honda-guy

iTrader: (55)

does anyone know the rear diff gear ratio for an Evo 7 and Evo 8?

i got a used t-case and from what Shepherd told me (sent him pics), it has Evo 7 ring and pinion. he told me to count the teeth and get the gear ratio of the t-case.

here's what i came up with.
original evo 8 t-case has: 43/13 = 3.30769
t-case with Evo 7 ring/pinion: 53/16 = 3.3125

i need to know the rear diff gear ratio of an Evo 7 to determine if the speed difference between the front and rear wheels, and will the speed difference large enough to cause problems.

thanks,

honda-guy

iTrader: (55)

^^^ up

honda-guy

iTrader: (55)

some one has to know where i can get the info.

94AWDcoupe

iTrader: (125)

the ratios you posted shows the evo 7 t-case is different ratio than 8. this means the centerdiff in the tranny will be spinning all the time to make up the difference between front and rear. its not designed for that and will likely lead a very short life. not sure how knowing the evo7 rear diff ratio would even help. the evo7 has active rear. the ring and pinion from it may not even swap into the 8 housing. Thats assuming the ratio of it would correct the offset.

honda-guy

iTrader: (55)

the difference in the t-case gear ratio is 0.00481, not sure if that’s a big enough difference. i want to figure out the speed difference between the front and rear wheels at cruising speed (75-80 mph). since the rear wheels will spin faster than the front wheels with the new t-case gear ration, it could possibly make the car more rear wheel drive bias. and considering that my center diff is viscous coupling, so it's not fully locked like ACD would be. viscous coupling only start to lock when there is a great difference in speed. this is all theoretical btw.

UT_Evo

iTrader: (5)

If a structural support beam on a bridge is off by .00481 inches the bridge is likely to collapse... Just food for thought. But if the way you describe it works and it just sends more power to the rear than the front you'll end up with exactly what you described (course, that's obvious, so I haven't been much help)

honda-guy

iTrader: (55)

if my math is correct (using 24" tire diameter), the speed diffrence between the front and rear wheels at 60 mph is .288 mph.

honda-guy

iTrader: (55)

This info is for reference in case someone else wants to know.

Shepherd did get back to me and confirm that rear diff gear ratio is the same for the Evo 5,6,7,8 with 3.307 and Evo 4 has a 3.323 rear diff.

So, it would be ok for me to use this t-case with Evo 7 ring and pinion gear.

Mauricio Evo IV

iTrader: (1)

Back to the life this thread.

In my case, I put it in my Evo 4 rear diff (3.323) an Evo 9 rear diff (3.125 I think).

The rus fine until I made the firts launch. I broke some parts (open diff), I broke before too with the original parts (AYC read diff). But I dont´know if this was the problem....

barneyb

Driving in a straight line on a smooth surface, all the wheels are moving at the same speed. The only thing running due to any difference in gearing would be the center differential.

94AWDcoupe

iTrader: (125)

gotta update my original post because I cant believe I wrote what I did. so here is the update.

there is no such thing as having a ratio mismatch for evo 4-9.

43/13 = 3.30769 and 53/16 = 3.3125. the two ratios only differ by .0048! they are the same! all four tires need to be same height on all wheel drive car. otherwise the center diff spins all the time to make up the difference. that is true. but front tires get smaller faster because they are turning sideways as well as rolling forward. so tires should be rotated frequently. the factory manual for early eclipses states tires can be up to 1/8th in diameter difference.

not gonna do the math for you but driving 200 miles without rotating tires would be more harmful to center diff , than a rear end to tcase mismatch of .0048. a mismatch tire set of 1/8 inch creates .4125 mismatch front to rear.

so even if you dont know what your ratios are worst case scenario is you have a .0048 mismatch . these are the possibilities tcase to rear:
3.125 and 3.125 perfect match
3.125 and 3.307 .0048 mismatch
3.307 and 3.125 .oo48 mismatch
3.307 and 3.307 perfect match

shane_evo7

I'm having a dilemma and I really need some help.

I have a evo 7 with oem acd tcase.
it needed to be rebuilt so i bought a new oem ring and pinion from Jack's trans.

from what i saw online i thought the evo 7,8,9 had the same ring and pinion bearing.

but the pinion gear is rubbing on the inside of the tcase and the shop cant reassembly the and install the tcase until its sorted out.

does anyone know what my issue might be?
the ring and pinion should fit fine shouldn't it?


Thanks for any input!

kaj

iTrader: (60)

Anyone want a Cusco RS 1.5 way rear diff? It eliminates AYC. New in box. Half price.
yeah...shameless plug...

barneyb

Reading through this old post I find all the worry about the center diff humorous. Hit a dip and the front wheels now have to travel a longer distance than the rear wheels and the center diff runs. Next the rear wheels hit the same dip and the same thing happens. In my town with crummy pavement and lots of winter the roads are heaved like a test track. My center diff should be destroyed according to common knowledge.