Any comments on changing the gearing on a 92 Chev K1500 Pickup
from 3.42 to 3.73 ? I know this is not much of a change but was
wondering if any real benefit would be gained.
Truck runs fair, has allot of miles but never really has been too
impressive with bottom end power, even before with stock tires.
350 engine with 7004R transmission.
Running stock wheels with 285-75R-16 Goodrich All Terrain Radials.
Not planning on changing wheels or tire size. I think the stock tire
size on this truck was 245-75-R-16.
Also on another note... Any comments on the Eaton electric locker
for the front on trucks like this?
I have an aftermarket Eaton limited slip in the rear.
Truck is spends more time on the pavement than off-road.
Gas mileage sucks anyway so I'm not concerned about any loss
of fuel mileage that this swap might alter.
I would regear it but I would not bother with a 3.73, you want atleast a
4.10, your tirediameter is about 33"s and you need a 4.10 here. It has
got to be a slug now in OD and so so in drive with 3.42's. The 700R4
(and 4L60) have a first gear ratio or 3.06 to 1 vs a THM400/4L80's 2.48
so it can make it feel perkier than it is at low speeds but OD on the
700R4 is .7 vs .75 on 4L80. Even with 4.10'a you will only be turning
1900 RPM at 65 in OD and the MPG will improve as well as engine
efficenct will improve at the increased RPM and not working as hard
(this is not a diesel and it needs to turn a few RPM to be most
efficent) If it was my truck I would consider 4.56's because it yeild
2100 in OD at 65 and pull OD really good and really get with the program
in lower gears or towing. When used properly, OD let you run a deep rear
axle gear for power and yet cruise nicely. If this was a non OD truck I
would say "maybe" a 3.73 as a compromise between power and MPG but not
in your case as you have a 700R4.
I am considering going with the 4.10 gear.... (current setup is the
stock 3.42) either I'm going to move to a 3.73 or 4.10. I can can't
see going any higher numerically over a 4.10, since this thing will
still need to drive on the pavement a reasonable speeds.
Throw out my question about the Eaton e-locker, sine the best I can
tell as of today is that Easton only makes a front e-locker for the
2500 and 3500 series trucks of the same year model.
My next question is how does one get the speedometer corrected for the
gear change. I believe my 7004r drives the speedo electronically, is
there a way to adjust for a gear change in the transmission? I know
with the old style you changed the speedo gear in the transmission, I
don't know what you do on these trucks with a electronic speedo? Also
does this impact the ECM....as far as it concerns true road speed?
Truck is a 1992 K1500 350 Engine 7004R trans with a 3.42 gear. I plan
to go with a 3.73 or 4.10 gear and it has 285-75R-16 tires on stock
I'll have to look at the truck later today or tomorrow to verify the
speedo issue, but I think it does drive the speedo via electronics
rather than a gear driven cable. I know what to do if it has a cable.
It is not the 700R4 that decides that it is electric, it is the truck
because 91 old sytle Burbs with not electric while 91 new style trucks
were. I know on thw later model (like my 2000 K3500) you can tweak it
easily with something like a hyper tech tuner.
THere is a BIG misconception about gear ratios. Untiel the mid 80's not
trucks had OD and still came with 3.73 and 4.10 gears and some did okay
MPG wise. Your 4x4 is a big heavy draggy truck and if you think that you
are goinf to get better MPG cruise with a 3.73's 33's and a .7 OD, you
are in for a surprize. It takes more than 1700 RPM in drive at 65 to
effiecently cruise that truck. Forcing the RPM to low for the load hurts
not helps MPG. Even with 4.10's it will only turn a slow 1900 RPM. I
used to have a 3/4 ton GMC with no OD and 4.10's with 32's I drove it
150 K miles and drove it across country twice cruising at 3000 to 3300
RPM (between 70 and 80) and more at times and got between 13 and 15 mpg
depending on how much a leadfooted it. Small block love to wind up and
make there best power above 2500 RPM or so and are not efficent at 1700
RPM. (it is not a diesel)
On the locker, I advise against it as you will have guiding problems and
they are hard on ujoint in straight axles and axle shafts too and with
33's you might break a axle in front with one. USe a true Trac type diff
up front and it will guide a lot nicer and not whip wheel as bad in
tight turns as the Ujoint next the spindles are not constant velocity is
a turn, the tighter the turn, the worse it is.
