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Thank you. Win some, lose some. At least now I know how to proceed, so any time spent on this car beyond this point is likely to make things concretely better.
The transmission control module indicator matches whatever position I move the shift lever to (except for 2nd, which it reads as Z4, but that's probably not central to the puzzle we're trying to solve).
I revved the car to 2000 rpm in both D and R while my tech looked at the inboard shaft flanges; neither moved.
Then your idea of checking and recording the speed sensor readings ... that pointed to the "smoking gun" ... the engine speed read as 2000 rpm or so, yet the input speed as per transmission speed sensor was ... zero. Output also zero. This was based on the G182 sensor reading.
That matches the "nothing feels like it's happening inside" sensation, as if there's no hint of movement when moving from P to R to N to D. If nothing inside the transmission is turning that would explain it.
So, since we know that the torque converter is moving, this means I have a broken input shaft, yes?
I gather the input shaft is part of the clutch A drum, which is a part that often fails on these units, and there's a variety of options for sourcing these parts, including "Made in China" which would presumably make an input shaft failure more likely than on an original ZF unit.
Today we learned that this is an FBC variation transmission on a car made 11/1999 which means it originally came with an ECF variation -- so someone has had this transmission out of the car and that makes it more likely that someone has messed with it, perhaps including with the clutch A drum, which makes the involvement of an aftermarket input shaft more likely, which makes the failure of an input shaft more likely, compared to if these had all been untouched ZF internals.
This seems like the likely hypothesis to me, anyway. :-)
Thank you for helping me get there.
Tanya sorry i'm late to this thread. I agree with drum A. It was possible it was from the pressure spike that happens all to often in these cars from the valve body failure. I've been through much of what you talked about, but mine at least still drove in limp mode before worse things could happen. I went from an ECF to an FUL. If you want/need parts or anything more in-depth from the best ZF trans guys in the states - call these guys, talk to Nat. Eriksson Industries. I have a few more shots of my work here: Bringing Bigfoot back to life - Saving a C5 4.2 from certain death
One question i had that i couldn't find the answer to, how many miles?
Hijacking my own thread with a rave about these cars
Hello Nick, Thank you for your input. It’s in a sense good to know that these cars fail so predictably in so preventable a way, as to the clutch “A” drum being damaged by the pressure spike due to the worn-out pressure regulator.
Whenever I get my hands on a C5 A6 4.2 V8 with a still-good transmission, I don’t even drive it until I’ve preemptively changed out the valve body housing with the pressure regulator, by installing a renewed unit from the ZF distributor. With the service (filter, gasket, fluid) added into the mix, I’m out at most $500 yet then I’ve most likely prolonged the life of the transmission significantly by removing the most likely cause of catastrophic failure.
Your picture series about “Bringing Bigfoot back to life” made me smile for many reasons. One of our project cars, a blue 2000 Audi A6 4.2 V8, has been driving in “limp home”mode for more than a year now. I understand the temptation to delay parking the car if it’s still operable.
As you evidently do, I love these Audi C5 A6 4.2 V8 cars. I’ve bought two more in the last week, so by now I’ve bought four silver project cars (all 2000 model year), a white 2001, a gold 2000, a blue 2000, and a black 2000 that’s my personal transportation. I'm told the color goes well with my mane of German blonde hair. I haven’t sold any of these cars yet, either. You can imagine what my shop parking lot looks like, with these Audi C5 A6 4.2 V8 cars parked neatly in rows. The local populace is quite puzzled at the ever-growing collection.
For part of my workday I’m an information technology geek making custom database software, and then I vanish to my shop and work with my techs on these C5 A6 Audi Quattro 4.2 V8 cars. Tonight we were raiding the gold car for parts and putting them in one of the silver cars, into which this week we installed a renewed valve body pressure regulator, fresh transmission fluid, a fresh transmission filter, and a new transmission oil pan gasket. Next we’re dealing with some crazy headlight wiring, a bad steering knuckle and a coolant leak. After that, the silver car should be ready to drive, and the gold car is looking ever sadder.
