3.9 vs 3.7

Subafury · Post by **Subafury** » Sat Aug 25, 2007 4:35 pm

i dont know too much about all this ratio stuff- ie what is faster acceleration ? etc. but ive just swapped my gearbox and think it may be a different ratio then the old 3.7 one, as i was having some trouble getting it out of 4wd and it seems to bind up more than usual in 4wd. (or 3wd i should say coz i have one shaft out- welded diff). in 2wd it drives nice.

did the touring wagons (my donor box) come with anything different than 3.7?

also i just tested to see if diff +gearbox spin at same rate. had the car up on a hoist, marked a line on tyres, and drove it in the air and then clamped the brakes. back wheels had spun a bit more than the fronts.

i may just all be in my head tho, as stuff like this has turned out to be nothing before

also i wanna know will this screw things up offroad? or is it better to grab a 3.9 diff too.

rtcb65 · Post by **rtcb65** » Sat Aug 25, 2007 4:58 pm

3.9 is faster off the mark. The bigger the number, the faster off the mark , but less top end. That is where you need to find the balance between torque and speed. Which you wont the most.

I take it that you know what ever you do with the diff , you also have to do to the front diff.

Subafury · Post by **Subafury** » Sat Aug 25, 2007 7:44 pm

yeh im certain its a 3.9 gearbox now. will change tomorrow before 4x4

AndrewT · Post by **AndrewT** » Sat Aug 25, 2007 8:10 pm

Yeah 3.9 is faster accelleration but less top speed. Although from what people say both changes in characteristics are barely noticable between the two types of L series gearboxes.

That gearbox came from my old Touring Wagon. I thought all tourers were 3.7 so due to the rear diff lacking the sticker I just assumed it was a 3.7. I guess either the 1985 models came out in 3.9 or maybe somebody swapped the gearbox in my car sometime over the last 20 odd years.

Either way the matching diff that was in the car is on my driveway ready for you to collect =) Gimme back an moustache bar and top mount sometime, I couldn't be bothered removing them this arvo.

90brumby · Post by **90brumby** » Sat Aug 25, 2007 8:37 pm

u wouldnt no wat ratio gbox u sold me was would ya

AndrewT · Post by **AndrewT** » Sat Aug 25, 2007 8:59 pm

nah I never had that one in a car...I would hazard a guess at 3.9 but really couldnt be sure - Subarino would have the best idea cause he had it in Hatchy for abit but it was a while ago.
Your dad rekoned he could find out by counting revolutions, there is a way - someone on here will know.

BaronVonChickenPants · Post by **BaronVonChickenPants** » Sat Aug 25, 2007 9:23 pm

You can pull the drain plug out and mark a tooth with white paint then count the number of teeth as you turn the input shaft, 39 is 3.9, 37 is 3.7.

Bit of a pain if it's already in the car though.

Also if the diff and gearbox are different ratio then it'll bind up in a straight line within a few metres, if you can drive down the street then its the same ratio.

Jordan.

90brumby · Post by **90brumby** » Sun Aug 26, 2007 12:03 am

BaronVonChickenPants wrote:You can pull the drain plug out and mark a tooth with white paint then count the number of teeth as you turn the input shaft, 39 is 3.9, 37 is 3.7.

Bit of a pain if it's already in the car though.

Also if the diff and gearbox are different ratio then it'll bind up in a straight line within a few metres, if you can drive down the street then its the same ratio.

Jordan.

thats a cool i only fitted it 2day will try 1 of these ways to wrk it out

Matatak · Post by **Matatak** » Sun Aug 26, 2007 12:33 am

Awwww subi will only have an Open Diff tomorrow when 4x4ing
to bad for him lol

hope u get the new one in in the morning

AlpineRaven · Post by **AlpineRaven** » Sun Aug 26, 2007 9:19 pm

So 3.7:1 is better for highway?
Cheers
AP

AndrewT · Post by **AndrewT** » Mon Aug 27, 2007 12:31 am

yep.
although the difference is negligible