[4XGore]

I saw this in GD and thought I would ask here where the experts are. How fast would be too fast in different conditions in both 4L and 4H? I have heard many different answers throughout the years but I haven't seen it asked here. Also what kind of damage could result in going too fast? I understand there are many different axles and TCs so I'm open to here about them all. So what do you guys think is too fast?

[byrinxx74]

I know from experince that in Four low I have pushed my xj at about 4300 roms going up a hill and that was about the limit. I heard that you should only go about 15 to 25 mile an hour on 4lo and ONLY FOR A SHORT TIME!!

[pscj5]

well i have a blown motor in my jeep because someone used it and thought they needed to mess with t case and drove it bout 7-10 miles in 4 Low at oh prolly max speed like 35 from what they told me wouldn't hit 45 then it started to throw oil and now the engine is making terrible noise like metal on metal literally sounds like a machine gun from the block the tcase actually still shifts fine and tranny shifts fine but the engine is crazy lol i might post a video for everyone to here. i was pissed because i had just gotten it like a week before, but 45 in 72 cj5 258 3spd and dana 20 tcase is bad news but in my truck i have run 20 on the trail for short bursts its all what the motor can take really the tcase usually will hold and so will the transmission engine parts break 1st because RPM's get so high so fast

[bigjoe]

Well in 4low you could "crawl" around all day going a low speeds in the woods or trails doing 5 to 10mph. Anything over that I would be in 4high and nothing over 45 or 50mph tops. If I can go 45 to 50mph do you really need to be in anything else besides 2high? And if I'm running on hard road or pavement as soon as there is no ice and snow it's out of 4wheel. That's how I have used it in my PU's and Jeeps. However, my 77' has Quadratrac in it and is always in 4 wheel drive. The xcase is like a big limited-slip rear in simple terms, transfering power from the wheels slipping to the wheels gripping, (sounds like a commerical). You can lock the case via the e-switch it has, but I never have. For what little bit of trail-running it did and driving in snow it does a fine job. When driving it I just watch how much skinny pedal I use.

[80cj]

I've run at 45-50 mph in 4 hi on beach sand with no ill effects.

[Saltydawg1]

Originally Posted by bigjoe

Well in 4low you could "crawl" around all day going a low speeds in the woods or trails doing 5 to 10mph. Anything over that I would be in 4high and nothing over 45 or 50mph tops. If I can go 45 to 50mph do you really need to be in anything else besides 2high? And if I'm running on hard road or pavement as soon as there is no ice and snow it's out of 4wheel.

This pretty well sums up my feelings.

[sevenlitre2002]

As fast as the engine will allow, in 4 high or 4 low

[4XGore]

I think most are in agreemant that if you can drive 55 you shouldn't need 4WD. So excluding safety and only considering mechanical ability of the 4WD system, what speed would cause damage?
Thanks so far far for all the input.

[sevenlitre2002]

I say the only limit is your engine, if it red lines at 5,000 rpm, that's how fast you can go.
The transfer case will still be working, long after you blow up your engine.

[4XGore]

So it's the engine that would be damaged first? I thought it would be the TC or Transmission or drive line. So it's just the TC keeping the engine at a certain RPM that does the damage?

[jumbojeepman]

Originally Posted by Hey_Lawrence

I think most are in agreemant that if you can drive 55 you shouldn't need 4WD. So excluding safety and only considering mechanical ability of the 4WD system, what speed would cause damage?
Thanks so far far for all the input.

I can think of plenty of situation where while driving 55 or more and running 4wd is perfectly reasonable. Smooth dirt roads come to mind, as does desert racing.

[4XGore]

Originally Posted by jumbojeepman

I can think of plenty of situation where while driving 55 or more and running 4wd is perfectly reasonable. Smooth dirt roads come to mind, as does desert racing.

Ok, so when it is reasonable 55 or more is possible without causing damage. Is that correct?

[Saltydawg1]

Originally Posted by Hey_Lawrence

Ok, so when it is reasonable 55 or more is possible without causing damage. Is that correct?

I will say that is correct with a stock Jeep setup in good condition. When people start modifying their jeeps and increasing drive line angles and tossing big tires and stuff on it greatly increases the stress on driveline components.
I wouldn't hesitate to run 55 for a time in my own Jeep but mine is only lightly modified and I am a professional mechanic by trade. My Jeep is in excellent mechanical condition.

There are a lot of Jeeps I've seen that I'd be scared to take to 55 under any circumstances .

[twmattox]

Well, with a full time transfer case, you can run as fast as you need...even on dry pavement. They have either a viscous coupler or internal differential and allow for the minor difference in axle gearing etc. I have run these at 65-70 in the winter. We pretty much leave the t-case in full time most of the winter.

A part time transfer case is the one I worry about more. Not from grenading at speed...but from binding. If I run at 35-45 and hit a patch of dry pavement I don't think it would be as bad as hitting that dry patch at 65+.

I can speak from experience that an '81 CJ-5 with a 304 can do 45 in 4-lo. It doesn't like it...but it will do it...

[gosupes]

Another vote for as fast as the engine allows (to a degree). Ditto to what saltydawg1 said, back when mine was closer to stock form, it wasn't a big deal to do 55 in 4H, mostly on hard sand or smooth snow. Putting lockers in, among other things, changed all that.