D40 auto loss of reverse

[Piston Broke]

Hi all, I've done a search but can't find the same problem to what we are looking for.

We have a 2006 D40 TD 4WD auto that suffered water contamination in the tranny from the radiator. We rebuilt the tranny (seals, filter etc), fitted a rebuilt transmission module and solenoids and fitted an external transmission cooler to separate the tranny from the radiator. Since then there was a faulty sensor on the transfer case which prevented the tranny from changing up through the gears. This sensor has now been replaced with another sensor we had in a box of spares. This got the vehicle back on the road,
While the success was celebrated, it was short lived. After 4 days of short drives around town, the vehicle will now not go in to reverse. When the gear shifter is moved to reverse, you can feel the box engage (revs drop and the vehicle feels like its in gear) however the engine just revs and vehicle doesn't move. At the same time, the 4wd light on the dash flashes. This is the 2 front wheels on the 4wd indicator light. There are no issues in all forward gears, and the 4wd light does not flash in forward gears.

There are no codes showing on the consult 3 during any of this process.

I did read online about a fault in these trannies where the circlip that holds the reverse gears together can shatter and results in the loss of reverse gear. If this is the case, why would the 4wd light flash and the feeling of engagement when put into reverse, or is there some other issue here? I'd appreciate any ideas before we go and pull the friggin tranny back out and strip again.

Thanks.

 

[Old.Tony]

It sounds electrical to me although I can't think of precisely what is causing it. This might be on the transfer case, which has sensors to monitor the position of the gearing within - a fault there will trigger the 4WD light. It may also be related to the ABS which impacts on the 4WD circuit too. I'd probably look closer at the transfer case, since that was necessarily moved around while the gearbox came out (and the ABS sensors weren't).

As far as I know, the transfer case doesn't operate uni-directionally - that is, once the drive is engaged through the case (specifically thinking about LO and HI here) then it doesn't matter about direction, it will do the same forward and backward.

Here's a question: can you engage 4LO in a forward direction? Do you get the lower gearing? What happens in 4LO if you engage reverse?

 

[Piston Broke]

Thanks for the reply. An update on todays proceedings, when it was cool this morning, the vehicle ran fine with all gears including reverse until about 2-3km down the street. Then after pulling into the servo there were problems with 3rd and reverse gears. We got it home and let it cool down again and this arvo we ran it around the block again where it ran fine until returning home where there was no reverse and the 4WD light flashing when trying reverse.

We are suspecting its heat related as it runs fine when cool but once it warms up this is when the problems start. We are looking at the tranny cooler to ensure its flowing and cooling correctly. We are looking at a bigger heavy duty cooler to see if that fixes the problem.

To answer your question, when it plays up, it goes in to 4WD in forward gears but while in 4WD, hi and lo, there is no reverse. Are you thinking of some other issue?

Thanks.

 

[Old.Tony]

I was wondering if perhaps the ABS system was impacting on it, perhaps through a faulty bearing on one of the front wheels (this has happened to me). You've pretty much nailed that it's not the case, any ABS fault would prevent you from putting the car in 4WD.

A better (larger/more efficient) transmission cooler may only prolong the time before the problem surfaces and will introduce other "features". We have a large tranny cooler on ours because we regularly tow a 2.5T caravan, and on cold mornings the gearbox will not engage the torque converter clutch until the coolant temperature (specifically unrelated, but used as a measure of how much driving has been done) exceeds 65 degrees.

It would be interesting to see what a professional scanner has to say about the gearbox when the vehicle is cold vs when it is hot. How much TC slippage, what kind of temps are being raised inside the gearbox etc. Is it a valve in the gearbox's valve body that sticks when it is heated beyond a certain level? Is it an electrical fault in or related to the TCM - this may not be reported by the TCM directly, but largely unexpected results from a scanning tool might indicate something wrong with the electrical connections.