Am I nuts or is this an issue? 4 lo shifting/power band (1 Viewer)

[THEIZZARDKING]

Hey guys, when I'm center locked in 4 lo and I give it gas it'll pull off the line and then lose power underload till it's @ 3k rpm then it'll hook up and drop into 2nd and be smooth power through the rest of the gears....

I understand there is a different shift map for 4 lo and that shifting at 3k is normal in that mode, but what concerns me is the loss of power in 1st when I get on the throttle a bit, I'm not talking WOT, but maybe around 50% load...

Is there some sort of throttle cut off or something that stops the drivetrain from engaging when in this mode...again, only happens in 1st and only when I get on thhe throttle a bit...on flat, STRAIGHT, paved ground?

Seems a bit strange...seems like it shouldn't do that, but I don't really know for certain as I'm a new owner and don't quite know how these things behave.

Also is the CDL button ok to use on the fly or do I need to do this in neutral like the transfer case lever to go into 4 Lo?

 

[ToHiHy]

Does a 2000 have TRAC? Yes CDL can be shifted on the fly in a straight line.

 

[THEIZZARDKING]

Does a 2000 have TRAC? Yes CDL can be shifted on the fly in a straight line.

Yeah, has atrac

 

[THEIZZARDKING]

Also thought it could be done on the fly, this guy tried to make me sound like an idiot when I was telling him it could be done on the fly.

Thanks a ton man, I'm really at a loss here

 

[ToHiHy]

I asked because I have occasionally felt the same thing and thought the TRAC was engaging. There is a Ton of torque in 4lo 1st gear.

 

[THEIZZARDKING]

I asked because I have occasionally felt the same thing and thought the TRAC was engaging. There is a Ton of torque in 4lo 1st gear.

You think that's what's going on here?

Is there a way of disabling Trac then...i prefer to be in control 100% of the time....never owned a vehicle with any sort of electronic off road controls, not sure I like it if that's the case...

Can I expect the same feeling when trying to go over an obstacle?

 

[Hayes]

It's not a TRAC thing.
I just think the way the torque and power curves sit in the low range shift point make first gear run long to get the most out of the gear, and make the shift from 1st to 2nd a little lurchy. I would speculate that this is by design--most low range crawling usually wants to stay on the same gear, and an up-shift at the wrong time could suck.
You can sometimes trick it into shifting to 2nd earlier by playing with the throttle.

 

[THEIZZARDKING]

It's not a TRAC thing.
I just think the way the torque and power curves sit in the low range shift point make first gear run long to get the most out of the gear, and make the shift from 1st to 2nd a little lurchy. I would speculate that this is by design--most low range crawling usually wants to stay on the same gear, and an up-shift at the wrong time could suck.
You can sometimes trick it into shifting to 2nd earlier by playing with the throttle.

I would expect that, my issue is that it feels like the truck in neutral at a certain point...then will lurch into 2nd.

It's like a loss of power almost...but only happens when you get on the throttle a bit..

 

[flintknapper]

It's not a TRAC thing.
I just think the way the torque and power curves sit in the low range shift point make first gear run long to get the most out of the gear, and make the shift from 1st to 2nd a little lurchy. I would speculate that this is by design--most low range crawling usually wants to stay on the same gear, and an up-shift at the wrong time could suck.
You can sometimes trick it into shifting to 2nd earlier by playing with the throttle.

^^^^^^^^^ Agree....NOT a Trac thing. My 80 series does the same thing. Holds 1st gear for a LONG time before shifting (around 3,000 rpm) with no commensurate acceleration (with respect to throttle applied) between about 2200 and 3000 rpm. When it does shift...it is pretty snappy, even more so now that I've increased my line pressure.

 

[Hayes]

Dunno. I think the torque probably falls off as it approaches 3,000 rpm, so despite the increasing revs it feels like the go power has stalled. I think it's pretty normal. My 80 did it too.

 

[Muddy Bean]

Interesting. I have more than once shifted to 4lo and accelerated full throttle on pavement and never had this happen with my '98. It just shifts through the gears faster than a rabbit with a hound on its tail. But no loss of power at all. I can squall all four rubbers and get to 45mph in a hurry in 4lo. It's a blast. And right now since I disconnected my front driveshaft, it's a tire burning machine.

Flintnapper. My '98 has always shifted soft from first to second. How did you increase your line pressure?

 

[flintknapper]

Flintnapper. My '98 has always shifted soft from first to second. How did you increase your line pressure?

^^^^^^^^^^ Did this on my 97 (80 series) but the Transmission is the same for both models (A343F).

If you drop your transmission pan to expose the valve body...you can access the primary regulator valve (no need to remove the valve body).

The regulator valve (for some reason) is adjustable. By pressing in on the valve (be careful to hold the retainer in place) you can rotate it either direction (clockwise for increased pressure, counter-clockwise for reduced pressure, assuming your factory setting is in the middle).

I have right at 300K miles on my transmission, so 'seat of the pants' feel of the shifts (in high range) is not dramatically different, but watching the 'tach' definitely shows I am getting 'quicker' shifts. Probably should have done this at 200K

 

[Muddy Bean]

Me likey. Now I have a fun experiment to do this summer. Awesome stuff. Much thanks. Sorry for the thread hikack OP.

 

[flintknapper]

Me likely. Now I have a fun experiment to do this summer. Awesome stuff. Much thanks. Sorry for the thread hikack OP.

Read this first: Improving Transmission Shifting

 

[Muddy Bean]

Wow. Very very awesome thread that I've never seen. Thank you so much. Apparently I still have much to learn.