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will i need gears for 30's on sierra ??
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Author:  rob45x [ Sun Nov 11, 2012 11:04 am ]
Post subject:  will i need gears for 30's on sierra ??
Hey guys. Wanted to upgrade to 30 x 9.5 tyres from stock tyres and wheels and just wondering if I'm going to need transfer case reduction gears ??
Author:  zukmeista [ Sun Nov 11, 2012 11:13 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
Yes, or a 1.0L transfer case. You can drive it with stock gearing, but it will suck big time.
Author:  rob45x [ Sun Nov 11, 2012 11:19 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
Yeah I've been looking for a 1L case. But it gets confusing. Switch no switch. Lol I just don't get it
Author:  Scrawny [ Sun Nov 11, 2012 11:30 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
Doesn't really matter about the switch. If you get hold of the driveshaft flanges from a 1L you can swap them onto your WT shafts and just bolt them straight up.
Author:  norcorider [ Sun Nov 11, 2012 11:35 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
no, you don't need gearing but you will be dumping the clutch a lot, so gearing would be better
Author:  zukmeista [ Sun Nov 11, 2012 11:38 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
Switch means you can use the flanges of your old tcase to make it bolt straight in. The non-switch cases have different size shafts so you can't do this.
Author:  31zook [ Sun Nov 11, 2012 12:05 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
And I'm pretty sure that non switch 1L are a smaller different size case
Author:  303zuke [ Sun Nov 11, 2012 1:18 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
rob45x wrote:
But it gets confusing. Switch no switch. Lol I just don't get it

No confusion at all, you have a 4wd light on your instrument panel, so you need a switch to operate the light!!! If you had read any of the posts about 1.0lt cases, you would have read that the switched case is the easiest to put in a WT. Mention of the Non Switched case is usually only that it is the case to steer clear of to avoid installation dramas. But as Scrawn said, if you also have the driveshafts with the non switch case, then it will bolt straight in using halves of the F and R driveshaft and the yoke off the jackshaft.
Author:  rob45x [ Sun Nov 11, 2012 1:23 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
Ok ill have to keep my eye open for a 1L case
Author:  pezz [ Sun Nov 11, 2012 3:37 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
Im going with 4.9's for my 30's
Author:  sideways [ Sun Nov 11, 2012 4:43 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
Depends how you wheel it. I ran 30s on my 1l Sierra with no gearing (it's probably worth noting that 1ls are quite a bit lower geared from the factory) and it was all right, a bit slow on the road but would still do highway speeds. For pretty much everything I did (lots and lots of sand) it was fine but the second you were doing technical stuff it was painful, but then it was on 26" tyres too. I always meant to fit some 4.556 diff gears but it doesn't look like that's going to happen now.

The non-switch tcase is geared roughly 10% lower than the switched case in low range but has the same highrange so that's the one I'd pick. It is harder to fit but if your unis need doing then it's practically no more work. :)

If I had the opportunity then I would have picked 235/75 mud tyres on sierra rims or 205r16s on LJ/16" sierra rims instead of the 30s on 15x7s.
Author:  rob45x [ Sun Nov 11, 2012 5:48 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
sideways wrote:
If I had the opportunity then I would have picked 235/75 mud tyres on sierra rims or 205r16s on LJ/16" sierra rims instead of the 30s on 15x7s.


I think i should be able to fit some 235/75's on 15x7 rims?
Author:  jimny_timmy [ Sun Nov 11, 2012 6:01 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
Yep you will^
Author:  rob45x [ Sun Nov 11, 2012 6:15 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
ok coolies. ive got some second hand rims organised. Just gotta hunt for the transfer case now
Author:  sideways [ Sun Nov 11, 2012 8:38 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
rob45x wrote:
sideways wrote:
If I had the opportunity then I would have picked 235/75 mud tyres on sierra rims or 205r16s on LJ/16" sierra rims instead of the 30s on 15x7s.


I think i should be able to fit some 235/75's on 15x7 rims?


Yeah but 7" rim is pretty wide for that size, a 5.5" rim will hold onto the tyre better and look more standard. :D
Author:  rob45x [ Sun Nov 11, 2012 8:51 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
i was told 235's need at least 6 inch wide??
Author:  sideways [ Sun Nov 11, 2012 9:23 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
rob45x wrote:
i was told 235's need at least 6 inch wide??


