Replace ZF6 HP26 with HP28 TRANSMISSION

[TDV6]

I am having issues with the auto box in my 2.7 TDV6, and was wondering if anyone has replaced their HP26 box with the later HP28 or an 8 speed box.

I will go down the Fuchs ATF 4400 route before ordering a new box, however if I am up for 8K and a HP28 will work with the 2.7L TDV6 then I think it would be the way to go.

We have replaced the ATF 2 month's ago using ZF Lifeguard and added Dr Tranny, without van on all is fine, but spits the dummy once the van is attached.

Ryall

[Slunnie]

Is the ATF cooler clear so the air can get through all of it?

[Graeme]

A different canbus architecture was implemented for the 2010 D4 so the gearbox ecu, which is located inside the gearbox rather than in the vehicle, is likely to be the stumbling block to fitting the HP28 or the 8-speed.

[CaverD3]

I think the HP28 was the one used in the V8 D3 all year models. More robust components but not sure if the mechatronics are the same. You could ask ZF exactly what the differences are.

[Graeme]

I thought the HP26 was upgraded to the 28 for the 3.0 but even if it was available for the old canbus, there might not be software suitable for use with the TDV6 with its dfferent torque and power characteristics to the petrol V8.

[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 (http://www.disco3.co.uk/gallery/thumbnails.php?album=5059)

Thanks,

Ryall

[TerryO]

I'd be interested to find this out as I reckon our auto is not long from giving up the ghost as well.

[Graeme]

As I recall the 28's torque converter can be locked at lower revs to allow better use of the 3.0's low-down torque. With the gear ratios identical there's not going to be much difference.

[jonesy63]

IIRC, the 6HP26 was on the D3 2.7/D4 2.7, 6HP26X was in the D3 4.4 and 6HP28 was in the D4 3.0. I doubt very much if they're interchangeable.

[CaverD3]

If the mechatronics and or transmission ECU could be swapped it may be possible.
Even if you get a D3 V8 one the ecu would need to be re-flashed (at the correct temp)
It is something that has not been done before I would think but if you want to be a guinea pig?

A no on disco3 but not much response or feedback

DISCO3.CO.UK - View topic - D4 ZF 6HP28 into D3 is it Posible !?! (http://www.disco3.co.uk/forum/topic95344.html)

There seems to be little definitive info as to whether the V8 trans mission was changed during the D3s run.

Sniegy might be able to find out.

[Graeme]

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.

[Rich84]

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.

[ak]

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?

[RR P38]

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 (http://www.disco3.co.uk/gallery/thumbnails.php?album=5059)

Thanks,

Ryall

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.

[TDV6]

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

[RR P38]

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.

[TDV6]

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

[dennis brine]

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

[TerryO]

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

[discotwinturbo]

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

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...

[dennis brine]

always let gearbox do its own thing
it is normally in 5th (about 1800rpm)- will sometimes go into 6th if a bit downhill.

[TerryO]

ok Dennis, do you use sport mode or normal drive?

The reason I ask is 85 kph is very slow and most auto gearboxes keep trying to shift up. Personally I would have thought 85 kph in fifth towing a heavy van would be putting quite a lot of strain on the auto.

I'll stand corrected if I'm wrong.

I find even with my 2.7 D3 that at around 110 to 115 kph the Disco drives a whole lot better when towing our 2.5 ton van and at that speed I'm usually in fifth.

[dennis brine]

hi Terry
thanks for your comments
leave box in normal mode
box shows no sign of wanting to shift up - can manually shift up but smallest increase in load causes it to shift back down.
dont understand why 5th would cause more load - need a certain amount of output torque from gearbox to keep van & car moving (to overcome rolling resistance etc). With higher gear reduction in 5th gear versus 6th gear this means less torque at torque converter = less load on torque converter.(this is from my engineering background).
Have towed at higher speeds & gearbox stays in 5th but I am retired & in no hurry plus get better fuel consumption.

But I am also interested in your experience re 6th gear - even when not towing, car lightly loaded & level road it does not want to go into 6th in normal mode - have to manually force it up. Have complained to dealer before but "no errors"

Also find box very slow to downshift on steeper hills when towing - revs drop to around 2000rpm or less, car is slowing, flat out accelerator & box does not want to shift down (eventually does just as I am thinking of a manual down shift before we stall)

car is a 2.7l disco 3 SE

very interested in your experience.

regards, Dennis