Register or Log In To remove these advertisements. |
|
|
|
Thread Tools | Display Modes |
08-04-2007, 09:35 PM | #1 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Speedometer does not read actual speed...
I have a 68 GMC with a stock 250. Some year ago I removed the 3 speed non synchronized trans for a synchronized one that came off a V8 truck.
I found out my speedometer is 10 mph off!!! Shows 20 mph and it should be 30 mph and 25 mph and it should be 35 mph (measured with another newer vehicle). Don't drive it much and usually on country roads. Also, I usually drive slow but I'm lucky I haven't been caught speeding. I read where they make gears to fix this, but can't find out where to get them. Any help appreciated. |
08-04-2007, 10:08 PM | #2 |
Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
|
Re: Speedometer does not read actual speed...
GM dealers still have them.
__________________
56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
08-04-2007, 10:19 PM | #3 |
Active Member
Join Date: May 2007
Location: SO CAL
Posts: 226
|
Re: Speedometer does not read actual speed...
Would also like to know my speedo is off a bit
|
08-04-2007, 10:33 PM | #4 |
Senior Member
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,572
|
Re: Speedometer does not read actual speed...
That is quite a bit for the speedo to be off by 30 percent. Still have the old trans? Should be able to swap out the drive gear.
|
08-05-2007, 05:32 AM | #5 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
|
Re: Speedometer does not read actual speed...
30% ewouldn't surprise me... mihne used to read 100 MPH at about 75, and now, with a blind gear swap, it reads 35 at about 70
|
08-05-2007, 08:49 AM | #6 | |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
Quote:
kwmech, I don't have the old trans anymore. I think I left it behind in one of my moves about 10 years ago. I have another question, if I find the gears, do I have to also replace the internal drive gear as well as the driven gear? I would suspect I will since it looks like they're a matched set... |
|
08-05-2007, 09:00 AM | #7 |
Registered User
Join Date: Sep 2005
Location: Villa Rica Ga
Posts: 889
|
Re: Speedometer does not read actual speed...
you can go to any transmission shop and get one off them. i lost my gear during tear down, i went to the local shop he just gave me one for free. go ask em theyll dig around and find sumthn.
|
08-05-2007, 12:27 PM | #8 |
Senior Member
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,572
|
Re: Speedometer does not read actual speed...
|
08-05-2007, 01:03 PM | #9 |
Hellasick
Join Date: Jul 2006
Location: Death Moans, IA
Posts: 876
|
Re: Speedometer does not read actual speed...
being off a set amount seems kinda odd, not what i thought gears would cause. would think gearing would cause a set percent. mine is off 10% because of oversized tires (not by much) 50 is really 55, 60 is really 66 ad nausium.
I came across a website on checking speedo vs. real speed with a stopwatch. basically it is 60 seconds for one mile at 60 (duh) and then one second more for each mph below 60 and one second less for each mph over 60. about every 5 mph it jumps 2 seconds 66 sec. @ 55mph 64 sec. @ 56mph 63 sec. @ 57mph 62 sec. @ 58mph 61 sec. @ 59mph 60 sec. @ 60mph 59 sec. @ 61mph 58 sec. @ 62mph 57 sec. @ 63mph 56 sec. @ 64mph 54 sec. @ 65mph I printed it off, but can't find it and I think it went further beyond this range. The more miles you cover the more accurate it will be. Spreads out any inconsistancies.
__________________
I keep two MAGNUMS in my desk. One's a gun, and I keep it loaded. The other's a bottle and it keeps ME loaded. I'm Tracer Bullet. (Calvin and Hobbes) This life was a test. It was only a test. If this had been an actual life, you would have received instructions on where to go and what to do. RED meat is not bad for you...FUZZY BLUE/GREEN MEAT is bad for you!!!!!!!!!!!!! BUILT FORD TOUGH WITH CHEVY STUFF--sticker at Goodguys |
08-05-2007, 07:26 PM | #10 | |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
Quote:
So, it may not be as exactly as she read it. I'll try it on a straight highway before I do any gear changing... |
|
08-05-2007, 07:48 PM | #11 |
Registered User
Join Date: May 2006
Location: virginia beach, virginia
Posts: 16
|
Re: Speedometer does not read actual speed...
