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Is the 3.31 final gear too tall for my 19t and AW71?

D

DET17

Reformed SAABaholic
Joined
Nov 1, 2009
Location
NW Georgia
Just began today with a surgical reconstruction of the DD, my 940 that has served me well the last 4 years.

Of course the 3.73 final gear is presently installed in the 1041 Dana..... Volvo seems to have chosen this ratio for all the turbo 7's and 9's with the AW71. I'm sure they had their reasons to do so.

I've got a low mile '92 complete rear end fitted with the Eaton LSD and ABS tone ring (a rare bird); my current plan is to pull the LSD, remove the 3.31 ring gear and install the 3.73, set the backlash & preload those carrier bearings. Much less aggravation to just install the carrier, rather than the full pinion install.

With her sky high sitting on 6ton jackstands, I wondered if the complete 3.31 rear end assembly swap wouldn't be less work... perhaps? I've set up ring & pinions, so no worries there. I know the 3.31 final gear would give some relief to my 70mph cruise RPM of 3100.

However I wonder if the planned 19t turbo will be negatively affected by that tall final gear.
I'm guessing that the last 2 series cars with the B21 turbo didn't offer an automatic option.... but I don't know that for a fact. If they did, were they also fitted with the 3.73?

Anyone tried it? Please share your experience.
 
Keep the 3:73 I went tru this. The 331 seem to lug the motor while the 3:73 seemed to keep it just on the edge of the sweet spot. Mpg also suffered. I reinstalled the 3:73 and swapped the carrier to keep the alb and correct speedo.
 
Well I had forgotten the granny first gear in the AW70/71..... must have had 700r4 on the brain (first gear is 3.06)

From WIKI:

Gear Ratios

Gear AW70/71 AW72
1st 2.45 2.83
2nd 1.45 1.49
3rd 1.00 1.00
4th 0.69 0.73
Rev 2.22 2.70

Typically first gear * final gearing = 10~10.5 for a performance application

The AW70/71 provides 2.45 * 3.73 = 9.14, still a bit low of target

The AW70/71 provides with OPTIONAL rear gear is 2.45 * 3.31 = 8.11, really low

The AW72 looks better yet with 2.83 * 3.73 = 10.55, right on target

I'll keep the 3.73 final gear and watch for a 95 AW72 at my local PnP ;-)
 
^Correct for USA market.

If you don't tow in 3rd a lot, I didn't notice much (if any) actual difference in cruise RPM (and really no MPG difference) with the 4.10 axle which I liked in the turbo car everywhere else with the auto.

16V converter and AW-71L with a 4.10 is nice if you want to have a nice compromise for power and economy. I thought the converter lockup speed and shift points were weird with the 3.73 and considered the 4.10 basically mandatory with a stockfish B230FT car with the AW-71L. The 8V stock AW-71L converter is woefully dreadful for performance use. Good for N/A MPG though....just very, very slow.
 
Kjets On a Plane said:
16V converter and AW-71L with a 4.10 is nice if you want to have a nice compromise for power and economy. I thought the converter lockup speed and shift points were weird with the 3.73 and considered the 4.10 basically mandatory with a stockfish B230FT car with the AW-71L. The 8V stock AW-71L converter is woefully dreadful for performance use.
Click to expand...

By the numbers, the 4.10 final gear with the AW71 first gear 2.45 is nearly at the performance target with 10.05 torque multiplication. K-J is right, with the lockup converter of the AW71L it would balance out nicely with that final gear.... better performance "running thru the gears" and cruise OD nearly same as a plain Jane AW71 and 3.73 final. If you know the P/N for the 16V converter, would be nice to have in this thread. Perhaps TASCA can still get it.....

Was it the 960s that got the 4.10?
 
a 3.31 rear end with a bigger then stock turbo and hotter then a T-cam in the head will be a dog to drive in top gear. 3.31 is way to tall.
if you want to accelerate from 50 to 75mph in top gear you will be forced to downshift because in top gear the engine will not turn in boost-rpm-range. If you mash the throttle in top gear you will be waiting, waiting, waiting for the boost to kick in and the real boost will only start building at speeds in excess of 75mph. That gets annoying realy quick.
3.73 is nice but a 4.10 will make the whole car even more punchy and enjoyable to drive. That would be my choice.
 
DET17 said:
....the 3.73 final gear is presently installed in the 1041 Dana..... Volvo seems to have chosen this ratio for all the turbo 7's and 9's with the AW71. I'm sure they had their reasons to do so..... I know the 3.31 final gear would give some relief to my 70mph cruise RPM of 3100.
Click to expand...

