93 leg 4EAT, Transfer ratio????

[Gloyale]

Quick ? about 4EAT tranfer gear ratios.

 

Some are 1:1, these type have excactly the same ratio rear diff.

 

others are under or overdriven IIRC SVX had 3.7 front and 3.54 rear???

3ats commonly had 3.7front/3.9 rear or 3.45front/3.7rear

 

 

I need to know, for a 93 Legacy 4EAT, with a 3.9 rear end what is the front diff ratio? Does it have other than 1:1 transfer ratio???? Listed in specification chart of the FSM

 

Want to know why, read my thread in the retrofit forum

http://www.ultimatesubaru.org/forum/showthread.php?t=84923

[Legacy777]

Yes, the 93 legacy 4EAT uses a 1:1 transfer gear. The front diff is also 3.90

[Gloyale]

Ok. Update. I counted today and as I originally suspected:

 

EA82 turbo 4EAT number of teeth ring/pinion = 37/10=3.7

 

EJ22 (legacy) 4EAT number of teeth ring/pinion = 39/10 =3.9

 

These numbers match the rear diffs for the respective cars. So it appears for at least these 2 models of 4EATs, The transfer ratio (or 1st reduction ratio a the FSM term it) is 1:1.

[idosubaru]

what do you make of that email then - you think that guy is mistaken?

 

or some EJ trans are different?

 

or being a trans from another country?

[johnceggleston]

my experience is limited to my legacy & outbcak, but i've never read or heard of the front and rear final drives being different. not in a sbuabu or any other car for that matter.

 

do some cars really do this? i can see where the right transfer ratio and the right final drive ratio could make it work, but what would the advantage be?

[Legacy777]

In the newer cars, the 02 WRX and I believe the newer models as well have an effective final drive ratio of 3.90

 

In the transmission though, there is a 1.1:1 gear reduction, so the rear diff ratio is 3.545. If you take 1.1 and multiply it by 3.545 you get 3.889 or something like that. I believe subaru did this to help reduce gear noise.

 

Also, the SVX did not have a 1.1:1 gear reduction to my knowledge. The final drive ratio was 3.545.

[idosubaru]

In the transmission though, there is a 1.1:1 gear reduction,

in which transmissions? does this effect swapping the front diffs?

 

i will be swapping an EJ automatic into an XT6 and trying to retain the XT6 3.7 final drive.

[Gloyale]

in which transmissions? does this effect swapping the front diffs?

 

i will be swapping an EJ automatic into an XT6 and trying to retain the XT6 3.7 final drive.

 

It was a no go for me. I had to swap the 3.9 diff from the EJ into my EA bellhousing/case.

 

Different ring and pinions.

 

 

I suppose if one wanted to keep the 3.7, you COULD have swapp the pinion shafts to keep the 3.7. that way the 3.7 diff could stay in the EA housing but you would have to get proper shims for the Pinion shaft, unless you got real lucky and it just fit perfect.

[idosubaru]

i'll probably have a shop do the diff swap, sounds over my head.

[Gloyale]

i'll probably have a shop do the diff swap, sounds over my head.

 

Other than being REALLY messy, It's not that hard.

 

The hardest part is setting the backlash for the R+P. I haven't finished this yet(waiting for stub shaft seals)

 

But unbolting the bellhousing and swapping diffs is easy. You could do that part and take it to a shop to adjust the backlash if you were worried. I may end up having a hop double check mine before it goes back in.

 

If you have a shop do the whole thing, I would go the extra mile and swap pinion to keep the 3.7. I actually will benefit from the 3.9 gearing for my bigger tires.

[idosubaru]

i'll have to ask more when i get there, but i'll be bolting the XT6 front diff to the EJ transmission. i take it that's not a direct swap - remove EJ front diff and install XT6 front diff?

 

i'll do as much as i can myself if it's straight forward and easy, then have the shop double check the backlash. i'm not interested in spending a ton of time on it so if it gets intense i'll pay someone else.

