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Old 10-09-2017, 11:12 AM   #1
holdenjp
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Default Advice for AW71L and rear diff. G80 LSD

Alright. Here's the situation. I have a 1991 245 b230ft swap with an AW71. There is a 94 940 n/a nearby that I could get drivetrain parts from. It has a 4:10 rear diff and should have a G80 and AW71L as well but I forgot to look when I was under it yesterday. There is also an 89 760 locally that I haven't checked out yet but it seems like it may have an LSD.

I've sifted through threads for two nights and I haven't found definitive answers for a few questions. I've found various threads that say which years/models have different ratios and diffs but even those are conflicting sometimes. There also seems to be conflicting experiences for people. For example one thread someone said the G80 was unpredictable in turns and loud. I obviously don't want the back end to fly out from under me when turning in rain.

My ultimate goal is to ditch the open diff for traction purposes, improve acceleration, and improve mpg on the highway. I know increasing acceleration and mpg generally don't go together well, but thought there might be some combination of AW71L, gear ratio, and locking diff that could do the trick.
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Old 10-09-2017, 12:04 PM   #2
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As someone who swapped an AW71L into his car with a 3.73...DON'T do it unless you retain the 4.10 gearing. With the 3.73 it is a dog at cruise. No part-throttle boost, ever. A 13C is necessary if you use the 71L with any other rear end...and I can promise you that you'll beg for a 4.10 eventually. I deleted the lockup on mine and I've never been happier.
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Old 10-09-2017, 12:32 PM   #3
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The DANA Powr-LOK LSD is pretty much hen's teeth.... best of luck in finding one! I bought a complete 7 series rear end assy. to get one for my DD.

When you begin swapping the complete carrier and then pinion, "you are entering a world of pain" (The Big Lebowski). IMO having BTDT several times, find the complete Dana rear end, be it 1031 or 1041, and swap the bugger. Then with the pinion OEM installed, swap your matching ring onto a TRUE TRAC or the unicorn feather LSD. You'll still have to manage the proper carrier bearing preload and R&P backlash, but should be good to go then.

Make some careful calcs about "cruising RPM" of your target setup, and then decide if your turbo will spool at that engine RPM, or if you'll have to downshift to obtain boost.
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Old 10-09-2017, 02:37 PM   #4
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I dunno, I've had solid luck on mine with stock gears and the 71L. Locked up it'll build 5psi almost instant from 70mph on up, builds pretty quick after that. It's really not any different than driving a manual with a comparable ratio once the converter is locked. Personal preference though I guess.

Can't help on the ratio for a diff for sure, but the 16v cars seem to have a 4.10 G80 in them.
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Old 10-09-2017, 03:27 PM   #5
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Originally Posted by gsellstr View Post
I dunno, I've had solid luck on mine with stock gears and the 71L. Locked up it'll build 5psi almost instant from 70mph on up, builds pretty quick after that. It's really not any different than driving a manual with a comparable ratio once the converter is locked. Personal preference though I guess.

Can't help on the ratio for a diff for sure, but the 16v cars seem to have a 4.10 G80 in them.
Stock gears as in 3.73? Does yours have a G80 or LSD? Or is it open?

Last edited by holdenjp; 10-09-2017 at 03:44 PM..
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Old 10-09-2017, 04:02 PM   #6
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Quote:
Originally Posted by gsellstr View Post
I dunno, I've had solid luck on mine with stock gears and the 71L. Locked up it'll build 5psi almost instant from 70mph on up, builds pretty quick after that. It's really not any different than driving a manual with a comparable ratio once the converter is locked. Personal preference though I guess.

Can't help on the ratio for a diff for sure, but the 16v cars seem to have a 4.10 G80 in them.
Up here in Canadia, our speed limit tops out at 62mph on the highway, so the AW71L with anything other than a 4.10 and 13C is just awful. Cruise is at 2000rpm.
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Old 10-09-2017, 04:33 PM   #7
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Originally Posted by Broke4speed View Post
Up here in Canadia, our speed limit tops out at 62mph on the highway, so the AW71L with anything other than a 4.10 and 13C is just awful. Cruise is at 2000rpm.
Maybe in your part of Canada, but I assure you you can find higher limits in at least BC.
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Old 10-09-2017, 04:33 PM   #8
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Originally Posted by Broke4speed View Post
As someone who swapped an AW71L into his car with a 3.73...DON'T do it unless you retain the 4.10 gearing. With the 3.73 it is a dog at cruise. No part-throttle boost, ever. A 13C is necessary if you use the 71L with any other rear end...and I can promise you that you'll beg for a 4.10 eventually. I deleted the lockup on mine and I've never been happier.
So the 16T or the 19T I have on the shelf wouldn't be a good match if it takes longer to build boost?
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Old 10-09-2017, 06:07 PM   #9
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Maybe in your part of Canada, but I assure you you can find higher limits in at least BC.
BC is the highest at 120kph. New Brunswick and a few others are 110. That's still not enough, IMO, to use an L wiithout a 4.10 rear.
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Old 10-09-2017, 06:09 PM   #10
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Originally Posted by holdenjp View Post
So the 16T or the 19T I have on the shelf wouldn't be a good match if it takes longer to build boost?
I was using a 16T at the time, so I can say it sucked lol. It would lock up at 50mph, which put me at 1800rpm. It was terrible, even with the 16T. This is on a 3.73 rear end.
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Old 10-09-2017, 08:12 PM   #11
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It's a terrible transmission when paired with a 3.73 and scarcely better with a 4.10.
I regret putting one in our '93 240+T. I should have used the non-lockup version.
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Old 10-09-2017, 08:21 PM   #12
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It's a terrible transmission when paired with a 3.73 and scarcely better with a 4.10.
I regret putting one in our '93 240+T. I should have used the non-lockup version.
This is exactly what I had planned to do about a month ago. So glad I never found one! I thought it would be ok since our speed limit is 70mph.
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Old 10-09-2017, 08:37 PM   #13
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Yes, mine has the 3.73's. Depends on other mods as to when your setup will spool, but at 60mph it is a definitely a little slow to spool since that puts it around 2k.

