Double Trouble - Transmission Digest

Double Trouble

In today's world of automatic transmissions we see several different types of solenoids being used depending on the strategy the engineer chose to employ. There are the typical on/off solenoids that could be normally closed or normally open. And then there are PWM solenoids, normally applied or normally vented.

Double Trouble

Technically Speaking

Subject: Solenoid modulating valves
Units: 722.9, AS68RC, RE5R05A, 09D
Essential Reading: Rebuilder, Diagnostician, R & R
Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Technically Speaking

  • Subject: Solenoid modulating valves
  • Units: 722.9, AS68RC, RE5R05A, 09D
  • Essential Reading: Rebuilder, Diagnostician, R & R
  • Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

In today’s world of automatic transmissions we see several different types of solenoids being used depending on the strategy the engineer chose to employ. There are the typical on/off solenoids that could be normally closed or normally open. And then there are PWM solenoids, normally applied or normally vented.

Some of these solenoids are fed with line pressure through an orifice so its flow rate is less than the exhaust rate. When the solenoid blocks the exhaust, pressure builds to stroke a valve. Other solenoids are fed un-orificed line pressure, which a PWM solenoid could used to directly control the application and release of a clutch.

Then there are solenoids that are supplied with regulated pressure from a modulating valve. The modulating valve typically is fed with line pressure, which it regulates down to a lower pressure to be used to feed the solenoid. In many ways, this modulator valve acts as an over-glorified orifice. The modulating valve controls the flow rate to the solenoid so that it is less than the exhaust rate. Should this valve be compromised in any way, it could either starve the solenoid of feed pressure or flood it with too much pressure.

In some instances, there are designs that require two modulating valves to sufficiently supply the increased number of solenoids being used. The 722.9, AS68RC and RE5R05A transmissions are several such examples. Another is the 09D transmission.

As you can see in Figure 1, solenoid modulating valve A supplies regulated pressure to the TCC, line-pressure and K1-clutch control solenoids.

Figure 2 shows how solenoid modulating valve B supplies the B1, K2, K3, N88 and N89 solenoids.

We all should know by now how modulating valves wear the bore they live in (Figure 3).

So with these types of transmissions using two modulating valves we now have “double trouble” on our hands with solenoid feed supply (Figure 4). With the 09D transmission, the most-common complaint seems to be harsh shifting during acceleration through a 4-5, 6-4 and/or 5-3 shift. In many instances bumpy coast downshifts occur as well – a telltale sign of modulating-valve bore-wear problems requiring reaming and new valves or a complete new valve body.

Just a thought – it seems to me that once a flow rate can be determined, a simple orifice feed can be the modified fix via a redesigned spacer plate or a bore-fit orifice.

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