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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #1 · (Edited)
After spending way too time tying to fix the runout problem in my old posi unit, I decided to update my carrier with a brand new Eaton/Detroit Truetrac and change my rear end ratio to a 373

So... during the past few weeks, I've been working on installing a new ring and pinion gear set into my Nova. I had some problems with a brand new US Gear ring and pinion (too much ring gear runout variations... and some other issues) and thought something seemed wrong. I had some questions about this gear set, so I contacted JBimmolate (Miles - Moderator on SNS) and he provided me with some very good guidance... and I wanted to thank Miles for taking the time to help me!

I contacted the company that sold me the gear set and exchanged the bad US Gear ring and pinion for another US Gear set.... and what a difference the new/replacement made during installation! Total ring gear runout was .002, and most of the ring gear teeth were within .001 of each other.

I started off with a .042 pinion shim, but the was too much (pinion was too deep into the ring gear)... so I switched to a .037 pinion shim with .009-.010 backlash and I think the contact pattern looks pretty good.

Turned the ring gear to get pattern. I did not put gear marking compound on all the teeth, some of the teeth shown are "Ghost Patterns". Both the Drive and the Coast patterns were "dead-on" consistent throughout the entire ring gear.

Drive .037 @ .009-.010 Backlash:
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Coast .037 @ .009-.010 Backlash:
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The ring and pinion gear mesh felt very smooth as I was turning the ring gear (unlike the previous set that felt kinda rough in some spots). Anyway, I just wanted to ask for some other opinions on the contact pattern before I move to final set-up
Thanks in advance!
 

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Let us hear how it works out. I did a Eaton/Detroit Truetrac, 30 spline, 373 on my 10 bolt but have not been on the road yet. My pinon depth was fairly easy to set up using a dial depth gauge, highly recommended, I was able to borrow one and got it on the first stab using the original factory shim believe it or not. Backlash took a couple tries. My biggest struggle was preload, we will see. Any pointers on preload is appreciated.

And BTW your pattern looks on.

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #4 ·

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #6 · (Edited)
Sorry pinion
When doing a ring and pinion swap, I always pull the rear from the car and secure it on my workbench within a large vise.
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I used a Ratech solid pinion spacer that includes a shim kit. I also have a 4 foot long steel bar with some holes drilled into it so it can be attached to the pinion yoke to keep it from turning while you tighten the pinion nut (see image below).
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I install the solid spacer + some shims from the kit and I tighten the pinion nut to 200 ft/lbs of torque... then measure the turning resistance on the pinion nut with an in/lb “beam style” torque wrench. You’re supposed to start with larger shims and work your way down to the smaller shims by “sneaking up on the correct turning resistance. It’s kinda trial and error... but once you find the correct shim combo thickness, you can keep reusing it for all of your set-ups.

If you are using a crush sleeve, it is not needed until you go for final set-up.
On your trial set-ups, you just tighten the pinion nut until you get the correct pinion bearing turning resistance. On final set-up, you insert the crush sleeve and tighten pinion nut until you duplicate the turning resistance from your trial set-up... but you’re going to need a long 1/2” breaker bar (and most likely a long piece of pipe inserted over your breaker bar) to get enough leverage to collapse the crush sleeve. Once you start getting close to the correct turning resistance (pre-load), you have to go very slowly while tightening the pinion nut so you don’t over-shoot the turning resistance. If you over tighten the pinion nut (too much turning resistance/pre-load), you need to start all over again with a new crush sleeve.
 

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1968 Chevy II Nova.
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Im just about finished with my MOSER 12 bolt total axle replacement.Auburn 3:73 posi. 95/140 normal gear oil with 6 oz auburn limited slip additive. In stalled the rear wheel disc brake conversion. Cross drilled and slotted rotors. Calibers from Right Stuff kit ar huge from a Cadillac Eldo! I used Hawk pads. Composite leaf springs. Factory F41 Rear sway all new bushings $4,200 for all parts

i need to complete a easy brake in session.

new drive shall being built 1350 yokes. $650. Connects to a Richmond racing 6
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Gigi should be on the road next week. I’ll post a video guys!
 

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #8 · (Edited)
Stroker Ace and J Mark, thanks for the feedback!

Below are some photos of the final set-up with preload. I also slightly thinned out the gear marking compound with a little bit of gear oil to produce a better gear mesh pattern. I tightened up the backlash slightly with the majority of the readings in the .0085 - .0095 range (figuring that my backlash will probably open up .001). The contact pattern (both marked teeth and "ghost pattern") remained consistent throughout the entire ring gear.
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I hope to have the rear end back in my car within a few days for proper gear break-in.
 

