Reduction gear options for a Sierra: pros and cons

[davidsuzuki]

Hi all,
Just after some opinions on reduction gearing for a Sierra.
I am interested in being able run 31"s and looking at different transfer case gear kits. Many people say that installing these aftermarket gears can make the car excessively noisy and this is something I'd rather avoid. There are 3 companies making these kits that I've found, each offering a few different reduction ratios. TrailGear(TrailCreeper Kits), Trail Tough and Calmini.

To reference an earlier thread on gearing there was some fairly in-depth information posted by gwagensteve in relation to running a Sierra with 6.5 gears and 31" tyres.
See below thread --
http://auszookers.com/forum/viewtopic.p ... tion+gears

From this is it would seem that 6.5s are both an excellent choice for 31's in high range mode, and will offer crawling speeds in low range mode. As I intend to use my Sierra on the highway quite a bit then these would probably be the best choice. I read the install pdf for the 6.5 Trail Creeper gears and these require grinding of the transfer case close to some of the thread holes (to provide clearance for the larger gears) which seems a bit dodgey, but for some reason grinding is not necessary for the 6.5 Calmini Kit which is wierd. I'm not sure about the Trail Tough kit, but its made in Japan which gives me some confidence they're well made gears.

Just wondering about experiences with these kits regarding reliability, excess noise, etc. Low range also offer a rebuild kit which includes all kinds of bearings, washers, gaskets and seals so these can be replaced while you've got the transfer case opened. Seems like a good idea?

Links below:

Calmini: http://www.calmini.com/detail.php?b=2&m=40&t=3&p=831&n=

TrailGear: http://www.lowrangeoffroad.com/index.ph ... e.html?p=1

Trail Tough: http://www.trailtough.com/index.php?pag ... &Itemid=53

[gwagensteve]

I can't comment on 6.X Calmini gears, but I bet they require grinding, otherwise the tooth counts required can't work.

I do know that TG and TT 6.X gears require grinding as I've installed both, and it's no big deal. It's 5 minutes work with a die grinder.

I chose the TT gears as they had the tallest high range, to work with my 5.12 diff gears, but it's only a % or so. 1.65-1.7

My TT 6.4:1 gears have been very quiet. They make a bit of noise now, but they have been filled with mud, run out of oil, and filled with water, so that's more abuse than you'd expect them to take. They were VERY quiet when they first went in. I can't comment on other brands.

I like TT gears as they come with Suzuki genuine replacement parts ( intermediate shaft/seals etc) whilst TG gears come with generic aftermarket parts. I don't think there's a big problem either way, but my preference is for SGP where possible. However, when I filled my case up with mud, I rebuilt it with a low range kit, which was all generic parts, and it's been fine.

There's no need to replace all the bearings when you replace the gears if they are quiet and in good condition. If your case is currently quiet, I would just buy the gear set - It comes with everything you need to fit the gears, only the large ball bearings are retained from your existing case, and if the case hasn't been filled with water/run dry they should be fine - they are pretty big and beefy.

Steve.

[jonfromhamilton]

My 6.4 gears on 33s are still too short in top gear (on the 616b)
I think with the standard engine they were a tiny bit too low so I had to constantly shift between 5th and 4th gear so anything under 33 would probably be perfect on the 6.4s
I don't know maths

[jono165]

My car has calmini gears. They're a bit noisey. I'd probably buy trail tough gears next time.

Mine are the 5.14 ratio which is nice for 31's. If you ever decide to go bigger than 31's 6.x gears are a better choice IMO

http://www.lepayne.com has a good gear calculator but note all sierras after 1988.5 ie widetrack have a 0.865 5th gear.

[gwagensteve]

I think I've heard before that the 5.1 transfer gears are noisy.

Steve.

[davidsuzuki]

Thanks for your input.
I'm leaning towards trail tough for the transfer case gears then. I've read more positive reviews of their kits than the other manufacturers, and less complaints about noise.
Actually I was browsing the TT website when I came across a technical bulletin urging zookers (such as myself) lusting for bigger tyres to change the gear size in the differentials first, and then make a choice about the transfer case gearing. I must admit my mechanical knowledge is not great in this area. Do 31" tyres require these kind of drive-train upgrades?? Also, to those that have performed this upgrade, how difficult was the process of changing the differential gears?? I have been lead to believe that the transfer case upgrade is manageable with standard tools and the use of a gear press.

[gwagensteve]

They're right, except if you can work out how to get the gearing right with 31" tyres and any combination of both diff and transfer gearing, go right ahead

All of the available diff ratios for suzukis aren't really compatible with using transfer case gears, at a 31" tyre.

The tallest readily available diff ratio to use is 4.6:1. These gears come from the front of a carburettor equipped automatic vitara. There is also an aftermarket option at 4.56.

These gears are almost exactly 20% lower, so they will perfectly offset 31" tyres on the highway. You speedo will read correctly, and the car will be really nice to drive. However, it will still be far too tall geared off road, so you'll need transfer gears.

