installing a gear
Thread Starter
Drifting
Joined: Feb 2009
Posts: 1,408
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From: Hoffman Estates Illinois
installing a gear
hi everyone im thinken about buying a 3.90 or 4.10 gear for my 04Z
what all needs to be done to successfully install a gear..
will i have to do a recalibration for the speedo and odometer..??
any tips and advice would be great!!
what all needs to be done to successfully install a gear..
will i have to do a recalibration for the speedo and odometer..??
any tips and advice would be great!!
Pro
Joined: Mar 2004
Posts: 653
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The PCM won't need a minor reconfiguration for the new gear, in order for the speedo and odometer to be accurate. (Thanks Mike Mercury for fixing me!)
For the gear set install, I don't recommend it as a DIY job. Unless you have a hydraulic press, pinion depth setter, and a lot of experience using them. I have no problems R&R-ing my engine, trans, clutch replacement, etc....but I don't touch rear diff gears.
For the gear set install, I don't recommend it as a DIY job. Unless you have a hydraulic press, pinion depth setter, and a lot of experience using them. I have no problems R&R-ing my engine, trans, clutch replacement, etc....but I don't touch rear diff gears.
Last edited by crainholio; Jul 2, 2009 at 04:40 PM. Reason: Correction thanks to Mike Mercury
Pro
Joined: Dec 2003
Posts: 654
Likes: 1
From: chandler az
The PCM will need a minor reconfiguration for the new gear, in order for the speedo and odometer to be accurate.
For the gear set install, I don't recommend it as a DIY job. Unless you have a hydraulic press, pinion depth setter, and a lot of experience using them. I have no problems R&R-ing my engine, trans, clutch replacement, etc....but I don't touch rear diff gears.
For the gear set install, I don't recommend it as a DIY job. Unless you have a hydraulic press, pinion depth setter, and a lot of experience using them. I have no problems R&R-ing my engine, trans, clutch replacement, etc....but I don't touch rear diff gears.
My guess is the info is out there somewhere, but it wouldn't surprise to find it all in German. Spreken ze Deutsch?
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
I have all that, but I've heard you need special tools that are very expensive. I have not been able to find any write ups on the internet so I gave up on the idea.
My guess is the info is out there somewhere, but it wouldn't surprise to find it all in German. Spreken ze Deutsch?
My guess is the info is out there somewhere, but it wouldn't surprise to find it all in German. Spreken ze Deutsch?
if you want to actually change just the actual gears in the differential--don't. these rear ends are a PAIN IN THE @$$ to set up correctly.
i'd strongly recommend you buy a rear end with the gears you want in it already and just sell the stock one. it will cost a bit more up front but it also turns the job into something you might could do on your own.
it isn't too hard to change the whole differential. basically you'll be dropping the rear cradle (which is like 4 nuts) and just unbolting the diff/unhooking any wiring. install new one in the reverse order and fill with correct fluid (usually GM syncromesh..or at least it used to be).
there are surely some write-ups around here somewhere but IMO that's the way to go.
(oh, and this car isn't from Germany
..so the instructions should be in English)
Team Owner
Joined: Apr 2001
Posts: 54,204
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From: S.W. Ohio. . . . . . NRA Life Member
on A4's, but no reprog is necessary on a manual shift C5.
for the new gear, in order for the speedo and odometer to be accurate.
INCORRECT ! 
there is no speedo/odo error induced when changing the rear axle ratio on any C5... PERIOD !
There's reasons to reprog for a rear axle ratio change on an automatic C5 (though it has nothing to do with the speedo or odometer). Manual shift C5's require no reprog at all. The OP has a Z06.
No need to guess at answers here; there's plenty of people here on CF that know the accurate details.
for the OP; here's some installation info:
http://mikemercury.home.att.net/342.htm
I agree with the others; replace the entire unit (carrier) . Leave the internal ring & pinion swap to the professionals. The Getrag differential is too unique.
for the new gear, in order for the speedo and odometer to be accurate.
there is no speedo/odo error induced when changing the rear axle ratio on any C5... PERIOD !
There's reasons to reprog for a rear axle ratio change on an automatic C5 (though it has nothing to do with the speedo or odometer). Manual shift C5's require no reprog at all. The OP has a Z06.
No need to guess at answers here; there's plenty of people here on CF that know the accurate details.
for the OP; here's some installation info:
http://mikemercury.home.att.net/342.htm
I agree with the others; replace the entire unit (carrier) . Leave the internal ring & pinion swap to the professionals. The Getrag differential is too unique.
