Off Roading Gear Ratio for dual use truck?

[Moab4x4]

My daily driver / occasional offroad mountain and slickrock climbing truck has 3. 54s in it. I drive this truck around town mostly, but do take on the interstate to meetings in SLC (250 miles) and Vegas ( 400 miles) from time to time, so mileage is a small issue.



I am looking at installing 35" tires and Lockers, Detroit in the rear and ARB in the front. As I need to change out the carriers anyway, what gear ratios do you all recommend for this type of use? 4. 10's? 4. 56?? or do I keep the 3. 54's and put in a 203 doubler?



Truck currently makes ~260 HP 640 torque, 5 speed Getrag.



the 3. 54s have me just a little faster than I feel comfortable with on steep slickrock with 33's. Lack of power has not been a problem.



Thanks for the opinions.



One of these days, I will need to build a dedicated trail vehicle... .

Ken

 

[MAllen1]

If you want a little more gear without going extreme w/the 4. 10s, look at getting something in the 3. 73-3. 90 range. My truck came with 3. 54 and the 5-speed, and, when I increased my tire size, the 3. 73 put me within the same r. p. m range as the 3. 54/stock tire configuration. The 4. 10s would be better for oversized tires and rock crawling, though.

 

[MickeyMiller]

Ken,

I don't know which transfer case your '92 has but why not consider a 'doubler'? Best of both worlds... highway cruise, regular low and super low low range. There are 205/203 and 205/208 doublers out there (and others, I'm sure). The aftermarket T-cases are also an option... but bigger $$$$.

 

[BWJensen]

You know what my answer is :-laf--------

MADDOG

 

[Moab4x4]

You know what my answer is :-laf--------

MADDOG

Yes, I have gone back and looked at those nicely polished NW Fab parts more than once. As I have the rest of the build. Yours actually makes my truck look small.



I have thought about the doubler. I am running a 205 and have thought about putting a 203 in front. How much should I budget for parts on something like that? I have spare 205's but no 203's in my stash.

Driveshafts, 400 ea by Tom Woods, with 1350 joints.

203

Custom stuff to hook the 203 to the 205

linkages

what else?

Exhaust mods. .



Unfortunately my wish list greatly outguns my fiscal resources. ...

It looks like the ARB is off the list till next time, so Detroit with 3. 54's will have to do me for a while.

 

[bjonesAZ]

I've done the Doll House section of Canyonlands with the LS 3. 54 and 6-spd, 305/70/16 w/o any issues.



My current set-up is with BFG A/T 295/75/16 and it's pretty sweet with the 3. 54s.



Bob

 

[Moab4x4]

Slickrock

Hi Bob, I did Hells Revenge with the RCC guys in October and it did fine, but with the Getrag, I didn't thing I really had the control to do the gate. I currently have open 3. 54s and 285's. I was debating on going to 295's, 305's, or 315's. I am pretty set on BFG AT KO's as I have had really good luck with mine.

It looks like I am going to get an RC and wheel it instead of the CTD. That might make me rethink some of my mods, but would make more sense.

Thanks

Ken

 

["Mad Max"]

fellas -



I'm stuffing a 6BT-518-203/205 in the RC, and keeping the 3. 55 gears and 35" tires, and my question is... how will down-hill crawling be in a vehicle like ours without 'normal' engine braking? I'm not planning to install an exhaust brake, and even if I did I still won't have a lock-up converter (or clutch) so an e-brake won't be very effective anyway. But, with a 4-1 doubler, will it really matter?



I do NOT want to screw around with a 47RE transmission just to get a lock-up converter and be able to use an e-brake just to slow myself down crawling down hill..... so would it really matter if I did have the 47 and e-brake???



- M2

 

[Moab4x4]

Hi Sam,

I look at it this way, the transmission slip shouldn't be any worse than the 727 behind the 440. Most trail rigs I see are non lockup autos. I would think that with the doubler you should be able to get the RPM's high enough to get that TQ to grip fine. I wonder if a high% efficient TQ would help in this matter.

This is one thing that has made me think maybe an ex brake might not be a bad thing, even with the 518. I've been thinking of the bt RC as well as I have most of the parts already. I have been tossing back an forth 6bt or 4bt.

6bt, I have, just needs built = good. Heavy = ??

Coming to EJS?

See ya,

Ken

 

["Mad Max"]

I'm actually less worried about the converter slop than I am the lack of engine braking potential in a Cummins. Without a 'carburator' or throttle body to suck against the Cummins has nothing to slow down the intake stroke except raw friction, wheras the gas engines do, which is why gas engines produce engine vacuum and the diesel's don't. Because of that, when decellerating the Cummins tends not to slow down a rig nearly as much as a gas engine would with the same transmission behind it. This is where an exhaust brake comes in - when closed an exhaust brake will slow down the exhaust stroke on the Cummins, which definitely slows down the engine, but, with a non-lock up converter (A518 transmission) there is no direct resistance between the engine and the wheels - ya have to have both a lock up converter and an exhaust brake. It is especially important for a tow rig.

Case in point - when towing the RC out to Maob last year, I had plenty of 'go' power - the DTT converter in my '93 tugboat worked great - but - without an exhaust brake, when going downhill... and with 18,000 lbs of truck and trailer/load... the Cummins simply started to rev up because there was nothing trying to slow it down (no engine braking). With an e-brake it would have been lots better, and with a lock-up converter it would have been fantastic - but, I had neither... and I had to gear down into 1st just to keep from losing the whole load coming down the big grades.

Now, factor in a heavy RC, in Low Low, but no engine brake - it'll just spin right through the governor. With an e-brake it'll want to spin slower, but without a lock-up converter it may not matter much.

I dunno - it's all theory... but I can say that it is because of this 'issue' that I am converting my '93 over to a 6-speed NV5600... and adding in an exhaust brake.

I personally don't think that with a 4-to-1 doubler and a good conveter the RC will have much problem... but that's only when crawling. When I'm on the road cruising at 75 mph hauling the trailer and the quads... I'm gonna want to have some engine braking. Hmmm - I'm gonna have to figure this out.

If I find a 47RH I'll build it and sell the 518. I'm just trying to determine how long I can wait before doing wither one...

- Sam

 

[Moab4x4]

The Answer

Well, the answer I seem to have chosen is to keep the 3. 54's in the truck so I have decent hiway legs. I just bought a 78 ramcharger to modify for the trail rig. Now I have a 203 to combine with my other parts so I think I will be going more along your way MADDOG. That way I will keep the legs and still be able to crawl. With the NWfabworks parts did you have to machine the 205 case to fit the larger bearing as the ORD website mentions? My 205 is from a 518 truck.

Thanks

Ken

 

[BWJensen]

Yes I did. It's an easy job for machinist.
While your at it have them shave the 205 shift rails, so that in the future you can triple stick it if you want.

MADDOG