Part-Way Rebuilt Used VW/Audi Quattro ZF 5HP-24A Transmissions

imag0421_01For $2,700 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 (C5 body style)
  • A8 1997-2003 (D2 body style)
  • S6
  • S8

We also offer it for the VW Phaeton.


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 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 “A” clutch 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 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 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? 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.

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 “A” clutch 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:

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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.

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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 rebuild.

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 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. 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: 

Buy from us a 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 3-year warranty on the most typical point of failure: the “A” clutch drum
  • Has the new, correct ZF-specified fluid
  • Has the new, correct ZF-specified filter
  • Has the new, correct ZF pan gasket
  • Has had its oil pan inspected & cleaned, and the magnets cleaned & positioned

These are either:

  • Units that drove fine, so we didn’t need to replace the “A” clutch drum, or
  • Units that had problems that we repaired as much as seemed prudent.

We believe 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.

We 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

  • Correct (if needed)
  • Prevent (with a renewed pressure regulator) and
  • Warranty (3 years 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, we hope that the rest of the transmission will continue to work too.  We own approximately a dozen 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.

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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 two 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. Items that we’re guessing will break next, hopefully far in the future:

  • The sprag clutch (affecting 1st)
  • The F clutch (affecting reverse)

We Offer 5 Buying Options

A. Traditional Exchange: You send us money, you pay the shipping, and we send you the transmission. Price: $2.700. The deal includes us providing a video proving the transmission worked in a car.

B. Traditional Rebuild: You send us money and your old transmission, you pay the shipping, and we repair it. You pay the shipping back to where you are. Price: $2.700. The deal includes you providing a video proving the transmission worked in a car except for the classic symptoms of clutch A drum failure.

C. Drive it, Buy it, We Ship it: You come visit us, and choose a used transmission by test-driving one of our running A6 or A8 cars. You can drive the car, your mechanic can drive the car, you can plug your laptop computer into the car and analyze it for fault codes. That way, you can observe the absence of problematic symptoms. If you like a particular transmission, you write down its serial number, and we hand you a permanent marker black pen. You sign the transmission personally, and that’s the one we remove from the car and ship to you. You pay the shipping or take it with you when you leave. Price: $2.700

D. Drive it, Buy it, We Install it in your car: You bring your car to us, and choose a used transmission by test-driving one of our running A6 or A8 cars, and we do the swap. We are licensed to repair transmissions but not cars, so as legally required we will outsource the relevant part of the work to a licensed auto repair shop two blocks up the road. We still take all the responsibility so you deal only with us.  Price: $2.700 + $1.350.

E. Bring your Car. We Repair it: You bring your car to us, and we verify the transmission works in your car except for the classic symptoms of clutch A drum failure.  We remove, repair and re-install your transmission, and involving the nearby licensed auto repair shop as legally required. We still take all the responsibility so you deal only with us.  Price: $2.700 + $1.350.

You would choose the options that rebuild your specific transmission on the “better the devil you know” premise, but if your transmission shows failure symptoms other the clutch A drum, the price will be more than $2,700.  We’ll negotiate the specific price up front depending on what the symptoms indicate.

Sales Tax

The $2,700 amount does not include sales tax, which for options C, D and E are 7.65%.

Core

We don’t charge you a core charge though as part of the deal, you give us the option of sending someone by within 30 days to pick up your old transmission and bring it back to us. How we get it transported back to us is our problem.

What your Mechanic Should Know

We include an already-done transmission service (a new filter, new pan gasket and new fluid, topped up to the perfect level and with the magnets cleaned and positioned correctly, and the pan bolts torqued just-so). That’s another $300+ value. Your mechanic doesn’t have to (and should not) drain the transmission fluid, nor change the filter.

We require that your mechanic formally certify that the transmission lines and the radiator have been cleaned as so any old (potentially contaminated) fluid.  To compensate for the fluid that’ll go from the transmission to fill the empty transmission lines and radiator, a minor top-up will be required as per the formal Audi procedure — and with the correct, honey-colored fluid … NOT red fluid.

Torque Converter

We most strongly recommend that as part of this, you send your torque converter to the US ZF distributor and pay them $300 to have it renewed.  That’s between you and them, and their price isn’t included in what we charge you.

Comparing to Buying a Used Unit

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 from someone else, then you’d be prudent to also spend on it:

  • $300+ on the service
  • $500+ on the pressure regulator renewal

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 3-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 the same part number there are variations that affect compatibility. Specializing has enabled us to be mindful of these variations, and their importance as to compatibility.

We chose the price point of $2,700 with the intent that our peace-of-mind deal is competitive relative to the gamble of used transmissions. If you don’t think ours is a better option than a used transmission, please tell us. We understand that there are occasional one-off deals but we’d love to know of any long-term options better than ours. If there are, we might well use them ourselves.

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 (being addressed if you buy a used transmission from us)
  • The timing chain 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 a 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.

Our Location

We’re based in Fallon, NV, about 60 miles east of Reno, NV — within a day’s drive of Southern Nevada, plus much of California, Arizona, Utah, Idaho and Oregon.

Please contact us and say hello!

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