If you're doing it by the book, plenty of people run them on standard rims though. A friend of mine runs them like that and it works really well for him. :)
Author:  rob45x [ Sun Nov 11, 2012 9:54 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
And they won't roll off a 5.5 wide rim when you drop the pressures ??
Author:  defibros [ Sun Nov 11, 2012 11:25 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
Sorry to jump in. What if I have a set of 15x7? If I run 235 75 15, does it also need gearing?
Author:  rick1970 [ Mon Nov 12, 2012 2:42 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
defibros wrote:
Sorry to jump in. What if I have a set of 15x7? If I run 235 75 15, does it also need gearing?


I run 235/75R15's on 15x7's with std transfer case gears and 4.1 (Maruti) diff gears. Its ok but still needs to be a bit lower geared IMHO, expecially in low range.
Author:  Reubs [ Mon Nov 12, 2012 8:28 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
rob45x wrote:
And they won't roll off a 5.5 wide rim when you drop the pressures ??

The narrower the rim - the more pressure applied to the bead = less chance of rolling the tyre off the rim when deflated.

IMO 15x7" is a bit wide for 235/75R15.
Author:  303zuke [ Mon Nov 12, 2012 4:10 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
sideways wrote:
The non-switch tcase is geared roughly 10% lower than the switched case in low range but has the same highrange so that's the one I'd pick. It is harder to fit but if your unis need doing then it's practically no more work. :)


1.0L non switch has a high range ratio of 1.590:1 and a low range of 2.558:1.

1.0L switch has a high range ratio of 1.580:1 and a low range of 2.511:1.

Nowhere near 10% lower!!!!!
Author:  JrZook [ Mon Nov 12, 2012 4:23 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
~1.9% lower.... :P
Author:  sideways [ Mon Nov 12, 2012 4:31 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
303zuke wrote:
sideways wrote:
The non-switch tcase is geared roughly 10% lower than the switched case in low range but has the same highrange so that's the one I'd pick. It is harder to fit but if your unis need doing then it's practically no more work. :)


1.0L non switch has a high range ratio of 1.590:1 and a low range of 2.558:1.

1.0L switch has a high range ratio of 1.580:1 and a low range of 2.511:1.

Nowhere near 10% lower!!!!!


My Suzuki FSM (early '80s) lists the low range ratio as 2.716:1. What are your sources?
Author:  christover1 [ Tue Nov 13, 2012 6:32 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
http://www.facebook.com/download/169959 ... mation.pdf

This info suggests a 12% reduction, except later model.
If it will open.
Author:  JrZook [ Tue Nov 13, 2012 9:41 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
Its a comparison between low ranges of the 1L cases chris. That source says the same as 303, with the 1L cases either having a 2.558:1 or 2.511:1 ratios. Nice doco tho!
Author:  SierraDan [ Tue Nov 13, 2012 7:33 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
I worked out a 1ltr trans was 12% reduction high and low when i ran one.
Author:  rob45x [ Tue Nov 13, 2012 7:52 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
SierraDan wrote:
I worked out a 1ltr trans was 12% reduction high and low when i ran one.


do you still run the 1L case or have u upgraded to Low range gears etc??
Author:  JrZook [ Wed Nov 14, 2012 8:48 pm ]
Post subject:  Re: will i need gears for 30's on sierra ??
What's your first gear ratio?

Overall drive ratio = Gearbox ratio*tcase ratio*diff ratio
Author:  sideways [ Thu Nov 15, 2012 12:39 am ]
Post subject:  Re: will i need gears for 30's on sierra ??
hillbilly wrote:
i've been inquiring into vitara diff centres into a sierra diff to try get the reduction i'm after ....the 1litre transfere is my final option, i was going to ask if anyone knows the equation ......if lj50 transfere is 3:1 (near enough)......what would my final drive comparison be with vitara 5:12 diff centres (i would like to keep running lj50 transfer if i could).....my current life expectancy out of a 50 transfer is 1 day


Just fit a bloody Sierra transfer before you mash all the LJ50 transfers in Aus. :?
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