A few Questions....

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BluePhoton2010
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A few Questions....

Post by BluePhoton2010 »

Well what started as a" brake job", then an "emergency brake job", then a "change the backing plates job" turned into a "change the outer rear axle bearings and seal job" and ultimately decided to be a "change the whole rear diff job " as I slid the axles back in after changing the outer bearings and noticed about a 1/4 inch of the cam gear in my G80 was missing teeth.... after researching parts and prices ( as we know you can't just change the cam gear without putting in new carrier bearings, clutch packs, ect, ect, ect on a 9 year old truck).. I researched and and googled and found the G80 is basically a piece of crap waiting to explode due to its design of locking up at 20 Km/h ( sorry, canadian here ) and giving the diff internals a good jolt when it does it....
nice design, " lets stick a metal bar into the gears at about 20kms to lock em together for traction guys ! errr wait we better throw in some clutches that will wear out and absorb the impact until the garantee expires .... All in favor , say Aye, those opposed to our profit making through parts sales plan ,pick up your final pay after the meeting " , Gotta love those early monday morning GM design team meetings !

Needless to say I found your new diff on sale on ebay at a great price, which is the Eaton True trac with the helical gears and no clutches and probably a result of a much better wednesday afternoon design team meeting.

As I await its arrival, I just want to verify that my old ring gears and pinion are OK to be re-used and although I've been a mechanic for 25 years plus, I haven't really dabbled in setting up diffs and have to rely on my memory from trade school , which was quite some time ago... so I'll post some pics and let the experts in the field take a look to see if anything catches thier eye thats out of ordinary....

http://i1149.photobucket.com/albums/o59 ... DC0104.jpg
http://i1149.photobucket.com/albums/o59 ... DC0103.jpg
http://i1149.photobucket.com/albums/o59 ... DC0100.jpg
http://i1149.photobucket.com/albums/o59 ... DC0105.jpg
http://i1149.photobucket.com/albums/o59 ... DC0102.jpg
http://i1149.photobucket.com/albums/o59 ... DC0101.jpg
http://i1149.photobucket.com/albums/o59 ... DC0106.jpg
http://i1149.photobucket.com/albums/o59 ... DC0108.jpg
http://i1149.photobucket.com/albums/o59 ... DC0109.jpg
http://i1149.photobucket.com/albums/o59 ... DC0107.jpg

Already changed the outer bearings and seals..
http://i1149.photobucket.com/albums/o59 ... DC0110.jpg

Since there's no clutches in my new diff thats comming, I assume just an SAE 80W90 gear oil will do ?
will the new diff come with die to mark the ring gear so I can check my patterns, or should I pick some up ?
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monzaz
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Re: A few Questions....

Post by monzaz »

Ok - WOW what a way to go...lol. Talk about an avalanche....lol....

Start easy first, This looks like an S-10 Yes?

If so, all 7.5 aftermarket and gm gears will fit NO Problem from housing to housing.
(exception are the monza Vega 7.5 rears They are totally different pinion diameter.)

Marking compound will not come with any ring and pinion or posi unit unless you ask for it from who ever is selling it.

REBUILD kits (master) will include that compound and all the rest of the shims bolts etc. you need.

Gears appear to be very good shape so you should not have any issues if they were set and running good before then bolt the ring to the NEW carrier and double check the backlash and adjust to what the gears were set before you disassembled. .007 .008 .009 ish GM good used.

IF you are going to beat on the rear you can tighten the backlash a bit BUT you could alos have a noise factor risk too if you get too tight .005 .006 area.

Hope I asked all the questions...If not let me know what I missed and will attend to them quickly. Jim

JD
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BluePhoton2010
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Re: A few Questions....

Post by BluePhoton2010 »

Its a GMC Jimmy so S10 Blazer, same thing...

No plans on beating it, it's my winter truck, my appologies for wasting a fine differential that could of gone into a nice street car, we can only hope it didnt have any aspirations of being a diff in a 10 sec 1/4 mile car.... lol.

So to confirm...

Spacing between carrier bearing and diff housing should be between .007 and .009 with as close to the original pattern as possible.
( I didn't check what it was before yanking it out : ( )

SAE80W90 should be fine for the Eaton True Trac #912A317 Torsen gear diff, do you recommend any additives at all ??

I need to know.....

What should be the torque on the bolts for the carrier bearings ?
( I'm purely guessing here but I'd figure 65 -70 ft/lbs ???)

I bought new bolts from GM for the ring gear( 7/16-20 left hand thread with blue GM thread locker on them already ), What should I torque them down to ?

I imagine a crisscross pattern for torquing down the ring gear and the carrier bearing caps is best ?

Should I torque down the whole thing, spin it a few times by hand, take it completely out and then re-install it and check my pattern and spacing to kind of preset everything under pressure and settle it , or put it straight in and start checking the pattern ?

Yes my gears look almost mint and from what I've read and seen of patterns look like they were set up perfect with almost full contact on both sides.. I only hope I can get it that good when I do it.

Thanks in advance for all your help !
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monzaz
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Re: A few Questions....

Post by monzaz »

Spacing between carrier bearing and diff housing should be between .007 and .009 with as close to the original pattern as possible.

????

This is called the backlash. It is the space between the pinion coast side to drive side. THE ROCK of the ring gear forward and backward. (as if you were putting the car in drive then reverse)

When installing used gear or any gears you need to start somewhere...So use the original shim set-up for now... You will NOT use the crush sleeve or need to replace the seal YET. Just install the pinion and outer bearing and yoke so there is a slight drag to the pinion yoke spin. NO in out play or up down play etc. NONE...
Then install your carrier with ring gear and try to install shim packs on the left and right. It will take some practice to swap out different sizes...YOU will probably need a carrier shim pack and a Pinion shim pack to help this go smoothly.
Dial indicator will be needed also.
You will keep trying driver side and passenger side shims till you get the correct preload and backlash of the ring and pinion.

