 Midnight Rider
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06-30-12 04:43 PM - Post#2243064
I've been working on installing a set of 3:73 gears in the 12-bolt housing for my '66 Bel Air. The gears are by Motive Gear, on a new Eaton posi unit.
I have the pinion at the 2.875" depth, as marked on the pinion. (would you believe that the cap parting surfaces are spot on the bearing centerline!?)
With the pinion out, I set the side-bearing shim packs to a preload that allows the ring gear and carrier to freely spin about 1 revolution (1 1/3, at the most).
Then, with the pinion back in, I proceeded to check the backlash. MG says it should be set between .008" and .012". I can get .006".
But if I lessen the shims from the left (driver) side, and move them to the right, I still get .006", or even down to .005". This just does not make sense. Any ideas on where I am going wrong?
Just for giggles, I decided to run a pattern at the .006" backlash I could achieve. Here are some shots of the drive-side pattern;
and the coast side;
Thoughts on the patterns?
I'm doing this myself, because this car in my project!  I don't mind redoing the steps, now that I know how it's done. (actually was getting pretty smooth at pulling the carrier out to adjust the shim packs, and had a nice routine with the press to change the pinion shims...  )
I am open to suggestions from any of you who have "been there, done that".
Thanks,
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone 
1989 Celebrity |
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slammed1
Contributor
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06-30-12 06:11 PM - Post#2243096
In response to Midnight Rider
Your gear pattern dont look real bad,Im having a hard time understanding why your getting the same backlash settings after moving shims side to side though.
What thickness shim/shims have you moved from the left to the right and vice versa?What was your pinion depth shim thickness?
.008 to .012 is usual backlash recommendations,I usually try to get .007 to .009
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leon phelps
Valued Contributor
Posts: 3018
Loc: Croydon Manor, PA
Reg: 06-04-05
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06-30-12 07:37 PM - Post#2243123
In response to slammed1
I would throw it in and drive it and see what is sounds like.
the wear pattern looks OK to me. I did my 10 bolt and it looked similar.
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impala
Senior Member
Posts: 1139
Loc: Pittsburgh, PA USA
Reg: 07-13-00
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06-30-12 08:23 PM - Post#2243138
In response to Midnight Rider
But if I lessen the shims from the left (driver) side, and move them to the right, I still get .006", or even down to .005". This just does not make sense. Any ideas on where I am going wrong?
It sounds like you don't have enough shims on the carrier bearings to begin with. By the backlash staying at 5 when you move shims from left to right confirms that as the carrier is staying in the same place.
Forget the spinning one turn method and pack the carrier as tightly as you can to the point where you almost need a case spreader to get the carrier into the housing. Then start moving shims as necessary from side to side.
impala
61 Impala Convertible, AACA senior
94 Jaguar, XJS, V12 coupe
11 Silverado
03 Impala Sedan |
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 jumbojim
"2nd Year" Platinum Supporting Member
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06-30-12 10:25 PM - Post#2243176
In response to Midnight Rider
Your drive side and coast side contact marking should be in the middle of the tooth but toward the small end (toe), So your marking looks pretty good to me.
I would go with 6 thou, if you increase the backlash the contact will go toward the large end of the tooth (heel). I think the post from 'Impala' suggesting that you increase the preload is a good idea. One way to measure preload is to wrap a long string around the crownwheel carrier and attach a springscale to the free end of the string. Pull on it at about 1 rpm per second to measure the pull. Should be about 4-5 pounds. Jim
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Midnight Rider
"6th Year" Gold Supporting Member
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Reg: 01-19-05
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07-01-12 01:44 PM - Post#2243373
In response to jumbojim
My thanks to everyone for their input.
Brian,
The initial setup for the preload had .239" on the left, and .236 on the right. When I dropped it back in on top of the installed pinion, there was 0 backlash.  Just as a starting point, I moved .007, resulting in .232/.243", which resulted in the .006" backlash. Then I moved an additional .002 (.230/.245) and ended up at .006 again (what the...  ). Tried another .002 (.228/.247) and saw about .0055 on the indicator. . Moved back to the .232/.243 shims, and again saw backlash at .006". That's where I ran the patterns.
