Gear change etc. ????

[70jimmy]

Time to change the gears in the diffs for better crawling

Rig 70 Jimmy with 350 TBI, 350, NP205 twin sticked, 37" Krawlers

Rear
14 Bolt FF with Detroit 4.10's

Questions
1. I am thinking 5.13 gear ratio, vehicle is driven on street some and to and from trails, some long range like 6 to 8 hour trips also. Input

2. How do I tell if I currently have thick or thin gears or if the carrier is 4.10 and down. Whatever that is. If I have the the 4.10 and up but need 4.10 and down then do I buy a new carrier. What is the carrier?

3. With the Detroit I have can I re-use it with the new ratio or do I need a new Detroit?

and no I don't plan on doing the gear setup myself at least not without the help of some knowledgeable hands and tools helping.

Front
10 bolt 4.10's welded. right now I wheel with one hub locked if needed and both locked when I have too. It does have crossover, high steer, upgraded shafts, and hydro assist.

1. Since it is currently welded what all will need replaced beyond the obvious ring and pinion?

2. I would like to go with a new traction device. recommendations? I was looking at an aussie locker or some other selectable type. I would love an ARB but prolly not in the budget.

Thanks for the input/advice, also if you have advice on best places to get the parts fire away.

 

[sweetk30]

well 14ff rear is same detroit per carrier. it just replaces the spider guts only.

and 4.10-down = thin gears
and 4.56-up = factory thin for the thicker case .

the front will be full new parts as carrier will be needed. and all that power/tires on 10 bolt better to do axle shafts aftermarket or just find and bolt in a 60 front and be done with it in stock form over a 10 bolt.

so you are good at this point as aftermarket gears for 4.10 down common carrier are far cheeper than factory 4.56-up carrier. so just order thick gears.

and if you want better crawl ratios and like the rpms on the road now mabye the better option in the end would be a doubler kit. 203/205 the 203 for the th350 setup is vary comon to find and cheep if not free to be had. then just need to get kit to bolt on to 205 and dependant on kit swap input on 205 and punch the 205 tcase hole out for bigger bearing. but real easy to do . read here for idea full reman http://coloradok5.com/forums/showthread.php?t=253000 or bolt together http://coloradok5.com/orddoubler.shtml

this will help front driveline angles a little. but alos shorten up the rear that much. also with the th350 its a simple bolt on as the 203 and 205 use the same tail shaft on the tranny. so no reman of tranny needed.

the 1.96:1 low in the 205 now x2 with the 2 to 1 low in the 203 range box will be great for lower ratios .

play around a little with this first . you can do all sorts of stuff and side by side comp of diffrent setups. http://www.grimmjeeper.com/gears.html

hope this all helps. if not just ask more.

 

[1BEATK5]

x2 on the doubler. 4.10s for highway use and 4:1 for the trails.

i have 42s and 4.88s and a t350. 2750rpm at about 60mph. 37s and 5.13s will be screamin on the highway.

th350/203/205 is a cheaper doubler to do. people almost give away 203s. you will need a different 205, or have yours modded to accept the bigger input gear.

 

[nvrenuf]

42's, th350 and 4.88's will be 2475 rpm, very livable.

37's, th350 and 5.13 will be right at 3000 rpm, no horrible but probably annoying for a 6 to 8 hr trip.

That said...I agree, keep the current 4.10's and buy a Doubler for the best of both worlds.

 

[1BEATK5]

42's, th350 and 4.88's will be 2475 rpm, very livable.

37's, th350 and 5.13 will be right at 3000 rpm, no horrible but probably annoying for a 6 to 8 hr trip.

That said...I agree, keep the current 4.10's and buy a Doubler for the best of both worlds.

according to my gps its 2750. 3100 is about 70mph. tires are shorter than the say therfore calculated speeds arent quite accurate.

 

[nvrenuf]

according to my gps its 2750. 3100 is about 70mph. tires are shorter than the say therfore calculated speeds arent quite accurate.

You know, I was poking around on the GrimmJeeper site looking at a bunch of different combos and didn't even think about the differences between advertised and actual tire height. Good point.

 

[1BEATK5]

i think if you wanted to be really accurate you would used the circumfrence of the tire and use math (ugh) to figure out the exact revolutions per mile or actual hight.

 

[sweetk30]

if swampers or most other tire brands. thay show on there sites specs on specific rim for act hight over advertised size. just go find it.

here is interco to help start you guys out. http://www.intercotire.com/tires.php?id=10&g=1

 

[1BEATK5]

they still tend to be a little optimistic. my 42s measure more like 40s when loaded. i measured one. but i think measuriing the actual tire and using revs per mile would be the most accurate.

another thing, what about convertor slippage. everybody guesses 200-250 rpm slippage. but i would think that an under-powered 6000lb. truck that sticks way up in the air attempting to spin huge tires will slip the convertor more than a stock height truck with small tires.