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Im just about finished with my MOSER 12 bolt total axle replacement.Auburn 3:73 posi. 95/140 normal gear oil with 6 oz auburn limited slip additive. In stalled the rear wheel disc brake conversion. Cross drilled and slotted rotors. Calibers from Right Stuff kit ar huge from a Cadillac Eldo! I used Hawk pads. Composite leaf springs. Factory F41 Rear sway all new bushings $4,200 for all parts

i need to complete a easy brake in session.

new drive shall being built 1350 yokes. $650. Connects to a Richmond racing 6


View attachment 428424


Gigi should be on the road next week. I’ll post a video guys!
Gorgeous car! Just curious about proper torque readings on your cap bolts without hardened washers under the bolt heads. Thought those were supposed to always have a washer beneath them against the cap... lubed with assy lube to get the proper torque and pre-loading on the bolts for distortion to the housing and shim squareness and retention...

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Gorgeous car! Just curious about proper torque readings on your cap bolts without hardened washers under the bolt heads. Thought those were supposed to always have a washer beneath them against the cap... lubed with assy lube to get the proper torque and pre-loading on the bolts for distortion to the housing and shim squareness and retention...
No different than factory bolts....they don't have washers either.

Factory engine main cap bolts and head bolts also don't have washers.
 

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No different than factory bolts....they don't have washers either.

Factory engine main cap bolts and head bolts also don't have washers.
I was always of the understanding aftermarket allen cap screws were supposed to have a washer between the faces. Hey, I guess if it works, it works.
 

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1963 Chevy II 2 door hardtop
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I've only done one diff. The advise was to make sure there was a load on the gears when turning to get the contact pattern.
After building my Dana 60 I learned a few things a) I would never attempt this with the diff in the car b) you need to build a stand and a few jigs and some dummy bearings and have a press C) there can be a lot of trial and error involved in setting a diff up unless you get lucky. I didn't have the original shims which might have made it easier. The housings with built in adjustable preload rings are a great idea. I wish I had one of those D) paying somebody to build it for me might not have been a bad idea :)
 

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #14 ·
Update: I am very happy to report that during my first couple “gear break-in” drives, there is absolutely no noise anywhere in the differential during various driving conditions (acceleration,deceleration, light throttle at different speeds, coast).

The new ring and pinion gear set feels great with my engine/trans combo and the Truetrac differential is unnoticeable (quiet + no binding) in operation.
 

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RifRaf, thanks alot for this info. I have a 12 bolt that i shortened and welded on the brackets for the CBR 4 link. Also welded on Torino ends and installed the Truetrac (3.73) with Dutchman 33 spline axles.

My brother setup the diff with the solid spacer and we used the specs off the ring/pinion for the setup. Havent broken it in yet since the engine isnt built yet. However, my marking compound pattern does not look nearly as good as yours. Also, I feel there is a little too much play just by rotating the pinion yoke back and forth. So, your information confirms that I'm not convinced mine is setup correctly. Next spring I will get back into it and may take the diff somewhere to have it professionally setup. I understand how to do it and do most of my own wrenching but i dont have an accurate inch/lb torque wrench and I dont have a super accurate bridge to go across the main cap saddles on which to setup my dial indicator.

Your info is gonna help alot. thanks
 

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #17 ·
So what gear ratio did you originally have and what do you like better about this ratio?
I’m went from 410 to 373. I know... not a big ratio change.
The 410s were better suited for the first gear ratio when I ran a turbo 350 (2.52).
The 373s feel better in the 2004R that I currently run (2.74 first gear ratio).

The car now feels like it is pulling a little better from a stop... and cruising at 75-80 mph will be a little more enjoyable with the lower rpm (2400-2600 vs 2700-2900).
 

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Mike - 74 Nova Baltimore, MD
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Discussion Starter · #18 ·
So, your information confirms that I'm not convinced mine is setup correctly. Next spring I will get back into it and may take the diff somewhere to have it professionally setup.
I'm glad my post was able to help!
I try to make it a habit to document/photograph any changes that I make to my Nova... and also post the results.

The main thing I learned with setting up new ring and pinion gears sets is that if something is not right > STOP and figure it out. I my case, I received a bad ring and pinion set (too much backlash variation with almost no carrier and ring gear runout). Instead of settling for these results, I contacted the vendor and and exchanged the gear set for another of the same make and ratio. Sure, it delayed things... but was definitely worth the wait!
 
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