New car, speedo off
08-31-2017, 05:10 PM
#1
TECH Resident
Thread Starter
iTrader: (8)
Join Date: Jun 2008
Location: south jersey
Posts: 958
Likes: 0
Received 0 Likes
on
0 Posts
New car, speedo off Hey everyone, not new to ls1's but its been almost a decade. I just purchased a camaro auto. I figured out quick the speedo is off. The car has i believe stock size 27t/40r17 on it. So that leaves the gearing or cluster off?? I took these recordings by hand, theh approximate but hoping someone on here can figure what gearing is in the rear. First test showed
at 2200 rpms i was going 80 but speedo showed 65
at 2000 i was going 71 and speedo showed 59
another time i observed 2000 rpms and going 72 speedo 60
last was 1600 rpms and going 55 speedo showed 45
at 2200 rpms i was going 80 but speedo showed 65
at 2000 i was going 71 and speedo showed 59
another time i observed 2000 rpms and going 72 speedo 60
last was 1600 rpms and going 55 speedo showed 45
09-01-2017, 05:34 PM
#2
Teching In
Join Date: Jul 2017
Posts: 18
Likes: 0
Received 0 Likes
on
0 Posts
yikes, with numbers that off I would say gears and the tires just add to variance as well.
Do you have any local portable speed traps set up? I usually drive by them to see what they say vs speedo on car. (I'm sure someone on here will have a story how that is not accurate yadda yadda but at least it gets you a ballpark of what your working with.)
The only other time I have ever seen gauges that off is when they replace the faces and people put the needles wrong. Do you have whitefaces or silverfaced aftermarket gauges cause that could also be the issue.
Do you have any local portable speed traps set up? I usually drive by them to see what they say vs speedo on car. (I'm sure someone on here will have a story how that is not accurate yadda yadda but at least it gets you a ballpark of what your working with.)
The only other time I have ever seen gauges that off is when they replace the faces and people put the needles wrong. Do you have whitefaces or silverfaced aftermarket gauges cause that could also be the issue.
09-02-2017, 12:04 PM
#4
Teching In
Join Date: Jul 2017
Posts: 18
Likes: 0
Received 0 Likes
on
0 Posts
09-02-2017, 02:42 PM
#6
TECH Resident
Thread Starter
iTrader: (8)
Join Date: Jun 2008
Location: south jersey
Posts: 958
Likes: 0
Received 0 Likes
on
0 Posts
If the cluster was just off, the difference from speedo to my "going" speed wouldnt flucuate correct? Say going 55 but speedo showing 45 is 10mpg difference and going 80 but speedo showing 65 is 15mph difference.
Trending Topics
09-02-2017, 07:21 PM
#9
What year is it ?
Factory option code sticker(glove compartment or on driver door) GU2=2.73 GU5=3.23 are what it could've come with.
275/40/17 is same rolling diameter as what it would've come with.
Cluster receives its' info from computer and computer receives its' info from sensor on output shaft of tranny. I'm guessing gears. Put rear of car up off ground(in a safe method),mark driveshaft and tire,turn driveshaft(by hand) and count driveshaft rotations to get one wheel rotation,accuracy is important.
2.73=2 3/4 turns 3.23=3 1/4 turns 3.42=3 3/8 turns 3.73=3 3/4 turns 3.90= 3 9/10 turns 4.10= 4 1/10 turns.
If driveshaft is steel,vehicle had 2.73s' originally. 3.23s' got aluminum driveshaft.
Factory option code sticker(glove compartment or on driver door) GU2=2.73 GU5=3.23 are what it could've come with.
275/40/17 is same rolling diameter as what it would've come with.
Cluster receives its' info from computer and computer receives its' info from sensor on output shaft of tranny. I'm guessing gears. Put rear of car up off ground(in a safe method),mark driveshaft and tire,turn driveshaft(by hand) and count driveshaft rotations to get one wheel rotation,accuracy is important.
2.73=2 3/4 turns 3.23=3 1/4 turns 3.42=3 3/8 turns 3.73=3 3/4 turns 3.90= 3 9/10 turns 4.10= 4 1/10 turns.
If driveshaft is steel,vehicle had 2.73s' originally. 3.23s' got aluminum driveshaft.
09-09-2017, 11:58 PM
#10
TECH Resident
Thread Starter
iTrader: (8)
Join Date: Jun 2008
Location: south jersey
Posts: 958
Likes: 0
Received 0 Likes
on
0 Posts
What year is it ?
Factory option code sticker(glove compartment or on driver door) GU2=2.73 GU5=3.23 are what it could've come with.
275/40/17 is same rolling diameter as what it would've come with.
Cluster receives its' info from computer and computer receives its' info from sensor on output shaft of tranny. I'm guessing gears. Put rear of car up off ground(in a safe method),mark driveshaft and tire,turn driveshaft(by hand) and count driveshaft rotations to get one wheel rotation,accuracy is important.
2.73=2 3/4 turns 3.23=3 1/4 turns 3.42=3 3/8 turns 3.73=3 3/4 turns 3.90= 3 9/10 turns 4.10= 4 1/10 turns.
If driveshaft is steel,vehicle had 2.73s' originally. 3.23s' got aluminum driveshaft.
Factory option code sticker(glove compartment or on driver door) GU2=2.73 GU5=3.23 are what it could've come with.
275/40/17 is same rolling diameter as what it would've come with.
Cluster receives its' info from computer and computer receives its' info from sensor on output shaft of tranny. I'm guessing gears. Put rear of car up off ground(in a safe method),mark driveshaft and tire,turn driveshaft(by hand) and count driveshaft rotations to get one wheel rotation,accuracy is important.
2.73=2 3/4 turns 3.23=3 1/4 turns 3.42=3 3/8 turns 3.73=3 3/4 turns 3.90= 3 9/10 turns 4.10= 4 1/10 turns.
If driveshaft is steel,vehicle had 2.73s' originally. 3.23s' got aluminum driveshaft.
Haven't had a chance to lift the car yet, however I checked the codes and it has GU2 meaning it came with 2.73.
I played with the different options on this website for gearing
http://www.andysautosport.com/learni...r/calculators/
and noticed my actual speeds match a 3.23 gearing the most but my speedo readings match a 3.90 gearing.
Is it possible who ever did the mail order tune on this car put in 3.90 gearing instead of 3.23 not knowing or just making a mistake? I bought the car used and was told it has a mail order tune on it, a "gm 2600 stall" but nothing about a gear swap.
I find it weird that the speedo it reading slower than my actual speed. What do you think about my idea the computer thinks I have 3.90s but really someone put in 3.23s? I know I'll have to confirm this in the morning by putting the rear up and spinning the tires to confirm the 3.23s are in it.
I don't know why else the speedo would read slower... and not faster.
