Which diff?

[kenhaw]

Hi

Can somebody tell me what diff I am running and if it is any good?

Best regards

Kenneth

[MonzaRacer]

i am assuming you have an Fbody, 70s up were mostly popul;ated with 10 bolt 8.5, some had 12 bolts, before 70 most had 10 bolts looks like 8.2 "chevy" because the center is open to look at it. IF it has c-clips its chevy, no c-clips its BOP.
But more info to determine its lineage.

[chicane67]

Kenneth... what you have is a GM 12 bolt differential housing with an aftermarket EATON limited slip differential... or quite possibly an OEM EATON with a replacement clutch pre-load pack.

Is it good ?? Hell yes... and it is also tunable and rebuildable. They are and were good enought for aGM to use them specificaally in factory performance applications... it's aka is the "GM Posi Traction" differential as an OEM offering all the way back to the early/middle 60's.

[big gear head]

Looks like an original Eaton posi in a 12 bolt to me. Probably a 3 series, but i can't tell for sure. The casting number is just out of sight in this picture. Judging by the thickness of the ring gear and diameter of the pinion I'd say it's a 3.07 gear. Looks like it has the 200 pound preload springs and the original cut differential gears. Looks like someone has been in it before because those differential shims don't look original. I'm guessing that it's a '68 or later Camaro or Nova rear end. It's hard to beat an Eaton in a 12 bolt.

[kenhaw]

Thx

[kenhaw]

Thx for the replies, great news for me.
I took some numbers of the cating, they are 30140PMI.
It sits in a 69 Camaro.
I lately noticed some clonking from both sides at very low speeds when starting after a stop, is that the gears resetting?
I know it is a 12 bolt with c-clips and it has 3.73 gears.
I want to upgrade the rear drum brakes with discs so I guess I will have to change the axles, any suggestions will be helpfull. I am leaning a lot towards the Wilwood Dynalite Pro Series, will they do the job. The car is only street driven.

Regards
Kenneth

[big gear head]

You don't have to change the axles to install disc brakes, but by the looks of that engine you should install some stronger axles anyway. The 30140 is a 3 series. Are you sure that this is a 3.73? It doesn't look like one. Count the teeth on the ring gear and the pinion gear. Divide the ring gear by the pinion. A 3.73 will have 41 on the ring gear and 11 on the pinion. The clunking noise might be coming from the clutches. When you put oil in it be sure that you put in a bottle of the GM oil additive. Also check the u joints.

[kenhaw]

I am not that sure but was told that was the gearing when I bought the car, it came with 2 other sets of ring and pinions.
So if I upgrade the axles I can still use the C-Clip system?
I will put the GM additive in the next time I disassemble the differential, or if I can find it down here in France i will empty the differential and add it now. What kind of oil is recommended. I am currently using a GL5 compatible differential oil, think I have read it needs GL6 but I am not sure?

Regards

Kenneth

BTW USA Rules

[big gear head]

GL5 is fine. The additive should be available at a GM dealer, part number 1052358. It needs the additive if you will be driving on the street.

You can upgrade the axles and keep the c clips. Many companies like Moser Engineering and Tom's Differentials make c clip axles that are about 30% stronger than the original axles.

[MonzaRacer]

Simply switch use synthetic diff lube and you shouldnt need additive.
Royal Purple and Red Line make great lubes, if you use regular oil ,non-synth, I have had best luck with Shell Spirrax and either the lubeguard or Kendal additive. Also Fords posi additive is very good, probably one of the best.

[chicane67]

...Except for the fact that EATON specifically recommends that you not run synthetic... as well as many builders like myself, will tell you the very same thing... I would just run the friction modifier.

Of the components mentioned... I would run the axles from Toms Differentials ( tomsdifferentials.com ) if you wanted to retain the c-clip function. The only thing that you will need to pay close attention to is the axle end play. You will want to keep this to no more than 0.005" (0.127mm).