3.73 is the shortest diff for your carrier, 3.91, 4.10, 4.30, etc. has a different carrier.

So you have AW71, 3.73 and that gave you cruise rpm of 3100 @ 70mph? That seem very wrong to me. Speedo, Tacho or Gearbox has a problem. With my 205/60x15", AW71 + 3.73 = 2670rpm, which is 16% less, very wrong.
 
Janspeed said:
a 3.31 rear end with a bigger then stock turbo and hotter then a T-cam in the head will be a dog to drive in top gear. 3.31 is way to tall.
if you want to accelerate from 50 to 75mph in top gear you will be forced to downshift because in top gear the engine will not turn in boost-rpm-range. If you mash the throttle in top gear you will be waiting, waiting, waiting for the boost to kick in and the real boost will only start building at speeds in excess of 75mph. That gets annoying realy quick.
3.73 is nice but a 4.10 will make the whole car even more punchy and enjoyable to drive. That would be my choice.
Click to expand...

Agreed, I think 3.73 for T cam, 4.10 for a decent street cam.
 
B20Paul said:
3.73 is the shortest diff for your carrier, 3.91, 4.10, 4.30, etc. has a different carrier.

So you have AW71, 3.73 and that gave you cruise rpm of 3100 @ 70mph? That seem very wrong to me. Speedo, Tacho or Gearbox has a problem. With my 205/60x15", AW71 + 3.73 = 2670rpm, which is 16% less, very wrong.
Click to expand...

Volvos all use the "3.73+" D30 carrier. They make up the difference with the ring gear thickness...

Ratios are pretty close on the O3-71 gears 1-3, except OD is a big jump from 3rd.
 
3.31 isn't that rare, 960's have em, some 940's got em, etc.

I swapped one in to offset the .75 OD from the 4L80e
 
B20Paul said:
So you have AW71, 3.73 and that gave you cruise rpm of 3100 @ 70mph? That seem very wrong to me. Speedo, Tacho or Gearbox has a problem. With my 205/60x15", AW71 + 3.73 = 2670rpm, which is 16% less, very wrong.
Click to expand...

Nice catch B20! Bad case of brain flatulence.... I was thinking of my 70 Malibu with TH350 and 3.55 final gear (3100 RPM at 70)

Here is the calculation from my Excel spreadsheet of trans. & gearing options for my 940; this option the AW71 and various final gears. Actually with the 3.73 final it calculates out just above 2400 RPM:

AW71%20rpm%20finalgears.png
[/URL][/IMG]

Last night I pulled the G80 out of the installed 1041, and it slid out with not much of a pull (preload on carrier bearings). Couldn't have been an .006" preload on those bearings, as is spec'd in the greenbook. Then I went into the donor 1041 with the 3.31 and removed this:

DSCN7385.jpg
[/URL][/IMG]

Now THAT guy had some preload! It took a good grunt with a pair of levers to disengage it from the housing. As K-J noted, this carrier should be good to accept all the Volvo ratios..... so that has me in a quandry. This discussion about how "peppy" the 4.10 final would be in my application..... only costs me another 240 rpm at 70mph cruise while hitting the performance target torque multiplication value of 10.05. DAMN it, y'all have me thinking to go find a boneyard 4.10!!!! I'm only 14 bolts away from having the 1041 housing out.

However, if the only donors are NA 740s and 940s, those have become suddenly scarce in these parts. I thought for sure there was also a 960 fixed axle that came with the 4.10 final gearing. The window is open right now, as I could put the rear work on the back burner while I source one. All help appreciated to confirm the exact suitable donors..... :nod:
 
I've got one in the back end of a 1990 740. swap the diff cover, chunk, and ring gear and roll out.

*to clarify, I've got a rear end. I've got no plans to use another volvo 4.10 any time soon for any of my current or future projects
 
Keen observation Simon! The G80 is sittin' on my workbench. Yup, only one of them thar' 48 tone ring LSD's that I've seen.

"Hoping" the AW71 will protect those cross shafts from exploding..... or I might as well install the TrueTrac 588.
 
cosbySweater said:
N/a lh2.4 740s and n/a 940s got them iirc. I think I still have a 4.10 r&p if you are interested
Click to expand...

verified, +1 on 940 na for sure, no more single tire fire.

personally, most fun gear there is. I love the mechanical advantage in the 60ft, never looked back since i put the na rear in my turbo wag. i dont know if anybody really commutes these cars much(distances), phuck miles per gallon. Smiles per gallon is where its at.
 
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