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View Full Version : JHM 4:1 diff tiptronic install



Flexcj5
09-26-2013, 01:13 PM
JHM has a great write up for the manual trans and tip isn't much different but here it is.

Tools:
3/8 drive ratchet
Two long extensions (wobble head helps)
T40 torx
6mm Allen
Bfh
Fluid transfer pump

Remove the 6mm Allen bolts holding the driveshaft to the tail housing, then attempt to remove driveshaft. Most peoples will require some coaxing from a hammer. Mine required 2 days, 2 cans of pb blaster, and finally an air hammer for ten minutes. It was completely seized/rust welded.

Once driveshaft is unbolted you can begin removing the 6 t40 bolts that hold the tail housing to the trans. 5 are fairly easy with the extensions. The very top bolt is a bit of a pain but it will come out.

When the bolts are mostly out, put a drain pan under the housing and break it loose from the trans. Gear oil will drain into the pan. About a quart I believe.

You can now remove the torx bolts entirely and slide the housing and diff off the tail shaft. It comes straight back a good ways and is fairly heavy so go easy.

Rear of trans
Note there is no spring like the manuals have
http://img.tapatalk.com/d/13/09/27/3ydyza6y.jpg

Diff inside housing
http://img.tapatalk.com/d/13/09/27/uta9u3an.jpg

Empty housing
http://img.tapatalk.com/d/13/09/27/asu6ejad.jpg

Old diff will lift out of housing and new one drops in onto the splines. Below is the JHM.
http://img.tapatalk.com/d/13/09/27/je9eremy.jpg

Install is reverse of removal. Fill the diff from the plug on the passenger side. Fluid pump makes it easier.

Driving impressions:
Butt dyno says torque transfer off the line feels very different, rear squats more under load. I'm gonna adjust my bilsteins to compensate for it.

The good:
Sharp turns from a stop (red lights) under hard throttle feel good. Very little under steer, hooks we'll and pushes through. I was squealing tires at wot. Mountain roads are a different kind of fun with this diff. It's closer to a rwd car handling wise. Highway driving and normal around town feel the same as it always has.

The bad:
I kind of expected this and it's hard to describe. Diff feels/sounds clunky. You definitely know it's there at low speed turns. It has the ratcheting feel of a locked rear end being used on the street.

I expect to see a lot more wear and tear on the rear end itself, cv axles and diff mount.

Would I recommend this mod? ABSOLUTELY! If you enjoy the twisties and spirited driving go for it. Car is a different beast now.

CorneliusRox
09-26-2013, 01:24 PM
Is that easy or what!

LoKisSpYdR
09-26-2013, 01:56 PM
Impressions after driving? Worth it? Remove understeer?

Audibot
09-26-2013, 02:00 PM
Good write-up! Bookmarked for when I [eventually] do this.

One question: I'm guessing all the lube on the gears stays in place when reinstalling?

DRAKLORE
09-26-2013, 02:07 PM
Awesome job Brad!

Flexcj5
09-26-2013, 02:55 PM
Lube on gears is assembly lube. It's fine to leave it there.

I haven't driven the car yet as I'm doing the apikol diff mount and replacing a front axle. Should be back on the ground tonight. I'll update everyone then.

Jake@JHM
09-26-2013, 03:51 PM
Looking good man! Thank you for sharing. [up]

Jake

CLEANA3
09-26-2013, 08:55 PM
Can't wait for your review

AudiTFSI3o3
09-26-2013, 09:09 PM
OP, how often do you track your car?

mec
09-26-2013, 10:49 PM
Deeeeecent! Nice writeup, looking forward to the build :)

Flexcj5
09-27-2013, 06:18 AM
Original post edited for more info

Flexcj5
09-27-2013, 06:34 AM
OP, how often do you track your car?

I rarely have time for track days with my job but spend a lot of time in the mountains of the east coast. I'll be making another trip to the Dragon very soon and will report back.

Flexcj5
12-18-2013, 05:45 PM
Well, three months later I have absolutely nothing but love for the 4:1 diff from JHM.

It corners well, handles mountain roads incredibly well and I really can't tell it's there for around town driving.

I haven't noticed any extra wear or nuances from the tiptronic trans either.

Jake@JHM
12-18-2013, 06:15 PM
Well, three months later I have absolutely nothing but love for the 4:1 diff from JHM.

It corners well, handles mountain roads incredibly well and I really can't tell it's there for around town driving.

I haven't noticed any extra wear or nuances from the tiptronic trans either.

Glad to hear you are loving it! [up]

Jake