The speedometer in My 1954 Buick Century is reading approx 5-10 mph fast. Speedometer gear in transmission is the original, never been touched. Speedometer working smoothly cable was lubed before I got it running a couple months back. I am running P225/70R 15 tires on the car. What should I be looking at to fix this?
Are you still running 'tall' cross plies? Sounds like a size reduction with modern tyres, like smaller modern radials, even if they're still on 15 rims
Could well have been off that far when new. And at what speed? 40, 70 MPH? And goodness knows what's going on after 60 years. Quick search says your current tires have a dia of 27.1 inches. The specced 7.60-15 have a diameter of 28.66 Going to this page http://www.summitracing.com/parts/cok-59400/overview/ and using the gear ratio calculator to solve for MPH using 3.23 axle ratio, 3000 RPM, and then plugging in the two different tire diameters, the result is a +/- difference of 5 MPH. Of course, you should use the actual numbers for your car, but you get the idea. Anyway, live with it, or go to an actual speedo shop and get it calibrated.
Well, living with it got Me a $150 ticket for being 10 over without knowing, so sadly that's not an option. Speedometer was reading 20 mph, cop told Me his radar clocked Me at 30
S-10 had a gear reducer that went in between the trans and the cable. it will adjust the speedo http://www.ebay.ca/itm/Gear-Ratio-A...m542e81c5cd:m:mgNv9fZ5LB8zTxQP6Jsmnbw&vxp=mtr the link is to ebay , so you can see what it looks like. most junkyards have them and you can switch the gears around to go either up or down, or you can go to an old trans shop and see if they might have different speedo drive gears for your tailshaft.
Easy enough to recalibrate your speedo to the shorter tires, just change the gear pictured below. Less than $20 delivered on Ebay.
This is 180* opposite of your initial statement......"my speedometer reading fast". Your speedometer is reading SLOW if it shows 20mph and you are really doing 30 mph. And the error is 50% off at only 20 mph indicated!! Smaller diameter tires, as discussed in prior posts, would cause it to read 'fast'. Something is very inconsistent here. Ray
Until you can figure this out mechanically, there is a free iPhone app called "Speedometer free speed box" that will get you better off than you are.
Looks like the normal GM style speedo gear like in the TH 350 and TH 400, I can check with some area transmission shops, one might have some lying around.
Yup. A 50% error at 20 mph is a lot more than a gear is going to fix as well. Of course the OP could have someone (or maybe 2 different) people with a recent factory stock car pace 20 mph and see who is lying - his speedo or the cop.
borrow a gps with a speedo in it and verify the real speeds, put masking tape on the speedo and write it in...............then worry about it later
You are not going to be able to correct the error with a driven gear change, it's to far off. By the police radar you're reading 33% slow. You need to run the car on a measured mile and see how many 1/10's you're turning in a mile, by the figures you gave you should be showing 7/10's in a mile. Run the car and give me the measured mile reading and I can build you a ratio adapter to correct the error. I explained the process in a previous post but couldn't figure out how to copy it to this thread, search I'm having speedo reduction issues and you can see how it's done and why it's best to use a measured mile as a base line. If your measured mile comes out correct then the speedometer needs to come out and be repaired.
This gear may not fit your transmission. I can say with certainty that Pontiac used a very different-looking gear in the 50s.
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How is your odometer working? If it is ok then you should consider having your speedometer rebuilt. Charlie Stephens