RPMs limited in 4L reverse?

[Limestone]

Really?
I guess my point is proven beyond any reasonable doubt, sheesh does anything ever sink into your dense skull?
"Because of the additional gear reduction when in low range, engine RPMs should be kept under 2500 (remember the planetary is turning at 4 times that rate 2,500 x 4.0 = 10,000 RPM). Severe transfer case damage can occur if this RPM warning is not observed "

Holy ... I'm done

If the 2500 rpm was a concern, why was it addressed by limiting rpms in 4L reverse and not when in 4L forward gears? Also, why would the Jeep owners manual not mention it at all? Also, the rpms are first limited at 3500. Perhaps you missed those points.

Sponsored

 

[Maximus Gladius]

Maybe there’s resistance for others to try because of some “damaging aspects” to the transcase at those high limited RPM’s?? Unnecessary to do as a test but action can be done if needed. ??

When it happened for me, I was trying to pull someone out of the snow bank and was in 4L lockers reverse to position the truck better, that’s when I noticed the higher speed at first until I let off, followed by a much slower speed when I needed more which was super annoying.

The test action is simple and when I leave for work in a bit, I’ll retry in the iced up alley to confirm. The more I do with my truck, the better I get to understand it and know it’s limitations compared to my unlimited demands.

 

[Maximus Gladius]

OP, Went out to the alley to perform 4L in reverse. Rpm went to 3500 and stopped there. Time and time again, it went to 3500. Never did it too out at 2500.

I engaged OFF ROAD+ and rpm’s topped out at 3500. Again, never topped out at 2500.

I engaged both lockers and tried reverse again…same thing.

 

[sharpsicle]

OP, Went out to the alley to perform 4L in reverse. Rpm went to 3500 and stopped there. Time and time again, it went to 3500. Never did it too out at 2500.

I engaged OFF ROAD+ and rpm’s topped out at 3500. Again, never topped out at 2500.

I engaged both lockers and tried reverse again…same thing.

Waiting for the "Thanks for responding. Now back to the original question. ? "

After all, this is the second time you're confirmed this for him...

 

[Maximus Gladius]

OP, There’s one extra thing you did and that was reverse for 1/2 mile until you let off the throttle and it then topped out at 2500. I won’t be doing that test but maybe that has something to do with it?

No thanks needed. It was fun! Never giggled so much in my life…. Well…there was that time with the wife….(record scratch)

 

[DankjeeP]

If the 2500 rpm was a concern, why was it addressed by limiting rpms in 4L reverse and not when in 4L forward gears? Also, why would the Jeep owners manual not mention it at all? Also, the rpms are first limited at 3500. Perhaps you missed those points.

Forward, reverse, the RPMs are the limiting factor of the planetary gears. No the quote is not from Jeep, but the principle is the same. Someone posted a paragraph from the manual alluding to the situation. Not sure if there is any mention of a rev limit, but it is pretty obvious by now there is one.

 

[Limestone]

OP, Went out to the alley to perform 4L in reverse. Rpm went to 3500 and stopped there. Time and time again, it went to 3500. Never did it too out at 2500.

I engaged OFF ROAD+ and rpm’s topped out at 3500. Again, never topped out at 2500.

I engaged both lockers and tried reverse again…same thing.

When at 3500 rpm, if I back off the accelerator and let the rpms drop below 2800 rpm, then try to accelerate, the rpms are further limited to 2500.
Thanks for tour efforts. You are the only one who actually tried this with their truck.

 

[Maximus Gladius]

When at 3500 rpm, if I back off the accelerator and let the rpms drop below 2800 rpm, then try to accelerate, the rpms are further limited to 2500.
Thanks for tour efforts. You are the only one who actually tried this with their truck.

And once it stayed at 3500, I dropped it down to 2000 then accelerated to 3500 then back down to 2000 then accelerated to 3500. I did that 4 times.

I’m wondering if your 1/2 mile at 3500 triggered heat sensors??and it brought it down to 2500 to protect it ??

 

[Limestone]

And once it stayed at 3500, I dropped it down to 2000 then accelerated to 3500 then back down to 2000 then accelerated to 3500. I did that 4 times.

I’m wondering if your 1/2 mile at 3500 triggered heat sensors??and it brought it down to 2500 to protect it ??

