RPM trnsmission
Thread Starter
Advanced
Joined: Jan 2007
Posts: 81
Likes: 3
From: Rocky Hill CT
RPM trnsmission
C5 RPM transmission just installed. along with a diff change 2:73 to 3:42, both from RPM. A short test drive to determine if I can drive it to a Corvette shop for a tune revealed it would not shift out of first gear
Drifting
Joined: Oct 2002
Posts: 1,773
Likes: 66
From: SoCal
With the rear gear change, it should still shift. It would probably shift short compared to what it used to, but it would shift. When you changed gears, are you sure you connected the VSS (Vehicle Speed Sensor)? Do you get a speedometer reading on your cluster? If you manually shift the transmission from first to second, does it shift then?
Check codes and maybe a wiring issue, blown fuse, loose connection.
Here is how to check for trouble codes
http://www.c5forum.com/ayc/dtcdic.php
Check codes and maybe a wiring issue, blown fuse, loose connection.
Here is how to check for trouble codes
http://www.c5forum.com/ayc/dtcdic.php
Last edited by RedRiderZR1; Mar 10, 2018 at 06:32 PM.
Thread Starter
Advanced
Joined: Jan 2007
Posts: 81
Likes: 3
From: Rocky Hill CT
With the rear gear change, it should still shift. It would probably shift short compared to what it used to, but it would shift. When you changed gears, are you sure you connected the VSS (Vehicle Speed Sensor)? Do you get a speedometer reading on your cluster? If you manually shift the transmission from first to second, does it shift then?
Check codes and maybe a wiring issue, blown fuse, loose connection.
Here is how to check for trouble codes
http://www.c5forum.com/ayc/dtcdic.php
Check codes and maybe a wiring issue, blown fuse, loose connection.
Here is how to check for trouble codes
http://www.c5forum.com/ayc/dtcdic.php
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Ok When making a rear gear change on a C5/C6 you DO NOT have to make a speedo correction HOWEVER you do need to make a shift point correction for both the P/T up and down shiftpoints and more importantly the WOT both UPSHIFT and DOWNSHIFT mph speed shift points!!
Going from a 2.73 rear gear to a 3.42 rear gear requires a -25% change on your WOT shift speeds both for WOT upshifts and WOT downshifts
IF you do not make these WOT corrections the trans will skip over the WOT RPM shift points and hit the "safety rev limiter" and NOT shift
It is rather more complicated than this however the basic starting point would be to SUBTRACT 25% to both the WOT upshift speeds and the WOT downshift speeds As an example if your 1-2 WOT upshift speed is 45 MPH then subtract 25% to that do that for the DOWNSHIFT speeds at 2-1 at WOT as well Do this for the 2-3 and 3-4 and the 3-2 and 4-3 WOT speeds as well--
Going from a 2.73 rear gear to a 3.42 rear gear requires a -25% change on your WOT shift speeds both for WOT upshifts and WOT downshifts
IF you do not make these WOT corrections the trans will skip over the WOT RPM shift points and hit the "safety rev limiter" and NOT shift
It is rather more complicated than this however the basic starting point would be to SUBTRACT 25% to both the WOT upshift speeds and the WOT downshift speeds As an example if your 1-2 WOT upshift speed is 45 MPH then subtract 25% to that do that for the DOWNSHIFT speeds at 2-1 at WOT as well Do this for the 2-3 and 3-4 and the 3-2 and 4-3 WOT speeds as well--
Last edited by tblu92; Mar 17, 2018 at 02:43 AM.
Advanced
Joined: Oct 2017
Posts: 81
Likes: 5
From: Lowell MA
Ok When making a rear gear change on a C5/C6 you DO NOT have to make a speedo correction HOWEVER you do need to make a shift point correction for both the P/T up and down shiftpoints and more importantly the WOT both UPSHIFT and DOWNSHIFT mph speed shift points!!
Going from a 2.73 rear gear to a 3.42 rear gear requires a -25% change on your WOT shift speeds both for WOT upshifts and WOT downshifts
IF you do not make these WOT corrections the trans will skip over the WOT RPM shift points and hit the "safety rev limiter" and NOT shift
It is rather more complicated than this however the basic starting point would be to SUBTRACT 25% to both the WOT upshift speeds and the WOT downshift speeds As an example if your 1-2 WOT upshift speed is 45 MPH then subtract 25% to that do that for the DOWNSHIFT speeds at 2-1 at WOT as well Do this for the 2-3 and 3-4 and the 3-2 and 4-3 WOT speeds as well--
Going from a 2.73 rear gear to a 3.42 rear gear requires a -25% change on your WOT shift speeds both for WOT upshifts and WOT downshifts
IF you do not make these WOT corrections the trans will skip over the WOT RPM shift points and hit the "safety rev limiter" and NOT shift
It is rather more complicated than this however the basic starting point would be to SUBTRACT 25% to both the WOT upshift speeds and the WOT downshift speeds As an example if your 1-2 WOT upshift speed is 45 MPH then subtract 25% to that do that for the DOWNSHIFT speeds at 2-1 at WOT as well Do this for the 2-3 and 3-4 and the 3-2 and 4-3 WOT speeds as well--
Last edited by Bruceb66; Mar 17, 2018 at 05:21 PM.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
On a new or rebuilt transmission you need to run it through every gear while filling it. I highly recommend you run run it and shift it while it's on the lift or the jack stands so you can hit every gear. Otherwise, If you just fill it in neutral it will end up low on fluid when it does shift into the different gears.
The last 4L60e rebuild I filled when in neutral got low enough in fluid that it lost line pressure once it shifted to second while on the jack stands.
The last 4L60e rebuild I filled when in neutral got low enough in fluid that it lost line pressure once it shifted to second while on the jack stands.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Hey tblu92 - Sounds like you have some expertise with this topic. I've also been planning to swap out my 2.73 diff with a 3.42 diff next month, actually bought the 3.42 diff last month. However, the more I've been reading about the intricacies of shift point reprogramming, I'm starting to get cold feet....For an experienced performance shop, aside from swapping out the differential itself which should be fairly straight forward, is the programming aspect more of an art than a science? Or should it be pretty basic stuff for an experienced tech? Thanks.
This will get you very close---all the P/T shifts will be spot on but sometimes the WOT up/down points may require another adjustment
The more modded your eng is the more chances it may skip over the shift point RPM and hit the safety rev limiter---
The thing they call the "split" the difference in RPM between the shift at WOT RPM and the actual MPH RPM on a stock engine is around 600 RPM---When adding HP and TQ ( lower rear gears multiplies TQ) and acts just like engine mods_ you may have to increase the "split " as high as 1000 to 1200 RPMs------
This is the technical explanation Simply said just LOWER both the up and down shift MPH's at WOT--1st by the 25% then again 5 % at a time until it shifts at WOT correctly