I'll try to provide some of my experiences and conversations with other
owners.
I had Cinnabar install the 3.42:1 ring and pinion gear two years ago
last month. After adding up the costs of all the parts, shipping, etc.,
which is around $1400 (including the speedometer gear reduction unit) as
I recall (going by memory as I don't have access to my paperwork at
work), I decided to have Cinnabar perform the replacement. Their labor
cost was approximately $100 dollars to install. Well worth it in my
opinion since they use a four post lift to raise up the coach that I
don't have access to and enough personnel to manhandle the differential
housing in an out of the coach.
In case you're not aware, the theory behind going to a higher
(numerically) gear ratio is to maximize the power output potential of
the engine where the rubber hits the road (i. e. driving wheels). In
the case of our GMC's, the engine torque curve rises very steeply with
increased rpm's and tops out at approximately 2800 rpm, according to the
chart I was furnished by Chuck Stoddard. What this means is that the
engine power falls off With the original ring and pinion gears (3.07:1),
2800 rpm would equate to a speed exceeding 75 mph, if I'm not mistaken.
With the 3.42:1 gears, 2800 rpm now equates to approximately 70 mph.
With my 403 cid engine, beforehand I was driving 60 mph @ 2200 rpm and
now the same speed results in 2450 rpm.
What will the 3:42 to 1 do????? Although I didn't make any checks
beforehand, following installation of the new gears, I went to a free
flowing exhaust system (Flowmaster mufflers and 3" exhaust piping).
While convoying with Bobby Moore (in his 76 GMC with a 455 cid engine)
from Louisville KY to the Boerne TX GMCMI Rally last year, about 25
miles s of Louisville on I-65, there is a long 3-4 mile sweeping S-curve
in the road that climbs a healthy grade toward Elizabethtown KY. As we
approached the S-curve, Bobby, who was in the lead, said over the CB
"set your cruise on 65 mph and lets see what happens". About two-thirds
of the way into the S-curve, I caught Bobby and passed him while still
on cruise That should give you some idea of the effect a 3.42:1 ring
and pinion gear will give you.
No longer do I loose speed going up hills while traveling, mountain
driving excepted.
Prior to installing the larger exhaust system, but after installing the
new ring and pinion gears, I was able to notice a definite change in
passing ability when pulling out to pass a vehicle in front of me.
Acceleration in that situation was much improved and noticeable right
off the bat.
As to other choices, Dick Crawford and his 73 GMC, installed the 3.21:1
ring and pinion gear then went to the 3.46:1 ring and pinion gears and
ran them for several years. Now he has the 3.66 or 3.67.1 ring and
pinion and tells me he doesn't notice any difference from the 3.46:1.
Leigh Harrison has been running Caspro's Power Drive (i. e. 3.50:1
ratio) for several years now with no problems, in spite of the vastly
increased power produced by his fuel injection system. A number of
people espouse that the Power Drive system overstresses the
transmission, but obviously Chuck wouldn't agree with that position.
Earlier, there were complaints with gear noise/whining, but supposedly
those have been ironed out now.
Incidentally, Chuck Stoddard feels that a 3.66:1 gear ratio is ideal for
the GMC. There is little or no difference in cost among the various
ring and pinion gears available now.
Paul Bartz
From: Gcbr [mailto:Gcbr]
Sent: Thursday, September 03, 1998 9:21 PM
Subject: Re: GMC: 3.42 drive
In a message dated 98-09-03 20:47:41 EDT, you write:
I realize that this may have been covered at one time, but I would like
to know people's opinions of the 3.42 Final drive offered by Cinnabar.
What kind of money would this improvement cost me, and is it really an
improvement? If any of you have opinions on the subject, and I bet you
do, please let me know!
MJ
I too would like to talk this one to death. I want to make the change to
another ratio--------but which one. Who is running what? Does it realy
work? Who is happy and who is sad. What is the buzz and what is the
truth. Heck I am driving a LeSharo when I picked up my GMC I thought it
kicked butt got away a lot faster than I am used to. Who has the magic
Cinnabar-----Caspro--------Gearmaster-------and the others??????? Love
to hear the skinny.
owners.
