Crawl ratios and junk?

skipnrocks · Jan 11, 2018

A buggy for the kids what is needed?

Ok here are the specs Lightweight (less than 2500LBS)
Engine 3800 out of a buick
4t65e trans
Ford 9 rear
Dana 60 Front
Trans ratio 1st 2.94:1
4th .70:1
Trans axle ratio (t-case) 3:1
Diff ratio 3.54:1

40 in bfg stickies.

So here is the dilemma. The axle ratio is what it is because that is how they came.
Now were heading to moab for a week. and I am thinking that it might be better to put a 5.38 in the axles to reduce stress on the trans axle, make it more controllable, and lower the top speed from 80 to about 50.

But if the trans axle will hold up and the it will climb without having to rev the crap out of it I would rather hold off on spending the money.

What are your opinions on if it will hold up, and if it will be controllable in its current state.

clemsonjeep · Jan 11, 2018

I'm thinking you'll be need more ratio. With the way its setup now I'd imagine the trans would build up on heat. Currently you're at 38.4:1 and I'd be looking for something more along the lines of 60-70 as a minimum for the type of rig you're talking about. However, it appears the best you'll be able to do is get around 47:1 with the 5.38's. You'd need something in the 7:1 ratio for a ring and pinion to get into the 60:1 final ratio range. The power to weight ratio should help out, but like you're saying I think the transmission/transaxle might end up hating life.

TBItoy · Jan 11, 2018

It'll be fast with 30:1 crawl ratio. Being that light, it'll probably be pretty peppy, but you might find a situation where it won't have enough power to stall the converter

Id gear it low (5.38) to run 40" tires

Sent from my iPhone using Tapatalk

TacomaJD · Jan 11, 2018

Are they really 40's or are you just calling 39's 40's? molaugh

I'm all for the lowest gear ratio imagineable. Your engine has plenty power to turn everything, not sure about the trans axle stress issue, but with kids driving, or anybody for that matter, lower gearing especially in a place like Moab will make the rig much more manageable in any sort of technical stuff.

I may be looking at something wrong, but you have a t case that is a fuzz lower geared than typical stock low range in say a Toyota truck. Paired with 3.54 gearing in axles, and a 39" tall tire. That sounds like it would be pretty high geared for crawling anything at all.

I had a 98 Tacoma, stock chain driven t case, 4:88 gearing in axles, and only 36" tires and it was terrible to manage crawling anything. It had the 2.7 engine which has significantly less hp than your 3800 6 cyl, but my gearing was lower in axles and tires were shorter - aslo reducing final drive ratio. It was the jerkiest thing ever to try to control over obstacles while crawling, and I can't imagine your build for the kids being much different....unless I looked at something wrong in your spec list. I wouldn't think adding 5:38's would make it just rev like hell climbing stuff. Seems like it would be more practical that way, if anything.

skipnrocks · Jan 11, 2018

TacomaJD said:
Are they really 40's or are you just calling 39's 40's?

I'm all for the lowest gear ratio imagineable. Your engine has plenty power to turn everything, not sure about the trans axle stress issue, but with kids driving, or anybody for that matter, lower gearing especially in a place like Moab will make the rig much more manageable in any sort of technical stuff.

I may be looking at something wrong, but you have a t case that is a fuzz lower geared than typical stock low range in say a Toyota truck. Paired with 3.54 gearing in axles, and a 39" tall tire. That sounds like it would be pretty high geared for crawling anything at all.

I had a 98 Tacoma, stock chain driven t case, 4:88 gearing in axles, and only 36" tires and it was terrible to manage crawling anything. It had the 2.7 engine which has significantly less hp than your 3800 6 cyl, but my gearing was lower in axles and tires were shorter - aslo reducing final drive ratio. It was the jerkiest thing ever to try to control over obstacles while crawling, and I can't imagine your build for the kids being much different....unless I looked at something wrong in your spec list. I wouldn't think adding 5:38's would make it just rev like hell climbing stuff. Seems like it would be more practical that way, if anything.

