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99 AWD BadAstro
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Discussion Starter · #1 ·
Hey guys, I have a lot of questions here, so here goes:

1. I have GU6 gearing which is 3.42, and I've read that 3.73 provides more torque on the highway thus better MPG. If I find a rear end that has the 3.73 gearing, how hard is it to swap the front as well to match? If that is a huge PITA I will likely stay 3.42.

2. I am getting a rear end whine, and it's been getting noticeably louder, that goes away when I let off the throttle. From what I understand it is most likely the pinion bearing, so that most likely needs to be replaced

3. I currently have an open diff, and I'd like to go limited slip. Full locking isn't probably necessary, I don't offroad a ton, and I do drive in snow climates, so a full locker might cause more issues in drivability than a limited slip. I've been looking for a G80 for years, without any luck, so at this point I am thinking I need to go aftermarket. What do you recommend?

4. I have a 3" lift and I'm using bilsteins, which seem to be extended all the way. I hate how the shock mounts hang downwards. Where do you get new shockmounts to weld on to the upper half of the axle tubes?

5. My Astro Trailer has a factory axle still in it, also GU6, so same ratio as my van. I was thinking about pulling this axle to rebuild, then swapping it into my van so I don't have any downtime. With the one I pull out of the van... can I gut the pumpking before installing it back into the trailer to reduce drag? How do you keep the axles from sliding out?

Thanks a ton in advance, I am a total newb about rear ends in general
 

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1998 LS AWD Forest Green metallic
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863 Posts
#5: You need the spider gears and retainer clips to hold the axles in place. You could probably pull out the pinion shaft and seal up the hole, but I think that would be a lot of work for very little gain.
Rod J
Issaquah, WA
 

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2000 Lifted 4x4 Astro 92 V8-350 Shorty
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1) Swapping a rear is not all that difficult... if you have the right tools, jacks, jack-stands.
The difference between 3.42 & 3.73 is not huge.. but it typically is an improvement.
I wish I had that gear ratio.

2) Some rear-end whines can be typical (in unloaded vehicles).. and might not be a huge problem.
But on the other hand, if the noise is getting worse, then there is likely an issue.
At the very least, you need to pull the cover and do an inspection, as well as test the pinion for play.
Fresh fluid refill is always a good thing too.

3) A G80 is a great option for "general" use.
Maybe you could find one with 3.73 and solve "3 problems" at same time.. with minimal expense.

4) Most performance companies (like Summit Racing) sell weld on shock tabs.
You'll need to know tube diameter.
I'm not sure if there's going to be an issue having it above the tube, vs hanging below.
I'd suspect there might be a reason almost all vehicles have them hanging below the tube.
Might not be worth obsessing about.. looks normal as is.

5) You will need (at the very least) the carrier inside the pumpkin to hold the axles in place.
The unloaded drag (either way) will be very minimal

Those are just my basic thoughts.. others may offer more detail
 

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99 AWD BadAstro
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Discussion Starter · #4 ·
thanks, but question 1 was about swapping the ratios on the front end of the van. I don't think I can keep the 3.42s in front if I go 3.73 in the back :p
 

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Common Sense + Critical Thinking
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thanks, but question 1 was about swapping the ratios on the front end of the van. I don't think I can keep the 3.42s in front if I go 3.73 in the back
No, you definitely can not. The front would have to be changed as well.

All depends on what kind of driving you do and what kind of weight you carry. If you mostly drive around an empty, stock tire size van at highway speeds the 3.42 is going to be more efficient for you. If you are heavy loaded, larger tires, mostly city driving then it might be worth the effort to change ratios.

But when you have a matching ratio rear end sitting there waiting to be put into service. Esp if all it needs is to have fresh seals installed or whatever.

Limited slip is a great way to go for street vehicles. The factory locker works well for a lot of purposes, pretty much anything other than heavy offroad driving.

If all you deal with is some snow and a muddy driveway, the factory locker is awesome!
 

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99 AWD BadAstro
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Discussion Starter · #6 ·
Only problem is finding one. I've been searching CL and FB for a g80 since I bought this thing 2 years ago, no dice. Can't really ship one. Whenever I'm at a junkyard I check the tags in the door; have never found a G80
 

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Just looked on flea bay they have one for 160.00. (3.42) Gov lock assembly. As far as the front diff and the rear unless you have experience painting the units then adding or subtracting shims. I would suggest hiring both diffs done. Where are you located? Maybe someone could look in there local yards or most yards have a finder system. I have scored several G-80 units complete rear ends for under 100 bucks. Any way you go we all wish you best luck.
 

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99 AWD BadAstro
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Discussion Starter · #9 ·
So I have a 99, is there anything special about spline count that I need to watch out for, or will any G80 for 7.5 work? I'm assuming I reuse my existing ring gear and whatnot.
 
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