Looking for advice on my "new" wrong RPM diff?
05-23-2010, 07:58 PM
#1
TECH Regular
Thread Starter
iTrader: (1)
Join Date: May 2008
Location: Iowa
Posts: 475
Likes: 0
Received 0 Likes
on
0 Posts
Looking for advice on my "new" wrong RPM diff? Hey everyone,
I've got problems and need advice what to do. I ordered from RPM transmissions in Indiana a new Stage 3 diff for my 02 C5 w/ hardened output shafts, carbon clutches etc with a 3.90 micropolished MG gears.... $2700 later and a bunch of troubles picking it up i got it. Well i now have it installed and i've been driving around with it and have had it on Speed inc's dyno and they dyno-tuned it and made the speed read correctly with a 3.90 gear.
Well i got it home and to make a long story short the Iowa highway patrol help me verify that the speedo is way off. At 70 I was going 80, well anyway i brought it back to Speed inc to fix the issue and Jim said speedo reads correctly with a 3.42 gear not 3.90. I thought it was weird but i did the test i read about when i put the car in 4th at 70 the rpms rear 3400 in which 3.42 gears........ My dad has a 02 C5 that is 100% stock with the same 3.42 gears so we were on the interstate Friday and in 6th at 70 both of cars are within 200 rpms of each other (1500-1700 rpms)
The problem is, the receipt i have from RPM says 3.90 and the RPM tag on the diff says 3.90 but its obviously not a 3.90
What in the world can i do or what are my options before i call RPM and flip out on them? Since its obviously wrong..
I've got problems and need advice what to do. I ordered from RPM transmissions in Indiana a new Stage 3 diff for my 02 C5 w/ hardened output shafts, carbon clutches etc with a 3.90 micropolished MG gears.... $2700 later and a bunch of troubles picking it up i got it. Well i now have it installed and i've been driving around with it and have had it on Speed inc's dyno and they dyno-tuned it and made the speed read correctly with a 3.90 gear.
Well i got it home and to make a long story short the Iowa highway patrol help me verify that the speedo is way off. At 70 I was going 80, well anyway i brought it back to Speed inc to fix the issue and Jim said speedo reads correctly with a 3.42 gear not 3.90. I thought it was weird but i did the test i read about when i put the car in 4th at 70 the rpms rear 3400 in which 3.42 gears........ My dad has a 02 C5 that is 100% stock with the same 3.42 gears so we were on the interstate Friday and in 6th at 70 both of cars are within 200 rpms of each other (1500-1700 rpms)
The problem is, the receipt i have from RPM says 3.90 and the RPM tag on the diff says 3.90 but its obviously not a 3.90
What in the world can i do or what are my options before i call RPM and flip out on them? Since its obviously wrong..
05-24-2010, 05:21 AM
#2
Give Rodney at RPM Transmissions a call. Rodney stands behind his products, and I'm sure he will help you out. Bob
__________________
ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
05-24-2010, 07:52 AM
#3
Changing from 3.42 to 3.90 is a increase in gear reduction of 12.3%. If you're dad's RPMs are 1500, then yours should be 1500/.877=1710 RPMs. Sounds like it's right on the money to me.
05-24-2010, 02:03 PM
#4
TECH Regular
Thread Starter
iTrader: (1)
Join Date: May 2008
Location: Iowa
Posts: 475
Likes: 0
Received 0 Likes
on
0 Posts
I called and talked to TJ @ RPM today he said that i need to do a test in lower gears compared to my dads C5, he said in 4th at 70 in my car should be 3400 (which it is) and my dads should be 3000 - We'll give it a whirl tonight and see where were are at. Thanks guys!
05-24-2010, 02:28 PM
#5
Sounds good! Bob
__________________
ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
ATI ProCharger and Moser Sales 260 672-2076
PM's disabled, please e-mail me
E-mail: brutespeed@gmail.comob@brutespeed.com
https://brutespeed.com/ Link to website
05-24-2010, 08:10 PM
#6
TECH Regular
Thread Starter
iTrader: (1)
Join Date: May 2008
Location: Iowa
Posts: 475
Likes: 0
Received 0 Likes
on
0 Posts
Here's the deal, its a 3.90 I did the test that RPM suggested in 4th gear and did the same to my dads and mine is 3400 at 70 and his is 3100 at 70 so we are good to go..... I'm calling RPM tomorrow and telling them there are no problems just a little confusion. I'm extremely relieved now.
Either way thanks to everyone helping me diagnose the issues!
Case closed
Either way thanks to everyone helping me diagnose the issues!
Case closed
