L322 ZF8HP70 gearbox problem

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kermit_rr

kermit_rr

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Any gearbox guru's here?
Most of the time i have no issues, no soup that i can tell but i do get a snatch between first and second gears, more so when it's warm.
The biggest issue i have is the tenancy to go into a 'neutral' at speeds under 20.. slow down slowly, it will drop to 2nd, then drop to neutral somewhere between 15-20mph, i don't mean the torque converter unlocks, i mean full on neutral. if i touch the accelerator, nothing happens for a second or so then it will bang into gear and off we go.
If i select D and let it roll downhill with no accelerator, it will stay in neutral until 8-10mph then bang into 1st.
I did an oil and pan/filter change just over 12 months ago and that made no difference.
I think the actual gearbox is ok, but i don't know the first thing really just that they are very complicated with the solenoids/valves/mechatronic etc but other than pay someone to step the lot down and check everything, is there any way to narrow down which bit is likely dead?
Could it be the torque converter that's not working properly? Any way to rule in or out the rest? There's no error codes.
I think it's getting worse, slowly. Id rather not get stuck one day especially far from home on holiday etc!!
 
Is it the same set up as the 6 speed with the mechanical selector on the side that seizes up?
 
'Not a fan' of gearbox flushes, the oil they use will 'meet the specification' - barely in most cases. You've already said an oil & filter pan change made no difference so we can discount the oil and the oil level if it made no difference...
If it's dropping out of gear / no friction on the clutch packs, to me, that sounds like a hydraulic valve issue. If it were the control electronics or the valve(s) have an electrical defect, then that would/should set a DTC as the valve current is controlled & monitored.
I would add that I'm by no means a auto transmission specialist, much of the dealer-level diagnostics across all the marques I've worked for (inc. JLR) are opaque in terms of the diagnostic flow process and usually results in an instruction to change the transmission or a sub-assembly, there is no process to strip, measure & repair the internals of an auto transmission in dealerships. Conversely, manual gearbox & transfer 'boxes are very hard to exchange as the repair instructions - and parts, are readily available.
 
If it's staying there, it's unlikely to the the trans. oil cooler leaking into the transmission - if it was constantly dropping, then it would be worth taking a sample for testing.
 
I read about low coolant being a split expansion tank and it drops to the level of the split.. but i don't think that's the case.
I should really figure out what it is though.
 
If the expansion tank were split, then the coolant system wouldn't pressurise correctly, leading to further coolant loss as the coolant expanded, along with steam & the aroma of baked-on coolant....
 
How is the engine running, any after market modifications?
Any issues with air flow or fueling problems?
Any stumbles or hangups of engine speed?
The reason for the question.
The shift pressure is always based on engine torque signal. BUT if the engine torque signal does not match actual torque being generated by the engine then the pressure used for the shift will be wrong.
The transmission should be consistent. If not it could well be the engine actual torque is not matching engine signal torque on some occasions.
 
Graculus said:
If the expansion tank were split, then the coolant system wouldn't pressurise correctly, leading to further coolant loss as the coolant expanded, along with steam & the aroma of baked-on coolant....
Click to expand...
Yes agree. Dunno, where is going though or why it only drops so far. I should bother to fix it
 
V8bob said:
How is the engine running, any after market modifications?
Any issues with air flow or fueling problems?
Any stumbles or hangups of engine speed?
The reason for the question.
The shift pressure is always based on engine torque signal. BUT if the engine torque signal does not match actual torque being generated by the engine then the pressure used for the shift will be wrong.
The transmission should be consistent. If not it could well be the engine actual torque is not matching engine signal torque on some occasions.
Click to expand...
It runs fine, but it's been de-dpf'ed. I don't know what was done to the software,/engine map etc or if anything else has been done. I don't know if it has been done 'properly'
 
V8bob said:
How is the engine running, any after market modifications?
Any issues with air flow or fueling problems?
Any stumbles or hangups of engine speed?
The reason for the question.
The shift pressure is always based on engine torque signal. BUT if the engine torque signal does not match actual torque being generated by the engine then the pressure used for the shift will be wrong.
The transmission should be consistent. If not it could well be the engine actual torque is not matching engine signal torque on some occasions.
Click to expand...
That's a good point - I was also considering turbine speed sensor as a possible cause but again, without reading actual values, you'd have to rely upon a DTC being set.
 
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