I had Cinnabar install the 3.42:1 ring and pinion gear two years ago
last month. After adding up the costs of all the parts, shipping, etc.,
which is around $1400 (including the speedometer gear reduction unit) as
I recall (going by memory as I don't have access to my paperwork at
work), I decided to have Cinnabar perform the replacement. Their labor
cost was approximately $100 dollars to install. Well worth it in my
opinion since they use a four post lift to raise up the coach that I
don't have access to and enough personnel to manhandle the differential
housing in an out of the coach.
In case you're not aware, the theory behind going to a higher
(numerically) gear ratio is to maximize the power output potential of
the engine where the rubber hits the road (i. e. driving wheels). In
the case of our GMC's, the engine torque curve rises very steeply with
increased rpm's and tops out at approximately 2800 rpm, according to the
chart I was furnished by Chuck Stoddard. What this means is that the
engine power falls off With the original ring and pinion gears (3.07:1),
2800 rpm would equate to a speed exceeding 75 mph, if I'm not mistaken.
With the 3.42:1 gears, 2800 rpm now equates to approximately 70 mph.
With my 403 cid engine, beforehand I was driving 60 mph @ 2200 rpm and
now the same speed results in 2450 rpm.
What will the 3:42 to 1 do????? Although I didn't make any checks
beforehand, following installation of the new gears, I went to a free
flowing exhaust system (Flowmaster mufflers and 3" exhaust piping).
While convoying with Bobby Moore (in his 76 GMC with a 455 cid engine)
from Louisville KY to the Boerne TX GMCMI Rally last year, about 25
miles s of Louisville on I-65, there is a long 3-4 mile sweeping S-curve
in the road that climbs a healthy grade toward Elizabethtown KY. As we
approached the S-curve, Bobby, who was in the lead, said over the CB
"set your cruise on 65 mph and lets see what happens". About two-thirds
of the way into the S-curve, I caught Bobby and passed him while still
on cruise That should give you some idea of the effect a 3.42:1 ring
and pinion gear will give you.
No longer do I loose speed going up hills while traveling, mountain
driving excepted.
Prior to installing the larger exhaust system, but after installing the
new ring and pinion gears, I was able to notice a definite change in
passing ability when pulling out to pass a vehicle in front of me.
Acceleration in that situation was much improved and noticeable right
off the bat.
As to other choices, Dick Crawford and his 73 GMC, installed the 3.21:1
ring and pinion gear then went to the 3.46:1 ring and pinion gears and
ran them for several years. Now he has the 3.66 or 3.67.1 ring and
pinion and tells me he doesn't notice any difference from the 3.46:1.
Leigh Harrison has been running Caspro's Power Drive (i. e. 3.50:1
ratio) for several years now with no problems, in spite of the vastly
increased power produced by his fuel injection system. A number of
people espouse that the Power Drive system overstresses the
transmission, but obviously Chuck wouldn't agree with that position.
Earlier, there were complaints with gear noise/whining, but supposedly
those have been ironed out now.
Incidentally, Chuck Stoddard feels that a 3.66:1 gear ratio is ideal for
the GMC. There is little or no difference in cost among the various
ring and pinion gears available now.
Paul Bartz
From: Gcbr [mailto:Gcbr]
Sent: Thursday, September 03, 1998 9:21 PM
Subject: Re: GMC: 3.42 drive
In a message dated 98-09-03 20:47:41 EDT, you write:
I realize that this may have been covered at one time, but I would like
to know people's opinions of the 3.42 Final drive offered by Cinnabar.
What kind of money would this improvement cost me, and is it really an
improvement? If any of you have opinions on the subject, and I bet you
do, please let me know!
MJ
I too would like to talk this one to death. I want to make the change to
another ratio--------but which one. Who is running what? Does it realy
work? Who is happy and who is sad. What is the buzz and what is the
truth. Heck I am driving a LeSharo when I picked up my GMC I thought it
kicked butt got away a lot faster than I am used to. Who has the magic
Cinnabar-----Caspro--------Gearmaster-------and the others??????? Love
to hear the skinny.