The pinion shim started at .018" (original from the 2:76 setup I pulled out of the housing. Ended up at .035", to put the pinion depth at 2.875", as marked on the pinion.
Leon,
I wish I could, but the ol' ride is still a long way from hitting the streets. 
Impala,
It sure seemed like I was treading on thin ice, trying to get the packs in as it was. If I understand what you are suggesting, I can try upping both side by a couple thou, tap them in (cringing all the way...) and check the backlash again. Worth a shot, and all it takes is a little more time, which I have. 
Jim,
I'll give the 'string test' a try. I like the idea of shooting for a specific measurement of some kind; it's so hard to know how hard to spin the darn thing.
More to come,
Thanks,
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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slammed1
Contributor
Posts: 669
Age: 42
Loc: Ark
Reg: 03-28-12
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07-01-12 02:10 PM - Post#2243382
In response to Midnight Rider
I like seeing all these 66 Belairs surface lately.
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jumbojim
"2nd Year" Platinum Supporting Member
Posts: 315
Age: 66
Loc: Melbourne, Australia
Reg: 09-25-11
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07-01-12 04:41 PM - Post#2243435
In response to Midnight Rider
You could fabricate a case spreader. You can spread the case up to 12thou.
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 JimKshortstep4x4
Chevytalk Moderator & "9th Year" Silver Supporting Member
Posts: 4162
Loc: Muskegon, MI, USA
Reg: 03-28-02
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07-01-12 04:55 PM - Post#2243438
In response to jumbojim
I am having a spreader made up similar to this one.
Jim
Member 65-66 Full Size Chevrolet Club
65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/350
71 Snow plow, 4x4, 350, TH 350
Current project, 72 GMC Shortbed, stepside, 427 |
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leon phelps
Valued Contributor
Posts: 3018
Loc: Croydon Manor, PA
Reg: 06-04-05
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07-01-12 05:44 PM - Post#2243459
In response to JimKshortstep4x4
so the nut mechanically spreads the case apart?
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 capricesport66
"3rd Year" Gold Supporting Member
Posts: 1208
Loc: Lafayette, Louisiana
Reg: 11-02-03
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07-01-12 06:05 PM - Post#2243470
In response to leon phelps
I absolutely hate rear-ends, on cars that is!!!! I bought the 3.73 richmond gears quite a few years back. I watched that video time and time again. Finally, I gave up on it. Brought it down to a tranny and gear shop and had them installed. About a year later, I changed the carrier to an auburn posi unit. That was actually easy to remove and install. I'm now looking at changing the old axles out to some Moser axles, but don't think I'll tackle this one on my own. I'll probably let the same tranny and gear shop install it. The little bit I'll pay for the added insurance that someone knows what they're doing with the adjusting makes me feel much better driving down the road. This is about the only part of the car that I absolutely refuse to touch.
I wish you success on getting everything right.
Gerald
Lafayette, La.
http://www.flickr.com/photos/95648804@N08/
'66 Chevy Caprice 2DR HDTP 496/4L80e/3.73, 20's, Console, Buckets
'06 Chevy 2500HD 4x4 LBZ Duramax/Allison
'08 Toyota Highlander "Hybrid"
'99 VW Jetta TDI |
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slammed1
Contributor
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07-01-12 06:13 PM - Post#2243476
In response to capricesport66
Swapping out axles is a snap if you have already done a Posi Unit.
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Midnight Rider
"6th Year" Gold Supporting Member
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Age: 54
Loc: Brooklyn Ctr, Minnesota
Reg: 01-19-05
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07-01-12 06:59 PM - Post#2243496
In response to JimKshortstep4x4
Jim,
How does the spreader attach to the axle housing?
