Test Drive one of our Used Audi Quattro ZF 5HP-24A Transmissions before you Buy it!

imag0421_01For $2,700 including West Coast delivery, we sell used, partially renewed, guaranteed, test-it-in-a-running-vehicle ZF 5HP-24A transmissions for the Audi Quattro with the 4.2 V8:

  • A6 1999-2004
  • A8 1997-2002

Is this what you’re experiencing … when you drive forward, your transmission slips?

In more detail:

  • The engine revs but the car doesn’t move forward
  • There’s a jarring bump
  • The instrument cluster display changes for the shifter position indicator, so that it is lit up in reverse video
  • The car moves forward but very slowly, as if it’s stuck in 5th gear
  • If you continue driving, the car can pick up speed gradually and eventually go as fast as you need it to, at highway speeds

Park, reverse and neutral work fine. It’s just going forward that’s misbehaving. You turn the car off, then start it again. The problem appears to have been fixed, going by the display. You try to move forward, and the same thing happens, every time.

The Bad News

This is a classic failure pattern for this type of transmission after 15 years or so. The pressure regulator in the valve body has worn out slightly, just enough to not contain the pressure perfectly all the time. Eventually, a pressure spike slips past it, and blows out the rim of the clutch “A” drum.

zf_bad_a12015-12-19-22-25-24This causes the first four forward gears to be unavailable since they all mechanically depend on that clutch. Only 5th gear works, because it doesn’t use that particular clutch. The transmission has input shaft and output shaft speed sensors, and the car’s computer compared these continually. When it senses the input shaft speed (engine speed) is high yet the output shaft speed is too low or zero, that means there is some serious slippage. The transmission control computer bypasses the first four forward gears. As a result, going forward you only have 5th gear. The instrument cluster display informs you that this special mode has been activated.

Some call it “limp home” mode like an injured dog limping home. It gets you safely home, which is a lot better than being immobilized in a bad neighborhood or bad weather. Granted, you have lousy acceleration from stops, but once the car gets up to highway speeds, it’s as fast as always.

Some Quick Tech Notes

Audi didn’t design or build this transmission. Porsche designed it (its essentials, anyway) and it was built by ZF, a massive German company with a long history of building high-quality automatic transmissions used by Audi, Bentley, BMW, Jaguar, Maserati, Peugeot, Range Rover, Volvo and VW. This particular model is a 5-speed. It’s a variation of the 5HP series specifically with an emphasis on high-torque applications such as Audi, BMW and Jaguar cars with an engine size of 4 liters or more. The rear-wheel-drive variant is named ZF 5HP-24, and the Audi Quattro variant incorporates the Quattro mechanism, and is named ZF 5HP-24A. The BMW X5 and Range Rover use the rear-wheel-drive variant and deal with the 4×4 issues outside of the transmission.

Just for the Audi Quattro version, the ZF 5HP-24A, there are close to a dozen variants of this transmission. For example, the variation of transmission for the Audi A6 Quattro 4.2 V8 through 2000 is different than the 2001 variant which is yet again different than the post-2001 variant. None of these overlap with the A8 variants (of which there are half a dozen or so) or S6 (high-performance A6) variant. So, as you pursue solutions, be clear as to which variation your car has, and what’s compatible or interchangeable with it. Some variations interchange, some do not. You might buy a perfectly good transmission from a rebuilder but it’s an incompatible variant.

Option A: Long-Shot Quick Chemical-Additive Fixes

We sometimes dismantle the transmissions on the cars we buy, and we see contaminated fluid due to someone trying a quick fix such as a fix-it additive. This can’t possibly help because the failure is serious and structural, like a broken bone in a person’s body.

Additives can, however, cause harm. The chemical composition of the fluid in the transmission has to be just right, and anything else is a problem. Additives don’t just contaminate the transmission (which is bad in its own right) but also the cooler lines and the radiator, so you’d then have to thoroughly flush those out before installing a good replacement transmission — otherwise its fluid will be contaminated too, which would make it likely to fail sooner.

Option B: Fluid top-up

The failure was caused by overpressure, so there was enough fluid to cause that. We have never seen low fluid level cause this sort of failure. Trying to top up the transmission can, however, cause damage unless it’s done correctly (which is hard to do), as explained in the “Service” section below.

Option C: Service

If you do a service, it won’t fix the serious structural problem, but it can cause harm. I’ve listed more than 30 points where a service can create problems, so approaching with the “can’t hurt” mindset is overly optimistic.

A service will cost you several hundred dollars even if you use non-original parts and do the work yourself, and since a service is pointless in this context, you’d be better off allocating that money towards another option.

How do we know this? By making most of the mistakes I’m cautioning you about. The others, we’ve inferred by seeing the damage in the transmissions we dismantle and analyze. A few others, we’ve read about. By and large, though, my cynicism is based on personal experience or observation.

