Crawl ratio

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Phils67
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Crawl ratio

Post by Phils67 »

I never really thought about crawl ratios before, is 48 a decent crawl ratio? I do very little offroad and occasionally snow. Planning my axle swap and want decent road gears but still be able to get traction in snow and mild mud. Current ratio is 55 but its not great on highway speeds. Feedback?
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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Stuka
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Re: Crawl ratio

Post by Stuka »

Whether a crawl ratio is good or not depends on the transmission and torque band of the engine, and the size of the tires.

With 35's, you aren't going to want any higher gears than 4.28's that you have now (assuming you have 4.28's by you saying you have a 55:1 with a T18a/D20). Especially with the T18a which is driven like a 3sp on the street.

A very handy site that I have used for years is http://www.grimmjeeper.com/gears.html

It lets you pick and choose gearing and tire sizes, and shows you what RPM you will run at given speeds. Just be sure to put in the tires actual size. For instance, most 35's have a rolling diameter of 34". To get the rolling diameter, measure from the ground to the center of the wheel, and multiply that by two.
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Re: Crawl ratio

Post by Phils67 »

I have 6.32 first gear, 2.03 low range and currently 4.27s on 35s. I want to regear to 3.73 since my donor rear is already setup with those and its in good shape internally
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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tedlovesjeeps71
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Re: Crawl ratio

Post by tedlovesjeeps71 »

Phils67 wrote:I have 6.32 first gear, 2.03 low range and currently 4.27s on 35s. I want to regear to 3.73 since my donor rear is already setup with those and its in good shape internally
Look at how you use the truck and gear according ly.
If you live where it's flat and you mostly highway drive, 373s may be better. If it's hilly you may find you lose fourth gear regularly from needing to downshift. If you do a lot of stop and go or around town driving, the deeper gears (4:27) will make getting going easier and you may find your clutch last longer. I'd stick with 4:27 if it we're me.
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Re: Crawl ratio

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I live in the Catskill Mountains. Alot of hills but also highway. I dont drive far often, mostly work and back which is a 5 mile round trip, but mostly i stay local BECAUSE of its highway manners. It doesnt go out in the snow unless im moving it around the property in winter soley because this crap they put on the roads destroys new trucks in 2-3 years. I have been battling mother nature as it is so i dont want to make it worse. Mostly local summer driving. I want to take more trips though in nice weather. Running 3000rpm(ish) at interstate speeds isnt enjoyable
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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Re: Crawl ratio

Post by Phils67 »

Guess ill have to build it one way and if it doesnt suit my needs i can always regear
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will e
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Re: Crawl ratio

Post by will e »

Phils67 wrote:I never really thought about crawl ratios before, is 48 a decent crawl ratio? I do very little offroad and occasionally snow. Planning my axle swap and want decent road gears but still be able to get traction in snow and mild mud. Current ratio is 55 but its not great on highway speeds. Feedback?
Yes, 48 is a very decent crawl ratio. Your big advantage is that very low 1st gear. Gear the rear for driving, don't worry too much about the crawl ratio because of that low first gear.
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Re: Crawl ratio

Post by Phils67 »

Thats what i am thinking also. I figure with detroits front and rear and the low 1st i should be ok. I really dont take it offroad but i still like knowing it will handle whatever i may throw at it in the future
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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Re: Crawl ratio

Post by Lumpskie »

In case it's helpful... here's a T18/D20 combo with 3.31s.
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Re: Crawl ratio

Post by will e »

Lumpskie wrote:In case it's helpful... here's a T18/D20 combo with 3.31s.
Cool video. Is that the wide range T18? Listening to the video I would have expected higher RPM's and slower speed if it had the 6.32 granny gear.
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Re: Crawl ratio

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My 6.32 gear is a snail even with the transfer in high. Its so slow that with the 4.0s throttle response it makes me jerk the gas pedal like crazy. In high or low range i dont even need to touch the gas. It just idles and goes wherever i point the truck. Its honestly impressive to me, thats why i dont want to lose it by going to a 3.73s from 4.27 gears. The jeep in the video must be the numerically lower range first, mine would have idled over those rocks like nothing
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Re: Crawl ratio

Post by 44bz »

I’m confused why you’re worried about crawl ratio when what you’re after is friendlier cruising speed, especially when you aren’t using the vehicle as a crawler. I’m sure there are lots of ways to build a capable, dual purpose rig. I just don’t understand how fretting about crawl ratio has any relevance for comfortable freeway speeds.

My 68 has the 327 which is a low revving engine to begin with. T18/d20 with stick 3.92s in the axles. My experience with 1st gear is very similar - top speed of about 8mph but will go on its own at idle. On the freeway I feel like 55 is the top speed I’m comfortable with and the engine rpm suggests any higher would just be too stressful.

The wilderness gladiator comes to mind for your what you’re talking about - the do all rig, but that thing had thousands of dollars dumped into it so that it could be driven comfortably to the trail, wheeled hard, then driven home.


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Re: Crawl ratio

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I overthink every little thing. No other way to explain it really. I want dual purpose although crawl isnt really an all the time thing. I want highway friendly and a decent riding rig but if one day i decide i want to drive up the wall of the grand canyon i want the confidance to point it at that wall and go (figuratively speaking of course). I still want the low end grunt to rip out tree stumps. I dont like getting stuck. I dont enjoy NY winters and want to conquer 10 feet of snow if i choose. But i also want to cruise 65 and decent RPMs with my 4 speed. Its really i want everything at once. Im weird like that
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Re: Crawl ratio

Post by 44bz »

I hear ya. I haven’t tackled axle or gear swaps yet. Mine drives and rides like a dump truck but I mostly keep it around town. I’m interested to see how your j20 axle swap goes.


