened up one of these diffs I cant really comment on technical details.

Here is what we found.

1. Drivers side seal was missing the retaining spring that is under the rubber jacket. This is very odd because we never opened this unit up before. Never had any fluid leaks.
2. The Pumpkins outer bearing races show groves and wear and extreme heat marks in localized areas. These are the separate pieces that pop over the end tapered roller bearings held in place by the U shaped end caps.
3.The End caps are the real mystery. Where they meet the bearing races the cast aluminum U has wear and groves. Now its my understanding that the outer races of the roller bearings should not move ever in this design but I can be wrong. The roller bearings have lots of movement.
4. Now one end cap had a stamped Spring Steel cap over it I assume to add strength but the other side did not. Whats the mystery here is that both end caps show wear from the screw heads when torqued down yet one side had a steel cap over it which looks to have been added after the fact. As if someone rebuilt this differential before.
5. The pumpkin has casting numbers of 3:27 which are crossed out with a pink paint pen.
6. The clutch packs inside the Posi show very uneven wear and they have lots of play with the shims in the case. Don't know if this is normal or not. There was lots of visible metal particulate matter under the shims, looks like grease which later proved to be metal, the size of sand particles.


I am honestly thinking my car was built with a rebuilt differential from a G8 or something because it was an early build. Maybe someone screwed up but I am dying to see photos of other units to compare. If any of the guys who have done these teardowns before can comment on what we found today its greatly appreciated.

If anyone wants to see photos Il try to add them to this thread. Very pissed off and confused on what I should do from here.

I can easily buy a new diff but what if I get another rebuilt lemon? Not building a drag car nor doing the 9 inch.

Any suggestions guys?

[BackinBlackSS/RS]

I'm confused. Is this the stock pumpkin you are talking about, or is this a new one you purchased aftermarket?

[55Designs]

Originally Posted by BackinBlackSS/RS

I'm confused. Is this the stock pumpkin you are talking about, or is this a new one you purchased aftermarket?

100% stock never touched until today when we opened it up

[BackinBlackSS/RS]

Originally Posted by 55Designs

100% stock never touched until today when we opened it up

Man, sounds like quality control on that one was on a coffee break.

[55Designs]

Some photos below:

If you see the Left and Right main End Caps the caps both have impressions from the mounting screws. One side, the tooth side had this metal cap over the aluminum cap for support of some sort. It is obvious the aluminum end caps were used, or installed prior or this metal cap was done afterwards by the ghost of differentials. How can a brand new end cap get impressions from screws if the steel cap was installed over it? MAGIC

If you search Google for the blown 4:10 from Lingenfelter it has the metal cap over the aluminum end cap. The end caps can alter backlash so why does one side get this while the other does not?

Also there is an article on Gm High Tech performance showing a Richmond installed on a BRAND NEW Carrier from the dealer and the brand new one does NOT have the stamped steel over the aluminum end cap. Very strange.

You can see the groves and heat transfer marks on the bearing race for the posi, the one that goes over the tapered end roller bearings.

groves also worn on the arch of the cast aluminum end caps proves the bearing race was not locked in place tight enough.

[jamesc1123]

Only thing I know of it carriage house customs made a point that the 3.27 was marked on the gears even though they were 3.45. I think I remember reading another thread that mentions only one side getting the stronger end cap. And the clutch packs...might relate to the one wheel burnouts on these cars.
So this is all "I heard..." stuff. I can't comment directly as I haven't torn one of these apart.

[v6sonoma]

[Eric Baker]

I know Ted at Jannetty designed new caps that he machines in-house to replace the "flimsy" stock ones. Maybe this is why. He also sells a posi mod that may take care of the loose clutch packs you're talking about. I plan on doing both this winter.

[Driveshaftshop]

Originally Posted by Eric Baker

I know Ted at Jannetty designed new caps that he machines in-house to replace the "flimsy" stock ones. Maybe this is why. He also sells a posi mod that may take care of the loose clutch packs you're talking about. I plan on doing both this winter.

Ted is one smart guy and looks out for the finest details in all parts, cant go wrong with that advice

[Badger]

Necrothread...I know..but just did a search...dealership just cracked open my diff for the 1st time to do a 3.91 gear upgrade and they found this same setup...I have an early build car...only 1 of the main caps (left side) had the steel strap on it..this cap had 1 bolt that was finger tight and the threads into the housing were stripped out...They are going to warranty the housing...but I am still pissed...Gm really did a piss poor job designing this IRS..I drive my car hard some times but never do clutch dumps or take it to the track for that matter....They tell me the torque is what does this and the aluminum can not take it?? Anyone else seen this happen? was it over torqued at the factory and stripped out? they also told me that the housing GM sent might be an updated one?? anyone hear of this?....sorry for the rant...Just pissed that everytime I do a mod on this car something else is found that needs to be replaced

[NEstyle]

I need to bump this old thread. I just took my rear apart, and it also has a steel strap over the left side carrier bearing cap. Is this a factory piece and does anyone know why all of the rears don't have it? It seems like a good idea in theory.

[Dbunch9]

This is weird cause I went through 2 stock 3.45 diffs, the original (car was built mid-late 2009 IIRC) didn’t have the steel strap and it was labeled a 3.45. Second diff I believe was a 2013 and was exactly the same. Now I have a 2015 1le diff and took the cover off to put an LPW cover on and looks the same as the the first two. I can say tho that these diffs seem pretty damn fragile as I’m on my 3rd and I’m only making 475whp.

[NEstyle]

Originally Posted by Dbunch9

This is weird cause I went through 2 stock 3.45 diffs, the original (car was built mid-late 2009 IIRC) didn’t have the steel strap and it was labeled a 3.45. Second diff I believe was a 2013 and was exactly the same. Now I have a 2015 1le diff and took the cover off to put an LPW cover on and looks the same as the the first two. I can say tho that these diffs seem pretty damn fragile as I’m on my 3rd and I’m only making 475whp.

Where did you get the LPW cover? A lot of places are out of stock right now.

[Dbunch9]

Bought it probably 3 years ago and waited probably close to 6 months to receive it from lpw. Didn’t put it in until 6 months ago