[kenhaw]

...Except for the fact that EATON specifically recommends that you not run synthetic... as well as many builders like myself, will tell you the very same thing... I would just run the friction modifier.


Of the components mentioned... I would run the axles from Toms Differentials ( tomsdifferentials.com ) if you wanted to retain the c-clip function. The only thing that you will need to pay close attention to is the axle end play. You will want to keep this to no more than 0.005" (0.127mm).

So you would run normal non synthetic oil and the add friction modifier?

Well I am sure that there is more play than that in the axles now. If I want to change into non C-clip axles what will that involve?

Thax for the feedback.

Kenneth

[chicane67]

So you would run normal non synthetic oil and the add friction modifier?

Well I am sure that there is more play than that in the axles now. If I want to change into non C-clip axles what will that involve?

Thax for the feedback.

Kenneth

Yes... a non-synthetic with the addition of friction modifier. I would also recommend using a straight weight 90 or a multi viscosity 90-140... and either the GM or Ford friction modifier. I personally believe that the Ford stuff is the ticket... but there's nothing wrong with the GM or RedLine stuff either.

As for your axle end play... I too believe that you most likely have more than three times that number currently. There are a few ways to combat this issue... from shimming the clutch pack and thicker c-clips... to installing an axle with press-on bearing's, like that of the kits available from Toms Differential and others.

The inhearent safety gained from a press-on style axle bearing is always good... but, the cost and effort envolved can be more than some want to afford. But... this would be the better solution as you gain many positives from the modification. What it takes to do this is that the housing will have to be removed, the ends cut off, the new ends jigged onto the housing, weld them up and then straighten the housing. Next will be the axles... which only requires a 'overall' measurement for the axle length and the proper retainer to work with whatever brake system you are going to use.

The old school way to fix the axle end play is to re-shim the clutch pack and to use thicker c-clips. But you really need a good differential guy that really knows his proverbial sh*t so that it gets done correctly. This is one component that you dont want to screw up and that you dont want to build a second time from cutting corners.

[minendrews68]

KENHAW, Please don't listen to Chicane!!!!! Unfortunately, he does not know what he is talking about! That rearend is one of Chevrolet's worst!!. If you would like to give it to me I will pay shipping to get it here. I don't always do things like this but I am going to make an exception this time. Please don't put that rear end under your car.......Let me put it under mine!.. All jokes aside Chicane is once again right on the money. Listen to him. By the way GOOD find. I wish I had one.

gotch'a Chi

Carl

[chicane67]

Carl... I do have one for sale...

[kenhaw]

Well I think the way to go for me is the C-Clips way with thicker clips and shims. My car is only street driven and never sees a track.
My problem is however that I, for the time being, am living in France where American cars are an unknown thing. So finding a mechanic that understands a 12 bolt might be a difficult thing.
I do however have an old Ferrari mechanic which seems very meticulous and does prime work, I might let him have a go.
Does this job include the whole setup "ring and pinion" again?
If I want new stronger C-Clip axles, what should I look for? I do a lot of buying from Summit, so if it´s one of their product, that would be nice.

Thx for all the replies, nice to have all this knowledge available for us guys not living in the US.

Regards Kenneth

[minendrews68]

Carl... I do have one for sale...

Sorry I'm just getting back, had a death in the family (my mother) and kinda been out of it lately.
Any way, What have you got? and how much? You know I'm poor right lol...

[minendrews68]

Sorry I'm just getting back, had a death in the family (my mother) and kinda been out of it lately.
Any way, What have you got? and how much? You know I'm poor right lol...

Hey Chi, Where are you?

[big gear head]

No, there is no need to bother the pinion gear. As for the ring gear, if you keep the shims in the locatioon that they come from then you will not have to reset the backlash. Just put them back exactly like they were and it will be fine. You can remove the posi, replace the clutches and reinstall it just like it came out.

[chicane67]

Most often in Vegas...

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