The problem is that all transfer gears reduce high range gearing as well, so even the least reduction, 4.1's, drop high range by 12%, which puts your 100km/h cruise RPM up to 4400 rpm when used with 31's and 4.6 diff gears. That's unnecessary and annoying for a small tyre like a 31.

As for cost/complexity, it's a fairly big and or expensive job to swap diff gears. It's a pretty advanced from a skills point of view and requires specialist tools. It's also a job most people also would choose to do at the time they fit lockers.

You could try to track down some 4.1 gears from the rear of a jimny or late model maruti, these are a 10% drop from what you have. These will work quite well but you're still up at 3840 rpm @ 100km/h, relying on difficult to find diff gears and with lots of money invested.

Installing gears doesn't require a press. It will require a die grinder or similar to grind the case, a set of gear pullers, and some tube to use as a drift to knock the gears on in place of a press. You'll also likely need a rattle gun to get the flange nuts off, they are too hard to undo any other way. I'm not even 100% sure a torque wrench is required, but it would be handy.

Personally, I think diff gears are important if you're running a 33" tyre or bigger. I run 5.12's and 6.4 transfer in my car, but I have 35" tyres. those of us with this setup with a range of engines and gearboxes are pretty happy. It's maybe a touch too low off road, but it's OK.

TT are correct though, spreading the load between diffs ad transfer is a good idea - mostly, it reduces the load on the transfer mounts, which are the weak link in the Suzuki driveline. We have a car in the club which runs 35.5" tyres with stock diff gears, and whilst the gears have been reliable, it's MURDER on transfer mounts. low diff gearing definitely takes the load off of everything upstream, for sure. There's not much point if it makes the car annoying to use though.

Some form of bracing is pretty much required. Low Range have just released what I think is the gold standard in transfer mounts:

http://www.lowrangeoffroad.com/index.ph ... radle.html

I haven't seen one in person yet, but it looks to address every issue with transfer mounting in a sierra.

I don't think that much bracing is required with 31's, We've run a bunch of cars with some reinforcement on the long side and a tag to pick up the front output bolts but that's a fabrication job, not a bolt in, and with the EOS mounts, you'd only have to do it once. Bent transfer arms and broken mounts are a pain, especially because they always happen on the trail.

Steve.

[davidsuzuki]

I see.
So the most reliable setup for my rig allowing for both on and offroad driving would be 4.1:1 diff gears (~10% reduction in both LR/HR) and 4.16:1 to transfer gears (~12% reduction in HR & 84% reduction in low range) giving me a 22% reduction for road driving and a 94% reduction for offroad driving. I like the sound of it, but I'm glad I haven't spent any money yet. I'm still costing the whole project but I think it's gonna be a fair bit more than I anticipated. I going to look into costing some genuine suzuki parts from a Jimny rear differntial.


This is getting complicated now so please excuse my lack of knowledge here.

Is it only the ring and pinion parts I would require from a Jimny diff??


Will both the front and rear differentials in the car require the same change, ie; a set of 4.1 diff gears from the rear of a Jimny installed into my Sierras front and rear differentials??

Do you know what year Jimny I would be looking at to get the desired gear ratio??

I should also really factor in the cost of having the diff gears professionally installed (is this what most people without car workshops do?) as I can't see myself doing it.
The transfer case upgrade sounds do-able when I eventually move into a house with a garage.

Cheers!
David

[gwagensteve]

What you're describing there is probably the "perfect" setup for a 31" tyre, but geez, it's an enormously expensive and complex way to achieve it. I imagine those genuine Jimny diff gears will be >$850 each per end. Greyghost who's at my place today reckons $1500 each end new genuine You'd be best to get some from a wrecked jimmy. I think all years have 4.1. The very newest ones might not be.

Yes you'd need two rear diffs, generally sold as the whole assembly as removed from the jmny axle housing (diff centre, gears, and housing) . The rear will bolt in like for like, so no need for gear setup. The front gives you two options, you can bolt the whole thing in as is, which will require upgrading the front axles to 26 spline "double tough" axles (a very good upgrade) or get the gears installed into your 22 spline centre.

What will be difference be in driving experience between 6.5 transfer alone and 4.1/4.1's on road though? I reckon almost nothing, and off road, the gearing will be more impressive with the 6.5's alone. That's why most people can't justify the cost and effort for a 31" tyre.

you've stepped from a set of $600 transfer gears, to a set of $400 transfer gears, two diffs (at least $150 each) A set of $345 front axles or the same in diff gear setup…

It's going to cost twice the money to get within 5% of your road gearing - 175rpm or so @ 100km/h, and loose a gear off road.

31's aren't going to cause that much stress on the mounts/transfer with stock diff gears, especially in victoria where we are traction limited, and even moreso without a locker. Throw some 6.5's in and call it good.

Steve.

[mika]

Throw some 6.5's in and call it good.

This.
6.5's or 6.4's, either will work well and do the job.