Option D: Repair

The only way we know how you can fix this internal failure is to remove the transmission, remove the parts that are in the way of the damaged clutch, then remove the damaged clutch, replace it, then put everything back together again. Then, nominally you’ve fixed the problem. However, the shrapnel from the destroyed rim of the clutch “A” drum are now somewhere in your transmission internals, and that can cause some more problems. For that reason, it’s prudent to strip down everything to find those small pieces of aluminum. Here’s an example:


At that point, you might as well replace the steel disks and friction surfaces. To reassemble everything, you also need new seals and gaskets. You should also shim the clutches to make sure the clearances are right. In other words, it means a full transmission rebuild.

Problem is, then you haven’t fixed the root cause, so the replacement clutch will soon fail again. To fix the root cause you must address the worn pressure regulator in the valve body.


This is a highly specialized and complex transmission. It’s notorious for requiring exceptional cleanliness in the work environment. It’s not the sort of thing a typical transmission repair shop or even a skilled amateur would be qualified to mess with.

Option E: Buy a rebuilt transmission

A rebuilt transmission of this type tends to be priced in the $3,500 to $4,000 range.

Will the rebuilder use original-manufacturer high-quality components, made by ZF, or will your Audi have a transmission with a “made in China” level of quality? Who reassembled the transmission? How skilled were they? How precise were they? Which parts did they replace?

How did they address the worn pressure regulator? The problem is that that aluminum bore has worn, so replacing the piston won’t solve the problem. The bore has to be precisely enlarged and an oversize piston has to be fitted. Either that, or the casting and piston must be replaced by all-new parts from the manufacturer.

Assuming you buy the rebuilt unit, then they probably ship the unit to your shop from their rebuilding facility, which might be hundreds or thousands of miles away. Odds are they won’t install the transmission in your car for you. Your mechanic does that. After installing it, if it doesn’t work, then what? Does the mechanic blame the rebuilder and vice versa with you in the middle, not knowing whom to believe?

Could be by then you’re out $5,000 and you still have an Audi without a good transmission.

Option F: Buy a transmission from a help-yourself junkyard

This is ostensibly the cheapest option, but by far the most likely reason that an Audi Quattro 4.2 V8 with this transmission would be in the junkyard is: transmission failure. So, odds are you’re buying another transmission that’s bad.

There’s also a core charge, as explained in more detail where we describe the next option.

Even if it comes with a warranty, the hassle factor is significant. You’d be taking a very long shot if you buy a transmission from such a source, and simply install it, hoping it’ll work. The alternative is to dismantle and inspect it, and then you’re well on your way to a rebuild.

Then again, if it’s in good running condition, it might well be due for failure caused by the pressure regulator.

Option G: Buy an off-the-shelf transmission from a junkyard or eBay

Some junkyard cooperatives share availability and pricing data, and so you could (as we did once, while exploring options) walk into junkyard A and they’ll tell you of a unit available at junkyard B, an unrelated company that might be a state away. On this circuit, a used transmission will sell for $1,800 or so, not including delivery. For that price, the seller guarantees it and claims it came from a running car. As to shipping charges, for a 300+ pound unit, these can be significant.

This can be a good deal but only if you choose a good vendor. It’s hard to tell them from the bad ones since they make a point of looking like good vendors.

We sell used transmissions, and we get some good feedback from our customers. We’ve been told some horror stories about how we contrast with junkyards who sell poor-quality units brazenly, and by the time a customer of such an outfit has finally gotten a refund, much money, time and energy have been wasted.

If it is a bad transmission then the only way you know it is by installing it and finding out. That’s a lot of work (or expense) that the seller won’t cover.

Also, junkyards tend to charge a core charge, meaning they charge you this up front and then after you ship your old transmission to them they’ll refund the core charge. Often a buyer will pay this and then forfeit it because it’s too much hassle and expense to send it back, or there is a delay and the window of time has passed. So, often you end up paying the core charge too. That can range from $100 to several hundred.

eBay is similar but typically the transmissions are priced around the $1,000 mark. An acquaintance of ours owns an Audi A6 Quattro 4.2 V8 and he went this route. He has so far installed two transmissions, and he’s by now out $5,000 and he still has an Audi that doesn’t run.

Regardless, even if the transmission is in good running condition, it might well be due for failure caused by the pressure regulator.

Option H: Transmission control computer

Perhaps your transmission is okay but the transmission control computer is bad.

On the A6, it is located under the carpet in the passenger front footwell, near the front of the seat. If you’ve had a rainwater leak, or cleaned the carpet with too much water, or spilled water in that area, maybe you simply have a bad computer. An acquaintance of mine experienced this. He swapped out the bad computer with a good one and within minutes his A6 was fine again.

