My DIY differential gear change

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cowger

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Sorry, man, not much progress. I've been on a business trip all week, but in that time I did get the blessing of Unitrax for my setup, so now I'm ready to proceed. With any luck, I'll have the car running again this weekend.

I also received my new 3/4" breaker bar (ebay find) last night, so I should be set. Stay tuned...

Bryan
 

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on setting up those gears just in case(it appears you know what you are doing) too loose and it will howl at light accel speeds, too tight and it will howl on deceleration
 
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on setting up those gears just in case(it appears you know what you are doing) too loose and it will howl at light accel speeds, too tight and it will howl on deceleration

Thanks. I'm definitely anxious to hear how this thing sounds. It's running smooth-as-silk on my workbench but obviously that's no guarantee that it'll be quiet in the car and under load. I've been spending a LOT of time (and conversations with Unitrax) thinking about the setup, backlash, etc., but I'm at least confident that it's about as close as it could be at this point.

I suppose the good news is that now that I have all the tools and technique down, I could take this thing out, adjust it, and have it back in the car in an afternoon. But hopefully that won't be needed...
 

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on setting up those gears just in case(it appears you know what you are doing) too loose and it will howl at light accel speeds, too tight and it will howl on deceleration

My 50k+ mile stock diff makes a slight whine at low load acceleration. I wonder if its at a loose condition now or if thats a sign that its on the way out. Outside of that I haven't noticed any ominous behavior.
 
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cowger

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My 50k+ mile stock diff makes a slight whine at low load acceleration. I wonder if its at a loose condition now or if thats a sign that its on the way out. Outside of that I haven't noticed any ominous behavior.

Hmmm, could be. FWIW, my 30k stock diff had a backlash of between 0.012" and 0.014". My new one is begin set up around 0.006" to 0.007"...
 

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My 50k+ mile stock diff makes a slight whine at low load acceleration. I wonder if its at a loose condition now or if thats a sign that its on the way out. Outside of that I haven't noticed any ominous behavior.
alot of rear gears now days are noisy, yes mostly loose tolerance- but will and can go a long time like this just for cruiseing-
 
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Wanted to bring everyone up to speed on where I'm at, and then my goal is to get the thing back together this weekend. Hopefully... :)

I would estimate I've tried about 8 or 10 different shim combinations by now. I started the pinion shim first, and had started that at 0.046", per Unitrax's recommendations. (Note that they also said "start with your existing shims", but not being sure, I flipped a coin and picked the wrong one.) As I've mentioned previously, I wanted to get the contact further down the tooth so I went first to 0.048" and then eventually back to 0.050", which is the thickness I had pulled out of the original setup.

BTW, here's the bearing puller I've been using to remove the bearing each time I've replaced the pinion shim:
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And here's how I had to mod it a bit in order to get it to work for me. The lip part of it that fits under the bearing comes very thick, ~1/8". If you use it like this (which I did with my old pinion), it hits and destroys the bearing cage as you pull the bearing. By grinding it down such that it can fit under the bearing (i.e. about the thickness of the shim), then it works like a charm every time.
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So here is what I ended up sending to Unitrax for their inspection. A close-up of the drive-side:
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And the coast side:
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The areas in yellow were my main question to them. I was/am seeing absolutely no contact in those areas, and didn't know if that looked okay or not. I spoke with the guy who does Viper rear ends there, and after a few back and forth questions, he thought I was in good shape. He liked that the contact was centered on the tooth, in both directions.


Next I wanted to work on the carrier shims and get those mocked up close. With an 0.132" shim on the gear side, I was getting good backlash (0.006-0.007"), but had virtually no preload. So I went a couple sizes thicker on the opposite side shim, which, as I expected, loosened backlash up to about 0.008". So, I split the thickness increase evenly on both sides, got the ~7 in-lbs carrier preload that I was looking for, with backlash back down in the 0.0065" range. I'll most likely go with 0.135" on the gear side and 0.129" on the opposite side, exactly 0.003" thicker on both sides then original.