I can have it limit to 2500 rpm by just backing up a100 feet or so in my gravel driveway. I wouldn’t think that heat sensors would be a factor. I’ll try letting the rpms drop to 2000 and see if it then limits to 2500 or 3500.

 

[Limestone]

I can have it limit to 2500 rpm by just backing up a100 feet or so in my gravel driveway. I wouldn’t think that heat sensors would be a factor. I’ll try letting the rpms drop to 2000 and see if it then limits to 2500 or 3500.

What I found about my truck was as follows:
1. In 4L reverse there is an rpm limit at 3500.
2. Once that 3500 rpm limit is reached the limit remains 3500 rpm as long as the rpms remain above 2500.
3. If the rpms drop below 2500 for about 3 sec or so, there is a new rpm limit of 2500 set.
4. The 2500 rpm limit remains even if the truck is brought to a complete stop (0mph, 700rpm) and then accelerated again in reverse.
5. Once the truck is shifted into a 4L forward gear and then back into 4L reverse, the rpm limit is again 3500.
6. These results were obtained on a level gravel road.
7. My truck (2021 JTR, Auto, 5 position t-case) results are somewhat different than those of Maximus Gladius.

Perhaps this information will be useful to someone.
Now, let the ridicule and name calling begin.?

 

[sharpsicle]

How fast are you trying to go in 4L? It's designed for torque output, not for speed. If you need to go faster, that's what 4H is for. This obsession with trying to get over 3500rpm is not making sense, unless you're trying to grenade your gears. This is exactly why they both exist, it's a tradeoff. Use the right setting for the right job.

I'm really confused on what the problem is here.

 

[ShadowsPapa]

the RPMs are the limiting factor of the planetary gears. No the quote is not from Jeep, but the principle is the same.

Planetary gears can handle some crazy RPM - racing transmissions, anyone?
Powerslide used in a lot of drag cars hitting RPM way over what these are capable of.
Even the TF998 is behind some 7,000 RPM 600+ hp engines.

That bit from the 3rd party is talking a reduction waay below what any stock Jeep is capable of.
It's aimed at that box, so really would not apply to a stock Jeep.

I would suggest that the RPM limit of the engine is for the engine's sake more than anything. It's basically unloaded due to the torque amplification of the transfer case.

 

[Limestone]

How fast are you trying to go in 4L? It's designed for torque output, not for speed. If you need to go faster, that's what 4H is for. This obsession with trying to get over 3500rpm is not making sense, unless you're trying to grenade your gears. This is exactly why they both exist, it's a tradeoff. Use the right setting for the right job.

I'm really confused on what the problem is here.

I don’t believe I ever stated that I wanted to go faster than 3500 rpms, but merely noted that an rpm limit seemed to exist at 3500 then at 2500 and asked if other members had noted those limits in 4L REVERSE. 3500 rpm in 4L REVRSE worked well for the snow conditions and slope I encountered. When the rpm limit reset to 2500, the truck was struggling to maintain momentum.

 

[Kevin_D]

Just for shits & giggles, I tried it with my Sport S today. No 4:1 transfer case, no lockers, no 4WD Auto.
4L in reverse the RPMs were limited to 3500, regardless of letting off of the throttle.

Kevin

 

[sharpsicle]

I don’t believe I ever stated that I wanted to go faster than 3500 rpms.

Yes, you did. This is what you've said. It clearly shows you want to go faster in 4L.

...the truck would not rev any higher than 3500 rpm, and when I let off on the accelerator a bit and then tried to increase the rpms...

..The rpms were limited to about 3500, then 2500 even when the accelerated was floored...

...once 3500 rpms is reached, the truck will not go any faster...The ground speed of the truck at 3500 rpm in 4L Reverse is about 6mph, and at 2500 about 5mph.

This is where you're getting all these replies talking about how it works and why you probably want 4H. Keep in mind you've posted up in the "Issues" section, which implies you have a problem. The problem, as you describe, is that you can't go faster in 4L reverse. I would recommend using 4H instead.

We're all here to help. But you gotta be honest with what you're trying to get out of this for anything to truly be useful. Right now, it just feels like you're yanking everyone around just for fun.

Sponsored