Low speed/high torque problem (1 Viewer)

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T

TacoLand

Joined
Apr 26, 2020
Threads
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Location
Helena, MT
When I'm in high range, my 80 is struggling to go up a mildly steep hill offroad from a stop. Similarly, it struggles to roll over a railroad tie from a complete stop in high and will do the same thing in reverse.

It feels like it's loading up and just can't get enough power/torque to get up and over. I did experience a loud pop once when trying to replicate the issue in reverse. No issues in low, CDL doesn't change anything. *edit to clarify CDL in H doesn't change anything*

For reference, I did resolve a shudder related to a short in the wiring harness this spring. I've checked that, and it's good. No noticeable shudder when trying to replicate the issue. I'm pretty sure the torque converter is locking up at speed, the trans isn't getting hot at highway speeds (except on a mountain pass when it's running 4k+ for a few minutes). I'm not noticing any slipping in the transmission. I thought maybe a bad fuel sock, but the pop makes me think I should be looking somewhere else.

Any thoughts?
 
Last edited:
TacoLand said:
If they're stripped, wouldn't they still be an issue in low?
Click to expand...
No, because when you put it in low and the CDL engages 50% of power is locked to your rear axle and that's what is driving you.

On my old 92 I blew my flanges on the trail. Like you mentioned there was a loud bang before it happened, but I was in low and the CDL locked so I didn't notice anything wrong till we actually got to the hard stuff and I couldn't get up it. Luckily the 91-92 came with a CDL button so I was able to drive home with it locked in high range.
 
Careful doing that in reverse.
These are known to blow a ring and pinion in reverse on the front axle.

One member blew it pulling a shrubbery from his yard.

Low range is there for a reason. Do it in low. As soon as you're over the obstacle, shift back to high range and move on.
 
wpns4l said:
No, because when you put it in low and the CDL engages 50% of power is locked to your rear axle and that's what is driving you.

On my old 92 I blew my flanges on the trail. Like you mentioned there was a loud bang before it happened, but I was in low and the CDL locked so I didn't notice anything wrong till we actually got to the hard stuff and I couldn't get up it. Luckily the 91-92 came with a CDL button so I was able to drive home with it locked in high range.
Click to expand...
Ah gotcha. Mine is still doing this with the CDL locked in high.
 
BILT4ME said:
Careful doing that in reverse.
These are known to blow a ring and pinion in reverse on the front axle.

One member blew it pulling a shrubbery from his yard.

Low range is there for a reason. Do it in low. As soon as you're over the obstacle, shift back to high range and move on.
Click to expand...
I shouldn't have to shift into low to roll over a 6-inch railroad tie in my driveway.
 
TacoLand said:
I shouldn't have to shift into low to roll over a 6-inch railroad tie in my driveway.
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Why? Your tires are at street pressure so there's no give. If you're at a dead stop, there's no momentum. What are you asking the truck to do, change the laws of physics?
 
jonheld said:
Why? Your tires are at street pressure so there's no give. If you're at a dead stop, there's no momentum. What are you asking the truck to do, change the laws of physics?
Click to expand...
Okay, maybe I'm really misunderstanding something.

It's normal for an 80 to be unable to roll over a rock, speed bump, or curb from a complete stop? That hasn't been my experience in any of my other vehicles (or my other 80) and is a new issue for this one.

The mildly steep hill I referred to in my original post was about as steep as a lot of people's driveways and was a dirt road. It seems like the truck should be able to get up without needing to shift into low.
 
TacoLand said:
Okay, maybe I'm really misunderstanding something.

It's normal for an 80 to be unable to roll over a rock, speed bump, or curb from a complete stop? That hasn't been my experience in any of my other vehicles (or my other 80) and is a new issue for this one.

The mildly steep hill I referred to in my original post was about as steep as a lot of people's driveways and was a dirt road. It seems like the truck should be able to get up without needing to shift into low.
Click to expand...
No somethings unusual. Try locking the cdl in high, I kinda wonder if the viscous couplers kinda cooked
 
Let's try this another way.

What year is your truck, what engine is in it, what has been done to it, how long has it been since regular maintenance?

If your truck stalls, the transmission isn't slipping; the engine isn't developing enough power.
 
Malleus said:
Let's try this another way.

What year is your truck, what engine is in it, what has been done to it, how long has it been since regular maintenance?

If your truck stalls, the transmission isn't slipping; the engine isn't developing enough power.
Click to expand...
Yeah that would have been good to list, my bad!

‘96 LX450, stock motor w/~250k. Recently baselined this spring, all new hoses, valve cover gasket, coils, plugs, dizzy cap and rotor, all fluids done except a full block flush which I still need to do. New u-joints, freshly retorqued driveshafts. Fixed the wiring harness in the spring (shorted wires causing cylinder 5 misfire), double checked it again trying to diagnose this issue. CDL switch installed. Lifted ~3 inches, on 315s with bumper, winch, GFC and light drawers. I wheel or camp with this truck most weekends, it started doing it this past weekend.

The truck isn’t stalling, it’s just loading up (revs increasing, vehicle torquing with motor) and struggles to move in those instances. As I mentioned earlier, I did hear a loud pop when loading in reverse, which is the point when I posted here. My initial thought was fueling, but the mechanical noise made me second guess.

Didn’t mean to come across as short earlier, but it’s a new issue. I’m not asking the truck to “change the laws of physics”, just to do something it has been able to, and should be able to, do.
 
That helps. I read nothing that sounded impolite.

So, increasing engine rpm without an increase in speed is a slipping driveline. Somewhere. How is your transmission fluid? Does it look red and smell like ATF, or is is black and either doesn't smell or smells burnt? FWIW, the torque converter isn't the problem at low speed.

Just to be clear, this is a new(-ish) problem? It hasn't been failing to perform in the past? Or, is this a problem you're just observing, because you haven't done this specific type of driving test(s) before?

And, as was said previously, it's a very bad idea to develop high torque in reverse; the gearset wasn't designed for that.
 
Malleus said:
That helps. I read nothing that sounded impolite.

So, increasing engine rpm without an increase in speed is a slipping driveline. Somewhere. How is your transmission fluid? Does it look red and smell like ATF, or is is black and either doesn't smell or smells burnt? FWIW, the torque converter isn't the problem at low speed.

Just to be clear, this is a new(-ish) problem? It hasn't been failing to perform in the past? Or, is this a problem you're just observing, because you haven't done this specific type of driving test(s) before?
Click to expand...
Yeah ATF is fresh with only ~2k on it or so. Still red and smelly.

This is definitely new. Started on some easy trail/forest service road driving this weekend. First instance was at the bottom of a small, mildly steep hill we had stopped at the bottom of to look around. Just wouldn’t go up in high. Tried to replicate it a few different times and in different ways and it’s consistent.

Definitely noted on the reverse testing, although I would think being able to back up a hill in high should be fine?
 
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