Thanks,
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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impala
Senior Member
Posts: 1139
Loc: Pittsburgh, PA USA
Reg: 07-13-00
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07-01-12 08:08 PM - Post#2243520
In response to Midnight Rider
Impala,
It sure seemed like I was treading on thin ice, trying to get the packs in as it was. If I understand what you are suggesting, I can try upping both side by a couple thou, tap them in (cringing all the way...) and check the backlash again. Worth a shot, and all it takes is a little more time, which I have.
The purpose of the spreader is to have the correct amount of shim without having to force them in there.
One test would be to leave the amount of shim you have in there now. Just snug the cap bolts. Set up your indicator to measure the carrier sideways and force the carrier side to side with a pry bar. Any indicator movement at all will tell you how much more shim you need to add. Now if you can, spread the case to install the additional shims and to make the side to side shim changes a whole lot easier. Remember , you want some pre-load on the side bearings just like you have on the pinion bearings and you won't get it simply sliding the shims in by hand. At the shop we have a huge assortment of the one piece factory shims which are a whole lot easier to deal with compared to a bunch of thin shims.
impala
61 Impala Convertible, AACA senior
94 Jaguar, XJS, V12 coupe
11 Silverado
03 Impala Sedan |
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jumbojim
"2nd Year" Platinum Supporting Member
Posts: 315
Age: 66
Loc: Melbourne, Australia
Reg: 09-25-11
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07-01-12 09:56 PM - Post#2243549
In response to Midnight Rider
Bill, Usually there is a hole about 3/4 inch diameter machined in the housing adjacent to each bearing cap. The arms of the spreader have the same size 'dowels' which fit into the holes in the housing. See the photo in previous post by JimKshortstep4x4. Jim
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JimKshortstep4x4
Chevytalk Moderator & "9th Year" Silver Supporting Member
Posts: 4162
Loc: Muskegon, MI, USA
Reg: 03-28-02
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07-02-12 04:33 AM - Post#2243569
In response to Midnight Rider
Bill,
As mentioned the spreader uses the two locator holes on the differential using dowels. The holes on the 1/2 ton trucks are 1/2" and 3/4" x 1 1/8" deep. Once the spreader is set up, the jack screw on the right side is tightened to cause the spreader to expand the housing making it easier to install the necessary shims needed for a preload.
I have broken quite a few shims driving them in so I am going with a spreader for future rebuilds.
Here is a picture of a 72 12 bolt truck differential showing the locator holes.
I really appreciate your sharing the process of assembling your differential. You certainly appear to have the needed patience for doing a rebuild!
Jim
Member 65-66 Full Size Chevrolet Club
65 Impala SS, 400sbc, Muncie M-22
66 Impala SS, 396, TH 400
69 El Camino, 350, TH 350
71 Short bed stepside 4x4, 350/350
71 Snow plow, 4x4, 350, TH 350
Current project, 72 GMC Shortbed, stepside, 427 |
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jumbojim
"2nd Year" Platinum Supporting Member
Posts: 315
Age: 66
Loc: Melbourne, Australia
Reg: 09-25-11
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07-02-12 06:16 AM - Post#2243587
In response to JimKshortstep4x4
Great photos Jim. Jim
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Midnight Rider
"6th Year" Gold Supporting Member
Posts: 623
Age: 54
Loc: Brooklyn Ctr, Minnesota
Reg: 01-19-05
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07-02-12 07:20 PM - Post#2243785
In response to JimKshortstep4x4
Jim,
Thanks for the pic, and the kind words. Now I gotta ask another one; what is that rod coming out at the upper right in the truck 12-bolt pic?
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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slammed1
Contributor
Posts: 669
Age: 42
Loc: Ark
Reg: 03-28-12
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07-02-12 09:51 PM - Post#2243831
In response to Midnight Rider
Panhard bar mount,as 67-72 trucks have coils and trailing arms.
