4.8 GRX transmission lockup speed

[Clem]

Guys, my 4.8 only locks up at almost exactly 120km/h (true speed per GPS, speedo reading just a shade under 130km/h). Now lockup appears to affect fuel consumption*, which means keeping it in lockup is desirable. But that implies being just over the speed limit all the time. Is there any way to adjust the lockup speed? Ideally I'd prefer it to be something like 100km/h.

* I get better fuel consumption travelling at a true 125km/h to 130km/h on the clock than at anything below a true 120km/h

[hugejp]

Subscribed!

[NMAD]

Releasing Lock-up
Throttle position

Lock-up “ON” Lock-up “OFF”
Throttle position Closed throttle 64 - 72 (39 - 45) 61 - 69 (38 - 43) Vehicle speed km/h (MPH)
Throttle position Half throttle 164 - 172 (102 - 107) 130 - 138 (81 - 86) Vehicle speed km/h (MPH)
+When throttle is closed, the accelerator opening is 1/8 or lower of the full opening, and the closed throttle
position switch is turned “OFF”.
+ At half throttle, the accelerator opening is 4/8 of the full opening

Lockup goes on on my Patrol around 105 km and if i slow down and drive at 90km/h (1500 rpm) it still stays on as long as the box is not been strained like going up a hill etc.

previously I also found that it only locked up around 120km hours and I discovered that my rear hand brake was not adjusted correctly and it had a lot of drag, I jacked up the rear axle so I could spin both wheels freely at the same time after adjusting the rear brake drums on each wheel.Now the rear wheels spin freely and since then it locks up correctly so I think it could have been the hand brake always been partly on which caused a problem.

If you have larger than stock tyres and I think it could also cause it to lock up later due to the inertia of the larger tyre?

[David]

Yes larger tires definitely plays a role but do your throttle position learning first as everything is related.

I have 33' s and find it sometimes worthwhile to rather put the auto in manual 4th when doing around 110km/h as the lockup and cruise control just works better.

[Clem]

My vehicle is 100% standard other than for a Bosal towbar and Connan bash plates.

My speedo cruise doesn't work other than in "D".

Interesting comment about the handbrake.

[IR_Eddie]

i know this might be a stupid question, but can you explain (in laymen terms) what you mean by transmission lockup speed?

[NMAD]

I am not a mechanic but I see it like this: the auto box has a torque converter and this locks when you are in top gear ie 5th and it almost acts like an extra gear as its lowers the revs more, so if you are cruising at 120km hour in 5th gear at say 2400 rpm and then the transmission locks up the revs will drop lower to say 2200 rpm and you will still go the same speed: it saves fuel but not sure how much.


https://en.wikipedia.org/wiki/Torque_co ... converters

Lock-up torque converters[edit]
As described above, impelling losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss.

The first automotive application of the lock-up principle was Packard's Ultramatic transmission, introduced in 1949, which locked up the converter at cruising speeds, unlocking when the throttle was floored for quick acceleration or as the vehicle slowed down. This feature was also present in some Borg-Warner transmissions produced during the 1950s. It fell out of favor in subsequent years due to its extra complexity and cost. In the late 1970s lock-up clutches started to reappear in response to demands for improved fuel economy, and are now nearly universal in automotive applications.

[David]

My speedo cruise doesn't work other than in "D".

Do the cruise in Manual Mode Mod

Works lovely when towing as you can gear up or down as necessary and use cruise control in 4th

[Clem]

NMAD's post is correct. That's what I'm referring to. I read somewhere (I cannot remember where, might even have been the manual) that when in "D" the 4.8 only locks up in 5th and then only at 120km/h. En sowaar, that seems to be the case with mine.

Unless there's something I'm missing. But I definitely use (quite a bit) less fuel exceeding the speed limit than staying below it and when you take your foot off, it stays locked to exactly 120km/h and then unlocks

[Clem]

Thanks David. I'll do that as soon as she is out of warranty (still below 30,000 km).