For $1,800, we sell used or repaired, improved, warrantied ZF 5HP-24A transmissions for the Audi Quattro with the 4.2 V8:
- A6 1999-2004 (C5 body style)
- A8 1997-2003 (D2 body style)
We also offer it for the VW Phaeton.
|Valve body pressure regulator renewal
+new pan gasket
|Warranty: one year||Most typical point of failure: “A” Clutch||The entire transmission|
* Excludes torque converter
Why The $400 Add-On
These are highly specialized transmissions, and many people shop based on price. If we could safely omit this extra $400 and viably just sell you a used transmission for $1,400 then we would. However, we are convinced it’s a bad idea to not prudently guide you as to attending to the items covered by that $400.
We own several Audis with these transmissions, and we have spent more than five years studying, specifically, this model of ZF transmission. We’re convinced that, without renewing the valve body pressure regulator renewal, it’s only a matter of time before the “A” clutch drum blows out and the transmission fails. That’s why we include an improved, renewed version of this part.
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. Normally the relevant letter (P, R, N, etc.) is illuminated on a dark background but in abnormal mode, the background is illuminated for all the letters, and they’re dark.
- The car moves forward but very slowly, as if it’s stuck in 4th 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, but forward gears are misbehaving. You turn the car off, then start it again. The problem then 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 “A” clutch drum.
This causes the first three forward gears to be unavailable since they all mechanically depend on that clutch. The transmission reverts to 4th gear, by essentially locking the entire rotating assembly together as one unit to create a direct 1:1 ratio, which is what 4th gear is.
The transmission has input shaft and output shaft speed sensors, and the car’s computer compares 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 three forward gears and puts you in 4th 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 VW & 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 VW & Audi Quattro version, the ZF 5HP-24A, there are more than 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) or S8 (high-performance A8) variants. So, as you pursue solutions, it can be useful to 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.
So, what are your options (including bad-idea options)?
Option A: Long-Shot Quick Chemical-Additive Fixes (Bad idea)
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, and ZF is adamant that these should not be used. 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 (Bad idea)
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 (Bad idea)
If you do a service, it won’t fix the serious structural problem, but it can cause harm. In analyzing this issue, I’ve noticed more than two dozen 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 if you have it professionally done, and it’s not cheap even if you use non-original parts and do the work yourself.
But, a service is pointless in this context. It’s like having an abscess and needing a root canal and then deciding to go get your teeth cleaned by a dental hygienist, or flossing them yourself. Yay for dental hygiene but you’ll still need a root canal.
You’d be better off allocating that money towards another option.
How do we know this? We’ve made most of the mistakes being cautioned about in this article. The others, we’ve inferred by seeing the damage in the transmissions we dismantle and analyze. A few others, we’ve learned about from other enthusiast reports. By and large, though, my cynicism is based on personal experience or observation.
The most typical mistake we see for this option is people using red transmission fluid instead of the precisely correct type. This makes the clutch disks more likely yet to slip and burn, plus you’ve contaminated the transmission cooler lines and the radiator, so when you install the replacement transmission, then some messy and difficult decontamination work will be needed so as to not affect the replacement transmission.
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 “A” clutch, replace it, then put everything back together again. Then, nominally you’ve fixed the problem.
However, you still haven’t fixed the root cause, so the replacement “A” clutch will soon fail again. To prevent that, you must address the worn pressure regulator in the valve body.
This is a 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 repair.
So, choosing this option can make sense if it’s done correctly, but that might well be difficult.
Option E: Buy a rebuilt transmission
When last we checked pricing in 2018 or so, a rebuilt transmission of this type tends to be priced around $4,000. The best-quality product is likely if you buy a rebuilt one from ZF. The shipping can add an additional $1,600 ($800 each way) to West Coast locations since they’re east of the Mississippi. .
Gary Ferraro is another rebuilder on the East Coast. highly skilled and with an exceptional work ethic, and high standards. I recommend him too. I don’t recall what he charges for a rebuild.
As to other rebuilders: will they 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 will they replace? We have sometimes opened up transmissions rebuilt by someone else and their quality was so iffy that we don’t even want to sell that unit as one of our used transmissions, so we strip those down and use them for the few salvageable parts they can contribute.
One major question: what does “rebuild” mean? Do they replace everything, including the case? No. So, it’s always a judgement call as to what they choose to replace, and what not.
Another major question: how did the rebuilder address the worn pressure regulator? The problem is that the 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. A vendor providing aftermarket solutions, TransGo, takes a different approach. Their approach might be adequate too, though it’s neither the approach we take nor the one recommended by the US ZF distributor.
Assuming you buy a rebuilt unit from someone whose reputation is less than stellar, they will 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, or someone used red fluid in it so the clutch disks have now slipped more, and are perhaps burned.
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 (both this one and other ZF transmissions), and we get some good feedback from our customers. We’ve been told some horror stories about how we contrast with junkyards that 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 and there’s no core charge. 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, or someone used red fluid in it.
