ZF 5 HP-24A Teardown: Step 11: Valve Body

With the transmission upside down, and the oil plan removed, the valve body is easily accessible. An electrical cable runs along the outside of the valve body, from an external connection plug, to the solenoids and the pressure regulators along the front of the valve body.

To separate the valve body from the transmission, we first removed the filter, by removing two T-27 Torx bolts.

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Then, we loosened the electrical plug. We identified and removed the T-27 Torx bolts that attach the valve body to the transmission.

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This is fairly tricky because we did not want to also remove the bolts that keep the valve body together. However, these bolts are the same color, and they are also T-27 Torx bolts. The difference is that that the T-27 Torx bolts that attach the valve body to the transmission have heads that have a slightly larger circumference.

We had a gentle, clean spot ready for the valve body after we removed it, so that we did not have to set it down on a hard surface. Doing so might not have been very good for the speed sensor and the other fragile-seeming parts.

ZF 5 HP-24A Teardown: Step 10: Oil Pan

At some point in the tear-down process, the valve body must be removed, and before that, the oil pan. We first removed the oil pump, clutch A and B drums, and front differential. That made a big difference in the weight.

With those parts removed, we lowered the transmission, took it off the transmission jack, and turned it upside down.

We removed the oil pan, by removing the Torx T-27 bolts around the lip. According to the ZF parts manual, these are 26 of them, and they are M6 22-mm bolts, and the oil pan for this transmission comes in three variants:

  • Part number 1058 203 019 for the early Audi A8 (1997, 1998) with transmission letter codes DPZ, DSM and DTE
  • Part number 1058 203 030 for the Audi S6 (2002-2003) and the 2000-2002 Audi A8 with transmission letter codes FBD and FBG.
  • Part number 1058 203 026 for all the Audi A6 models, and the models of the A8 not covered above. Transmission letter codes ECF, FBC, FUL for the A6, and EDG, FBF, FUN for the A8.

The other parts in the oil pan are the same for all the models that use this transmission. The parts are:

  • Gasket
  • Fill plug (hex)
  • O-ring for the fill plug
  • Drain plug (hex)
  • Magnets, four of them

With the oil pan removed, the valve body was nicely accessible.

Here is a picture of the inside of the oil pan. The large light-covered circle towards the right is the top of the fill plug. The small light-covered circle towards the right is the top of the drain plug. The magnets are toward the lower left; three of them clustered together, and one further down.

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Here is a close-up picture of the magnets:

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ZF 5 HP-24A Teardown: Step 9: Clutches A and B

We removed the A clutch, B clutch, input shaft and the intermediate shaft as a unit.

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Here is a picture of the assembly, being held above a drip tray, intermediate shaft pointing upwards.

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Here is a picture of the assembly, being held above a drip tray, input shaft pointing upwards. The picture also shows the bearing that fits between this assembly and the oil pump.

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Here is what remains of the transmission afterwards.

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ZF 5 HP-24A Teardown: Step 8: Oil Pump

To remove the oil pump, we removed the eight T-27 Torx bolts that are arranged in a circle, with the bottom two accessible via the holes recently vacated by the two black rubber plugs.

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The input shaft is a composite, with an outer shaft and an inner shaft. The outer shaft goes to the oil pump. The inner shaft goes to the clutch A drum, which is behind the oil pump. So, to pull out the oil pump, shaft and all, one yanks it out very precisely, dead-on forward, towards the front, by pulling the outer drive shaft while pushing down on the front edge of the inner shaft. Problem is, how?

So, my clever assistant sent me shopping. I bought 4 separate pullers from the local NAPA store, hoping one would do the trick. I also bought two short M4 bolts. The bolts go into holes on either side of the outer shaft. Some cleverly placed rubber bands hold the bolts in place.

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Then, using a puller with a sharp central point that keeps it located into the (fortunately) hollow front edge of the input shaft, the puller then grabs the bottom of the two bolts and exerts pressure. It worked perfectly.

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Here is a picture of the oil pump just starting to move outwards, no longer flush with the housing.

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Here is the oil pump, after removal.

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Here is what the transmission looks like with the oil pump removed.

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This picture shows the holes on the driver side of the casing right by the oil pump, by which the fluid leaves the transmission to go to the radiator to be cooled, and then flows back again.

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ZF 5 HP-24A Teardown: Step 7: Oil Pump Rubber Plugs

Near the bottom of the oil pump are two round, black, hard rubber plugs, with each of them maybe the size of a dime or smaller.

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After the differential pipe has been removed, and the plug can be accessed from the back, the process we should have used is to tap or push the plugs through from the front to the back, and catch them as they fell out.

Instead, we pulled them out and destroyed them in the process. Good thing the rebuild bundle we bought comes with a fresh set.

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Here is a picture of the oil pump, with a blue light behind it to show what the area looks like with the two plugs removed.

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Here’s a close-up picture of one of the damaged plugs.

