Replace ZF6 HP26 with HP28 TRANSMISSION

What would you hope to gain from fitting a HP28? Is the ability to keep the torque converter locked at quite low revs (eg 1000 rpm) of any use when mated to a 2.7 when the TCM is going to change down anyway when the engine can't produce sufficient torque?

An 8-speed would be nice but I suspect they cost a great deal more than a rebuilt HP26, they're programmed for different engines' torque and power and the changed canbus means that its not going to work anyway. Replacing a HP28 with an 8-speed would be another matter, which I may consider if my HP28 needs to be replaced when the 8-speeds aren't so new.

How exactly is your gearbox 'spitting the dummy' TDV6?

I note sometimes if I hook up a trailer with LEDs I get a "Transmission Fault" message. The trailer can be empty and it still does it randomly.

Yet I can hook up our camper trailer with LEDs which is three times heavier, and it won't have any problem for thousands of km.

What are the problems with the D3 Auto trans? I also noticed in the market place a D3 listed with 265K and the owner saying the Auto was rebuilt. I was not aware the Auto in the D3 had problems. Could anyone please enlighten me?

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Originally Posted by TDV6

Thank you all, yes the ATF cooler is in clear cold air flow about 2 inches in front of radiator, was told by one auto trans tech that oil can quite readily reach 170 degrees C when towing.

Will be asking questions of ZF etc of differences between HP26 AND HP28. looking at ZF pdf file there appear minimal changes between them.

PDF file copied from bbyer gallery see ; DISCO3.CO.UK Photo Gallery - ZF 6HP26 Automatic Transmission in LR3

Thanks,

Ryall

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If your trans fluid reaches 170c it will be RS after a few minutes at this
temperature.
Your trans ECU should be defaulting to a cool down mode as well at about 125c ish.

There were two fault codes listed P0730 and P0735 plus the "F" in the dash display, there were also two other codes listed for the torque converter, but I don't know what they were.

I towed the van 750k last week, annual fishing trip, caught 10 yellowbelly and one jewfish, reading on scangauge showed marked increase in horsepower required when "F" on display and engine temp rapidly raising to 106 Centigrade then returning to 90 at idle. Car would really slow up with "F" display. It was defiantly temp related as long hills, on single lane bitumen with engine temp around 100-105 generally resulting in "F" display and just limping over crest of hill.

Park with motor at idle for a few min then turn moror off and back on quickly to continue cooling wait a few min then slowly resume trip, after watching engine temp and trying to keep below 100 degrees we were able to get another 100k or so before the next "F" event.

Clear all faults with MSV2 and car is happily touring along with another 600k since returning and no other faults returning since the van was disconnected.

I now have a digital temp guage ready to fit to the outside of the pipe sending hot oil to the oil cooler, to be fitted as close to the transmission as can get it.

I will be also replacing the seven pin trailer connector on the van, to prevent any electrical problems that may upset the tranny (thanks Rich84).

After all that I will establish and record baselines, having changed scangauge to read engine temp, rpm, map and voltage as well as new auto trans temp gauge, then hitch up van and see what happens, if it plays up I will change ATF to Fuchs 4400 adding DR Tranny as well to see if it helps, if it's still not working, get new transmission fitted. I will be watching for RPM fluctuation while in same gear.

Costs I've been quoted are 4550 + GST for ZF Reconditioned from ZF re-manufacturer and 7000 for brand new HP26 filled with oil plus 1100 fitting. I don't know if Reconditioned means new valves and Mechatronic unit. Reconditioning at local auto trans shop says depending on parts but under 9000.

Thanks all, will update as I go.

Ryall

OBD Code P0730refers to;
This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows: Torque converter slip ratio = A x C/B A: Output shaft revolution signal from speed sensor (revolution sensor) B: Engine speed signal from Engine Control Module (ECM) C: Gear ratio determined as gear position which TCM supposes If the actual gear position is higher than the position supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.
Symptoms
Possible sumptoms of OBD code P0730
- Engine Light ON (or Service Engine Soon Warning Light) - Incorrect transmission shifting
Causes
Possible causes of OBD code P0730
- Low transmission fluid level - Dirty transmission fluid - Shift solenoids - Shift solenoids harness or connectors - Transmission mechanical problems - Transmission hydraulic control circuit The Error code is generally activated on detection of the following conditions: The TCM has detected that the transmission is trying to mechanically shift to a lower gear than intended.

OBD Code P0735refers to
This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows: Torque converter slip ratio = A x C/B A: Output shaft revolution signal from revolution sensor B: Engine speed signal from Engine Control Module (ECM) C: Gear ratio determined as gear position which TCM supposes If the actual gear position is higher than the position (5th) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.
Symptoms
Possible sumptoms of OBD code P0735
- Engine Light ON (or Service Engine Soon Warning Light) - Incorrect transmission shifting
Causes
Possible causes of OBD code P0735
- Low transmission fluid level - Dirty transmission fluid - Shift solenoids - Transmission mechanical problems - Transmission hydraulic control circuit The Error code is generally activated on detection of the following conditions: P0735 is detected when A/T cannot be shifted to the 5th gear position even if electrical circuit is good.

The ATF was changed last month when the additional ATF oil cooler was added.

I hope to hitch the van up next week for a short run down the highway up past Nambour which has several nice hills and not too far from home.

Ryall

I am very unhappy about the zf26 transmission - tdv6 from new
first failed at about 60k & lr reluctantly repaired under warranty (incl new torque converter) & problems started again at about 120k.
I tow 3 tonne van & after first failure added extra tranny cooler & temp gauge. fluid has been changed after 20k with lifeguard fluid.
tow at about 85kph, tranny temp normally about 55c - never seen over 90c (& then for short time). always let box do its own thing (as recommend)
basically believe transmission can not handle load from towing 3 tonne vans or similar.
think ZF really should be forced to upgrade transmission or have to replace under warranty - some hope I guess but it is obviously not suited.
looking at alternative vehicles but most have ZF transmissions which I will not touch.
welcome any coments

Out of interest Dennis, what gear do you tow in when your driving at 85 kph?

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Originally Posted by TerryO

Out of interest Dennis, what gear do you tow in when your driving at 85 kph?

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I don't know if there is much mechanical difference between my Touareg 6HP26A and the LR 6HP26 but my Touareg has lugged around 3.5 tonne for 5 years very regularly, and transmission has coped without any complaints during this time, even to the point of the oil transmission test at 120k advising no need for change.

ZF are in a huge number of vehicles.....most of them being high torque motors.

I guess it comes down to how the manufacturer programs them ?

My VW 6HP26A has always had better engine breaking than my Disco, sport mode is significantly better, but normal mode is slower to react to throttle input than the Disco.

When I was looking at buying my D4 and realised that the D4 had a similar transmission to my VW this was a good point for me, but there is definitely a difference.

Brett...