With all that done, I did a cleanup of both gears to remove the Prussian Blue. I know I'll have some more on there to verify the final setup, but with all the trials, there was quite a bit. I cleaned up the pinion in the solvent tank, but didn't want the solvent inside the differential, so I just cleaned that up with a rag.
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Tomorrow: The Crush! :)
 

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Gotta love HF tools. Inexpensive, so putting a grinder to them to make them work right is a simple decision.

Thanks for sharing all you've done so far. I really admire your patience and ability to get things right.
 
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Big day for this build -- final assembly!

First thing is to install the pinion seal, but first it's important to put both the front bearing and the little washer in:
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Here I'm getting ready to press in the pinion seal:
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Then the pinion goes back in, but this time with the crush sleeve on it, just below my thumb:
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Now you have to get the front bearing pressed down onto the pinion without damaging the seal. Again, heating up the bearing beforehand helps.

Install the ****** and then the new washer and nut:
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Now the fun part. I torqued the nut down to as high as I could go on my torque wrench (250 ft-lbs), and just as Allan had stated, that didn't even come close to setting the bearings -- the crush sleeve was spacing the bearings out, too far apart, still uncrushed. So out came the heavy-duty equipment:
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That's a 3/4" breaker bar on a 1-5/16" socket, with a 3' cheater pipe. With this setup, I was able to start crushing the sleeve, but it wasn't easy!


Allan, this one's for you, bud:
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I know it looks like I'm dorkily trying to grimace for the shot, but I'm really not faking anything. I'm probably putting between 300 and 350 ft-lbs on that nut at this time, turning it bit-by-bit in order to get it crushed just the right amount.

I'd read that when it reaches the correct preload, it happens quickly. Now that I've done it, I'll add some exclamation points and an underline... it happens quickly!!! I probably ended up turning the nut maybe 1-1.5 turns past my 250 ft-lb point, in about 10 steps, and for 9 of those, there was zero preload on the bearings, meaning that the pinion was just spinning freely and I could still feel the slop in the bearings. Then, with just one little turn of the nut, maybe a 10th of a turn, it was suddenly up at 30 in-lbs of rotational resistance on the pinion. I was going for about 25, so I backed the nut off just a little, and was now showing about 25 in-lbs:
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It amazes me how stiff and tight it feels to turn the pinion with this preload setting on it, but I guess that's what it takes to ensure that there's no slop as they wear in.
 

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Thanks!.....the picture is worth a thousand words. There's just no way to describe the experience of that procedure accurately. You don't need a gym membership, just build a few differentials now and then. ......Also bench pressing transfer cases in trucks is good for you as well. :)
 
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cowger

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Okay, sorry for the delay -- had to take a break to watch that Niner game (wow!)...


With the pinion in, in went the carrier with the shims that I had pre-selected during mock-up phase. Torque the bearing cap bolts to 65 ft-lbs:
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I measured backlash and it came in nice and tight -- four readings of 0.006, 0.0065, 0.0065, and 0.006. I was going for something in the 0.005-0.008" range; I realize there's some risk that this will be too tight, but I'd rather err this way and have a stronger setup; the risk is that I have to pull it and ease up on the backlash. Time will tell.

Then one final check on the contact pattern. Drive side:
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And coast side:
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They both look good to me, so now to verify carrier bearing preload:
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This is reading about 31 or 32 in-lbs. With the pinion alone at about 25 in-lbs, that puts the carrier bearings themselves at about 6-7 in-lbs, which is what I was looking for. I figured to match the preload on the pinion, at 25 in-lbs, you would divide that by 3.55, given the gear reductions.


With all that verified, time to put the cover on. Small mistake here... I originally read the instructions for how to apply the RTV sealant that came with the gear set -- those said to stay on the inside of the holes. After doing that, I checked the instructions that came from Unitrax, and those were different and read: "Circle the holes and go straight from hole to hole." AND, they mention this as a Critical Step: Be sure to apply sealant to the bearing caps. The caps press against a portion of the cover that apparently provides them with support, so apparently the adhesive there bridges any gap and helps provide that support.