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Midnight Rider
"6th Year" Gold Supporting Member
Posts: 623
Age: 54
Loc: Brooklyn Ctr, Minnesota
Reg: 01-19-05
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07-03-12 05:18 PM - Post#2244145
In response to slammed1
Brian,
Thanks. The old farm '66 C-10 I grew up with had coils and arms too, but I don't remember something like that on the diff. Of course as I get older, there are more things that happened that I can't remember, and more things I remember that didn't happen...
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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slammed1
Contributor
Posts: 669
Age: 42
Loc: Ark
Reg: 03-28-12
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07-03-12 05:27 PM - Post#2244150
In response to Midnight Rider
I think they started it in 63 or 64,couldnt remember though.My memory escapes me even more lately also. 
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63nutty
Forum Newbie
Posts: 2
Reg: 07-05-12
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 07-05-12 07:38 AM - Post#2244687
In response to Midnight Rider
Iam new to ChevyTalk so I might be a little late in commenting on your diff specs.. I have been a Chevy tech for about 40 years and engine and drivetrain was my specialty.Your pattern looks perfect so technically nothing else matters because the pattern will move around according to pinion depth and backlash. I would have to agree with one comment I read; how many thousandths are you moving from side to side and what was your pinion depth shim? Have fun!
P.S. I am restoring a 63 impala SS and Iam finding out this is a hobby for rich people!
chevys rule
63nutty
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leon phelps
Valued Contributor
Posts: 3018
Loc: Croydon Manor, PA
Reg: 06-04-05
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07-05-12 09:10 AM - Post#2244709
In response to 63nutty
63nutty, welcome.
could not agree with you more. I love when my car that I have probably 40k into pulls up to a light and someone tells me it is gonna look great once I start to put some real money into the body work.
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Midnight Rider
"6th Year" Gold Supporting Member
Posts: 623
Age: 54
Loc: Brooklyn Ctr, Minnesota
Reg: 01-19-05
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07-24-12 06:56 PM - Post#2251843
In response to leon phelps
Hi, me again,
Another installment in the journey.
While checking over some of the next parts that will go on, I noticed this slight difference;
The original washer is on the left, with the original nut in the middle. The new nut, from the install kit for the gear set, is on the right.
Clearly, the new nut is no where near as deep as the original. In fact, even the new nut and original washer is still not quite as high as the original nut alone.
Does this seem right? The threads are the same, so it's not like the nut is for a Pinto diff or something. I'm thinking the nut is an item that should be replace during the rebuild, but I don't want to put in any sort of weak link.
Any thoughts on this?
Thanks,
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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leon phelps
Valued Contributor
Posts: 3018
Loc: Croydon Manor, PA
Reg: 06-04-05
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07-24-12 08:05 PM - Post#2251863
In response to Midnight Rider
depends on the original part having threads on the washer part molded in it.
I would guess no threads in the washer part so it should be fine.
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ss3964spd
"6th Year" Gold Supporting Member
Posts: 3014
Loc: Fairfax, Va
Reg: 12-21-00
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07-25-12 08:19 AM - Post#2252014
In response to leon phelps
Bill, I'd be inclined to use the original, especially if the treads run the length of the nut and it's integral shoulder. Once you finish mocking it all up and you do the final install put some loctite on the threads. It won't go anywhere.
Dan
If I recall correctly my memory is excellent. My ability to access it is not.
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Midnight Rider
"6th Year" Gold Supporting Member
Posts: 623
Age: 54
Loc: Brooklyn Ctr, Minnesota
Reg: 01-19-05
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07-25-12 06:08 PM - Post#2252178
In response to leon phelps
Thanks guys,
The threads extend maybe one turn more in the original, but they do not extend to the bottom of the integral shoulder. So thread engagement should be about the same, just a bit farther in on the pinion.
Perhaps I'll use the 'digital decision maker'
when the time comes for final reassembly.
Bill
Midnight Rider
1966 Bel Air 2-door sedan
1985 Impala Now gone
1989 Celebrity |
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