The Official 1LE 3.91 gear swap thread

[blazzin1]

Originally Posted by stikSS

Ok.... I just posted on another 3.91 thread in this same section yesterday. I just done my swap this past weekend, and don't believe everything you read or see. While I do agree that if this is your first rodeo with gears... you may want to have a differential mechanic on retainer, but it's not near as bad as what I'm sure some of you and myself have read about doing gears.

Now I will do my best to give you as much detail as I can into my swap, and I do apologize for not having pictures, but when I'm working on my car... the camera is the farthest thing from my mind.

Tools - if you are lucky enough to have a lift.. that will make this very easy, if not, jack and stands will work just as good. You will need a 18mm socket and wrench, 10mm wrench, and a 15mm socket and wrench. Most of the bolts in the rear of the car are 18mm, but your exhaust if you remove it will be 15mm and the 10mm wrench will be used to remove the little bolt holding your brake line and the sensor that hooks into the hub, and a 32mm socket to remove the axle nut.

After removing the wheels, remove the axle nut... you may need a cheater bar to break it loose, then use the 10mm and disconnect the brake line attached to the upper control arm, and the sensor behind the rotor that hooks into the hub. Next, you will remove the bolts from the upper control arm, the upper trailing arm and the lower trailing arm, this will allow you lean the hub outward from the car so that you can remove the axles. Take a hammer and a rachet end or rod and hit the end of the axle to push it out of the hub. Once you have the axle loose from the hub, If you have someone helping, one needs to get under the car and the second person needs to work the axle out of the hub and then start the removal from the carrier. All you need to do is give a few good tugs and it will come out, but make sure you don't damage the seals pulling the axles out. That is where the 2nd person is important... make sure they support the axle as it's being taken out of the carrier from underneath the car. No axle grease will come out, or if it does it will be very little. You will do this on both sides.

Next, there are 3 bolts connecting the driveshaft. You will more than likely need to either set the parking break or make sure the car is in gear when removing the bolts. All 3 can be removed, the shaft will still be supported by the pinion. Now, you may have to drop the exhaust, that depends on what you have. I have Corsa, and I removed the back half of mine. This will give all the room you need to get the carrier out. There are 3 bolts holding the carrier, and there is a small vent tube connected to the carrier, just pull it off. Get a jack and support the carrier before you start taking bolts out, so you can start lowering it down. Once you start the lowering process, one person needs to slowly work the driveshaft out. I will basically seperate itself as you lower the carrier. That pretty much sums up the removal, and the install is the same methods as this just in reverse.

Onto the gear swap....... This is where i think it will surprise alot of people. I didn't actually do my swap, but I was taught and watched it being done by my mechanic. Pretty much, Chevrolet has the carrier machined so well that its a take out and put in method. The gears will come with new ring bolts, and crush sleeve. You will need to get the pinion out of the housing and press off the pinion bearing and removed the crush sleeve, and then same process to install the new sleeve and you should be able to reuse the same bearing as long as you don't damage it taking it off the original pinion, and install it back into the housing. Now, replace the ring gear and reattach with new bolts, use the existing bearings on both sides of the ring gear if they look good, basically you're ready to re-install that back into the housing. The fit is very tight, and what we done was stood the carrier up on the end and held everthing together and slowly worked back into place. It takes a little force to work back in, but once its in, bolt the caps back on and pretty much its done. No shims or backlash adjustment was needed. The gear was lined up perfect. We assumed that since this is OEM parts, that it was machined to fit prefect without any adjustment. My mechanic was very impressed with precision that is used since there was no need for shims or bacK lash. We used grease to double check the position and it was lined up dead perfect in the center of the ring gear. From there.... it was put the gasket on, and replace the carrier cover.... and then back in the car same way it came out.

By far.... one of the easiest mods I've ever done on my car and very worth the money. I paid 248 for the gears and my mechanic charged 150 for labor. The labor charges i've seen for these swaps is crazy... unless you're doing an aftermarket gear, then those will require shims and back lash setting.

I'm glad that you are satisfied with your install, and I sincerely hope it lasts. But it sounds like your mechanic never even checked the pinion depth or backlash measurements at all. Just because you use the same pinion and/or carrier shims that were installed with the stock gears does not mean it will be correct upon installation with new gears, especially with new gears that are of a different ratio. I know taking everything out of the rear end and putting it all back together with different gears seems easy, and I'm sure it is. But it just seems like your mechanic completely disregarded some very critical measurements. Did you guys check the pattern at least? What is your backlash measurement?

I mean you guys can obviously do whatever you want....it's your car. But I would have a really hard time advocating these procedures to the typical novice mechanic. I sincerely hope not, but I would think we're going to see some problems with these gear installs if they are done this way with blatant disregard for ensuring the proper tolerances are measured and adhered to. Okay, enough said, you guys do what you want....

Lastly, setting the parking brake cable with your axles removed is NOT going to prevent the driveshaft from turning!!!! Okay, I'm done!

[stikSS]

No problem guys. Just for time frames... We had my carrier out in an hour and half, and the gear swap took about 2 hours, and the install was an hour... So in reality, you could do it in a day easy, provided you have all the parts and a press.

I really hope everyone's install is as easy as mine was... I don't think I got the "magical" set of gears... but I can't see where there is any need for adjustment.... its CNC'd perfect. I say it goes along with the rest of the car and how GM made it so easy to work on.