Mine has a TruTrac in it, has for a long time, originally open, then G80, then TT.
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Old 10-09-2017, 11:55 PM   #14
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Thanks for the help. Sounds like the 71L may not be a good fit.

Does it get much better highway mpg?

Anyone have any idea what the chances are that an 89 760 gle would have an LSD In it? I don't really want to mess with changing out the ring and pinion or cutting the axle to fit the G80.

Last edited by holdenjp; 10-10-2017 at 12:31 AM..
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Old 10-10-2017, 12:48 AM   #15
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Saw 2-3mpg increase on highway runs.
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Old 10-10-2017, 01:11 AM   #16
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Anyone have any idea what the chances are that an 89 760 gle would have an LSD In it?
Slim to none.
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Old 10-10-2017, 02:36 AM   #17
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16V or Canada 940T converter and 4.10 are basically mandatory with a stock(ish) B230 car at vaguely normal speeds. The ~1800-2000rpm N/A 8V converter is god awful and the lockup is worthless at any legal/daily speed and makes the car a pathetic dog or snapping down 2 gears to get anywhere just to gently pass while climbing.
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Old 10-10-2017, 03:30 PM   #18
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16V or Canada 940T converter and 4.10 are basically mandatory with a stock(ish) B230 car at vaguely normal speeds. The ~1800-2000rpm N/A 8V converter is god awful and the lockup is worthless at any legal/daily speed and makes the car a pathetic dog or snapping down 2 gears to get anywhere just to gently pass while climbing.
What's the difference in stall speed between the US n/a '71L's and the 16V/Canadian turbo models?
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Old 10-10-2017, 04:30 PM   #19
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For what it's worth I put an AW71L in my 940 with the 3.31 rear axle. And you guys state that 3.73's would be horrible... :-) it did an honest 110 mph at 3500 rpm.
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Old 10-10-2017, 04:35 PM   #20
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1800rpm or whatever in the green for the N/A US 8V cars to 2450-2600 or so for 16V and little less for the turbo converter. It's pretty notable.
They really went for fuel econ with the 4.10 and stock n/a 8V cars and made them shift as lazily as possible. And if driven like the average octogenarian N/A 940 driver with the cruise control set at 49.5mph on flat ground with no wind just fast enough to keep the converter locked, excellent fuel econ might be achieved.
If ANY other variable or other driving style is present, however (hills, wind, elevation) it still can barely pull it, despite them giving them a 4.10, but lower stall speed with steeper gears is usually better for economy in mixed driving overall.

It is so sluggish that the stock N/A 240 with even only another lousy 200rpm stall speed and no lockup with the 3.73 that's also pretty pathetically lazy actually feels maybe a little better (240s are a little lighter too)

For most with even fairly gradual hills to climb on the interstate or even the occasional lazy pass, trying to stay in vacuum 55-70ish mph (common enough USA speed limits) and burn a reasonable amount of fuel, at least 4.10 and 16V converter might be nice to have better all around use of power and keep economy/ease of light load drivability intact.

Always wondered if anyone would adapt the 03-71LE valve body that allows converter lock in 3rd for towing so you don't cook the trans, and one could maybe alter the shift points and also retard the timing on shifts to keep the thing alive/not having to make shifts holding more than ~200-300ft-lbs or whatever, once the shift's completed one would imagine they'd hang onto 4-500ft-lbs reasonably well. That would allow just unlocking the converter for a second for a sort of a "lazy pass" but still pretty light load in OD (OD is pretty weak/don't put significant load on AW-7x in OD) or "don't cook it" with prolonged towing in 3rd with the converter locked. Has junkyard recombine cheapskate and electronics tweaker appeal...

Technically, rebuilt (thrust washer issue fixed), the ZF auto box is kinda the stronger and better of the two (more for DD or towing use anyway, ratio spread and strength of the torque converter clutch and OD).

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Old 10-11-2017, 08:53 AM   #21
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Yeah I never had any issues with the 71L in my cars with 3.73 final drive (or taller), but if you plan to spend a lot of time sub 2200 rpms in OD, I guess it could be a dog.
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Old 10-12-2017, 11:13 AM   #22
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Yeah I never had any issues with the 71L in my cars with 3.73 final drive (or taller), but if you plan to spend a lot of time sub 2200 rpms in OD, I guess it could be a dog.
I’m in Indiana so there’s not exactly a lot of uphill climbs on my daily commute. And my OD is already blocked off. Really looking for better mpg without losing the fun of the turbo.
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