Thats a good thought thank you. Yea the tires are 40s, not sure how tall they are mounted but their the bfg race stickies.

skipnrocks · Jan 11, 2018

I MAde up my mind. I'm going to do a 5:38

RustyC · Jan 11, 2018

Go here and enter the all the numbers. (http://www.grimmjeeper.com/gears.html)
I entered the numbers you gave above and took a screen shot of the mph vs engine rpm vs gear.
3.54 ratio on the left 5.38 on the right

gottagofast · Jan 12, 2018

Do you have room to squeeze in a t case?

gottagofast · Jan 12, 2018

.....

nightcrawler4x4 · Jan 12, 2018

6.16 or 7.17 in the axles would help alot.

LightBnDr · Jan 12, 2018

In my opinion running a small rig like I do, I'm not far from the size of a small child, gearing OPTIONS is THE way to go.

I would put a crawl box in line behind that trans long before I geared those axles that deep. Meaning deeper than a 5.38.

Then forever you'll have options in the future of output speed. If you gear those axles deep you end up with an output that is incredibly low and an axle that nobody else could ever use should you part it out 8 years from now.

Look at northwest fab. You can build a DIY case with dang near any configuration in gearing for just about the same price as gearing 5.38s in that axle.

skipnrocks · Jan 12, 2018

RustyC said:
Go here and enter the all the numbers. (http://www.grimmjeeper.com/gears.html)
I entered the numbers you gave above and took a screen shot of the mph vs engine rpm vs gear.
3.54 ratio on the left 5.38 on the right

That's a sweet chart. I really think the 5:38 would be best. It gives a decent crawl ratio especially with a good power to weight ratio.

If I raised the motor I could fit a tcase. But I like keeping it simple light and the cog way down low in the chassis. Plus it gives a great driveline angle. If we get back and it still doesn't seem enough I'll look at putyting a case in. But the ratios aren't far off from my buggy. 5:13. 4:1. 2.7:1. But the weight is over 1 k lighter

Stuntman Autoworks · Jan 12, 2018

Why not use a regular trans and tcase setup instead of the transaxle? I dont like transaxle buggies for being limited on gearing options and no 2wd option.

skipnrocks · Jan 12, 2018

nightcrawler4x4 said:
6.16 or 7.17 in the axles would help alot.

That would for sure but I think 5.38 is the lowest for a lp 60

skipnrocks · Jan 12, 2018

Stuntman Autoworks said:
Why not use a regular trans and tcase setup instead of the transaxle? I dont like transaxle buggies for being limited on gearing options and no 2wd option.

.

There were a few reasons I went this way. I wanted a rear engine for the kids to see good out the front. I liked the packaging and simplicity. They won't need to be in and out of 4x4 so thats not a concern. Just wanted simple. Reliable. I'm happy with my gear option and it's final ratios. I have never had a trans axle rig before. I suppose if I don't like it I can simply mount a typical combo in there. But a lot of people seem to like the setup?

bjeep · Jan 12, 2018

SBJeepn said:
That would for sure but I think 5.38 is the lowest for a lp 60

Nope 7.17 is.......

muddinmetal · Jan 12, 2018

SBJeepn said:
That would for sure but I think 5.38 is the lowest for a lp 60

That is the limit for a HP 60. Like stated above, 6.17s and 7.17s have been around for LPs for years, but they are best for low speed and low power :****:

skipnrocks · Jan 12, 2018

Oh cool. I think that may be a little too low though. If I go 5.38 it will be a good ratio if I went traditional trans and tcase down the road also.

Dirt700 · Jan 12, 2018

http://www.crawlpedia.com/crawl_ratio_calculator.htm

leeadam94 · Jan 13, 2018

Stuntman Autoworks said:
Why not use a regular trans and tcase setup instead of the transaxle? I dont like transaxle buggies for being limited on gearing options and no 2wd option.

My Honda transaxle is awesome. Wheels speed is great and 3 gears is all you need. And I also have 2wd. (Rear disconnect)

Sent from my iPhone using Tapatalk