[JohnnyBfromPeoria]

Originally Posted by blazzin1

But it sounds like your mechanic never even checked the pinion depth or backlash measurements at all.... Did you guys check the pattern at least? What is your backlash measurement?

He said they "used grease." That's all. Not even Prussian blue. And it looks like no backlash or pinion depth measurements were done, am I right?

John B.

[stikSS]

Originally Posted by blazzin1

I'm glad that you are satisfied with your install, and I sincerely hope it lasts. But it sounds like your mechanic never even checked the pinion depth or backlash measurements at all. Just because you use the same pinion and/or carrier shims that were installed with the stock gears does not mean it will be correct upon installation with new gears, especially with new gears that are of a different ratio. I know taking everything out of the rear end and putting it all back together with different gears seems easy, and I'm sure it is. But it just seems like your mechanic completely disregarded some very critical measurements. Did you guys check the pattern at least? What is your backlash measurement?

I mean you guys can obviously do whatever you want....it's your car. But I would have a really hard time advocating these procedures to the typical novice mechanic. I sincerely hope not, but I would think we're going to see some problems with these gear installs if they are done this way with blatant disregard for ensuring the proper tolerances are measured and adhered to. Okay, enough said, you guys do what you want....

Lastly, setting the parking brake cable with your axles removed is NOT going to prevent the driveshaft from turning!!!! Okay, I'm done!

My mechanic has been in the business for over 30 years... and has been doing differential for as long and have no doubt in his judgement. Basically what I was saying is that there is no room for shims, and the crush sleeve basically sets your placement for you. I'm in no means saying don't check your tolerances... and he did check for any adjustments but none was needed.

He asked me to get an install kit and prepare for shims and new bearings.... well... Good luck finding that... cause nobody around my area had anything... they couldn't event find the bearing numbers for the car including the dealership.

Lastly... I set my parking brake to remove the axle nut.. and then took it out of gear to roll the driveshaft when removing the bolts... I guess you need numerical step by step instructions.

[stikSS]

Best thing I can say... is take yours apart and see what happens. GM obviously had a plan and if they send you everything you need to do the swap and that only includes the pinion, ring, bolts and crush sleeve... then what else do you need? Unless you foul up your bearings taking it out.

[Rhino79]

Those thick spacers on each side of the carrier are shims. If the backlash is wrong, they need to be replaced with the correct size with oe or aftermarket adjustable shims. Also the pinion shim in most cases will be correct for pinion depth but pinion depth must be verified always. The crush sleeve isn't for pinion depth, its for bearing preload.

[ssmike]

So if I were to have a local speed shop do the swap where do I find the specs for backlash, torques, tolerences, etc? Can someone post them so we can make sure our installers are doing these to specs?

[stikSS]

Right.... but what I'm saying is that everything went back in as it came out and in the end the placement and back lash was the same as it was with the original gear with nothing special having to be done. I don't expect that to be the same with everyone but I think alot of installers will be surprised at how precise everything is.

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[Ucantctchme]

I performed my 1le gear swap. I have all of the special tools available to me. Most mechanics will tell you the same thing I'm about to say. I would rather install the gear set with the factory pinion shim and side bearing spacer to see where I stand. With the 1le gears my backlash, bearing preload and pattern were all perfect. I did have a shim kit available but sold it because I didn't use it.
Your best bet is to take the rear assembly out and let a pro set it up. If you don't, you need a dial indicator, a small beam type torque wrench for setting preload. 1/2" torque wrench for ring gear bolts and bearing caps and some type of marking compound. White grease can be used. A pinion depth tool is not necessary as long as you understand your pattern.

[429]

^ I bought the shim kit from you, and we needed to use two of the shims to get the pattern right.

[SC2150]

Originally Posted by 429

Unless you have a case spreader, depth and backlash micrometer, and working knowledge of gear patterning, you have no business doing this install by yourself. Pull the pumpkin and take it to a specialty shop (differential shop, 4x4 shop, speed shop)

A DIY guy can remove the diff assy, but reading the detailed step by step of the ring & pinion itself an extremely important step was left out so I'm with you......lets see the results.

Originally Posted by Ucantctchme

I performed my 1le gear swap. I have all of the special tools available to me. Most mechanics will tell you the same thing I'm about to say. I would rather install the gear set with the factory pinion shim and side bearing spacer to see where I stand. With the 1le gears my backlash, bearing preload and pattern were all perfect. I did have a shim kit available but sold it because I didn't use it.
Your best bet is to take the rear assembly out and let a pro set it up. If you don't, you need a dial indicator, a small beam type torque wrench for setting preload. 1/2" torque wrench for ring gear bolts and bearing caps and some type of marking compound. White grease can be used. A pinion depth tool is not necessary as long as you understand your pattern.

Again, excellent info and accurate.

Once the gears are run, if the pinion depth or backlash is off and it whines, odds are it will be noisy forever. Proper pattern and setup is critical.

[willhe64]

If this is your first go at it. Take it to someone who has done lots of installs. You really need to know what you are looking at when you check the tooth pattern using prussian blue. Both front and back side. I've seen them perfect on the drive side but off a bit on the back and then they howl when you let off the throttle. Once you see it once you'll have it but there is a bit of an art to getting them perfect. And you want perfect.

[Caswell239]

There's no art to it. Just have to know when moving the pinion or te crown what affect it has on your pattern. After your back lash is set of course.


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[willhe64]

The art is in looking at the ink pattern and knowing it is right.

Edit: And if it is not, knowing by the look of the pattern what to correct.