90 corvette vss and gears
Thread Starter
Cruising
Joined: Jan 2013
Posts: 14
Likes: 0
90 corvette vss and gears
Just drove my 90 after installing new memcal. Runs good but GPS said speedo was 5 mph fast at 50. Now the fun begins. This car came with a 2.73. Buildsheet says the prom was programmed for a 2.73. I turned the driveshaft and counted one tire revolution-3.07. Took out the vss and found a red drive gear and green driven gear. Chart says red-blue is correct for a 2.73. Chart says red-green is correct for a 3.07, but......counted teeth on green gear (four times), 38 teeth. Chart says green gears have 42 teeth, blue gears have 38 teeth. The color is wrong, but the number of teeth is correct for a 2.73. Also bad news because 38 or 42 require a different vss. Can someone help me sort out this mess?
Team Owner
Joined: Sep 2003
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'vert has nothing to do with anything! That's just an WAG guess that's usually correct regarding the 2.73!
Disregard "colors" - for a 3.07 you need a 42 tooth driven and YES it does require a different VSS to get the gear pitch correct. The PROM in your case is "incidental" it's ID by the 2.73 and all 'verts got the 2.73 by default in the build. It has nothing to do with "error" you're seeing. You're seeing something at a 10% error at 50 and that should be consistent percentage wise at any speed. (35 - 38+, 40 - 44, 60 - 66+ etc)
You need to try and find a correct VSS and a 42 tooth gear..
It could likely be done by changing both the drive and driven using the VSS you have but that's a nuisance!
If someone had a '90 M6 on the ground it would have a correct VSS.
Disregard "colors" - for a 3.07 you need a 42 tooth driven and YES it does require a different VSS to get the gear pitch correct. The PROM in your case is "incidental" it's ID by the 2.73 and all 'verts got the 2.73 by default in the build. It has nothing to do with "error" you're seeing. You're seeing something at a 10% error at 50 and that should be consistent percentage wise at any speed. (35 - 38+, 40 - 44, 60 - 66+ etc)
You need to try and find a correct VSS and a 42 tooth gear..
It could likely be done by changing both the drive and driven using the VSS you have but that's a nuisance!
If someone had a '90 M6 on the ground it would have a correct VSS.
Last edited by WVZR-1; Feb 15, 2013 at 07:29 PM.
Pro
Joined: Jun 2007
Posts: 626
Likes: 2
From: Coquitlam British Columbia
If you had your VSS out; there is a stamping of the tooth size...2:59 and 2:73 have the same VSS with stamping of 34-39 in relation to drive gear tooth no. A 3:07 and up has a VSS stamping of 40-45. I have a 1990 Vert also and I went to 3:54 gears from the 2:73's a few years back and had to hunt down a used 3:07 VSS as they are not made anymore just the other VSS. With the correct drive and driven plastic gearing and the right VSS ; I am right on the speedo with a GPS check. Had to research it out for the right combo..forgot the colors of the gears but I remember the driven gear was 43T and if I went with 3:73's like some people have done the driven gear would be a 45T. Dont remember the drive gear tooth no.Just a little more info on your question.
Bill
Bill
Pro
Joined: Jun 2007
Posts: 626
Likes: 2
From: Coquitlam British Columbia
'vert has nothing to do with anything! That's just an WAG guess that's usually correct regarding the 2.73!
Disregard "colors" - for a 3.07 you need a 42 tooth driven and YES it does require a different VSS to get the gear pitch correct. The PROM in your case is "incidental" it's ID by the 2.73 and all 'verts got the 2.73 by default in the build. It has nothing to do with "error" you're seeing. You're seeing something at a 10% error at 50 and that should be consistent percentage wise at any speed. (35 - 38+, 40 - 44, 60 - 66+ etc)
You need to try and find a correct VSS and a 42 tooth gear..
It could likely be done by changing both the drive and driven using the VSS you have but that's a nuisance!
Disregard "colors" - for a 3.07 you need a 42 tooth driven and YES it does require a different VSS to get the gear pitch correct. The PROM in your case is "incidental" it's ID by the 2.73 and all 'verts got the 2.73 by default in the build. It has nothing to do with "error" you're seeing. You're seeing something at a 10% error at 50 and that should be consistent percentage wise at any speed. (35 - 38+, 40 - 44, 60 - 66+ etc)
You need to try and find a correct VSS and a 42 tooth gear..
It could likely be done by changing both the drive and driven using the VSS you have but that's a nuisance!
Bill
Team Owner
Joined: Sep 2003
Posts: 25,397
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Pro
Joined: Jun 2007
Posts: 626
Likes: 2
From: Coquitlam British Columbia
. I replaced the VSS after the install and finally got the right VSS from a forum member in Arizona. Once installed all was well with the GPS check.If memory serves me I used "MASTERSET" to figure out the gearing which I also got from a forum members site (thanks Vader). Thats all I remember
Bill
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Race Director
Joined: Apr 2002
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From: Anaheim CA
This might be helpful for situations like these:
There are two VSS versions. One has the shaft in the center. The other is for the larger driven gears and has an offset to move the shaft away from the drive gear.
There are two VSS versions. One has the shaft in the center. The other is for the larger driven gears and has an offset to move the shaft away from the drive gear.
Thread Starter
Cruising
Joined: Jan 2013
Posts: 14
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I see a simple way to rotate my old vss 180 degrees if that will properly space a 42 gear (which I found on ebay but haven't received yet). Has anyone had any success with this conversion? I suspect there is really only one vss , because the shaft on my 38 gear vss is not centered. If I rotate it 180, the offset goes from the "top" to the "bottom" if you were looking into the transmission with the drive gear at the top of the hole, so to speak.
Instructor
Joined: Oct 2006
Posts: 213
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From: Mandeville Louisiana
If you're willing to have someone burn you a new tune, it can be adjusted in the tune without having to change any VSS gears. It could potentially cause a real nightmare for someone down the road if you sold the car though.
Jep
Jep
Thread Starter
Cruising
Joined: Jan 2013
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Actually, I am the person down the road who is attempting to return everything to stock. I drew the line at going back to the 2.73, however, so I am correcting the speedometer gearing that wasn't changed when someone put in a 3.07. I had a new memcal burned before I realized the rear had been changed, so it is going to stay programmed for a 2.73. As far as I know, at least through 1993, the. computer does not calibrate the speedometer in a C4. I believe in 100% disclosure when I sell a car. Since I consider myself a "restorer", I know how maddening it can be trying to undo someone's "modifications."
Team Owner
Joined: Dec 2000
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From: Phila., PA burbs
Team Owner
Joined: Sep 2003
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Team Owner
Joined: Dec 2000
Posts: 21,094
Likes: 282
From: Phila., PA burbs
