Overdrive / Transmission Lock HDJ81 questions (works or not?)

[83bj60]

Hey Folks,

Since my fuel consumption appears fairly steep and since I have no tech info about this new truck (sept 1991 HDJ-81 VX LTD), I was wondering if perhaps something was not wroking right with the overdrive or transmission lock.

First of all, I noticed that I can't kickdown the transmission when in top gear unless I manually switch to 3rd gear or when the engine goes to below 1,500 RPM. That doesn't seem normal.

I just noticed the red button on top of the drive selector above Park which I suppose controls the overdrive. I does nothing at all when I push on it, no feel whatsoever. It seems to be a momentary on switch. Shouldn't it be a push on - push off instead? There is no indicator in the dash when I actuate it.

Is this the overdrive control? I presntly do 2050RPMs on my 285/75R16 (33") tires at 90kph.

Or is that the transmission lock in high gear?

Any ideas? I'm kind of lost!

Chris

 

[lshobie]

That is a transmission unlock button, so oyu can take it out of gear when the keys arent in the ignition.

 

[83bj60]

That is a transmission unlock button, so oyu can take it out of gear when the keys arent in the ignition.

Allright! I've learned something uselful today

Thanks for answering my post, Ishobie

Chris

 

[Martin White]

Can you not kick the tranny down at all or is it just really difficult? Most of these trucks seem resistant to kick down, but they will go. I've found you need to be right near the floor at times to make it happen. Also, what is your fuel consumption? Are you using GPS for distance?

 

[83bj60]

Good Point!

Can you not kick the tranny down at all or is it just really difficult? Most of these trucks seem resistant to kick down, but they will go. I've found you need to be right near the floor at times to make it happen.

No, it simply won't kick down, unless the RPM has come down to say 1,500 or so. I have noticed that I can't push the throttle all the way to its maximum, had my son push all the way down and noticed at the engine I could still rotate that lever another 15 degrees or so.

Is there an adjustement that can be made at the transmission to force an earlier kickdown? I'm a complete newbie when it comes to automatic transmissions...

Also, when in 3rd or lower gear, there seesm to be no problem at all kicking down. At least that's how it feels...

Also, what is your fuel consumption? Are you using GPS for distance?

I measured the distance with a chronometer and two distance markers on the autoroute, separated by exactly 2 km. The speedometer indicated for the duration approximately 90-91KPH. 2km took exactly 76 seconds. In one hour there are 3600 seconds so in one hour (3600 seconds) at this speedometer indication (approx 90-91), I would have done (3600/76)x2km, which is 94.7 kph. Divide that by 90.5 and you get a correction of 4.7% because of tire size.

Knowing that my tires are 285/75R16 I get a diameter of ((285x.75)x2)+(16x25.4)mm or 833.9mm, and the OEM tires are 31.5 inches or (31.5x25.4)mm or 800mm, the increase in size is a ratio of 833.9/800.1 or an increase of 4.2% in diameter compared to the OEM, whcih means, my speedometer rating is very accurate (error of .5%).

From this I assumed the odometer reading was accurate as well in the same manner and I extrapolated the figures from the odometer, applying the speedometer corrections to it...

Darn! I could really be wrong! Speedometers are independent from odometeres, aren't they? And I thought I had my methodology well covered... I guess I have to make the trip again and compare the odometer to the figures on the mile markers... How much does a GPS cost anyway? Hopefully it's inexpensive as I'm kind of broke at this point!!!

Thanks for your very pertinent question

Back to do some more field testing...

Thanks for your reply, Martin

 

[Martin White]

I did a bunch of calculations as well, just like you, but when I tested them, I found they didn't quite work. One thing to be careful of is that some GPS systems are more accurate than others. I used a friends system with an external antenna and checked it several times to get my odo calibrated. GPS units can be out, especially when they lose signal for a little bit. But still with your tires, you should find you are close to 9%, unless an adjustment was made in Japan before your truck was shipped out (and I doubt very much that it was).

 

[83bj60]

with your tires, you should find you are close to 9%, unless an adjustment was made in Japan before your truck was shipped out

Is there a way to adjust the odometer and speedometer for the tire in use, some sort of variable resistor in the instrument cluster, or am I hoplessly dreaming?

 

[Martin White]

I have seen adjustment gears (not sure how they work) but only in two sizes, neither of which is enough for a 9% change. I think you're better off to just borrow or buy a GPS and adjust mentally. Works fine for me.

 

[83bj60]

I have seen adjustment gears (not sure how they work) but only in two sizes, neither of which is enough for a 9% change. I think you're better off to just borrow or buy a GPS and adjust mentally. Works fine for me.

Are you saying that the HDJ81s have a mechanical gear and flexshaft drive to the speedometer like the old 60 series?

Hmmm... This thing is so modern I'm actually surprised it doesn't have an electronic pickup instead of an old whirring flexshaft (which tend to be very noisy at -30C )