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1G Matching gearbox w/ rear differential

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YoYo_4G63

15+ Year Contributor
187
3
Sep 5, 2008
Carolina, Puerto_Rico
Why DSM needs a matching Front Differential w/ the rear Differential? I've read you "can't" use a EVO 1-3 gearbox with DSM 3.54 diff or auto 3.30, neither a DSM gearbox with a EVO 3.90 rear :confused:



Could someone put a link to a thread with info please
 
Explanation is easy. Front and rear ratios must mstch becsuse we have a limited slip center differential. Same reason on a rwd limited slip car you can't run different diameter tires in the rear as a spare. You will burn up the differential in short order.
 
Explanation is easy. Front and rear ratios must mstch becsuse we have a limited slip center differential. Same reason on a rwd limited slip car you can't run different diameter tires in the rear as a spare. You will burn up the differential in short order.

But what if my center is welded?

You can change these ratios so that they match. Itv4equires complete transmission disassembly.

(I have EVO gearbox)
I tought, to swap an auto rear diff ring, to make the rear 3.90 instead of change the front differential.

Auto is 43/13 ...Std is 39/11, so if I use the 43ring w/11pinion it should be 3.90 right?
 
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The gears are cut differently. One gear set will have thicker or thinner gears with a longer or shorter toot and larger or smaller valley between teeth. Facts are facts. I don't have to try it to understand it won't work.
I don't have a link. Just do a quick Google search and there is plenty of info.

Ohh ok I see :thumb: thanks.

But!!! could've be something wrong, if I have a welded center, using my rear 3.54 with the evo gearbox
 
differential gears need to be replaced as sets
sp just replace ring and pinion to match
 
But what if my center is welded?



(I have EVO gearbox)
I tought, to swap an auto rear diff ring, to make the rear 3.90 instead of change the front differential.

Auto is 43/13 ...Std is 39/11, so if I use the 43ring w/11pinion it should be 3.90 right?
Even worse if your center is welded. The car wont even roll. The very nature of a differential is well...that it differentiates speed differences from one side to the other. In the case of the center its front to back.
Whatever you choose it needs to match.
 
you can just replace the front diff in your tranny with the dsm one

or track down an evo ring and pinion, stick it in your car not easy or cheap
 
Last edited by a moderator:
Even worse if your center is welded. The car wont even roll. The very nature of a differential is well...that it differentiates speed differences from one side to the other. In the case of the center its front to back.
Whatever you choose it needs to match.
Well the car drives normally, maybe the EVO gearbox have a DSM front diff already :/ is there a way to know, like spining the wheels x turns, without removing/opening the gearbox ?
 
There is a way to sort it out. I dont remember remember the exact method but you can remove the transfer case and then rotate the shaft or the wheel a certain number of times before the other makes one complete rotation. That tells you the diff ratio. I think you can find the video on jacks transmissions if it's still there.
 
tcase ratio must also match.
DSM 3.54 has
57 tooth ring in trans matches 1.074
58 tooth matches 1.090
for EVO 3.909
63 mates to 1.074 case
64 mates to 1/090 case.

then with EVO only the trans with non-LSD do ring gears swap with DSM. if you have a LSD trans the DSM ring ger will need machining to fit LSD.

the EVO LSD also uses special long CV cup. without this long cup the axle will pop out.
 
There is a way to sort it out. I dont remember remember the exact method but you can remove the transfer case and then rotate the shaft or the wheel a certain number of times before the other makes one complete rotation. That tells you the diff ratio. I think you can find the video on jacks transmissions if it's still there.

Ohh ok... I'm going to search that, thabks

tcase ratio must also match.
DSM 3.54 has
57 tooth ring in trans matches 1.074
58 tooth matches 1.090
for EVO 3.909
63 mates to 1.074 case
64 mates to 1/090 case.

then with EVO only the trans with non-LSD do ring gears swap with DSM. if you have a LSD trans the DSM ring ger will need machining to fit LSD.

the EVO LSD also uses special long CV cup. without this long cup the axle will pop out.

Is a EVO I non LSD
 
if your rear diff is non lsd and you have a welded cd you should be able to lift one side of the car and turn one wheel and watch the other
in neutral
ive never done this but it should work
ive never had welded cd so ive never tried
its really a big issue with dsm our cars are old you never know what combo might be in them
 
if your rear diff is non lsd and you have a welded cd you should be able to lift one side of the car and turn one wheel and watch the other
in neutral
ive never done this but it should work
ive never had welded cd so ive never tried
its really a big issue with dsm our cars are old you never know what combo might be in them

I did that and both tires moves
 
haha
the idea is to check if they move the same amount
mark the tires and rotate a few times see if they match
 
Anyway I ended up, removing the gearbox today. I'm going to change the diff. Thanks to all for the help
 
even if you have a stock lsd rear itll still turn

if you dont have a welded center diff this will not work as a method of measuring, or everybody would do this
 
did you even check the rear diff?
maybe whoever put the evo trans in it changed the rear diff too
 
haha
the idea is to check if they move the same amount
mark the tires and rotate a few times see if they match
Yes the did rotate at the same time
haha
the idea is to check if they move the same amount
mark the tires and rotate a few times see if they match
Yes they do rotate about the same time, I marked both tires etc
 
then why pull the trans?
sounds like you dont have a problem
it probably has a dsm front diff in it already
i personally have done this swap, its out there somewhere there is probably many around
 
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