I have a 1997 A6, 2.8 Quattro Wagon. It's got the ZF 4HP18 4 speed auto tranny with no torque converter lock-up. Hence there is always some slip. I'm seeing 13% slip at 65mph. (3000 rpm instead of 2600 rpm). Is this normal or high? (105,000 miles on this tranny). Can anyone else post their RPMs @ 65mph? (With standard size tires).

Simon

 

If I'm in 5th gear going 65mph my RPM's without my foot on the gas, stay around 2,000 - 2,100 RPM's. If you release your foot off the gas and your RPM's drop down suddenly your TCC solenoid probably locked itself to prevent further transmission damage.

TCC's going bad in 1998-2004 V6 Auto Tanz Audi's is unfortunately common. Got mine replaced at 125,000, cost $1,500! But it shifts like it's brand new now.

If you don't have P0471 code you should be good, change the trans fluid, filter & clean the pan. Audi claims its "lifetime" fluid. But they tell many fairy tales of such nature. Bastards.

 

I looked at buying a newer C5/A6 like yours, and calculated the correct RPM at 65 to be about 2200. The C5/A6 has a ZF 5HP19 tranny, which has a lock-up. My older C4/A6 has the ZF 4HP18 tranny, which as far as I can tell does not have a TCC (lock up clutch), hence will always be slipping somewhat.

Apparently there is a rubber seal in the 5HP19 tranny that was poorly designed and goes bad, leading to the TCC slip - make sure when it's changed that you put in a revised seal to ensure it doesn't happen again.

Audi calling it 'lifetime' fluid has destroyed many transmissions. Even quite a few Audi dealers believe that 'lifetime' fluid does not need to be changed. The ZF recommended interval is 40k miles! Don't skip changing the fluid!

 

The C4 auto tranny does lock up. My 1993 did anytime I was driving on the highway or at a steady speed in 4th. If yours is not locking up then something is wrong. It has been so long since I owned it I no longer remember the revs at 65mph.

 

How did you calculate the rpm? At 65 my car reads about 2400 fwd

 

For your particular car and tranny you need to know the gear ratio for top gear, the gear ratio for the final drive, and the tire size. There are calculators online that will calculate tire RPM given the size for any speed. Then divide the tire RPM by the 2 gear ratios, and you have the theoretical speed at the engine if nothing is slipping.

 

What car was your 1993? I'm pretty sure there is no lock up clutch in the ZF18HP - at least I don't see one in this service manual:

http://www.transdetail.ru/assets/sit...ch%20Guide.pdf