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Is a 3:31 diff too much for an AW71 B230 240?

drj434343

drj434343

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Joined
Feb 22, 2010
Location
Portland, OR
Is a 3:31 diff too much for an AW70 B230 240?

RSI is helping finish a rebuild project on my 1993 245. Stock rebuild B230 NA with a bit more squish, nothing fancy. AW70 transmission. I opted to leave in the 3:31 G80 rear end.

I've had someone warn me that 3:31 is way too low for the AW70 in this configuration. Kickdown cable won't be able to be adjusted correctly, and it will put quite a bit of load on the transmission.

Has anyone run this setup? Should I consider higher gearing?
 
It will be a dog. I drove my 242 around with that setup before swapping the rear end to a 3.73.
 
I had planned on swapping gears from 3:whatever in my 240 to what I had presumed to be 3.73 from my 745t, when I swapped the g80. Gears ended up unusable and I thought I had read somehwere that a 3.73 g80 couldn't be used with 3.54 and lower, however it all swapped over... gearing is definitely lower in the 240 though, I hang around 3k rpm @ 75-80, where I would've been around 3.5k in the wagon at that speed. leads me to believe both were a lower ratio than I had thought.. but that's a lot of speculation. Anyways, what I believe to be a 3.31 in my 240 gets me great highway mileage but sucks at the drag strip. Then again, I'm not n/a
 
I think it'll be a slug, but not nearly as bad as if it were a lockup torque converter.
 
So slow it can't hardly pull it on the flat in OD, no notable fuel savings. Lots of multiplying torque against the converter, which 240s already do a lot of to cruise on the highway with a 3.73. After all, a 3.73 with .69 OD (AW-71) is actually taller than an M46/47 with a 3.31 and .80 or .82 OD.

Swap in 3.73 or shorter. It will physically drive at all with the 3.31, but really luggy on the engine (pings more than it would with a shorter axle), heat up the trans fluid a ton, and a total dog (and my standards are very lax on this, I drive a Diesel 265 (M46 at least), honda insight 3cylinder (manual trans again), and previa 4cylinder van mostly (auto, and with tow bar...slower than snot).

Volvo never paired the 4speed auto with anything taller than 3.73, even in V6 cars. Even the ZF 4-speed with a shorter OD got 3.73 and shorter.

Even the 3-speed autos, only with the diesel or V6 or B30 get taller than 3.73 gearing in the back, but shorter 1st gear and higher stall speed so they'd actually move at all, and real real dogs with the 3-speed auto...the pairing in the B30 164 and Diesel basically sucks any and all of the life out of the car.

It works at all, probably is fairly unlikely to burn out the motor/trans in the immediate future, especially with the turbo AW-71 trans. Not ideal for economy or anything else. Swapped a couple stick-->auto and drove them around a bit with the 3.31 axle, that ~14% taller tipped the scales to "necessary" before giving the car back.

If you want a mileage miser, install AW71L from 93+ 940 N/A and 4.10 gears. Super slooooow stall speed on those, very slow in the slightly heavier 7/9 car, but slow stall speed/more direct drive to the wheels and lockup is good for mileage.
 
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My set up is a 940turbo with aw 71l and rear out of 960 with 3.31 ratio...no slug,great mpg...And I tow a tow dolly behind it for volvo recoveries
 
The snail kinda takes the slug out of a 3.31. NA/3.31=slug T/3.31= slug with moments of excitement. I'm NA/3.73 and it's got pep. Probably a turb with 3.73 or up would be giggly.
 
centason said:
Probably a turb with 3.73 or up would be giggly.
Click to expand...

Yeah that's the idea. I was on the hunt for a 4.10 gearset with locker for a while before other things took priority. Now that I've realized how much it hinders a good launch at the strip, it's making its way back up the ladder again.
 
Well this is strange, counted teeth on the old r&p and it's 3.73. Thought the g80 wouldn't swap from a 3.73 to a taller gearset... I might have to swap this thing into the car, just gotta clean the threads up a bit
 
turbotankshane said:
Well this is strange, counted teeth on the old r&p and it's 3.73. Thought the g80 wouldn't swap from a 3.73 to a taller gearset... I might have to swap this thing into the car, just gotta clean the threads up a bit
Click to expand...

It will. I recently put one in a 3.31 rear end.
 
Mileage?? A quick way to check is to mark the drive shaft, mark the tires and turn the tires one complete turn and count the turns of the shaft. That will give the ratio of the rear end without taking the cover off.
 
I'm not horribly worried about what's in it currently except that its definitely taller than the gearing was in the wagon with the same motor and trans. And I need to shave a few tenths off to win a friendly rivalry
 
^they have an ID sticker on the driver axle tube and it is listed in the original owners manual as well.

Towing in 3rd it might get better mileage.

Ive seen optional 3.54 with higher stall speed and trans cooler for towing in 3rd. Extremely rare optional arrangement.

I've only had the swap stick to auto experience with the n/a cars with a 3.31. Drove them a couple days and thought they were fairly hopeless. Small hills on the interstate you couldn't really pull. That's kind of true of the 5 speed 3.31 cars too: Hardly climbs a hill in 5th on the interstate, especially a 245 with stock 185(80)R14 tires. Really healthy high compression B23F I've had are about the only N/A car with enough torque to pull up much of a hill on the interstate, or a really strong '86-'88 car w/manual trans and 3.31.

Try it out, see what you think.
Maybe add optional trans cooler:
http://forums.turbobricks.com/showthread.php?t=301813
/shameless.
 
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