This was posted when I asked the same question on speedo changes
Your DRAC is attached to the computer behind th glove box. Don't buy a
DRAC from a dealer, their part numbers are wrong. Go to this site and
follow the links and you should be able to modify your system for no
I don't believe you can alter the speedo setting like you are talking
about on your truck as compared to this 92.
I know on the newer trucks you can "program" the ECM... older ones you
can't. My 92 truck is just like the old style ECMs where you were just
only able to change the chip.
I was looking at the elocker because you can turn it off and on and I
would only have it on off road. But anyway it turns out that they only
make them for 2500 or 3500 series for the front. I'm not sure at this
point, but it looks like the front may just stay "open". I drive this
thing on the road and the only type of posi / or locker would be
something that I can turn on and off. I don't want anything working
in the front while on pavement.
I should have the 4.10 gears installed within a week or so..
I follow the gearing... and the idea about mechanical advantage....
certainly aware that a small block makes power in the upper rpm range.
Gearing not a big deal to me, except that I'm not going below 4.10
with the setup I have now. I don't expect great mileage out of a
truck like this....but then again I don't want to be limited in the
on-road derivability either. IF it were truly a serious off road
truck then I would consider something numerically higher in the gears,
but then again I would most likely be dealing with a different
vehicle with a solid axle up front.
I'm just looking for decent performance, and somewhat of a compromise
between something that has to drive on the pavement reasonably well
but will also perform reasonably well off-road.
I believe your suggestion to run 4.10 gears makes sense with this type
of transmission and tire size. So thats what I'm looking to do.
On a 1992 you should have a electric speedometer. even if the gauge
it's self is analog read out. There is a DRAC unit(should be in the dash
beind the radio & glove box area). There is a Speedometer drive gear set
(much like a small ring and pionion set up). Where there would be a
cable comming out on older transmissions, your transmission will have 2
wires. The ECM (Engine Controll Module) has nothing to do with
speedometer calibration in that year.
Ok here is a follow on to my own post.
Anyone know if you install a K2500 front differential
into a k1500 pickup? The only difference I know
as of this writing is that the 2500 has a 9.25 differential
and the 1500 has a 8.25. The shop manual makes no distinction between
the 1500 and 2500 so I assume the housing is the same.
The reason I might consider this is that for the 2500 differential you
can get an Eaton e-locker, for the 1500 you can't get anything because
apparently no-one makes it. I don't know what other differences there
My only strategy at this point would be to run the 2500 front
differential housing to take advantage of the ability to install
the e-locker. For all I know at this point the two housings are
the same externally.
I don't have access to a 3/4 ton 1992 K truck so I don't know if the
differential actually mounts the same, (I assume it does). The goal
would be to just use the carrier housing and guts and keep the same
1500 drive axles and brakes etc...
anyone done this or tired it? It would have to be a total bolt in
type job, otherwise I'm not going to attempt it because I plan on
driving this thing on the road.
FYI on gearing
1992 GM K1500, 5.7, Auto Trans
Tire Size 285-75R-16
Old ring & pintion 3.42
New ring & pinion 4.11
Truck does not have an OEM tach so I don't know specifically what the
rpm "range" is but from driving the truck I can run 75 all day long.
The transmission shifts better and does not hunt back and forth
between lockup , and 3rd and 4th gear like it did in the past.
Overall I'm glad I changed the gears (front and back). More usable
power, transmission functions better...etc.
FYI on posi units for the front axle .....there are none available on
a 1/2 ton GM IFS front end.... Zero!!
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thanks... Been there before to check it out. Good info.
Looked there and also used my GPS to compare truck speed. Looks like
its about 5mph off. Speedo says 65mph GPS says 60mph. I'm not too
concerned about the speedo being really accurate. Given this truck
I'm not sure what you can do to adjust for a tire change and a gear
I think the mph error may increase as speed gets above 65mph. At
least it looks that way in comparison to the mph displayed on my GPS
unit (Garmin 76S).
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Ok, I'm in agreement with your opinion on the gearing... I used 4.11
and I think 4.56 with that tire combination would work too.
My next question is where to you get your speedo recalibrated? I've
seen some devices and reprogramers but I they all seem to work for
different year models, mine is a 1992 K 1500, 5.7, 7004R. Any
experience on this? Maybe I've missed it, but I've not seen anything
for a 1992 truck.
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