Manual Transmission Crunchier in 4lo

This may have been the case all along and I just noticed it recently. I spent 12-16 hours this weekend driving around mostly in 4lo and I noticed that gear shifts are less smooth in 4lo than in 4hi. I heard and felt a lot more crunch. I notice the crunch especially when shifting from 1st to 2nd while descending a steep incline (20+ degrees). I thought it was because I was shifting faster, not pushing the clutch in far enough, and/or not timing things as well, but I think I ruled that out.

As an aside, can anyone explain why it whines so much in 4lo? It never really bothered me before, but after so many hours it started getting on my nerves and also sparked my curiosity.

 

Yeah. You have to be extra slow on shifts. I think it there is a lot more rotational mass and the syncros can't slow it fast enough.

The gear whine is from the straight cut low range gears. Just a fact of life for strength.

 

I can't explain why, but will affirm the fact that its different. I spend days in 4 lo in my 2nd gen that has been converted into a orchard spray truck. I've done this for 2 seasons though with no ill effects so its been so far, just an annoying nuance.

 

That makes sense, I was being pretty aggressive in 4lo. The trails I was on allowed for a bit of speed in spots, I installed King shocks a couple weeks ago, and I started thinking my Taco was a Polaris Razr. I stopped short of catching any air. I did have a bunch of loose crap in the bed (hi lift jack, 20' log chain, 70 lb toolbox, etc) that I didn't want to toss on to my head.

By "low range gears", I assume you mean in the transfer case.

The other thing I noticed is that it sure seemed like the throttle is more responsive in 4lo compared to 4hi. After reading some info on the ovtuned website about how the ECU interprets gas pedal position, it got me thinking the ECU might be tuned differently in 4lo vs 4hi. In general, 4lo seems to be the old-school/hard-core mode. For example, it defaults to turning off several of the safety features. So it wouldn't surprise me if throttle control safety features were disabled as well.

Except for crunchy shifts and loud whining, it is lots of fun driving aggressively in 4lo off road with King shocks (until you reach about 25 mph and run out of gears),

 

Definitely sounds normal. I would imagine the whine is from the reduction gears in the t-case, and the crunchiness is cuz from the synchros as mentioned.

The throttle response feeling is mainly from the gear reduction, you have 2.57x the torque at any given rpm in lo range. I have the 2 wheel drive lol range mod, and im pretty sure my 4 banger can roast the rear tires in 2lo 1st gear

 

For the MTs, we can redline in 6th, which is around 60mph. Not a great thing to do, but it is possible.

I've cruised at 35 a couple times versus the full stop to get out of 4Lo.

Yes. Engine regulation defaults to off in 4Hi / 4Lo. The extra gearing in low range magnifies it.

Any 4Lo time is a good time.

 

I’m aware of the effect of gear reduction, but it still seems like the engine reacts quicker when I hit the gas.

 

The answer to all your questions is "because low range". The whine, the shifting, and what *feels* like throttle response are just part of the simple reduction gearing.

 

When I am talking about throttle response I am referring to the discussion on this page about torque dynamics response, power demand response, and throttle calibration response. The article doesn’t mention that the ECU uses a different tune for 4lo vs 4hi, but it seems like it might or maybe it’s just a faulty perception.

https://www.ovtuned.com/blogs/news/...as-abilities-through-the-power-of-electronics

 

It likely is mapped slightly different if for nothing else than the ground speed vs rpm relationship is different. However, no matter what, the engine now has much more leverage over the drive train so any bit of engine output increase (resulting from pushing the go pedal) will be more quickly turned into engine acceleration as the engine has 2.57x the normal mechanical advantage.

 

You are stating the obvious. What’s not so obvious to me is if the the throttle response is different in 4lo. Perhaps “throttle response” is a poor choice of words. I mean the way the gas pedal position relates to actual engine throttle. As the evtuned article points out it is not a linear relationship.

 

Are you referring to engine regulation that is part of VSC?

 

Yes. We generally refer to it as the TRAC system overall with VSC being a component / function of it.

 

Ok ya, I’m not talking about VSC, TRAC, auto-lsd, or ATRAC. I’m talking about how the gas pedal position relates to engine throttle as described in the OVTune article. The engine regulation in VSC is similar but is more dramatic and only activated when the wheels spin (I think). It might also get activated when the truck is traveling forward with yaw. I know the ABS brakes get fired under those circumstances, but not sure about the engine throttle regulation.

 

I get you. I am just saying that the overall term for all the ABS and ECU controlled aspects is referred to as TRAC around these parts. VSC is a part of that.

Yes. I understand that you are looking for some reference that the 4Lo throttle map is different than 4Hi / 2Hi. I cannot really help you there. Myself, even with OVT 2.0 SFOB, the throttle is responsive in all modes and doesn't throw me any curveballs.

Prior to 04B13 and OVT, there was a confirmed suspicion that the engine responded differently in 2Hi with the long press of the TCS Off button. I felt a difference myself, but it was subtle. I would often forget to do the long press.

 

Not that it really matters a lot, but I have not seen the term TRAC used as an all encompassing term. It’s confusing non the less.

https://www.tacomaworld.com/threads/3rd-gen-traction-control-modes-explained.530695/

 

It was an informal thing so that we could all keep the terms straight and consistent in the thread that spurned that one:
https://www.tacomaworld.com/threads...-non-trd-offroad.437814/page-11#post-16964403

 

I'm not sure what you mean by "straight cut low range gears". I assume you mean gears in the transfer case, but looking at the diagrams in the service manual I see that the transfer case is a chain drive type and I don't see any straight/cut spur gears. Could the whine be coming from the chain drive? The sprockets in the diagram look similar to spur gears.



FYI: I educated myself on spur and helix gears here:

https://en.wikipedia.org/wiki/Gear

 

The chain drives the front shaft, whether 4Hi or 4Lo. Low range is reduction gear set.

 

Ya never mind duh. That was a brain fart.

This is perhaps the diagram I should be looking at. Is this the reduction gear set?