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Re: Crawl ratio

Post by Stuka »

You mention you want to be able to drive in snow in the winter. But you also say you want detroits front and rear. Detroits front and rear will make the jeep undrivable on hardpack snow on the street. Even just having a rear detroit can make things a bit quirky in the snow. If you really want to be able to drive in the snow, leave the front open, and put a selectable locker in the rear.
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Re: Crawl ratio

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44bz wrote:I hear ya. I haven’t tackled axle or gear swaps yet. Mine drives and rides like a dump truck but I mostly keep it around town. I’m interested to see how your j20 axle swap goes.


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Its been an extremely slow project. Ive been just tinkering little by little. The rear is down to brakes and the locker. Front is still just a housing on the bench thats slowly being gone through. Winter time i plan to pick up the pace.
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Re: Crawl ratio

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Stuka wrote:You mention you want to be able to drive in snow in the winter. But you also say you want detroits front and rear. Detroits front and rear will make the jeep undrivable on hardpack snow on the street. Even just having a rear detroit can make things a bit quirky in the snow. If you really want to be able to drive in the snow, leave the front open, and put a selectable locker in the rear.
Currently the front 44 has a yukon lunchbox locker and a the 53 rear is welded like a spool. Its bearable in snow to me. Guess im just used to it now so driving it in snow doesnt seem difficult at all. I have a full detroit ready to drop in the new front 44hd, the rear ive been considering a TruTrac. My biggest regret overall is welding the rear. The turning radius is bad enough with a closed knuckle front. How i have not grenaded that rear by now baffles me. 53s were tough imo. The fact it has held up as long as it has like this is impressive enough to me. As far as selectable lockers, i have considered them but would rather keep the internals as mechanical as possible.a full detroit up front wouldnt even be noticed until the hubs are locked and the transfer is engaged. Its basically sitting idle until used. A TruTrac in the rear 60 would basically be a style of limited slip/posi. Itll put the power to the wheels that require it. At snowy conditions speeds itll be similar to a full locker but not as bad as a spool on dry roads
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Re: Crawl ratio

Post by Lumpskie »

Phils67 wrote:I never really thought about crawl ratios before, is 48 a decent crawl ratio? I do very little offroad and occasionally snow. Planning my axle swap and want decent road gears but still be able to get traction in snow and mild mud. Current ratio is 55 but its not great on highway speeds. Feedback?
Phils67 wrote:My 6.32 gear is a snail even with the transfer in high. Its so slow that with the 4.0s throttle response it makes me jerk the gas pedal like crazy. In high or low range i dont even need to touch the gas. It just idles and goes wherever i point the truck. Its honestly impressive to me, thats why i dont want to lose it by going to a 3.73s from 4.27 gears. The jeep in the video must be the numerically lower range first, mine would have idled over those rocks like nothing
I thought you wanted feedback on a 48:1 crawl ratio because you were considering longer axle gears so you could drive on the street. So, I posted a video I took showing same t-case/trans with longer axle gears (48ish:1 crawl ratio).
1989 Grand Wagoneer - Rebuilt 360, 2" Alcans, 10" travel Gabriel Guadian shocks.
1996 Land Cruiser - 1HD-T Diesel, Gturbo (23psi), Wholesale Automatics 442f, F/R ARBs, 35" Duratracs, ARB Rear Bumper, OME 2" lift, home built sliders and aluminum belly skid
2000 Honda Civic - Integra GSR engine, transmission, shift linkage and axles, 200hp, 33 combined mpg
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Re: Crawl ratio

Post by Phils67 »

Lumpskie wrote:
Phils67 wrote:My 6.32 gear is a snail even with the transfer in high. Its so slow that with the 4.0s throttle response it makes me jerk the gas pedal like crazy. In high or low range i dont even need to touch the gas. It just idles and goes wherever i point the truck. Its honestly impressive to me, thats why i dont want to lose it by going to a 3.73s from 4.27 gears. The jeep in the video must be the numerically lower range first, mine would have idled over those rocks like nothing
I thought you wanted to get longer axle gears so you could drive on the street. So, I posted a video I took showing same t-case/trans with longer axle gears. Looks like I missed the mark on this one.
I do. The jeep in the video was impressive with those gears. Guess i got side tracked talking about the first gear ratios. What 1st ratio did that t18 have? My hopes are to still have the "idle over everything" ability yet be more blacktop friendly as well
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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Re: Crawl ratio

Post by Lumpskie »

Phils67 wrote:
I do. The jeep in the video was impressive with those gears. Guess i got side tracked talking about the first gear ratios. What 1st ratio did that t18 have? My hopes are to still have the "idle over everything" ability yet be more blacktop friendly as well
Haha, I get side tracked all the time too. The Cherokee has the granny first gear, like yours. But, it has only been driven that one weekend in the last 15 years. So the carb on the 360 had some issues idling when hot. I think that was the issue you were seeing in the video. If it could idle, I think it would be able to idle over those rocks as well.
1989 Grand Wagoneer - Rebuilt 360, 2" Alcans, 10" travel Gabriel Guadian shocks.
1996 Land Cruiser - 1HD-T Diesel, Gturbo (23psi), Wholesale Automatics 442f, F/R ARBs, 35" Duratracs, ARB Rear Bumper, OME 2" lift, home built sliders and aluminum belly skid
2000 Honda Civic - Integra GSR engine, transmission, shift linkage and axles, 200hp, 33 combined mpg
2006 Mitsubishi Lancer Evolution 9 - 437hp/447ft-lb
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