Valve body repair ZF 8HP45 8HP55 8HP70 (Audi BMW)

ZF 8HP - a series of automatic 8-speed transmissions manufactured by ZF, first introduced in 2008 and already from 2009 these boxes were actively installed on almost the entire BMW model range, then there was a modification for the front and all-wheel drive Audi A7, A8 and Q5 cars.

In addition to the mentioned BMW and Audi, such boxes on our market are found on Jaguar, Land Rover, Range Rover. Chrysler is installing a slightly modernized analogue of the ZF 8HP in its vehicles under the 845RE marking.
The name of the transmission is decrypted as follows (for example, ZF 8HP70):

    8 - the number of gears
    H - hydraulic
    P - planetary
    70 - permissible input torque (700 Nm)

In general, the engineers managed (in comparison with their predecessors, a 6-speed automatic transmission from ZF) not only to maintain physical dimensions, but even to reduce the weight of the unit. In 2009, the ZF 8HP was perhaps the most modern automatic transmission - the Start-Stop system, which allows you to start moving for 350 ms after restarting the internal combustion engine, an adaptive strategy for working in different temperature conditions, and the possibility of sequential and non-sequential gear shifting.

Today we’ll talk about the repair of the valve body of the 8-speed ZF transmissions. Let's start with testing. We have a new stand that allows you to completely simulate the operation of the valve body as if it were installed in an automatic transmission and the repair specialist can see in real time how the hydraulics and solenoids work. This test method allows for the most detailed diagnostics, in contrast to a simple vacuum test with a tester, since some problems (jamming of plungers or incorrect operation of solenoids) occur only after warming up.

The valve body we received from the client has the following symptoms:
 

•     Thump when turning on DRIVE
•     Thumps when shifting from first to second and from second to first gears
•     Hard torque converter lock up

Check on the stand


                                                                                               Our new stand for valve body diagnosis

Installing a suitable adapter and fixing the valve body

                                                Entering the valve body model and the tests we are interested in, in this case there will be full testing

We start the stand and immediately see the problem - in the second photo there is a jet of oil from the booster of the main pressure valve, this should not happen and this indicates that the valve body cannot stabilize the pressure.

The valve that controls the main pressure and its booster is the weak point of all ZF boxes, from 4 to 9 speed gearboxes. When we discussed with the client the problems of the valve body - it was already clear from the verbal description that it would be necessary to do, practically every valve body with a mileage of 90-120 thousand has the Main Pressure booster seriously worn out, this can be determined by the following symptoms:
 

•     Diagnostics show high pressure errors
•     Drive turns on with a thump
•     If the booster is in order, but the valve itself is worn out, the drive, on the contrary, will turn on too "sluggishly" and slowly.

There are such repair options:
 

•     Repair valve pressure regulator (Oversized Pressure Regulator Valve) ZF 8HP45 8HP55 8HP70 - repair valve with booster, installation requires a reamer
•     The pressure regulator valve booster (in the original size | gen 1) (Pressure Regulator Valve Boost Sleeve) ZF 8HP45 8HP55 8HP70 is the original size booster for the first generation ZF 8HP, if the valve itself is in order, you can simply fix the problem by replacing the booster.
•     The pressure regulator valve booster (in the original size | gen 2) (Pressure Regulator Valve Boost Sleeve) ZF 8HP45 8HP55 8HP70 is the original size booster for the second generation ZF 8HP, if the valve itself is in order, you can simply fix the problem by replacing the booster.

Also, 8HP valve bodies have problems with end caps, if the vacuum drops to 16 inches of mercury and lower, pressure losses are waiting for us, which at first leads to jerks or vice versa slow switching, and ends up with burnt clutch packs. We ALWAYS check them and, if necessary, replace them with new ones:
 

•     Valve body end caps (in original size D 13 mm) ZF 6HP19 6HP21 6HP26 6HP28 6HP32 6HP34 8HP45 8HP55 8HP70
•     Valve body end caps (in original size) ZF 8HP45 8HP55 8HP70

Test results in the graphs below. A preliminary verdict is the following- we will repair the Main Pressure and TC Pressure valves, the latter showed very poor results during the test.

Repair start - disassembly

We disassemble and simultaneously inspect the separator plate and accumulators for the presence of wearout and damage. An interesting fact is, in 6HP, the replacement of accumulators is almost a mandatory attribute for repairing the valve body, but in 8HP they are in good condition in 95% of cases.

Solenoids removal

Solenoids (electromagnetic valves)

About solenoids - there are 9 of them in the block; repair technology does not currently exist. If there is a problem with them - either change to new ones, or rinse. You can rinse in 2 ways:

•     Ultrasonic flushing
•     Rinsing on the stand is a rather interesting method - we set the stand for checking solenoids to manual mode, set the opening / closing frequency (100 times per minute, for example) and serve the oil.

8HP solenoids are extremely sensitive to the purity and temperature of the oil, so we recommend changing it more often. An interesting fact, the fine tuning of the solenoids and the mechanism of self-adaptation of the box work so that even dirty oil can negatively affect the operation of the solenoids and cause shocks or slippage during shifting.

Vacuum testing and hydroplates visual inspection

Checking TC Pressure valve. Very low vacuum, only replacing the valve with a repair one will help.

Checking the vacuum zone of the Main Pressure booster. It will be enough to replace the booster, the valve itself is in perfect condition.

Hole reaming, oversized valves installing, repeated vacuum testing

We use reamers and valves of our own production for repair, the assortment for ZF 8HP can be viewed at the links below:

• ​Oversized valves ZF 8HP45 8HP55 8HP70
• Reamers ZF 8HP45 8HP55 8HP70

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                                                                                                                Fixing the hydroplate on the drilling machine and reaming the hole of the TC Pressure valve

We take the repair valve, install and repeat the vacuum test. Excellent result, we collect the valve body.

Final check on the stand

Testing. Pay attention to the Main Pressure booster again, it no longer passes oil.

Schedules of testing after repair.

The repair is over, the valve body works perfectly, you can pack and send it to the client. Now about pricing. We do not have a fixed repair price, it is calculated based on the number of replaced parts as follows:

Typically, repairing an 8HP valve body costs in the range of 330-375 $, but options are possible - the greater the mileage, the greater the likelihood that you will need to replace more than one valve but 3-4, or the solenoids will not work after washing.

Also there are already regenerated valve bodies on sale:

• Valve body ZF 8HP with solenoids (1 gen / electronic parking/ separator plate A048) — regenerated

If you need repair parts, you can purchase it from the links below:

• ZF 8HP45
• ZF 8HP55A ZF 8HP65A
• ZF 8HP70