Speedo gears

[ScottD]

The speedometer on my 86 GLHS has always been about 5mph slow at highway speeds. It has been this way since I put the car together and started driving it
years ago. The car has the original gauge cluster in it.

I'm getting ready to convert the car from 525 rod shift to 555 rod shift. I took the speed sensor out tonight and the pinion on it is white. Based on what I read
below, this is the correct color for the Dunlop Direzza 205 50 15s I have on the car.

http://minimopar.knizefamily.net/speedpinions.html

I'm wondering if I should go to a blue gear. Has anyone else had this issue with the speedo being slow and solved it with a blue gear?

[cordes]

I haven't tried it with another gear yet. I have 205/50r15s on my blue Omni and it reads slow too. So did my black car. I think that my black car is an issue with the OD of the tire to an extent. It's an autocross tire on a 7.5" wheel and I think it's shorter than most normal 205/50s would be on a stock wheel.

[85boostbox]

They do that from the factory. Every manufacturer does it.

[ScottD]

They do that from the factory. Every manufacturer does it.

Really? Then how come the other 4 vehicles I have that I drive regularly, the speedos in each of them are accurate?

[85boostbox]

Proven fact? If so how did you do it?

[85boostbox]

Cause I know the one in my SS is off past 75. The one in my s10 is off by about 5mph. My escort is also off. Not sure by how much but it is off. And mind you my SS is a 03

[ScottD]

Proven fact? If so how did you do it?

There's a "safety zone" on Rt. 15 near where I live where the speed limit drops to 50mph. There's a speed camera with a display there. I've driven through it with every one of my vehicles many many times.

[85boostbox]

http://www.caranddriver.com/features/speedometer-scandal?redirect=no

So out of 200 cars they were ALL off. You must have some freak cars then ;)

[ScottD]

http://www.caranddriver.com/features/speedometer-scandal?redirect=no

So out of 200 cars they were ALL off. You must have some freak cars then ;)

The articles says at a true 70 the average of the test cars was 71.37mph which isn't horrible. I'm sure none of my other cars (92 Spirit R/T, 04 SRT-4, 06 Dakota, 12 Mazda 5) are 100.0% accurate, but they are within 1mph of where they should be. The problem is my GLHS is about 5 miles per hour off, which I would like to resolve. I'd like to be doing 65 (or 64 or 66) when I see 65 on the speedo, as opposed to the 60 I see now at a real 65mph in the GLHS.

[shadow88]

I've varified speedometers on new cars using the police force. They often set up speed traps across the street from the dealership I used to work at. I haven't yet seen one that was more than 2 kms/hr off. These vehicles were wearing the correct size tires and correct transmissions.

On to the speedo drive gear... I have always had a blue gear in my shadow. As far as I know, the A-520 that came in the car was the correct and original transmission. Also the door sticker and owners manual and sales brochure all cal for 205-50-15 tires and yet it has always had a blue drive gear. I've run it up against a radar trap to varify accuracy and it's fine.

[cordes]

Most of my cars have always been within about 2mph of radar machine indicated speed at ~50mph unless there has been a tire size change. The L body speedometer error is pretty extreme IMO.

[ScottD]

Thanks 88 Shadow - that was helpful.

Cordes - I had an 85 Turismo 2.2 (you know, the carb'd one that I would always refer to when you had carb'd GLH questions) and the speedo was accurate in it. Now that I think about it, I ran 205 50 15s on that car, but I can't remember if I touched the speed pinion on that. Hmm, maybe I should look at my project log to help my memory, though a small change like that I may not have mentioned.

[cordes]

You may be on to something then Scott. All the natural/white gears I've had with the 205/50 tires on them have been too far off for my liking too.

[ScottD]

I just went through my p-log on the Turismo and as I suspected it made no mention of whether I did anything with the pinion on that car. At this point I'm leaning towards rummaging through my collection of speed sensors and finding a blue gear and trying that out.

[cordes]

I just went through my p-log on the Turismo and as I suspected it made no mention of whether I did anything with the pinion on that car. At this point I'm leaning towards rummaging through my collection of speed sensors and finding a blue gear and trying that out.

If you need one please let me know. I know that there is a loose one in my garage.

[tryingbe]

My white gear is pretty dead on on my A555/A520 hybrid with the 205/50R15 tires I have.

[ScottD]

If you need one please let me know. I know that there is a loose one in my garage.

I do need one. In checking my speed sensor supply last night, all I had were white and yellow gears.

[cordes]

I do need one. In checking my speed sensor supply last night, all I had were white and yellow gears.

PM me your address and I'll try to get one out to you soon.

[GLHNSLHT2]

My 205/60 15 daytona's speedo is DEAD nuts with the blue gear. Verified with radar readouts and GPS, but the Odo is 10% low based on those distance/speed testing lines they put on the highways in the middle of no where.

My 205/60 15 New Yorker with it's A413 Auto reads 1-2MPH low with it's blue gear and the odo is about 3% low based on GPS on Ulysee Speedo app for android. Gotta love smart phones :) The new yorker was 3mph high when I 1st got it, can't remember if it had a white or yellow gear originally.

[4 l-bodies]

By doing a little homework with factory service manuals and factory tire sizes this is what I have concluded.
22.5-23.5" White gear 21 tooth
23.6-24.5" Blue gear 20 tooth
24.6-25.5" Yellow gear 19 tooth
BTW all my GLH's speedo's are pretty accurate with 23.0 tall tires using the white gear. Like Jay, I have also found odometer is about 9-10% slow using 205/50/15's
Todd

[ScottD]

Thanks Todd!

[supercrackerbox]

FWIW, I have the blue gear in my Charger, running 205/50/16 tires (24" advertised height) and a 1990 Omni cluster, and it's dead on according to every roadside radar display I've come across.

I have the yellow gear in the Daytona (stock size 205/55/16) and it too is 5mph slower than the gauge reads at all speeds.

[ScottD]

By doing a little homework with factory service manuals and factory tire sizes this is what I have concluded.
22.5-23.5" White gear 21 tooth
23.6-24.5" Blue gear 20 tooth
24.6-25.5" Yellow gear 19 tooth
BTW all my GLH's speedo's are pretty accurate with 23.0 tall tires using the white gear. Like Jay, I have also found odometer is about 9-10% slow using 205/50/15's
Todd

I am running Dunlop Direzzas on my car. According to Dunlop's site, the diameter is 23.1". I really think the blue gear will be the way to go, I'll post back results once I have the car back together.

[cordes]

I am running Dunlop Direzzas on my car. According to Dunlop's site, the diameter is 23.1". I really think the blue gear will be the way to go, I'll post back results once I have the car back together.

I forgot to mention it, but Joy sent the gear out on the 24th. I'm anxious to see how this turns out as I think I've got another blue gear in the garage which I could use. I'm running the same tires as you so this will be great!

[ScottD]

Cordes - I received the gear today. THANK YOU!

I have the 555 installed in the car and still need to adjust the shift linkage, put axles in, etc. We just had some snow out here and they salted the road, so until we get a good rain it might be a while til I drive the car. I will def report back though once I have the car out.

[cordes]

Glad you received it. Joy said it was just in a thick paper envelope or some such so I was a bit worried it could go through the package and be lost in transit!

[mander1976]

I have a 83 Ford F100 that originaly had a C6 when i got the truck it had a rebuilt C6 out of a 78 Ford F250/350(trans tag says 250 or 350). The speedometer says im going 55mph when im going about 70mph. I do not have oversized tires. does anyone know which speedometer gear would be the right one? for example... how many teeth.