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, this might well have damaged the computer. An acquaintance of mine experienced this. He swapped out the damaged computer with a good one, and within minutes his A6 was fine again.
On the A8, the computer 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.
Option I: Swap in a 6-speed Manual Transmission
This is typically motivated by the premise that the ZF 5HP-24A is fragile, and we disagree with that premise.
But, yes, converting to manual is an option. However, we don’t offer that option. The Audi C5 A6 4.2 V8 is a complex car. It can be difficult even to replace a part with an identical-but-newer unit.
The work involved in converting to a manual transmission is best done by those in the upper echelon, as to automotive skills.
Buy from us a used transmission that:
- Works in every gear and by implication, has a working “A” clutch drum
- Has had its pressure regulator (in the lower front housing of the valve body) renewed by the US ZF distributor to protect the “A” clutch drum
- Has a one-year warranty on the most typical point of failure: the “A” clutch drum
- Has the new, correct ZF-specified filter
- Has a new pan gasket.
- Has had its oil pan inspected & cleaned, and the magnets cleaned & positioned
These are units that were in cars that drove fine, so we didn’t need to replace the “A” clutch drum. We have found much industry opinion to the effect that the ZF factory knew best when it built these transmissions, and every time we (or our competitors) disassemble, renew then re-assemble something, there’s a risk of making things worse, not better.
Our used transmissions are for those who see value in the “if it ain’t broke, don’t fix it” premise: don’t renew things just to renew them. If a part doesn’t have a specific recommendation for preemptive replacement, and it shows no sign of failure, then we prefer to leave it alone. We are heavily focused on the item that is, for these transmissions, by far the most common point of failure: the “A” clutch drum. That’s the failure we
- Inspect for (on used transmissions)
- Prevent (with a renewed pressure regulator) and
- Warranty (one year against “A” clutch drum failure). Specifically, if the “A” clutch drum fails, then we’ll refund your money, calculated proportionately over the warranty period.
Of course, on our used transmissions, we hope (with a proven basis for being hopeful) that the rest of the transmission will continue to work too. We own several Audis with these transmissions, and we drive them on occasion to verify that the transmissions we offer for sale are in, literally, in good working order.
One specific car, a black 2000 Audi A6 Quattro 4.2 V8 with its ZF 5HP-24A transmission, is driven extra hard and long distances, including:
- Having been entered in the Virginia City Hill Climb hosted by Ferrari Club, with the hard uphill driving being harsh enough to trash a complete set of good tires in two days
- Back and forth across the Sierra Nevada, including in sub-freezing winter cold and in winter storms, and rainstorms
- Back and forth to Las Vegas more than half a dozen times, including in summer desert heat
- Rally-style off-roading in the desert, harsh enough to trash the front lower section:
… and even though by the time of this writing we have been doing this for about four years, the car’s transmission is still running strong.
Our basic point: these transmissions are not fragile. As long as the pressure regulator does its job, the clutch A drum doesn’t break — and so far we haven’t managed to break any other part of the transmission either. The most-fragile item that tends to break next is the “F” clutch (affecting reverse).
For those who would rather spend the extra money and get the “F” clutch renewed too, we offer the “repaired” option. That includes:
- A new “F” clutch piston from ZF, with an improved design
The “F” clutch is at the very back of the transmission and necessitates taking essentially the entire transmission apart from both directions (front to back and back to front).
The “repaired” option also includes:
- New friction disks from ZF for all six clutches
- New seals where we deem it prudent
- New piston rings for the “A” clutch
- A new bearing for the most-likely-to-fail candidate just forward of the “C” clutch
- Adjusted end float
Typically, new steel disks from ZF add close to $1,000 to the pricing for all six clutches. This is expensive even by the standards of our ZF distributor, who has told me he does offer just the individual steels I’d need for a specific rebuild. I value the nuanced professionalism of this ZF distributor so very much. One of the reasons is: they understand that the problem is as much economical as technical.
Saying “just go replace everything with new stuff” is an oversimplification since the economics would kill most projects. So, for example, as to the steel disks, we do not use new steel disks. Our experience after much inspection suggests they are normally very much re-usable. So the rebuild does not include new steel disks, but rather: good, inspected, re-useable, re-used steel disks for all six clutches.
I prefer using “repaired” rather than “rebuilt” or “renewed” because the latter two might imply an “everything is new” premise that would be misleading. I renew specific parts, many of them preemptively — but no, I don’t replace all the parts with new ones. Most parts don’t need replacement, a large subset of those are best left undisturbed, and our price reflects our policy as to what we choose to replace with new items vs. not. Regardless, our one-year warranty on “repaired” transmissions covers the entire transmission, excluding the torque converter.
“A” Clutch Drum Controversy
Some have argued that the solution to the classic failure pattern is to beef up the “A” clutch drum. Various aftermarket solutions are available as such. We don’t have a problem with any of the good aftermarket “A” clutch drum vendors but until we see proven merit (as in, formal engineering field tests) we continue to use the ZF “A” clutch.