I have a new tech who until recently was into speed-tuning Detroit iron and Japanese cars; hard-core stuff like stuffing so powerful an engine into a Mustang that after its first (and only) drag strip run the body was irreparably twisted from all the torque. Horsepower outputs in the high three digits (900 or so) are not unusual for her work, and she’s even built some 1,000+ horsepower engines. Her work includes reprogramming the electronic control units with code that she writes herself. Now and then (mostly, actually) her stories strain credibility but then she takes out her phone and shows me video clips to illustrate her story. Her tech skills reconcile well to her stories, so I’ve had to accept that I now have a true horsepower freak as one of my techs. As you can imagine, she has very high standards. Even so, her exposure to these C5 A6 Audi Quattro 4.2 V8 cars has inspired her to favor one of these cars as her own personal transportation and she's already started mentioning S4 camshafts in (by her standards) casual conversation. These are, truly, inspiring vehicles.
It wasn’t until recently that I realized how the C5 A6 Audi Quattro 4.2 V8 is like the original 1960s Pontiac GTO. Someone in a large corporation took a mild-mannered mid-range sedan and stuffed a massive and powerful V8 into it, widened the stance and made it all fit and work.
The work on your C5 A6 Audi Quattro 4.2 V8 car is textbook admirable, wow. Your chariot looks magnificent. Sadly, I’m on the opposite side of the normal curve as to finances, so I’m trying to improve these cars on a shoestring budget. It’s sort of fun, in its own way, though.
I agree that Nat Wentworth of Eriksson Industries, the ZF Distributor, is a rock star. Over the last two years, he has patiently helped me through a myriad of issues and supplied me with a high-quality stream of parts. In a subtle way, he has also inspired me to go for original ZF components even if they cost more and even though my budget is limited. Just yesterday I mailed him yet another valve body housing for renewal of the pressure regulator.
As to your implied question: the silver car that inspired this thread has just over 170,000 miles on it.
I own a 2.7 Turbo and I wish I understood it better. So far I have learned (hopefully correctly) that it doesn't use the ZF 5HP-24A as in the 4.2 model but instead it uses the 5HP-19FLA which has a different set of urgent preventative maintenance requirements and is quite different in many ways, though they are both fundamentally based on the 5HP-30.
I would most warmly recommend Nat Wentworth as a good resource for answering your question -- as well as a good source of part. He's a formal ZF distributor:
In all the valve body changeouts, did you find any issues with the manual valve itself that slides in and out to select gears (is it intact)? And I've seen one post where someone missed getting it lined up with its actuating mechanism and it didn't actually move inside the valve body, even though the switch on the outside of the trans called out the correct selection.
I (we, technically) didn't find any issues, and I was (um, we were) looking for trouble there because if the transmission isn't being told to go into D or R, then ... well, it won't. As the valve body was originally, it didn't work. With the replacement, it still didn't work. Nothing seemed out of the ordinary ... but I also should add that I didn't do that part of the work personally. I was in the car moving the shift lever while my tech was under the car, checking the movement. Then again, he's put in several of these valve bodies without the shift lever aspect being messed up so I doubt he missed something twice on the same car.
Now you have me thinking, though. It's going to be a lot easier to beat the "shift" lever/cable issue to death instead of removing the transmission. Maybe it's time to swap the cable on the side of the transmission, in case it's subtly messed up ... just enough.
We have another similar car whose transmission oil pan we'll probably be pulling this week, and on the well-shifting car we can glare at the valve body and register what we see while the gear shift lever is being changed. Then we can apply that experience to the supposedly-dead car and compare. Thank you!
i would feel very silly removing the transmission if indeed the shifter were the issue, so I tried to beat the presumably-dead horse some more today, so as to rule that out more diligently yet.
With the pan off the car, my tech and I analyzed the valve body on another Audi C5 A6 Quattro 4.2V8 whose transmission does work. I sat inside the car and moved the shifter while my tech was in the pit, under the car, and he looked closely to see what a healthy mechanism looks like when functioning.
Then, the ailing Audi C5 A6 Quattro 4.2V8 whose transmission does not work was put over the put and its pan removing. I was inside the car moving the shifter again, and my tech was below, comparing the effect. His conclusion from observation: the shifter is working just fine. So, the problem is indeed elsewhere.
