Wagon Rear End Change Help

2
0
0
Decatur, IN
Buick Ownership
'96 Roadmaster Wagon
Thread starter #1
Hi all. I've owned my '96 Roadmaster wagon for about 7 months now and feel I need to change the rear end. It's a factory 2.56 non-posi. I don't get the gas mileage to justify such tall gears plus it's very sluggish. The one tire fire is what aggravates me the most. Therefore I want to install shorter gears and a posi/locker, ideally 3.73's. I know I have a series 2 carrier, and those gears aren't a factory option. What exactly do I need to do this? I've read somewhere that you can put spacers in a series 2 and install series 3 gears. I've also read that any 8.5 series 3 carrier will bolt in. I'm willing to buy new parts or pull something from a junkyard if gears out of a pickup or something like that would work. Just looking for advice from someone who was done a swap like this or witnessed firsthand. Thanks.
 

Dirtybob

Junior Member
34
3
8
Buick Ownership
95 RMS
#3
I wouldn't use a ring gear spacer, known a few guys that had the bolts shear under abuse...

I went with a (fleabay) Yukon Duragrip and 3.42s in my RMS, didn't bother with the abs reluctor since I had previously deleted the system. Trying to keep the abs functional will limit your choices on gear sets plus you will need to source the appropriate reluctor. I used eehack & tunerpro to recalibrate the pcm after the swap.

80 mph highway driving is down 1.5 mpg (22 mpg now, 23.5 before) vs. the original 2.56s (might not be as drastic if one were to drive a bit slower). City mpg is the same or better and the car is much nicer to drive in town (where I do 95% of my driving anyways) plus the posi makes rain/snow much less of a hassle.

Other options include sourcing a factory gov-bomb (G80 code "locker") from a later model truck. My $.02 on the gov-bomb is don't, they're not a 'real' posi and have been known to grenade the diff under abuse (have done that personally more than once). The guts from anything with an 8.5" rear and 30 spline axles should work as a donor (pay attention to the bearings when swapping). You could also find an open diff, series 3 carrier/gears from a donor and throw in a luchbox locker (i.e. richmond no-slip or clones) but I dunno if that would cost any less than what I paid for my Duragrip.
 

Dirtybob

Junior Member
34
3
8
Buick Ownership
95 RMS
#4
FWIW, eehack/tunerpro (FREE) will only work on '94 & '95 pcm. You will need to find someone to recalibrate your car for the gear change, swap to a '94/'95 pcm, or purchase tuning software usable on your '96.
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2
0
0
Decatur, IN
Buick Ownership
'96 Roadmaster Wagon
Thread starter #5
I'm impressed you get that mileage. I get 16.5 no matter what, and that's 2 up from before I did plug/wires/filter. I drive 70/30 highway/city. One tank I babied it best I could, next tank I left it in 2nd gear anytime I drove (even down the highway at 70) and holeshotted every stoplight. 16.5 both times, kinda disappointing but it's a boat.

I'll probably go with a ebay carrier and gear set like you and won't worry about abs. Front sensors are bad anyways and the brake lines are trash so I'll just replumb the whole system and delete abs.
 
174
6
18
Ironton,(southern)OHIO
Buick Ownership
'96 Roadmaster Collector's Edition
#7
I've got a 96 RMS with the 2:56 gears and I also want to switch to a quicker geared posi. I've never gutted a diff before, but I'm pretty good at figuring things out and I'm sure I can do it if I have to. I can't afford new parts right now, so I need the cheapest option available. I don't even care if it goes out in a couple thousand miles, I just want a quick posi for cheap till I can afford to do it the way I want. What is the cheapest way to get a quick posi unit for my RMS? Thanks, Adam
 

HotZ28

Full Member
6,132
26
48
Buick Ownership
1996 Roadmaster Limited Collectors Edition 58k - 1996 PAU
#8
I just want a quick posi for cheap
Sorry, but there is no such thing as a "cheap" posi & gear change. Parts would run about 1K plus $400.00 labor for someone who knows how to set backlash & wear pattern between the ring & pinion. . You may be better served looking at a doner Impala SS, or police cruiser with the same lower ratio rear-end. Used Impala SS posi complete 3-rd member with a lower ratio, can be found for about $400.00 if you do some research. Good Luck!!
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Last edited:
174
6
18
Ironton,(southern)OHIO
Buick Ownership
'96 Roadmaster Collector's Edition
#9
Sorry, but there is no such thing as a "cheap" posi & gear change. Parts would run about 1K plus $400.00 labor for someone who knows how to set backlash & wear pattern between the ring & pinion. . You may be better served looking at a doner Impala SS, or police cruiser with the same lower ratio rear-end. Used Impala SS posi complete 3-rd member with a lower ratio, can be found for about $400.00 if you do some research. Good Luck!!
Okay, thanks for the info. I guess I'll just have to wait till I can afford to do it right. I was just hoping there was a cheaper option.
 
34
3
8
Buick Ownership
95 RMS
#10
I was being budget minded when I did my gears/posi but also wanted to avoid ending up with a junk gov-lock or a used up auburn (Impy unit). Ended up spending $550 for a Duragrip/3.42s/install kit from ebay and paid another $350 for a professional install.
By the time I would've bought the necessary tools and drove myself nuts trying to perfect the gear pattern that extra $350 sounded like a deal to me.
 
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