Speedometer question

[zane2513]

Got a speeding ticket the other day my speedometer read 30 but the cop wrote me a ticket for doing 39. Maybe it just wasn't my day.
My question is what is the best and most accurate way to check the speedometer?
I have been searching here and finding all sorts of things about the speedometer, drive gear and all that but what is the best way to check the accuracy.
I am only 17 so I have limited knowledge about some of this stuff. I drive a 66 Chevy lwb with 327 and a powerglide transmission. The needle does bounce some at lower speeds. The PO had the transmission rebuilt about a year before I got the truck, haven't had any trouble with or anything just wanting to know how to check it and what my options are if it is off.
I have read this forum just about every day and learn something new every time.
Thanks for any help you can give me.

[bama63]

use a gps like garmin that displays mph and compare

[geezer#99]

Go for a drive with your buddy in his car or truck and you in yours. Tell him to drive at 60 and you compare at what speed you're going. Sounds like you should show about 45.
Your speedo is about 33% slow. You can change the drive gear in the tranny or the driven gear or buy a ratio adaptor to correct it. Adaptors are about 65 bucks on Ebay.

[zane2513]

Thanks for the good information guys I will try that tomorrow. Then I will go from there.
Zane

[rcnutt]

gps X 2
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[1Bad62Pro/Street]

zane2513,

Like the guys says use a GPS.
When you know the speed difference you will need to change your speedo gear on that Powerglide to compensate for the difference.

http://www.tciauto.com/Products/Tech...eedo_gears.asp
And it sounds like you need a new Speedometer Cable too...

TH350C, Powerglide and Muncie 4 Speed: Speedo driven gears have from 17 to 25 teeth. Each tooth added lowers the speedo reading about 5%. Each tooth removed raises the speedo reading about 5%. In our example, we are reading 15.4% high so we would need to add teeth to spin the speedo cable slower. Remember, one tooth = 5% so we need to add about three teeth. (15.4%/5% = 3.1 teeth).

At this point, pull the speedo gear out of your tranny tail housing by removing the small bolt and clamp that retains the speedo gear sleeve and pulling on the speedo cable. Then count the teeth, subtract or add to the number of teeth and select a new gear from the chart below. Use color only as a cross check. Plastic gears immersed in tranny fluid for many years will be stained and off color. You often see the speedo driven gear referred to as the "pencil" gear and the speedo drive gear the "circle" gear.
http://chevelleengineer.home.comcast...eer/speedo.htm


The Powerglide was available primarily on Chevrolet automobiles from 1950 through the early 1970s, although some Pontiac models also used this automatic transmission.

There were two primary versions of the Powerglide. The Powerglide transmission introduced in 1950 had a cast iron case and is known as the "Cast Iron Powerglide". The "Cast Iron Powerglide" was used until 1963, when it was revamped as "Aluminum Powerglide" where its case and several of its other parts were made of aluminum. The Aluminum Powerglide was used from 1962 until it was replaced with the Turbo-Hydramatic series of transmission in the early 1970s. The Aluminum Powerglide is still used today as a racing transmission of choice by many racers mainly for the fact that it only shifts once, and for its extreme durability. It is also possible to purchase all the parts needed to build an Aluminum Powerglide from scratch from most racing parts vendors.

When introduced on upper-level Chevrolet models in 1950, the Powerglide represented the first automatic transmission offered in a low-priced automobile; in contrast, Ford did not offer their automatic transmission until 1951, while Plymouth car buyers had to wait until 1954. The transmission was simple and very durable, which satisfied customers. The 1950, 1951, and 1952 Powerglide transmissions did not automatically shift between low and high (direct drive) which made for very sluggish take-offs and many drivers started in "Low" and shifted to "Drive" at about 30–40 mph (48–64 km/h), which was hard on the transmission. The 1953 and later units when in "Drive" started in low and automatically upshifted to high at a speed determined by the throttle opening. By the mid-1950s, more than half of all new Chevrolets were sold with Powerglide. In 1962, GM started building Powerglides in aluminum (primarily for use in the new model Chevy II, which required a light weight transmission for the compact body) and discontinued the cast iron Powerglides in 1963. A heavy duty version of Aluminum Powerglide was offered for 409 V8 equipped passenger cars, and Chevy light trucks using a 1.76:1 reduction planetary gearset, instead of the usual 1.82:1. With a 3.31 axle, Car and Driver magazine noted a full-throttle upshift speed of 76 mph (122 km/h) to direct with the 409-4bbl 340 hp (250 kW) engine in a contemporary road test. Most of the V8/Powerglide transmissions came with the 1.76 gearset. One notable exception was the export version of the transmission, which used only the 1.82 ratio and was used by Holden in Australia behind their Australian built 6-cylinder and V8 engines. Holden vehicles fitted with Chevrolet V8 engines used the 1.76 ratio gearset.