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ZF 5 HP-24A Teardown: Step 6: Front Drive-Shaft Guide Pipe

The front differential for the Quattro functionality is on the passenger side, and from there the power gets transmitted to the driver side along a long steel shaft that runs from the passenger side through a tunnel in the transmission all the way to the driver side.

The tunnel is the inside of a pipe, and that pipe can and must be removed as part of the dismantling process.

The pipe has a thicker portion and a seal on the driver side, and so the only way to remove it was by having it exit on the driver side.

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We needed some way to gently inspire the pipe to exit the transmission on the driver side. My clever assistant dismantled part of the bathroom sink, and she used that part as a basis to spread the force of the impact, and then she gently whacked the passenger side of the pipe with a rubber mallet. It worked perfectly.

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ZF 5 HP-24A Teardown: Step 5: Front Drive Shaft Inner Attachments

Inboard of each front drive shaft is an attachment point that ties it to the front differential. The part that provides that must be removed.

The passenger side is more complex because that is where the front Torsen differential is. To remove it, we removed twelve T-40 Torx bolts and then pulled the part away from the transmission.

Differential oil was going to leak out, so we had drip trays ready.

And wow, by our standards this part is VERY heavy.

Here are some pictures that show some of the process.  The red-and-black strap is to keep the transmission attached to the transmission jack (red).

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Here’s the passenger side of the transmission after the front differential has been removed.

2015-12-19 17.49.59Here’s the part, sitting in a drip tray.

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The driver side part is more simple. To remove it, we removed six T-40 Torx bolts and then pulled the part away from the transmission. Along with it came a speed sensor, and a long shaft that runs from the driver side, through the transmission to the front differential on the passenger side.

Here’s the part, sitting in a drip tray.

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ZF 5 HP-24A Teardown: Step 4: External fluid lines

Both lines come off together. We removed the 13 mm bolt that holds the lines in place, and then gently jiggled the lines at that attachment point, while pulling them away from the transmission.

LINES001

Below is a picture of the lines’ mounting point, with the bolt removed.

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Here is a close-up:

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There is also a bracket that keeps the lines in position right by the transmission bell-housing, but the bolt that keeps that bracket in place will have been removed as part of separating the transmission from the engine:

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Here’s a close-up:

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Removing the lines no sooner was a cleanliness issue because we first wanted to have the transmission clean, elevated to hip height on a transmission stand, and in a clean environment, to minimize the risk of dirt getting into the transmission or the lines.

Removing the lines no later was a safety issue because with this part removed, it was easier to move around the transmission, and we were less likely to be poked in the eye.

Here is a picture of what the lines look like, removed:

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Here’s a close-up of the radiator end:

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Here’s are some close-ups of the transmission end:
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ZF 5 HP-24A Teardown: Step 3: Side Mounts

We removed the transmission mounts on either side of the transmission.

Each side was attached with (as I recall) three Torx T40 bolts.

Before or after this step is a good time to raise the transmission up on the transmission jack, because from here on concerns about dirt contamination increase significantly. We made the mistake of centering the considerable weight of this transmission on the transmission jack, and then as we started dismantling the transmission from the front, the center of gravity moved significantly towards the rear and we regretted not having anticipated, and compensated for, that sequence of events.

ZF 5 HP-24A Teardown: Step 2: Torque Converter

We removed the torque converter from the front of the transmission, by pulling it forward and away from the transmission.

The input shaft for this transmission is a two-piece unit, with one shaft inside the other. The torque converter slides onto this shaft. Here’s a picture of the shaft (not of the torque converter):

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From what we saw in the repair manual, the torque converter locks up in both 4th and 5th gear. No electrical signals run to the torque converter though the process is no doubt initiated by an electric signal to a solenoid that changes the hydraulic fluid pressure.

The input shaft is the only way that the torque converter connects to the transmission, so the fluid pressure must come from the shaft. We have not yet figured out the fluid flow path; e.g, does the fluid flow into the torque converter from the inside of the inner shaft, and then out in the space between the inner shaft and the outer shaft? We don’t know.

When we remove a torque converter, we like to have, at the ready, a round drip pan with strong vertical sides, slightly taller and with a smaller diameter than the torque converter. That way, after removing the torque converter from the transmission, we can put the torque converter onto this drip pan and allow the fluid within to run and drip out.

We removed the torque converter while the transmission was on a large drip pan that in turn was on a wooden pallet, off the floor by a few inches but still low, so that if we were to drop the torque converter by mistake, it would not have far too fall.

We removed the torque converter after we’d thoroughly cleaned the outside of the transmission, to reduce the risk of dirt getting inside the torque converter or into the input shaft.

From what we see in the ZF spare parts catalog, all the C5 A6 Audis that use this transmission have an identical torque converter. Informally it’s known as the P35, with ZF part number 4168 026 394. The C5 S6 Audi, being a more-sporty model, has a different torque converter: Q35, with ZF part number 4168 026 395.