From: Neil E. Amrhein (neil@compu-powr.com)
Date: Fri Nov 07 2003 - 04:54:25 PST
OK, first I'm curious: What is a grass truck?
All of the CUCV pickup truck based vehicles have 4.56 gears. With the stock TH400 transmission, run about 2700rpm at 55mph. That is a decent cruising RPM that provides good HP. Without sound deadening material under the hood, it makes the engine sound like it's REALLY screaming. Plus, many units removed the floor mats, which would normally also help deaden the sound inside the cab.
There really is no cheap answer. Changing the transfer case is probably not the answer. It is merely transferring the power from the transmission to the rear. The only way a change here would help would be if you got an aftermarket T-case that has lower than a 1:1 ratio in the high range. I think that would probably cost a few grand. The real problem is that the TH400 does not have overdrive. When you combine this with the 4.56 gears, you have the speed vs. rpm issue. You could swap in a later model 4L80E, but you'd need to get the computer to control it, and that will cost $$ too. The other option is an aftermarket OD (Gear Vendors, etc..). These are not cheap either. Plus, they work better on crew-cab 4wd trucks. On a regular cab 4wd, they will extend the driveline enough that you will probably have to compensate for the increased driveshaft angle with a CV joint.
In my opinion, your best bet would probably be to have the ring & pinions swapped out with 3.73's. They are a good compromise gear. You will still have good power, but you will pick up some top end, too. 4.10's are OK, but it's only a 10% improvement. That means you can run about 60mph with the same rpm. I have them in my civilian 1-ton 6.2L crew-cab 4wd, and I don't run it over 65mph (usually not above 60).
I know there are a few who run their CUCV pickups at 70mph all the time. I just don't agree that it will have no, or minimal, impact on engine life. There are virtually no regular production engines designed to run at max rpm all day long. The strain on the engine increases dramatically as RPM increases. There's a reason that racing engines cost more than regular production engines. They are designed to run at max rpm all the time....
My $.02,
--Neil
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1987 Chevrolet M1028A3 CUCV
1963 Kaiser Jeep M274A1 Mule
----- Original Message -----
From: "Adam Suess" <ajsuess@hotmail.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Thursday, November 06, 2003 11:18 PM
Subject: [MV] M 1028 top speed?
> Fire dept has a M 1028 Chevy dually grass truck. Works pretty good except
> it's geared way to low and top speed seems to be about 55 mph. Speedometer
> don't work on the Chevy but the XM 813 keeps up to it just fine. Is there a
> way to get higher gearing for it or a better top speed with out spending a
> fortune? Change the transfer case? what’s top speed of the M 1008? Other
> military Chevy’s that parts could be swapped to go faster? Top speed is
> irritating but the real concern is the very high rpm’s the engine has to go
> to get to that speed. Thanks, Adam Suess
>
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