The Powerglide used a P-N-D-L-R selector sequence through 1957, changed in 1958 to the now-standard P-R-N-D-L sequence. The earlier sequence had been criticized on safety grounds for placing reverse after a forward gear, instead of having neutral between reverse and the forward ranges. For example, a driver could easily overshoot L and go into R, possibly causing permanent damage and/or catastrophic failure.

From 1957-1961, Chevrolet also produced the Turboglide, a triple turbine continuously variable automatic transmission with concurrent ratios whose design was similar to that of Buick's Flight Pitch Dynaflow, subsequently called Triple Turbine (full technical description). The Turboglide, only offered with V8 engines, was more expensive (by about $50) than the Powerglide and did not have wide acceptance, in part due to failures in 1957-'58 models, which were addressed by a significantly upgraded version for 1959.

Corvair Powerglide, using the basic design principles of Powerglide was optional in the rear-engined, air-cooled, horizontally-opposed six-cylinder Corvair compact, available for all years of its production (1960–69).

The Powerglide continued to serve as Chevrolet's main automatic transmission through the 1960s, when a new three-speed automatic transmission called Turbo-hydramatic 400 (1965 introduction) began to be phased in (the Turbo-Hydramatics were introduced in Buicks and Cadillacs a year before).

Usually, Powerglides were coupled behind small-block Chevrolet V8s and their third-generation inline six- and four-cylinder engines. By the late 1960s, demand for two-speed automatic transmissions was dwindling as buyers were demanding three-speed units (Ford, Chrysler and American Motors had already switched entirely to three-speed automatics by this time). In 1969, the three-speed Turbo Hydramatic 350 was introduced as a light-duty companion to the Turbo Hydramatic 400, and made available on virtually all Chevrolet cars and trucks with six-cylinder or small and medium sized V8 engines, as well as intermediate sized cars of other GM divisions. The Powerglide lingered on as a low-cost automatic transmission option primarily for six-cylinder Chevrolet Nova and four-cylinder Chevrolet Vega until it was phased out after the 1973 model year. They were also used in the DJ-5 'Dispatcher' jeeps sold for light commercial use, and best known for their service with the US Postal Service.

Although it is a very old design, the Powerglide still has a strong following in drag racing due to its strength and simplicity. Powerglides are also popular in mud racing and monster truck racing. In the first few years after introduction, they became known as the "Slip-N-Slide Powerglide" (due to the fluid coupling, as opposed to the mechanical coupling of a clutch-driven gearbox) and the "Positive-Pop transmission." This last is due to the characteristic "bump" or "pop" which occurs as the transmission is put into gear from neutral, and begins to load the driveline.

[zane2513]

1Bad62Pro/Street
that's a lot of info it will take me a while to digest it all. That's why I come here and read this stuff, you guy are so full of knowledge. I have a lot to learn.
I did the GPS thing and found out my speedometer is only off by 3 mph. It reads 3 mph slower than what the GPS said, I also tested the GPS in my dad's 2003 Chevy it was dead on in his truck.
Is 3 mph worth messing with?

[1Bad62Pro/Street]

I would not worry about it if it's just off 3mph.
My 2006 Ford F150 is off 3mph because I have a taller set of tires on it now.
Just have to keep it mind that I am going 3mph more than my speedometer says.
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[raycow]

Originally Posted by zane2513

I did the GPS thing and found out my speedometer is only off by 3 mph. It reads 3 mph slower than what the GPS said, I also tested the GPS in my dad's 2003 Chevy it was dead on in his truck.
Is 3 mph worth messing with?

It might be, if you can get a speeding ticket because of it.

Ray