On the A8, it is located in the plenum (cowl) area. Its drains can get clogged, so water damage is possible there too.

We offer a transmission control computer testing service. You send us your computer and describe the problem you’re having. We install the computer in a compatible car and see if we experience the same symptoms. We send you a report, and your unit back, whether it’s good or bad. We charge $150 for this test.

OUR OPTION: Drive it, then Buy it

We offer a used transmission that you can test in one of our running A6 or A8 cars. You can drive it, your mechanic can drive it, your Audi dealer can drive it, you can plug your laptop computer into the car and analyze it for fault codes. That way, there is no question as to the transmission working correctly.

Also, your mechanic removes the transmission from my car, so you know it’s the right one. From that point on, you can be certain that whatever might go wrong with the removal and replacement, the problem is not with the transmission.

But wait — there’s more. On each such transmission, we have had the pressure regulator problem formally addressed by sending the valve body housing for renewal to the US ZF distributor. This means that the typical cause of failure has been removed from the list of things that can kill off this transmission. That’s a $500 value. I’ll even guarantee that this removes the danger. If the clutch “A” drum fails, then we’ll refund your money, calculated proportionately over the warranty period.

There’s no delivery fee since the transmission arrives at the transmission shop in a working car. We’ll remove our car on a trailer when your mechanic is done with the work. For getting a 300+ pound transmission delivered to your mechanic, you might well have been looking at $300 in shipping charges.

We don’t charge you a core charge though we do expect to take your old transmission with me when we take our car away. As explained above, a core charge could be in the $100 to $200 range, say an average of $150 and many people forfeit due to the hassle and shipping cost involved. We do want your old transmission back as part of the deal, but we pick it up from your mechanic, so there’s not hassle for you and no core charge to forfeit..

We’ll even include a transmission control computer test in the deal (a $150 value). That way we can rule out you having a bad computer, so if the mechanic installs the transmission and it doesn’t work, you know you can look to the mechanic as the person who introduced the problem. We suggest you negotiate things up front as such too.

We’ll also include an already-done transmission service, and that includes a new filter, new pan gasket and new fluid, topped up to the perfect level. That’s another $300 value. Your mechanic doesn’t have to (and should not) drain the transmission fluid.

So, the extra value items are:

  • $500 (pressure regulator renewal) +
  • $300 (no shipping) +
  • $150 (no core charge) +
  • $150 (transmission control computer test) +
  • $300 (service)


  • $1,400 extra-value items

With this included, we charge $2,700 for a partially renewed, used transmission.

When it comes to money, it’s hard to compare apples to apples, which is why we list the total for the transmission, downstream of the torque converter, ready to be installed in your car.

If you’d bought a used unit, then you’d be prudent to spend another $1,400 on it, so if we subtract that from our price of $2,700 that means buying from us is the equivalent of you buying a used unit for $1,300 with the additional peace-of-mind benefits to you of

  • You get to thoroughly test it, by driving the car with the transmission in it
  • You buy from someone who specializes
  • You have very few hassles

We’ve tried to price our offering competitively. If you don’t think ours is the best option generally available, please tell us.  We understand that now and then there are occasional one-time unbeatable deals, but we’d love to know about it long terms there are better deals than ours.

Don’t give up on your Audi

Often when this sort of catastrophic failure occurs, an owner figures that more and more big-ticket items are probably going to keep failing and it’s probably prudent to just get rid of the car.

We love using these cars as our daily drivers, and we know them well. The main points of failure are:

  • The pressure regulator blowing out the rim of the clutch “A” drum in the transmission (being addressed if you buy a used transmission from me)
  • The timing chain and water pump failing (which might cost you $500 in parts if you DYI and $1000 if you have a shop do it … money well-spent either way)
  • The front brakes. Don’t let the brake disks wear down to the metal!
  • The seat bottom leather. This is tricky because the seats have air bags so a seat cover isn’t ideal. We like to wedge a color-coordinated towel between the seat bottom and seat back. That has some other benefits too such as the leather not being too hot in the summer.
  • The coolant reservoir eventually cracks. It’s easy to swap out and costs less than $100 new.
  • The central instrument cluster display loses contrast. When it’s cold, it’s legible for a while. We don’t have a fix for that as yet.

In our experience that’s pretty much it. Address the above, and you have a magnificent and reliable chariot.

Our Location

We’re based in the greater Reno, NV area so (on a good day) our service area spans Nevada, California, Arizona, Utah, Idaho and Oregon.

We love road trips but sadly we don’t have a large staff available for driving Audi Quattros all over the West, much as that would be a dream job. The farther you are from Reno, the less likely we are to drive to you soon, or ever.  But, you never know. Please contact us and ask.