 

do they do that with the entire transmission in hand bolted back together or can they do that with just the front diff in hand? they use those axle stub retainers to adjust the backlash and what exactly is being measured? i can't imagine access to measure anything with it all bolted back together.

[Gloyale]

i'll have to ask more when i get there, but i'll be bolting the XT6 front diff to the EJ transmission. i take it that's not a direct swap - remove EJ front diff and install XT6 front diff?

 

Swapping the EJ diff into the xt6 Bell housing is easy. Everything but the front portion can be left intact. All nessecary adjustment is done using the screw in bearing retainers on the, after swapping in the EJ diff.

 

Swapping the XT6 diff would require using the XT6 pinion shaft as well. Removal of the tail section is needed to get the pinion shaft out. Maybe a good time to put in new transfer clutches? But if the pinion shafts are even a few .000s different length, new adjusting shims need ordered and fitted. 100% doable though.

 

 

do they do that with the entire transmission in hand bolted back together or can they do that with just the front diff in hand? they use those axle stub retainers to adjust the backlash and what exactly is being measured? i can't imagine access to measure anything with it all bolted back together.

 

They either need the whole trans on the bench, or more ideally the diff section and the front pump w/pinion shaft installed. What is being measured is the excact *centering* of the ring gear to the pinion gear.

 

The centerline of the pinion shaft lies on excacty one vertical plane, perpendicular to rotational axis of the differential.

 

Using the bearing retainers, the ring gear must be positioned excactly on the plane of the pinion gear. And also, should have just a hair(.012) of movement side to side. In otherwords the bearings should only be *just so* tight.

 

It all sounds harder than it is.

[johnceggleston]

someone posted a great write up on it pictures and everything. i thought i bookmarked it but i can't find it now.

 

in a nut shell you adjust the ring gear assembly from side to side untill you get it bear just right onb the pinion gear. they sell some stuff to apply to the gear teeth so you can see where they are bearing. then you back off one side a certain amount and tighten the other the same amount to move the ring gear a little in one direction. then you lock down the retainers.

 

this give you the right clearence, and the right wear on the teeth.

[johnceggleston]

gary, i found the info, but it's a pdf file. send me your email and i'll send the file title: transaxle assembly.

[Gloyale]

gary, i found the info, but it's a pdf file. send me your email and i'll send the file title: transaxle assembly.

 

Can I get a copy of that too? sent to:

 

LoveYourSubaru@yahoo.com?

[idosubaru]

gary, i found the info, but it's a pdf file. send me your email and i'll send the file title: transaxle assembly.

grossgary

(@)

yahoo

(dot)

com

[johnceggleston]

grossgary

(@)

yahoo

(dot)

com

mail sent, both.

 

in addition to the assembly instructions, there is some heplful tips on the last 2 pages after the exploded parts views.

 

a question you'll soon know the answer to, is the pinion in the 3.7 different than the pinion in the 3.9? the gearing difference is the 37 vs. 39 treeth on the ring gear, the question is did they make a different 10 tooth pinion to match. it sounds like they did according to gloyale.

 

same question applys to the 4.11 vs 4.44 in the legacy auto (9/37) vs. outback auto (9/39). does the different size ring gear need a different size pinion tooth. it seems a no brainer that they would use the same 39 tooth ring in the 3.9 you're working with and the outback auto.

 

obviously this is an engineer/parts question but i'd check before i pulled the pinion. it sounds like a lot of work.

[Gloyale]

a question you'll soon know the answer to, is the pinion in the 3.7 different than the pinion in the 3.9? the gearing difference is the 37 vs. 39 treeth on the ring gear, the question is did they make a different 10 tooth pinion to match. it sounds like they did according to gloyale.

 

 

Both use a ten tooth pinion, but the excact bevel and pitch of the teeth is different, to match the respective ring gears.

 

It's not a difference you can see. It's tempting to think they are the same and don't need to stay matched. But from everything I've read, they are not.

 

Think about it, to fit 39 teeth on the same diameter ring a the 37, the excact size and pitch of the teeth have to be changed. The pinion must match this pitch excactly.