So, here's a picture of my first sealant attempt (which was easy to wipe off) and then I've overlaid a drawing, in brown, of where I believe the sealant should go:
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The brown is what I did the 2nd time, but forgot to take a picture...


Torque the cover bolts to 30-35 ft-lbs:
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Finally, I filled it with oil while it was on my bench -- I figured it was much easier here than under the car:
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That's it for tonight. Next will be the install back into the car...
 
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Thanks!.....the picture is worth a thousand words. There's just no way to describe the experience of that procedure accurately. You don't need a gym membership, just build a few differentials now and then. ......Also bench pressing transfer cases in trucks is good for you as well. :)

Thank YOU, Allan. Through your multiple warnings, you had me adequately prepared for that step, both in tools and in mental attitude. Both made a huge difference! :)
 
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cowger

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Diff back into the car

Last step is to get the differential installed back into the car and the car reassembled.

First, I lifted the differential back up into the frame, put one of the cover “arms” into the frame, then the ****** up resting on the exhaust, and finally the 2nd arm into the frame. Obviously this would be a lot easier if you’ve already eliminated the crossover exhaust (my next project):
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I used my floor jack to hoist the differential up into its approximate position, though biased a bit toward the driver's side. Slip the passenger side halfshaft back onto the output spline (a little grease will make it easier to remove for the next guy). Move the differential into its final position, reattach the upper bolts / nuts, and torque to 100 ft-lbs (21mm sockets).

The lower (pinion) mounts go through the differential mounting point, up into the frame, and then into what they refer to as a “flag nut”, basically a nut with a long tab integrated into it (there's an up and a down to it). That just floats loose in the frame so you’ll need to guide the bolt into that until it’s started:
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Then torque those bolts to 80 ft-lbs (18mm socket).


Reinstall the clamps for the e-brake cables to get them out of the way for the next step, which is to reattach the driveshaft.

Note the difference in the new kit versus the old:
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My 3/8" drive 6mm hex adapter wouldn't fit, given how tight it ends up against the driveshaft itself, so I had to make a long 6mm hex adapter out of a hex key and a 6mm socket:
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That allowed me to get to the bolts (with thread lock) and torque them to 24 ft-lbs:
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Now get the driver side halfshaft back on and (loosely) reinstall the upper A-arm bolts. Here's how I pre-loaded the suspension before torquing those to 75 ft-lbs.
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BTW, it probably goes without saying, but all these torque settings are from the '05 factory manual -- if your car is a different year, definitely verify what your settings should be.


Finally, a couple shots of the diff back up in place, ready to go:
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Last steps:
- Reinstall the bolt on the brake line retainer
- Reinstall the wheel -- torque to 90 ft-lbs
- Reinstall the belly pan -- torque to 40 ft-lbs


Done! Now I'm just waiting for a decent weather day to do the first drive. I'll let you know how it goes / sounds...

Bryan
 

cashcorn

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Awesome job! Was wondering? Would the 0 - 60 times be much quicker or is it more "in the seat of the pants feel"? again, great post!
 
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cowger

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Awesome job! Was wondering? Would the 0 - 60 times be much quicker or is it more "in the seat of the pants feel"? again, great post!

Great question, but unfortunately I won't be able to answer this for 500 miles, as I break in the new gears. I've read that it makes it a lot more fun, gives you that "new girlfriend smile", etc., but I don't have any real numbers...
 

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Excellent Post Bryan ! Thanx for sharing , and to those who contributed ! Very Professional ! :2tu: :2tu: :2tu:
 

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Awesome job! Was wondering? Would the 0 - 60 times be much quicker or is it more "in the seat of the pants feel"? again, great post!
I don't know first hand, as I still run stock 3.07 gears, but I'm pretty sure that changing the gear ratio will make the 0-60 time worse even though the car will accelerate harder and faster. With a lower gear ratio, the Viper will require a 2nd gear shift to hit 60. The shift time will negate the benefit of harder acceleration. Also from a dead stop, without drag radials, it's gonna be hard to keep the car pointed straight.
 