LOL that happened to me when I bought my truck. It was a rainy day, not too many other cars on the road, I drove it and man it was quick! Like a scalded dog quick... I drove it back to the guy and he leaned toward me and tapped me on the arm and said, "What'd ya think? huh? huh?" I said, "Man that thing sure is fast!" The next day driving it home the speedo said 70 but cars were passing me left and right! I have been told it's the same thing as your problem. I was going to take it to the speedo calibration shop tho... the trans guy around me is kinda greedy!
|
08-06-2007, 12:01 AM | #12 |
The Older Generation
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,582
|
Re: Speedometer does not read actual speed...
-
Here are a couple of web sites you might take a look at.... http://www.bgsoflex.com/speedo1.html http://www.transmissioncenter.net/sp...n_______va.htm Actually everything you ever wanted to know about speedo gears..... LockDoc
__________________
Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 08-06-2007 at 12:09 AM. |
08-06-2007, 08:54 AM | #13 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
LockDoc, thanks for the sites... That's what I was looking for.
|
08-06-2007, 01:47 PM | #14 |
The Older Generation
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,582
|
Re: Speedometer does not read actual speed...
-
No problem... Great board 'aint it..... LockDoc
__________________
Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
08-06-2007, 01:53 PM | #15 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
Don't mean to keep this one going, but I thought I'd keep some of you that are having problems with speedometer not reading correctly updated.
I just stopped by the chevy dealer and threw the old 22 teeth driven gear on the counter and asked the guy if had some of these. He said, yes, he had them. I asked if he had one with fewer teeth on the driven gear (mine has 22 teeth). I figured less teeth = faster rotation on the driven gear which will increase my speedometer reading. He brought back a white one with 19 teeth. Cost was $6.00. Since I was messing with all this, I noticed the rear end drive shaft seal and the transmission seal were leaking. And since I was going to remove the shaft to replace them, I went ahead and got u-joints. When I get it all back together again I will try it to see if that brings the speedometer closer to the correct speed. I'm not worried about a few mph over or under. |
08-06-2007, 10:18 PM | #16 |
Registered User
Join Date: May 2003
Location: Shreveport LA
Posts: 3,170
|
Re: Speedometer does not read actual speed...
http://novaresource.org/speedo.htm has the math and charts to figure out exactly what you need.
|
08-06-2007, 11:15 PM | #17 |
Sheetmetal Psycho
Join Date: May 2005
Location: athens PA
Posts: 515
|
Re: Speedometer does not read actual speed...
hmmmm - suddenly my speedo at 35 when I'm doing 55 soesn't seem so bad. I went to the dealer down the road and they said it was too old to get the gear. I never bothered look anywhere else since I don't drive it out of town a whole lot
__________________
I didn't say you were stupid, but I was thinking it... I need a check up from the neck up! Project "Rigginstine's Monster" 1971 C-10 longbed 355/4spd Future mods: 67 front clip Webby's Rigginations - where everything has potential! |
08-11-2007, 09:26 PM | #18 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
Continuing with update.
Got the rear end and transmission seals in, new u-joints, new speedometer cable (the old one was cracked) and put the new 19 tooth speedometer driven gear into the transmission. Had my wife follow me on the same road and this time I was 5 mph off at 25 instead of 10 mph off. In other words, when I was going 20 my wife was doing 25. I'll have to try it at faster speeds later on. I can live with this for right now... |
08-11-2007, 09:46 PM | #19 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
|
Re: Speedometer does not read actual speed...
Try another dealership, the parts guy at the one you went to is either a lazy bum, or is afraid to open a book.
They are still avalible. |
08-12-2007, 07:58 AM | #20 |
chrome makes it go FASTER!
Join Date: Feb 2007
Location: Cleveland Tennessee
Posts: 2,884
|
Re: Speedometer does not read actual speed...
And that right there ticks me off. Remember when parts stores were helpful?
__________________
She can't cook and she won't clean. But she looks good in a skirt and she brings me beer. She can stay for now. EDIT:: But she left me anyway, So forget her. 1962 GMC Stepside V6 4 speed My rolling resto thread http://67-72chevytrucks.com/vboard/s...d.php?t=324226 My old farm truck http://67-72chevytrucks.com/vboard/s...=1#post3465005 |
08-12-2007, 09:37 AM | #21 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Speedometer does not read actual speed...
Longhorn Man is correct. Sometimes of these guys say that they're obsolete as soon as you say the year of our trucks. It's true that most parts are, but some of them applied to other year vehicles as well and are still available...
|
Bookmarks |
Thread Tools | |
Display Modes | |
|
|