iowaan

I'm having a problem starting out from a stop. Starting a couple weeks ago and possibly getting more frequent, in drive the car won't move for a half second, then jumps into gear with a bang.

i checked the transmission oil level with the engine running, a small amount came out at ~40C.

I checked with the Ross-Tech tool and there are no codes, but i was fooling around with the transmission measuring blocks and noticed one time after shifting into D, the input speed was 0, then i got the bang and i had input speed about half the engine rpm. Later, input speed was always the same as the engine. What's up with that?

I bought this car about five years ago with ~100,000 miles on it. i changed the transmission oil and filter, and wiped out the sludge in the pan. I have about 20,000 miles since then.

SloopJohnB@mac.com

The 5speed auto has 5 or six solenoid-operated valves (one for reverse?) that you can see when you drop the pan….wires lead up to them, etc., on the valve body. The transmission speed sensor is on the top side of the valve body…you drop the valve body to get to it and to remove/clean out the solenoid-operated valves.
One guy on the forum has done this and posted pics.

STF

iowaan

i suspected sticky solenoids first. i found this pdf showing the solenoid locations and which ones operate for each gear: http://vwts.ru/pps/pps_951903_01v_01...ssions_eng.pdf

removing the solenoid valve cartridge and physically removing the deposits is the only way to cure this?

the input speed sensor failure would cause this problem? it only occurs after a complete stop. it bothers me that there were no codes, if the sensor or its wiring were intermittent, why would there not be a code? OTOH, how could the RossTech tool show zero input speed with the engine running unless the sensor or wiring were not faulty?

i see there is a post on replacing the output speed sensor wiring, is there a similar issue with the input speed sensor wiring?

MP4.2+6.0

By sheer chance, just checking in here from a A6 4.2 owner who posted on the timing belt engine timing issue. I gave him some tips w/ some messages back and forth. I'm not a frequent visitor here these days.

First, here is the ZF 5HP24A parts catalog. Has lots of diagrams, some how to's on fluid change, etc.: http://www.zf.com/media/media/docume...a_4/5HP24A.pdf

I used to own a 2000 A6 4.2 from new until I sold it to my inlaws. Still on road. Unfortunately tranny was weakest part of vehicle, as many former D2 and C5'ers have concluded. My original tranny went to just about 100K until it blew its clutch basket brains out and I had it rebuilt via ZF. That one has stayed trouble free, now at maybe 170K. I wasn't happy both ZF and Audi seemed to have hidden ball that tranny had a variety of issues. As I found out when mine was rebuilt (more below), ZF quietly made a variety of running changes in late 2000. Thus they told me on the rebuild about all the "better" parts it now had.

Before the rebuild, I had various shifting issues. I may be the guy referenced here about the output speed sensor; that was in the wiring leading to it, and I finally fixed it after years of needle in a haystack searching by jumpering from the sensor to the TCU. As noted, the input sensor is on top of the valve body. The output sensor sits by itself on the outside of the case so was much easier to get at. I don't recall, but the wire for the input sensor probably comes through the main valve body harness. But also because of that, seems les likely it would have an issue in the wire itself. See below though about the main connector.

Consider a few ideas:

1. Just change fluid, with filter the first time only. New fluid with new additive pack may also get deposits dissolved and freed up. Maybe two cycles to get most of it changed--first cycle with pan drop will only be about 70% max because of what is in torque converter. After first time, assess if it is any better. If so, maybe again. If not, maybe proceed to next ideas which will require another fluid drain anyway.

2. If need be, get in there and clean up valve body. You have several choices. Solenoids can actually be pulled from underneath if you are careful--pan dropped but valve body stays bolted in place. Done basically by just removing a solenoid retaining bracket and the harness and cleaning each individually with something like brake cleaner. BTDT along the way. But you are saying issue may be w/ input sensor or wiring, which this won't fix.

3. Pull valve body and get at speed sensor. Plus chance to replace harness if you want. But, not for faint of heart to pull it. I did. If you want to re do parts, get them from a ZF distributor, not Audi. Audi doesn't sell a lot of the piece parts anyway and marks them way up. I used Eriksson Industries in Old Saybrook, CT. Back when ZF had lead distributors by major car line, that was Eriksson.

4. Have valve body rebuilt. I did this on my C5 on way to later finding output speed sensor wire issue. It did nicely firm up shifting at the time. I pulled it, shipped it to them right before a vacation, and had it back on return 10 days or so later.

One other possible to look at, though it's been years--the basic shift position sensor and cable/harness bolted to outside of tranny. Along way I looked at that too; hard to get out and in. You would have to search posts on it to see if any symptoms might overlap. Was another failure area on some of these, but seemingly not mine.

Also, at least as of 6 or 8 years ago, 5HP24A knowledge was much deeper on D2 board than C5 board. You might search there. Plus, by definition all D2 A8's were the V8's, while here you have the V6's with the 5HP19. TozoM8 who was over there was the king of these things, who also did tranny work in the Chicago area as I recall.

As one last one, on very early 2000 A6's (even below mine at VIN ending in 0795 IIRC), there was a TSB on a wiring issue to the tranny. It was water ingress in main connector maybe? Search for it; by chance it is where I got the jumper I cannabilized for my output sensor wire redo, though that was coincidental. In any case, consider getting under there and removing the main connector (from outside), cleaning and re attaching--if you continue to suspect connection issues that is.

iowaan

Ok, there probably isn't any thing wrong with the speed sensor. When you apply the brake the torque converter stalls out so the input to the transmission is zero, duh.

iowaan

i almost just changed the fluid and filter, but when we inspected the filter we found metal particles.

The pressure regulator bore wore out causing excessive pressure to break a clutch plate carrier. Replacing the broken parts, new valve body, bearings seals, etc. cost me a little over $3000, plus someone else did the labor.

It really appears that Audi and ZF have decided the useful life of these cars is going to be ten years. If i had to rely on Audi dealer parts and labor i could never afford to run one.

Prospeeder

I think it does the poor transmissions no good running 100k on the same fluid. According to ZF it should have been changed twice by the time it got to you, and again at 120k. The V8 is too much for the trans, and never fluid changes its doomed for early death. The original fluid isnt even full synthetic.

SloopJohnB@mac.com

It's one big black mark against Audi when they go against ZF's recommendation. The fact that they're not alone (BMW sins also) and probably FICA (whatever Chrysler is these days…) as well as any manufacturer who uses ZF transmissions.