Allan

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COWGER, You really got to get rid of that exhaust crossover. All that thing is, is a 30lb cabin heater that gets in the way when your swapping the diff. :nono:
 
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cowger

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Excellent Post Bryan ! Thanx for sharing , and to those who contributed ! Very Professional ! :2tu: :2tu: :2tu:

Thanks, Jay!

Now that you've watched me go through this process, I gotta ask: Are you still thinking about doing this yourself?
 

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I don't know first hand, as I still run stock 3.07 gears, but I'm pretty sure that changing the gear ratio will make the 0-60 time worse even though the car will accelerate harder and faster. With a lower gear ratio, the Viper will require a 2nd gear shift to hit 60. The shift time will negate the benefit of harder acceleration. Also from a dead stop, without drag radials, it's gonna be hard to keep the car pointed straight.
So what is exactly the point of going with shorter gearing then? How will this new gearing affect the shift skip? Common wisdom would imply taller gearing is there to take advantage of lots of low end torque
 
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cowger

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So what is exactly the point of going with shorter gearing then? How will this new gearing affect the shift skip? Common wisdom would imply taller gearing is there to take advantage of lots of low end torque

My 2 cents: Allan answered one specific question, which was 0-60. If that was my only requirement for my car, then I agree with you -- don't make the change.

However, he also states (which matches my expectation) that the shorter gearing will cause the car to pull harder and accelerate faster, at the expense (perhaps) of top-end speed. Since I don't care if my car can only do 150 vs. 165 (or whatever), I'd rather have more fun in the speed range where I spend all my time...

As far as skip-shift, I've already eliminated that, so it doesn't really matter. But if it were still enabled, I'd expect that it would make it slightly less annoying, meaning that when you did have to shift into 4th gear at low speeds, the engine wouldn't be lugging quite as much.

Bryan
 

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viper is drag limited, only base hardtop would be affected, I think... I was just curious what possible motivation people could have to go with shorter gears on a high torque, (relatively) low revving motor. BTW, where are you in nor cal? I am in Sacramento.
My 2 cents: Allan answered one specific question, which was 0-60. If that was my only requirement for my car, then I agree with you -- don't make the change.

However, he also states (which matches my expectation) that the shorter gearing will cause the car to pull harder and accelerate faster, at the expense (perhaps) of top-end speed. Since I don't care if my car can only do 150 vs. 165 (or whatever), I'd rather have more fun in the speed range where I spend all my time...

As far as skip-shift, I've already eliminated that, so it doesn't really matter. But if it were still enabled, I'd expect that it would make it slightly less annoying, meaning that when you did have to shift into 4th gear at low speeds, the engine wouldn't be lugging quite as much.

Bryan
 
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cowger

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viper is drag limited, only base hardtop would be affected, I think... I was just curious what possible motivation people could have to go with shorter gears on a high torque, (relatively) low revving motor. BTW, where are you in nor cal? I am in Sacramento.

Auburn!

After my diff is broken in, let's get together and you can answer your question for yourself in my car... :)
 

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Auburn!

After my diff is broken in, let's get together and you can answer your question for yourself in my car... :)
That sounds like fun-as soon as my car sees all four wheels at the same time, LOL. Like you, I am busy with a little project that seems to be stretching into a few months.
 

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Funny you should ask Bryan , I was going to pay someone to do it . But since I have the tools and experiance from my Big Block Dodge Days from 30 years ago , I thought why Not ? ....lol ! I almost forgot how sweat equity could be rewarding !...lol ! You may have started a Trend !.....lol ! ;) Great Post and Nice Work !:2tu: :D
Cheers ! Jay
Thanks, Jay!

Now that you've watched me go through this process, I gotta ask: Are you still thinking about doing this yourself?
 
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