My auto box has a problem unlike any auto I’ve worked with before. When warm and in D, 2 or L, if you mash the throttle the box can’t hold on to first and jumps into second. I noticed this problem when I test drove the car and to be honest it doesn’t tend to cause a problem given my rather relaxed driving style in the ‘Cruiser, but it can be annoying.
If you’re gentle, it’ll hold first and progress through all four ranges as you’d expect. Stamp on it and first becomes anathema to it – it’s almost like an anti-kickdown 🙂
So, simple things first: check the throttle / TV cable. If it’s disconnected or loose not only would it be slipping (the cable regulates box line pressure, dictating how much force is applied to the clutch packs) but it would also be very premature in its shift points.
Once out of first the box behaves impeccably and hence I couldn’t believe that was the problem. It wasn’t – the cable was correctly adjusted. Winding the adjuster on some more to pull the cable further just firmed up the shifts and if anything caused the first gear issue to get worse. Hmm…
In perusing around the interpipe I found that Julian from Overland Cruisers is a dealer for Wholesale Automatic Transmissions who do various uprated solutions for the A442F, most notably their A442F extreme rebuild. Whilst I feel the entire package is a bit overkill, the extreme valve body on its own adds various benefits such as allowing lock-up in the top three gears as well as providing firmer shifts and applying greater pressure to the clutch packs. If it turns out to be a real valve body issue, I reckon the extreme valve body could be a neat way of both fixing the problem and providing a stronger box. Julian’s prices are good for these, so if you’re interested I’d get in touch with him 🙂
Anyway, back to diagnosing what’s going on with my box. The factory service manual is quite verbose here in how to narrow down the myriad possibilities, but it doesn’t directly cover my symptoms in any of the various flow charts. Following are the various check I’ve undertaken and the order in which I performed them:
1 – Fluid change
My past experience with auto boxes has proven two things, firstly that correct fluid level is critical, and secondly that more often than not they tend to be forgotten when servicing the rest of the vehicle, usually because they tend to be very reliable.
My car was no exception with respect to the second point: although the fluid had been topped up, when I took ownership of the car the fluid wasn’t quite as cherry red as it should have been. So, first thing – change the fluid.
Doing a fluid change on an auto is easy but not a one-step operation: the hydraulic system holds approximately 15 litres of ATF, but only six litres of that will drain out in one go. As a consequence (and without resorting to various levels of disassembly!) the best you can do is perform a couple of changes and hence dilute the old fluid with new. The procedure I undertook was as follows:
- Take the car for a bit of a drive round to get the fluid warm: ensure the temperature gauge is in the middle of the range. Conveniently I have quite a few steep hills within a couple of minutes of my front door, so a couple of trips up and down those soon get the vehicle up to temperature.
- Apply the hand brake, stick the transmission in park and kill the engine.
- Shove a bowl under the transmission oil pan and remove the drain plug.
- Leave it for a few minutes to drain down. It might be worth moving the shift lever through all of the ranges to see if it drains any more fluid out of the various pistons and clutch packs, however I’m unable to confirm if this has any effect or not as I was on my own when doing this operation. I figured it couldn’t hurt 🙂
- After the majority of the fluid has drained out, replace the sump plug. Take your bowl of used ATF and roughly measure how much fluid you collected.
- Refill the transmission with as much new ATF fluid as you drained out. A small funnel stuffed into the transmission dipstick tube appears to be the accepted way to replace the fluid.
- Start the engine and firmly apply the footbrake. Move the gearshift through each of the ranges, pausing for a few seconds in each to allow all of the fluid passages in the valve body to refill. Finally, move the shifter back to neutral and leave the engine running.
- Check the transmission fluid level with the dipstick. As the transmission is at an indeterminate temperature, you can’t really rely on either the ‘hot’ or ‘cold’ marks – you just have to trust your measurements were vaguely accurate 🙂
- Go for another drive again to get the tranny back up to operating temperature, but pay attention to how it feels. It might be worth taking some fluid with you in case you feel it slipping (which is usually caused by a low fluid level).
- Once warmed up again, repeat the above procedure.
- After two changes, do another drive round, but this time perform another level check. As the fluid is now warmed up, you should be able to trust the ‘hot’ mark. Make sure you top it up to the top of the ‘hot’ range.
Once all that was done, I went for another drive round and tried mashing the throttle from a standstill. Unfortunately, there was no difference whatsoever in the box’s behaviour and it jumped straight into second again. Not something very simple, then…
2 – Gear shift link check
Apparently one of the things that can cause first gear not to be held (at least in position ‘L’) is a badly adjusted shift linkage. There’s a neat little procedure on LCOOL explaining how to check and adjust this – it’s essentially lifted from the service manual, however it has been annotated in places.
After checking this again there was no change. Worth a try though…
3 – Line pressure (TV) cable adjustment
Easy enough to check: with the TV cable connected to the throttle linkage and the throttle at idle, make sure the following adjustment is as pictured below:
4 – Throttle position sensor
The TPS check is a nice easy test, requiring just a multimeter.
Locate the ECT diagnostics port – it’s attached to the bulkhead to the right of the engine. Flip open the cap and attach the multimeter as follows:
Switch on the ignition (but don’t start the engine!), then grab the throttle linkage and slowly move it from idle to flat out. The reading on the multimeter should increase in a series of steps:
If the voltage leaps around as the throttle is opened, it’s probably either a dirty or defective TPS. If not enough steps are read, consider that the TPS may be misadjusted.
Again, unfortunately, mine was behaving fine and was correctly adjusted, so on to the next test…
5 – Mechanical shifting test
This one is quite entertaining as it involves putting the box under full manual control, and is again quite easy to do. The idea here is that you remove all electrical inputs to the box and rely instead on the shift lever to change ranges. Without the ECU providing drive to the solenoids, only first, third and fourth are available and no automatic shifting will take place. If, however, all of the ranges engage correctly, this to a large extent rules out malfunction of the gearbox mechanics.
So – the procedure:
- Engine off, handbrake on, gearbox in Park
- Under the passenger side of the vehicle, locate the solenoid harness connector (approximately half-way up and half-way along the gearbox). Push in the locktab and remove the connector.
- Go for a drive 🙂 Reverse should work correctly, however forward ranges are now completely under driver control:
- ‘L’ gives you first
- ‘2’ gives you third
- ‘D’ gives you fourth (overdrive)
- Check that each range works correctly, but remember that there will be no torque converter lock-up over 40MPH and as a consequence be mindful that you don’t overheat the transmission by maintaining high speeds (> 50MPH) for any period of time.
Success! The transmission behaved correctly, and it was incredibly pleasant to experience full-throttle first gear from a standing start 🙂 The box held first quite happily without any fuss whatsoever. Based on this, I’ve either got an electrical issue with the ECU or a malfunctioning shift solenoid. This is good as, on the scale from “expensive” to “f***ing expensive”, it would appear we are on the lower end 🙂
Conclusions so far
Well – it would appear that it is not a core gearbox problem but something on the periphery, namely the electronic control system or the valves directly connected to it.
My next step is to test the solenoids. I’m sure they’re working otherwise two of the four gears would be completely absent, but it feels as if one of them either isn’t opening or closing completely allowing fluid to pass, especially at higher line pressures – i.e. when the throttle is pressed harder. In the FSM there is a convenient table:
Based on this, if solenoid 2 leaks in any range when 1 should be on and 2 off, this will result in second gear. This looks like a good suspect 🙂
So – next job is to create a bit of a test harness to see how the box behaves under manual control. As it stands it’s late and I’m knackered – I think I’ll have a play with this at the weekend…