Allison trannies off road...

Thanks, I really appreciate it.

Once I have completed my repairs to get my K5 back on the road, I will resume my search for parts to build it up for better off-road capability. I also want better performance on the road, so something like this would make much sense to me.

If an Allison would let me go with a lower axle ratio without suffering the gas-mileage effects I'd seriously look into making the switch.

I am planning on going overkill to some degree, but that's just a personality defect ;-P That and I'm tired of seeing the same old stuff in the 4x4's I see in the magazines. I gotta be different.

Thanks again, ~jp

Allison trannies are the toughest automatic ever made. Infact, they are the only OTR (over the road) truck transmission manufacturer to make a fully automatic transmission for large diesel trucks. They are tried and true. And JP, you are correct, the reason for the extra OD is for that very reason. The Allison trannies used in the chevy heavy series is just a sized down version of the 1200 ft.lb. torque tranny used in med. duty large trucks. They are rated for 600ft.lbs of torque (I think). I am trying to remember this from my Heavy Equip. class a couple semesters ago. Let me talk to one of my instructors (master ASE OTR truck tech) and I will get back to you on this.

Pk

Also if you properly build a 700R4 it will handle a lot of power and give you a deeper first gear (about the same as a ally, 3.06 vs 3.1 and

2.48 on 4L80) and a taller OD too (actaully a bit taller than the 5sp ally too (.7 vs .71 and .75 on 4L80)

Ally is a good tranny but it has a long road to go before it replaces the THM 400 as best tranny made. I used them drag racing years ago running over 700HP and never had one fail to handle it. (blew some engines but not the tranny)

Well actually I want to start at the same first gear ratio and end up in a higher overdrive, hence the 5 speed Allison idea...

I figure running lower axle ratios would let me have a stronger 1st while keeping the RPMs the same when using the higher overdrive.

What are the stock gear ratios on the 700R4 and the Allison 5-speed auto?

~jp

A 700R4 and 4L60 have a 3.06 1st, 1.6 2nd, 1 to 1 3rd and a .7 4th/OD (taller than a 5sp ally) a ally has about a 3.1 1st, 1.8 2nd, a 1.4 3rd,

1 to 1 4th and a .71 5th/OD

Then according to your numbers, if I wanted a stronger first gear keeping the axle gear ratio the same and swapping to an Allison would do it...but it doesn't seem like much difference. 3.06 vs 3.1.

It seems the 5 gears of the Allison more or less have closer ratios that allow lower-RPM shifting. I can see how this would be useful for diesels that produce high-torque at lower engine speeds, but not necessarily practical in my application...or not. I can't imagine needing to get my engine beyond 3000 RPM in most situations. And I am planning on getting a camper to tow around at some point.

But I'd be willing to bet building a badass 700R4 would be a lot cheaper that buying, rebuilding, and more importantly installing the Allison in my K5.

~jp

Go with a 4L80. Stock it should last, tougher then a 4L60/Th700. Charles

I agree and the nice thing about a 700R4 is that it is not ECM controlled and easy to beef up too plus is weighs less as well than the ally which is computer controlled too. I have 175k on a stock 700R4 in my 89 4x4 burb that I have had since new and it still works like new.

Greetings,

Visit this link:

It's a spec sheet from an older Allison 1000 series, and I believe that the most recent 6-speed version tranny's have much the same gear ratios but higher power and torque capacities.

Cheers - Jonathan

It is rated at 650 ftlbs or torque capacity and first 5 gears are the same with a added OD gear of .61. In the link below you will find some info on it, the Dmax upgrades and the planned V10

See now...that .61 sounds good to me. But still, I suppose it doesn't make much sense to me to make the swap to a bigger, heavier tranny, just to get a little lower first. I'm actually pretty happy with the OD for now. Further testing is needed though.

Either way, I still wish there was a 5-speed automatic available that had either a lower 1st or a higher OD.

I know I'm hoping for the best of both worlds, and it's not always possible, but still...

Thanks,

~jp

There is the 6L80 used in the vette (6speed hydromatic) and it will be coming to P/U soon. Some info on it in link below

WHOA! My research turned up a 4.02:1 first gear ratio on that thing! And a .67:1 sixth gear. Now THAT is what I'm talking about.

Now how much is this thing gonna cost...?

~jp

There are bolt-on overdrive and underdrive units from the aftermarket that you can check into. I don't know if they would be good for four-wheeling but it is a solution that I've seen folks who haul heavy 5th wheels use.

Cheers - Jonathan

Well, I had the same idea but soon realized the the problem with that is that if it were bolted onto the back of the transfer case there would be an extremely short driveshaft. Not only that, but it'd only affect the rear wheels.

I suppose one could be mounted between the tranny and transfer case, but that would push the t-case back very far, again requiring a very short rear driveshaft and a ridiculously long front driveshaft.

But thanks for the suggestion...

~jp