[Legacy777]

in which transmissions? does this effect swapping the front diffs?

 

i will be swapping an EJ automatic into an XT6 and trying to retain the XT6 3.7 final drive.

 

The one from the 02+ WRX

 

If you're not using one from a 02+ WRX, you don't need to worry about the rear transfer gear ratio not being 1:1

[Gloyale]

The one from the 02+ WRX

 

If you're not using one from a 02+ WRX, you don't need to worry about the rear transfer gear ratio not being 1:1

 

Cool, good to know.

[the_postie]

Swapping front diffs on ej auto's is easy.You can even swap ratio no probs,4.44 or 4.11.The pinions that came with the diff gear stays with it.You don't even need to reshim etc.Basically if going from 4.11 to 4.44

you use the donor 4.44 diff housing complete and you keep the pinion gear/shaft and bearing and shims from the 4.44 .The hardest part is believing you can do it.Shoot me down if you like.I have and know of several boxes built this way with plenty of miles and still running strong.

[johnceggleston]

the difference between the 97 legacy 2.2L auto with the 4.11 final drive w/ 195/70/14 and the 97 outback 2.5L auto with the 4.44 final drive w/ 205/70/15 is none. the difference in the final drive ratio is made up for in the tire size.

 

so if you put the right size tire on the svx you might be able to live with the 3.9 ratio. this, of course would be the easy solution not the best. 2 tire sizes would more than do it, one tire size would would almost do it (roughly 60%). if there is enough tire clearance it might work. so if you didn't need to swap the bell housing to fit the engine maybe you could save some work.

 

just a thought. probably no clearance and it might look funny too.

[Gloyale]

Swapping front diffs on ej auto's is easy.You can even swap ratio no probs,4.44 or 4.11.The pinions that came with the diff gear stays with it.You don't even need to reshim etc.Basically if going from 4.11 to 4.44

you use the donor 4.44 diff housing complete and you keep the pinion gear/shaft and bearing and shims from the 4.44 .The hardest part is believing you can do it.Shoot me down if you like.I have and know of several boxes built this way with plenty of miles and still running strong.

 

Well, I don't know about not needing to shim. I suppose if you get lucky and the excact length of both cases is the same, you could get away with it. Also the excact spacing of the pinion shaft centerline to the ringgear is CRITICAL.

 

I would never reassemble a diff without at least rechecking the backlash. All of my experience shows me that it's rare that no adjustment i needed. Every pinion shaft and every diff/ringgear is slightly different, and should have all clearances verified and adjusted. ALWAYS.

 

In this case I am not only changing ratios, I am using the EJ trans with an EA motor. So the Bell from my GL turbo is needed.

 

It's true, I could have swapped the 3.7 pinion shaft from the GL trans, and kept the 3.7 diff in the housing. But I wanted the 3.9 so I left 3.9 Legacy pinion in the legacy trans. I installed the 3.9 diff into the GL(ea82t) bell housing.

[Gloyale]

the difference between the 97 legacy 2.2L auto with the 4.11 final drive w/ 195/70/14 and the 97 outback 2.5L auto with the 4.44 final drive w/ 205/70/15 is none. the difference in the final drive ratio is made up for in the tire size.

 

Well, there absolutely is a difference in the ring and pinions, and the final gearing.

 

I see you're point however,that the overall RPMS would be similar at the same speeds based on the bigger tires. That is excactly what I want. This is going into a GL Turbo with 27x8.50s on it. It originally had a 3.7 final drive. Swapped to the Legacy 3.9. The lower ratio will help me turn my larger tires.

 

so if you put the right size tire on the svx you might be able to live with the 3.9 ratio.

 

I'm not putting this in an SVX. I mentioned it as a reference to the overdriven transfer ratio some 4EAT and old 3AT used.

[idosubaru]

Also the excact spacing of the pinion shaft centerline to the ringgear is CRITICAL.

i only know of one person that has done this to an XT6 - i gave him the differential to do it. it didn't last very long, i assume he didn't get something set right.