FireRescue

Ok, guys changed the rear diff in my 2005 C6 A4 car from stock 2.73 to 3.42.

Since the swap I have had nothing but problems, p0700 and p0894 codes, limp mode--hard shifts and 3 gear neutraling out.

Are you required to tune the trans after a swap like this or does it auto correct? Could not having it tuned cause the problems mentioned?

I took it to a tuner before I started driving the car a lot and he said nothing needed to be done. All he did was change a rev limit. 3 hours later....well transmission problems.

Thanks

stanger383

yes it needs to have the tcm tuned. rescaling all the shift points thru all tps readings included

FireRescue

Thanks for reply.

Since a tune was not done. Could it account for my transmission problems?

jim2092

I believe that you need to change the rear end ratio in your tune (TCM) so that your speeds and rpms match for shifting your auto transmission or else will play havoc with your shifting.

stanger383

I'm sure it can do all kinds of strange things

Norman Lane

How did you get a 3:42 gear to work in that carrier, I have a 2005 A4 C6 corvette,the only gear that will fit in that carrier is a 3:90 gear, that maybe why you are having transmission problem,and throwing codes

FireRescue

No this is not true. Any 2005 rear diff will mout up to the 2005 auto transmission. I changed out the whole rear diff. Mounts up perfectly.

I believe my problem is the TCM needs to be tuned for the gear change. Having it done as I type. Will let all know the outcome.

Dragracer_Art

Well ? How'd it work out ?

HEADWEST59

Would like to hear how it turns out. I have the same fact. year and trans. Thanks

Crazy4HP

I'm having the exact same issue with my 05 a4. I just recently installed a 3200 stall converter, 3.42 gears, and a beefed up rebuilt 4L65E. I purchased a DiabloSport Trinity and a custom tune from Diablew but he told me he didn't have anything in his software to change parameters for a stall converter and gears. So I drove the car for a couple days and got 3 fault codes: p0700, p0741, p0894. did you ever get the issue resolved?

jim2092

A friend of mine had a lower rear end put into his A4 C5 and he had the same trouble. The speed shop did not change the rear ratio in the tune. I changed it for him and that fixed it. The auto transmission shifts are controlled by speed and rpm's. You can see where a different rear end would play havoc with these parameters. You need a competent tuner to make these changes. Can be done with HP Tuner software and probably EFILive.

FireRescue

Yes, I had to get a tune. If you know what your doing you can use EFI or similar. Best bet to get a competent tuner.

GhostC6

I just had my A4 rebuilt and upgraded and had my converter upgraded and the stall was changed to work with the car and specific upgrades including other standard converter upgrades and am getting the P0700 code after a few trips and key cycles.

When the CEL comes on it defaults to max pressure and I have very hard shifts. I can clear the code, even while driving and it works normal again until it throws the code again.

What exactly did they change or do to fix this for you? I was told in HP Tunes and some others they can turn that code off which prevents the CEL and stops the max pressure which would solve the issue but would like to hear what they did in your case and with what tool or program. Thanks.

jim2092

After installing a new higher stall speed torque converter, changes to your tune may be required to get the shift points, shift firmness, TCC lockup speeds and modulation, spark advance, and drivability improved.

Was this done?

GhostC6

No it was nice not, I don't know a good tuner in my area

dennis50nj

you need to have the converter slippage settings changed to a number it will never reach I had my gears changed to 373 and a couple converters know problems the last converter change was 3800 vig to 3800 yank and it was slipping after a couple brake stalls and shifting hard so i called Norm and he told me what was wrong, Julio was on his way to the track and as i hung up with Norm he pulled up and i told Julio he said no problem and made the adjustments and never had the problem again

GhostC6

How are those changed, and with what tools? Can a transmission guy with a TCM tuner do that or does it need to be HP or Diablo or what? Is this the same as decreasing or turning torque management off?

jim2092

I have several great tuners in Kentucky. Looking for a great one in Tennessee. PM me.

GhostC6

Anyone know a great, good or reputable Tuner in northeast Tennessee around Johnson City, Kingsport, Bristol? I can do as far away as Knoxville if they can do it same day, where I take the car there and hang out while it is getting done then drive it back home.

One that is aware of this type issue and can resolve it?

Question? Would simply disabling the code from being thrown fix the problem? Not simply preventing the light but disabling the code which also prevents the max-pressure and other issues since the code was not thrown?

Thanks again everyone.

brewcitygymratt

Couldn't the TCM tune for gears/stall be done remotely via email with Hp tuners if there are no local tuners. I know I originally used ECS when I was bolt-on only and they were using the EFI Live Autocal for ecm/tcm tuning. Then I purchased hp tuners pro after headers and ported fast 102 for local dyno tune. Then after installing a Circle D stall Circle D recommended I use Pat G for a remote TCM tune via Hp Tuners for the new stall.

Sadly I've probably spent 2k on tunes over the past 4 years as my mod goals changed and I had to transition from EFI live to Hp Tuners pro for better compatibility with tuners.