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From: Central Jersey
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I have seen the set up tools go between in the $1200-$1500 range and sometimes a bit cheaper. I would suggest letting a shop like RPM set them up for you.
Pro
Joined: Mar 2004
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On the LS1s I've worked on, the PCM only reads reluctor pulses from the Vehicle Speed Sensor which tell it how many rotations the output shaft has turned. The PCM then calculates a miles/hour speed based on two configured variables:
1.) Tire diameter.
2.) Final gear ratio.
If you alter either of those two, the PCM will incorrectly report vehicle speed. Are C5 manual-trans PCMs configured differently, such that they use a different input for vehicle speed?
I can imagine the ABS reluctors would provide reasonably-accurate vehicle speed input independent of gear ratio...but they'd still be thrown off by changing tire diameter.
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
Can you direct us to an authoritative source for this finding?
On the LS1s I've worked on, the PCM only reads reluctor pulses from the Vehicle Speed Sensor which tell it how many rotations the output shaft has turned. The PCM then calculates a miles/hour speed based on two configured variables:
1.) Tire diameter.
2.) Final gear ratio.
If you alter either of those two, the PCM will incorrectly report vehicle speed. Are C5 manual-trans PCMs configured differently, such that they use a different input for vehicle speed?
I can imagine the ABS reluctors would provide reasonably-accurate vehicle speed input independent of gear ratio...but they'd still be thrown off by changing tire diameter.
On the LS1s I've worked on, the PCM only reads reluctor pulses from the Vehicle Speed Sensor which tell it how many rotations the output shaft has turned. The PCM then calculates a miles/hour speed based on two configured variables:
1.) Tire diameter.
2.) Final gear ratio.
If you alter either of those two, the PCM will incorrectly report vehicle speed. Are C5 manual-trans PCMs configured differently, such that they use a different input for vehicle speed?
I can imagine the ABS reluctors would provide reasonably-accurate vehicle speed input independent of gear ratio...but they'd still be thrown off by changing tire diameter.
On automatics though of course it needs a little more information to correctly calculate what's going on in the tranny. Comparing axle speeds, RPM and what gear the tranny is in is useless if it doesn't know the rear end ratios. But, for M6's it doesn't matter since the computer doesn't do anything in regards to shifting.
Last edited by schpenxel; Jul 2, 2009 at 02:41 PM.
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Team Owner
Joined: Apr 2001
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From: S.W. Ohio. . . . . . NRA Life Member
this is such old news that the only people that get it wrong are those that try to "reason" to get the answer.
I believe the problem is that you are indeed relying on others
Can you direct us to an authoritative source for this finding?
Team Owner
Joined: Apr 2001
Posts: 54,204
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From: S.W. Ohio. . . . . . NRA Life Member
the VSS sensor picks up notches from a reluctor wheel - located inside the rear carrier (differential) - attached to one of the output shafts. The only thing that will throw this accuracy off is a change in rear tire heigth.
Pro
Joined: Mar 2004
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this is such old news that the only people that get it wrong are those that try to "reason" to get the answer.
I believe the problem is that you are indeed relying on others
to give you the info. Instead; this time find it out yourself. All you need do is see where the VSS is physically located on the C5. Then you don't hafta rely on others to give you the accurate info.
Those cars acquire VSS data from the output shaft of the transmission itself, using a magnetic sensor installed in the T56 and 4L60E trans tailshaft housing. Installing a different rear gear ratio will very much throw off the PCM calculation of vehicle speed in those systems.
I recognize that the Y-body is a different animal. I left room in my statements for some difference in Y-body data acquisition, and hoped you might clarify.
Team Owner
Joined: Apr 2001
Posts: 54,204
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From: S.W. Ohio. . . . . . NRA Life Member
In fact, the source of my data is my own direct experience with the LS1 powertrain in both F-body cars as well as the GTO.
Those cars acquire VSS data from the output shaft of the transmission itself, using a magnetic sensor installed in the T56 and 4L60E trans tailshaft housing. Installing a different rear gear ratio will very much throw off the PCM calculation of vehicle speed in those systems.
I recognize that the Y-body is a different animal. I left room in my statements for some difference in Y-body data acquisition, and hoped you might clarify.
Those cars acquire VSS data from the output shaft of the transmission itself, using a magnetic sensor installed in the T56 and 4L60E trans tailshaft housing. Installing a different rear gear ratio will very much throw off the PCM calculation of vehicle speed in those systems.
I recognize that the Y-body is a different animal. I left room in my statements for some difference in Y-body data acquisition, and hoped you might clarify.
The Corvette is indeed different than other users of the LS1. Sometimes we're proud of that... other times we curse it