So, this still means: the input shaft. Tomorrow, we plan to start pulling the transmission, to find out.
We removed the transmission today, from the car that didn't want to move at all, in any gear, even while the engine was being revved. We discovered that the input shaft had indeed been sheared clean off.
From a conversation with the previous owner, I know that he liked to drive the car hard. So, he probably put a lot of torque on the shaft, which explains to some extent why it snapped: under the massive amount of torque generated by the A6 4.2 V8 engine. However, that input shaft should be able to handle such torque. These transmissions are also used in the S6 4.2 V8, which generates much more torque yet, so certainly with an A6 engine, a ZF input shaft should not have failed.
From the mess that my tech saw while removing the transmission, I conclude that this transmission had been out of the car at some point prior. Indeed, the ID plate shows it's type "FBC" which wasn't standard on the 2000 model year of the car that we're working on. So, I'm guessing that the original transmission had failed, and then someone had bought this replacement transmission from a junkyard, perhaps in badly-rebuilt condition. I say this because when I compare the details of the snapped input shaft to a true ZF input shaft, there is a slight difference. Both are hollow but the snapped shaft has a larger inside tunnel, hence would be weaker, all other things being equal. Conclusion: the input shaft that snapped isn't an original ZF unit but an aftermarket part.
Before becoming infatuated with ZF original parts, I'd bought an aftermarket input shaft more than a year ago. I like the seller, Cascade Transmissions in Oregon. The owner cautioned me that there are multiple aftermarket input shafts, and their quality varies greatly. The issue comes down to, essentially, a made-in-the-US shaft (one manufacturer only, as I recall) vs. a made-in-China shaft (several manufacturers), with the former being much better quality. I bought the made-in-the-US shaft, and it's still on the shelf in my shop, so I compared it to the sheared-off input shaft. The chamfering is markedly different, so the shaft that had snapped is not the made-in-the-US shaft. So, my best guess is that whomever had rebuilt this transmission had used a cheap made-in-China shaft with inferior quality.
Assuming I'm correct then this is a very solid object lesson: a rebuilt transmission is only as good as the quality of the parts that were used in the rebuild.
I am experiencing an error message when I try to upload the pictures, so I'm adding a link to the entire tech article here. The pictures are all at the bottom.
I have some good news to announce and I owe the nice people who advised me a BIG thank you.
After 50 miles of test driving, I'm ready to say that the 2000 Audi A6 Quattro 4.2 V8 ZF 5HP-24A transmission remove+repair+reinstall project was a success, yay! On this car, the project has only been a few months in the making, but as to the project as a whole, it has been two years in the making, as in I started analyzing the issues in the summer of 2015. It’s been a long road to victory ...
This is the car I bought for $600. The engine started and ran but the car didn’t move forward. The input shaft integral to the clutch “A” drum had sheared off. So my tech and I removed the transmission to swap out that part, but in the process we found that someone else had already messed with it including internally.
We removed the oil pump, clutch A/B assembly and the bearing just outboard of the C clutch, then renewed whatever seemed to make sense (I’m glossing over a lot in that statement but there was some reason to the process) and put it all together again. It felt SO good to do that first test drive and have the car behave well. I did some cautious slow driving at first and then got more and more gung-ho and yet everything seems functional even with some very hard driving. Yay!
I’ve worked with other automatic transmissions before, but this is the first ZF 5HP-24A that I’ve removed, rebuilt (only partially) and replaced – and much of the work I didn’t personally do; my tech did. Even so, I’m delighted. A formerly kaputt Audi has been restored to its former glory as a rocket-ship. More importantly, I have hope for doing this again and again. As to this particular transmission, I didn't trust myself to be able to dismantle the entire transmission and re-assemble it again; I'd already tried once and got overwhelmed. This time around, I'm more hopeful so this same transmission might well come out again and be dismantled with additional work being done, including a focus on the "F" clutch because reverse gear isn't as crisp as it should be.
The guidance and insights of my AudiWorld board of advisors (so to speak) were very valuable but so was the psychological effect.
I hope the "Thank you AW Friends" in the attached picture is legible enough.
03-27-2017, 06:05 PM
