Thread: Questions about Drivetrain for 4WD Sand Rail Build

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Hello All! This is my first post on this forum, and I hope I've got the right section!

I am doing a project for school, and I have decided to take it to the extreme and build a sand rail. It will be a 4WD 4 seater made from 1 3/4 mild steel (I'm fabricating the frame myself)l, so it will have a little bit of weight to it. It will also be running a set of 37" mud tires.

My intended use: Summer only, to drive short distances around town, or to the "desert" area where we can do small rock climbs, run through sand, or just have some all around trail cruising fun.

I have been doing a lot of research on what I should put in it mechanically. Here is where I sit right now.

Engine: Mid 70's to Early 80's Chevy 350 Small Block
-After considering a TBI, I would like to stay carbureated
-Engine mods to build it up to 300 bhp


Transmission: 4L80-E
-A lot of people have recommended the Turbo 400 as it is a ridiculously strong transmission. However, I would like to be able to get up to 60-70 MPH and cruise at those speeds occasionally. After further research, I decided that the 4L80-E would be better as it has an overdrive gear. Its ratios are as following: 1st- 2.48 --- 2nd-1.48 --- 3rd-1 --- Overdrive- 0.75

Charting this out on a calculator with my other parts gave me 72 MPH at 2100 RPM, which I think is an acceptable cruising RPM

Axles: Dana 44's
- Since I plan on running 37" mud tires, it was recommended that going with Dana 44's would be a good fit based upon the intended uses (crashing into rocks and trees). Also, if I went with something bigger like Dana 60's I wouldn't break the bank if they need a repair. Dana 44's are much easier to find where I live.
I then picked my ratio that I was looking for based off what I wanted for a cruising speed, which I demonstrated in the last paragraph (72MPH at 2100 RPM). This left me at a gearing ratio of 4.10.
-If I find out that I need more power, I plan to upgrade my engine more to get some more torque from it.

I'm not looking for crazy power. Just something thats unique and fun to take my friends out in that has a little go to it.

My questions are:
1. Does this spec out seem like a logical approach to my intended application?
2. Is the 4L80E overkill for a Dana 44? Should I be looking at a lighter transmission? I figured since the vehicle will be pretty light overall, the weight isn't a big factor to me, and it will be absolutely bullet-proof.
3. What do I do about a transfer case?
4. I am disc brake dumb. Whats the a good disc brake system for what I am doing? Braking is very important to me. I like being able to stop just as much as the next guy.
5. Any comments?


I have access to a shop at my ready (my friend owns a massive shop, and has graciously lent me a bay and welding equipment to build my frame and assemble the parts). I have also sourced our a machine shop for any extensive engine work that might need done (boring and honing) and another shop that can make the driveshafts for me.
Other things like race seats, pedals, power steering, lights, cooling, etc still need to be figured out, but I want to make sure I am solid on my drive train before I start on secondary systems.

Any comments are appreciated! Thanks!!

Welcome to the forum! I'd go with a D60 first off. You might have plenty of access to d44s, but how much torque will a d44 take with the wheels cranked and 38s? For the money invested in a d44 to make it strong, I'd just get a 60 and put in some Spicer non reasonable joints, good lock outs, and rock it. The 4l80e is a great trans, but may need some upgraded hard parts to live in an off road rig. It may not either, I haven't messed with any in an off road rig.

On the tcase, do you want a doubler, atlas, or just a plain 205?

For a rock crawler, you might reconsider EFI. Crazy angles can interfere with the float bowl operation.

Welcome to the forum. A couple of things jumped out at me, having done my share of off-road playing with the Jeep over the years. First you mention mild steel tubing - you want to use 1020 DOM tubing for strength, not seam welded tube. I'd use minimum 0.156" wall DOM for the main chassis waist band tube and rocker tubes, and minimum 0.120" wall DOM for everything else. You're putting your life on the line with your chassis & roll cage, so do it right.

Second, you mention "...rock climbs" but then you say "(crashing into rocks and trees)" is your intended use. Are you building an extreme trail buggy, meant to tear through anything at max power for the fastest time, or a rock crawler? There is a distinct difference, especially in the use of the machine. Rock crawling is finesse driving, doing established trails with minimal impact to the environment, while the extreme trail buggies have no concern for leaving the trail as it was when they arrived - they're there to "conquer the hill".

Ryan has given you some good comments, and some added questions about your direction on drive train. Most of the dedicated guys have gone to EFI over carbs, due to the difficulties of maintaining a consistent float bowl fill at extreme angles, but there are carbs that work better for off-road than others if you insist on going that direction. Bottom line, have you looked at Pirate4x4 - link Pirate4x4.Com - The largest off roading website in the world. Those guys are into everything from lightly modified OEM's to the most extreme all-wheel steer buggies and power you'd not believe. Just be prepared for the flaming if you go in asking rookie questions and acting like you know it all.... Just about every question has been asked before, and their search engine actually works.

In my opinion, you should consider the current state of off road/rock crawling and go from there. The key to decent performance is a lightweight platform with a low center of gravity. I have an aluminum bodied jeep with an injected (MEFI) 350 and dana 60 axles from Dynatrac front and rear. With a tube freme, etc, mine weighs over 4000 lbs....maybe good for 10 years ago but not the latest thinking. Some bullets:
1. engine needs to run when car is at extreme angles....injection good, carbs bad
2. 700R4 has lowest first gear of easily found trannys Use a cable shifter. Current cars have powerglides with LOTS of mods
3. Atlas transfer case. Any stocker is a pig. You want to have front wheel drive only option when you come off a steep bank
4. 37" tires and taller need power brakes if possible or better yet, hydroboost. I have 4 wheel discs (Wilwood) and on a steep downhill, two feet on the pedal barely stops the car with 40" goodyears
5. For your app, unless you are going full hard core, dana 44s are fine...you can buy lots of parts to beef them up. Stock junk from Tahoe fronts will probably break at a full lock turn and full torque
6. Keep the center of gravity LOW. Nimrods with a jacked up vehicle can barely do a side hill or much else. Jacked up trucks are for mud maybe but not rock crawling.
7. Your gear ratio 4.10 is about right for 37" tall tires.....I have 40" tires and 4.56 and I seldom need low range when in first gear.
8. You cant have too much for tranny coolers. Climbing in first gear dumps a LOT of heat from the converter....it goes into the fluid. External coolers with fans are a must.
9. Buy Goodyears or Goodrich T/A rock crawling tires....I run 4.5psi off road and 12 on the road. Use some good bead lock wheels.
10. Consider using ARB lockers front and rear.
11. Hydraulic assist steering is great. You can do hydraulic assist using a GM box...you can buy it modified or do it yourself. It is great for putting the tire against a rock and turning the steering wheel to move the vehicle sideways. Full hydraulic steering is illegal on the road but ram assist is OK since there is a mechanical link in the system.

Welcome to CHR, sounds like a neat project you're planning. I'm not much on off road 4 X 4 stuff, but from drag racing and playing on the street, I've to to agree with the guys suggesting to upgrade for a 44. They break way too easy!

I'd also offer the only 2 true rules of building a Hot Rod;
1. It's going to take longer then you thought.
2. It's going to cost more then you thought.

Sounds like you have the facilities, tools, and equipment lined up, go for it!!!!!

Lilke Roger said, becareful on Pirate. Those guys are brutal. For the money it'll take to keep a D44 alive, I'd just 60 it. I have a friend who just went through this in his jeep. He is switching from a upgraded D44 to a D60 now, and he can't get half his money back on his D44. I've been there, I'm jusst trying to save you some money. These guys have given you some great info and thoughts too.