The tremendous pressure caused by a failed pressure regulator should be taken very seriously, so as in the “irresistible force meets unmovable object” paradox we choose to resolve the “irresistible force” aspect. We prefer to offer the set of solutions formally provided by the ZF distributor, and we have found this approach to be rock solid on our personal vehicles.
You choose a carrier and pay it for the shipping, in one direction, unless you’re sending us your own transmission to rebuild, in which case you pay for the shipping in both directions.
We Offer 2 Buying Options
A. Used: $1,800
B. Repaired: You send us money, and you send or bring us your old transmission, and we repair it. We also replace several additional items with new ones. This is typically a good idea only if we don’t have in stock the exact variation of transmission that you need. Price: $3,400. That price applies across-the-board — even to the S6, S8 and RS6 variations.
The sales amount does not include sales tax, which is 7.65%.
If you buy a used transmission we don’t charge you a core charge as part of the deal, but informally we’d appreciate being able to get your old transmission, if it’s viable for us to get it to our location somehow.
We include a new filter and new pan gasket with the pan magnets cleaned and positioned correctly, and the pan bolts torqued just-so. That’s another $200+ value. We legally may not, and do not, ship these transmissions with fluid so your mechanic will have to add the correct, honey-colored fluid to the oil pan: ESSO LT 71141 or something that’s chemically comparable. For example, Blauparts offers a comparable fluid by the Ravenol company. Last we checked the correct part number for them was “G 052 162 A2.” That’s another $150 or so you spent, not included in the price you pay us.
Do not use red ATF. It is not compatible, and voids the warranty.
We dislike companies that void a warranty without there being cause-and-effect between what the customer did and the failure that gave rise to the warranty claim. But using red fluid instead of the correct honey-colored fluid introduces the wrong viscosity, so the clutches are more likely to slip hence more likely to burn, so red fluid is not OK. If your mechanic insists on red fluid, get a better mechanic. Red fluid voids the warranty, period.
Filling the transmission fluid to the correct level involves a fairly complex procedure for that. We trust you will choose a mechanic whose skills are up to the task.
We also cannot ship the transmission with differential oil, so your mechanic will need to fill that, too. There’s a special type for that, too: 75W-90 synthetic gear oil with Positraction additive (a.k.a. limited slip additive). Valvoline offers this; so do some other companies.
We most strongly recommend that as part of this, you send your torque converter to the US ZF distributor and pay them $300 or so, to have it renewed. That’s between you and them, and their price plus their shipping charge isn’t included in what we charge you.
However, we have a good business relationship with them and we’ll be happy to make the introduction.
Compared to Buying a Typical Used Unit Elsewhere
When it comes to money, it’s important 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 from someone else, then you’d be prudent to also spend money (probably $500 or more) on the items required to enable this transmission to have a good chance of longevity.
This assumes your mechanic is competent as to these transmissions, and doesn’t make a crucial mistake. We see many mistakes when we dismantle these transmissions — some of them very glaring mistakes.
Most used units from elsewhere don’t come with a one-year warranty, as ours does.
Also, not everyone who sells these transmissions is aware of the many subtleties. One example: the ZF 5HP-24A transmission cannot be removed and blindly replaced with another unit marked as a ZF 5HP-24A. Within that basic part number there are many variations that affect compatibility. Specializing has enabled us to be mindful of these variations, and their importance as to compatibility.
We chose our price points with the intent that our peace-of-mind deal is competitive relative to the gamble of typical used transmissions.
Many more Happy Years with 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 disagree. 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 (which is addressed if you buy a transmission from us)
- The timing belt and water pump failing (which might cost you $500 in parts if you DYI and $1,000 if you have a shop do it… money well-spent either way)
- The front brakes. Don’t let the brake pads wear down to the metal…
- The coolant reservoir eventually cracks. It’s easy to swap out and costs less than $100 new.
- The central instrument cluster display loses contrast in hot weather. There’s a $150 fix for that.
- Control arms: Not trivial but not the end of the world.
- The vacuum-controlled front bellows on the 40-valve engines. There’s a $300 fix for that.
- The mechanical fan bearing: $200 plus a few hours of work, if you have the right tools, which at most should cost you $100.
In our experience that’s pretty much it. We address the above, and have magnificent and reliable chariots, in many ways still comparable to the A6 Quattros and A8 Quattros being sold at Audi dealerships nowadays for $65K or $100K respectively. By keeping your classic Audi going, instead of buying a new one, you avoid the expensive taxes, DMV fees, insurance and depreciation … and long-term you are more in control of your repair bills.
We’re based in Fallon, NV, about 60 miles east of Reno, NV.
Please contact us and say hello!
Happy customer M.M. from Farmington, UT:
I made it home and the car was perfect. I’m at a loss for words to describe the feeling. Thanks so much! — October 2018
Happy customer E.H. from Long Beach, CA:
All in all it went well and I’m so glad to have my 2000 D2 A8 running like a champ again. The transmission was in superb condition just as foreseen — December 2019