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5/22/12 9:02pm - Original Message: 'More Speedo Problems'
manget1 Lifetime Member
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Indianapolis, IN - USA

Vette(s):
Silver 1974 Convertible - L82 4 speed Low miles (was only 8,900 when I bought it in March 2006) - Now 42K miles. Original owner bought it as an investment for son's college expenses. 2008 Jetstream Blue Convertible - DAILY DRIVER!!

Joined: 9/3/2006
Posts: 2383

Although my brake light switch is in close competition, I don't beleive anything on my car has given me as much trouble as the speedometer.  After many replacements and rebuilds, I finally gave up and bought a brand new one from Mid America last year.

I reset the odometer to match actual miles, and had the shop doing other work on my car install it.  As I got about a mile from the shop, it stopped working.  I took it back to them, and the mechanic said he experienced the same thing - he got it working again, but on the test drive, it stopped working again.
 
He even went as far as to replace the white plastic gear that connects the cable to the transmission (http://www.C3VR.com/member_uploads/9201_9300/9258/Speedo-Gear.jpg) but that didn't get it.  He told me that if he hooked up the cable to a drill, the speedo works fine.  He told me that the white gear seemed to "float" in the tranny as though it wasn't fully connected, even though it was.
 
The current theory is that there's an issue with where the gear connects to the tranny.  Does anyone have a picture of what the trans should look like there where the speedo connects?  Or are there any other ideas on what the issue might be?


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5/22/12 9:56pm - Reply: 'Re: More Speedo Problems'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
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The speedo drive gear, on the trans tailshaft, is pressed on the shaft. It can work loose, or move out of position. It's rare for that to happen, but possible. The only way to be SURE it is in place is to remove the tailhousing...which means pulling the trans out.
Has he checked the speedo adapter, and verified IT is not the problem?


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Joel Adams
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5/23/12 5:02am - Reply: 'Re: More Speedo Problems'
VikingVette
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Greer, SC - USA

Vette(s):
1978 Black with Viking mural painted under hood AM/FM/CB radio, T-top and a 2013 Cyber Gray Grand Sport Coupe, 2LT for my daily driver

Joined: 3/13/2012
Posts: 264
Joel,
Is there anything you don't know?  Maybe we can start a new online gaem called "Let's TRY to stump Joel"!!!!  Sheeeeesh


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Warning: The surgeon general has declared that it is NOT unhealthy to smoke your competition AND I just discovered that my corvette is a hybred.  It burns gas and rubber! 
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5/24/12 4:29am - Reply: 'Re: More Speedo Problems'
manget1 Lifetime Member
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Indianapolis, IN - USA

Vette(s):
Silver 1974 Convertible - L82 4 speed Low miles (was only 8,900 when I bought it in March 2006) - Now 42K miles. Original owner bought it as an investment for son's college expenses. 2008 Jetstream Blue Convertible - DAILY DRIVER!!

Joined: 9/3/2006
Posts: 2383
Whenh you say Speedo adapter, are you referring to the 90 degree adapter?  If so, yes, I believe the checked that too.
 
Is there anything that you should (or shouldn't) be able to see just looking where the cable goes?  Hate to pull the tranny (again) if there's another way, although my guess is that's the problem.
 
My shop handed the tranny over to another shop when the drivetrain was out last month.  There were some leaks and they were to seal it up.  If they opened it up, is it possible the gear in there either came loose or out and they wouldn't have noticed?


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5/24/12 9:51am - Reply: 'Re: More Speedo Problems'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19457
Yes, I wuz referencing the 90 deg adapter. Those are actually ratio adapters, and they change the ratio of the speedo gear-set to match the speedo calibration.

If you (or your tech) has a borescope, you might be able to sneak a peek up in there and see what the drive gear looks like, and it's location. Remember, you're talking about a hole that's only about an inch in diameter, and it's not exactly in a "line of sight" location. It's possible the gear has moved on the shaft just enough to not mesh properly with the driven gear...or maybe they dint get it back in the correct location when they worked on it before. Like I said, the only way to know for sure is to look. A borescope might at least give ya an idea, without pulling the unit back out, but if the gear is out of place, broken, or otherwise damaged....out she comes.Cry

Another idea...have your tech check the speedo "bullet"..the housing that the small(white) gear fits into...the bore in it may be egg-shaped, and allowing the driven gear to flop....

Marshall, here's a link to a parts breakdown on the BWST10 trans, with the speedo gear circled. It shows there are two snap-rings that hold the gear to the shaft...I don't remember ever taking them off, but I s'pose it's possible they are there. The speedo gear doesn't have to come off to repair/rebuild the trans, so I may have just never taken them off. This might be the problem...one(or both) of the snap-rings are out of place, damaged, or who knows what. That would allow the gear to move out of position, and cause yer speedo issue....if it is, you'll still have to remove the trans...Ouch

http://s77.photobucket.com/albums/j54/aapple2/Misc%20pics/350%20Trans/4speed%20stuff/?action=view&current=bwST10.jpg


|UPDATED|5/24/2012 7:51:53 AM (AZT)|/UPDATED|


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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