Now once you have that ...you can install the caps (no need to torque them just install them so they are seated all the way to the case. This way you know the carrier in in all the way to the saddles.
NOW take that pattern reading -

Once you see where the pattern is shallow or deep yopu will add or subtract pinion depth and start all over again with the backlash .. :) Fun huh?

Torque rating
caps 60 foot lbs.
ring 60-65 foot lbs.
retaining bolt lock tight (20-25 FOOT LBS... OT TO A GOOD TIGHT KNOCK WITH THE PALM OF HAND) LOCK tight will hold it.
pinion 20 inch pound rotating torque (constant)
carrier with out anything in the housing 1 to 1.5 spin of carrier...This is a very touchy questionable area along with the pinion preload rate. It usually a feel and experience area that will get you in the right spot. A lot of common sense works here.

TIPs - IF you can pull the carrier out by grabbing the ring gear and pulling straight out the preload is NOT tight enough IF you have to hammer the carrier out with a pry bar or break shims installing them then the carrier preload will be too tight. With a J bar a good pop with the palm of your hand should knock the carrier out about 1/4 to 1/2" then continue tapping will bring it all the way out.
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BluePhoton2010
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Re: A few Questions....

Post by BluePhoton2010 »

Sorry for the measuring backlash mistake, a retarded moment on my part, obviously you want to measure the gap between the pinion and ring gears as they mesh together, too little and it pushes out the oil and they overheat and can break, too much and they make noise and can break.... and you measure it perpendicular to the top of the gear tooth

1) I never removed or disturbed my pinion and with the carrier out there was no side to side or in and out movement and I'm re-using the same ring gear, Am I correct to assume I should only be concerned with the backlash and that the pinion depth , bearing preload and everything associated with the pinion set-up should still be fine ?? ( and can be verified by simply checking the pattern seen on the ring gear at the end of the install ) ???

2) to give the ring gear the preload needed to check the pattern can I just slide in the axles and re install the brakes and rotors and apply the hand brake untill the pinion only turns with about 40 -50 ft/lbs of torque ???

3) If I do all that and the pattern seems fine but the backlash reading is at the high end, should I go with it or rip it all out and re-shim to get a reading thats more in the middle of the road ?? ( ex : If I read the backlash and its .009 with a good pattern, Is it better to try to get a .006 or.007 ) ???


I'll start tomorrow and when I'm done take some pics and post, I'd greatly appreciate it if you could check out the pattern to see if its acceptable or not.
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monzaz
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Re: A few Questions....

Post by monzaz »

iF THE the rear was running fine and all you did was remove the carrier and replaced it you should not have to check anything.

I am a bit lost in the subject matter EVEN after re reading all this.

What rear are you rebuilding?

You ordered one and while waiting for it you sound like you are rebuilding the one you took apart...??? Is this correct? Or are you now on to a third diff.

???

Trying to help but this is all over the place. :) LOl
J D Race
BluePhoton2010
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Re: A few Questions....

Post by BluePhoton2010 »

2003 GMC Jimmy....

http://i1149.photobucket.com/albums/o59 ... DC0125.jpg

Short version : After changing outer axle bearings noticed about a 1/4 inch of cam gear were missing in the G80 carrier where the govenor connects to, removed just the G80 carrier, never touched pinion at all, ordered an eaton true trac #912A317 off of JD race on Ebay.

Eaton 912A317 arrived, transfered old ring gear from G80 onto it, installed with original shims to start with and this is what I get ( see pics )

I havent done a diff before but I think I see a near perfect pattern with a backlash reading of 0.0068 inches... this was taken with the axles put in and the hand brake slightly on to give me some load on the carrier ( I guess the idea there is to mimmick as close as you can to it being on the road and attempting to move the vehicle to get the most accurate pattern as possible ??? )

Tell me what you think...

http://i1149.photobucket.com/albums/o59 ... DC0112.jpg
http://i1149.photobucket.com/albums/o59 ... DC0117.jpg
http://i1149.photobucket.com/albums/o59 ... DC0116.jpg
http://i1149.photobucket.com/albums/o59 ... DC0115.jpg
http://i1149.photobucket.com/albums/o59 ... DC0113.jpg
http://i1149.photobucket.com/albums/o59 ... DC0114.jpg
http://i1149.photobucket.com/albums/o59 ... DC0123.jpg
http://i1149.photobucket.com/albums/o59 ... DC0124.jpg

If thats OK, is there anything I should check or do before closing her up and filling it with fluid ? and is just SAE80W90 gear oil all that's needed for the 912A317 or does it need an additive ?
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monzaz
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Re: A few Questions....

Post by monzaz »

Ok Now I got it.
If your gears were correct with the gov lock you are correct in that all you need to do is the backlash NO pinion depth. You pattern does look pretty good and where it should be for a quiet running gear.

I do not like where the plunger is on the gear set. We run it off the drive side face and try to keep the angle of the plunger as true to the gear rotation as possible. Meaning a straight drive of the plunger into the dial. IT is not to hard if you have a magnetic base and at least 2 arms to get the dial indicator in the correct position.

You can open the backlash up to .008 .009 to get the best quiet running gear. You will probably be fine where you are also.
Just be sure the carrier can not be removed by pulling it out with your hand. Pre-load must be correct on the carrier so the carrier runs true under load.

Looks like you are on a good path and appears it will all turn out very well. :) Jim

Torque the caps to 60 Foot lbs. Lock tight the retaining bolt for the pinion cross shaft and you should be good to go. Jim
J D Race
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