Need Speedometer Calibration Help

[84toy]

After looking through the archives I thought I would take my speedo apart, clean it and access the calibration screw and set it using my GPS. My speedo runs 10% fast.

I can not find a calibration screw anywhere in this unit. Did they change the design in later years? Mine is a 84 (160mph speedo). Any help appreciated

[afterburn 549]

Mine dose the same thing.......i am going to watch and see what you get for a ans.... ....... ......... ............

[no substitute]

http://www.pelicanparts.com/techarticles/Mult_gauge_repair/mult_gauge_repair.htm

[Aussie]

I just had mine recalibtrated at a VDO centre, as mine was 15% out.

They need to install a ratio box. Once they have installed this they can adjust it to give your speedo the correct reading.

[RoninLB]

this is what I did/non profesional/weekend wrench style for the elec speedo
I pulled speedo
I removed screws from rear of speedo that holds a plastic mount for wires.
I gently moved plastic wire mount so I can see inside
look inside using removed bulb sockets and thru hole under plastic wire mount look for an itty bitty screw the size of eyeglasses hinge screw/or smaller..the screw is almost invisible in there. Drill a hole on speedo case to be able to access itty bitty screw with itty bitty screw driver. use new drill bit and be gentle.
A small adjustment of the screw will affect the speedo reading..lets say a move from the 1 o'clock position to 2 o'clock position may affect a 5mph difference in speedo reading..I believe clockwise increases the speedo reading..don't remember the exact direction..but I think I'm correct. The pros adjust for 30mph and 60mph, I believe. I would start adjusting for your routine speeding ticket areas against a newer car with cruse control on a flat straight road. Some people have said that you can't adjust for high and low speeds by the itty bitty screw..that if you adjust for high speed your low speed will not be accurate. I believe I'm correct for high and low speed..not sure how finely tuned the speed is..will check it at next smog test..It's 10X better than before the surgery..and on big roads, such as flat Kansas, when you know that the mom and pop sedan is on cruse control at speed limit I'm accurate ..

The white is where I drilled. Use the plastic wire mount for a bearing.

[84toy]

Thanks for the reply. I have the speedo completely apart. I polished the lens and cleaned it up. I looked at the circuit board inside and there is no "pot" to adjust, just some resistors and a chip. I can not find anywhere that looks like an adjustment. Anyone done an 84 era speedo?

[RoninLB]

Originally posted by 84toy
I can not find anywhere that looks like an adjustment.

I thought all elec speedos were the same. Maybe confirm because it's an itty bitty screw and difficult to see in the mass of electrics. I'm gonna have to try a dig pic at the eyeball end of my borescope some day. sorry no pic.

[1980SC]

Here's a fuzzy picture I took of my SC's speedo. The needle is pointing to the trimpot. I doubt the Carrera speedo would be much different.




-Rob
1980SC

[RoninLB]

Originally posted by 1980SC
Here's a fuzzy picture I took of my SC's speedo.

Rob.. is it fuzzy only because you had to shrink it to post ?
Is a big bit pic available ?

[RoninLB]

'76-'89 911 Speedo pn 911.641.517.00

[1980SC]

No, my camera just won't do closeups. The original sized pictures are just as blurry. One day I'll buy a new camera...

-Rob
1980SC

[84toy]

Thanks for the pic Rob. My circuit board does not have nearly that many componants on it. Mine has about 4 pieces on the board. They must have changed the board at some point. I guess I will have to send it out. 10% off is too annoying for me.

Since we are talking about speedos, what kind of rpm do you get at say 60 mph (actual speed) with stock tires?

Thanks for the help guys

[RoninLB]

Originally posted by 1980SC
No, my camera just won't do closeups.

there may be a "macro" option ?

[Aussie]

Since we are talking about speedos, what kind of rpm do you get at say 60 mph (actual speed) with stock tires?

Thats going to depend on what gear you are in hehe.

[RedRoseRomer]

I have just bought a 911SC and I got two speedometers with it. One is broken (the needle is loose) but it appears to be much like the one in the photo above. The one in the car is reading about 10% up on the speed although the odometer appears to be about right.
It doesn't have a trimmer in the same place as the earlier one. Has anybody solved this problem?
David

[E Sully]

Many don't have the trim pot. This is from one made in 1983 that does, shown by the arrow. I read that without the trim pot, it can be done by changing a resistor, but that would be a bit of work to get right.

[RedRoseRomer]

I think I may have to live with it and just mark up the glass to avoid those speed cameras!
David