Speedometer Adjustment for tire size?

[CBRacerX]

http://www.abbott-tach.com/era.htm

Has anyone tried this device on the G-50 911's?

Looks like an easy way to get the speedo accurate again, if compatible with the 911 signaling. I know this works on the 944 platform.

Thanks,

Chris

[RoninLB]

CBR..never used anything like that, but I did adjust my speedo. I matched my speedo against a car with cruse control on at 30mph, 60mph, and 70mph..will check it again when I get a smog test in the shop ............Ron

[laddsc]

I am having speedo problems as well and wonder if this might correct it also. I have an 83 SC and my speedo is running 9 mph fast at 60 mph even though I have stock tires, gear ratio, etc. Speedo shops here in Salt Lake are baffled. Is there an adjustment they just don't know about?

[ChrisBennet]

Originally posted by RoninLB
CBR..never used anything like that, but I did adjust my speedo. I matched my speedo against a car with cruse control on at 30mph, 60mph, and 70mph..will check it again when I get a smog test in the shop ............Ron

How did you adjust your speedo?
-Chris

[Early_S_Man]

The 911 electronic speedos from 1976 - 83 have a trimpot on the circuit board.

[FlaCarrera]

And, lest we not forget, high reading speedos are racking up odometer miles faster than normal. Where is the trim pot again?...which circuit board?

Ted
86 Carrera

[ChrisBennet]

Originally posted by Early_S_Man
The electronic speedos have a trimpot on the circuit board.

Do I need to open the speedo or is there an access hole for the pot?
TIA, Chris

[RoninLB]

Warren is correct...the last time I posted on this subject all hell broke loose and I was the devil..the routine feeling around here is to send out the speedo to a pro..............Ron

[Rot 911]

Originally posted by Early_S_Man
The electronic speedos have a trimpot on the circuit board.

Warren, don't leave us hanging here! I thought I needed to send my speedo off to be adjusted. Could you give us a step by step for adjusting the electronic speedos? Ron, I remember your prior post, but can't find it in a search.

[RoninLB]

Gentleman..this is what I did/non profesional/weekend wrench style
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 ...........Ron

[Rot 911]

Ron, thanks! I'll try your method out. I have a very accurate portable GPS that I can take in the car to see if the changes reflect the correct speed.

[CBRacerX]

to give this a try. I've got a spare speedo (with only 5K miles..) so I'll try it on that first.

Thanks!

Chris

[RoninLB]

Kurt..you will be actually be doing me a favor by adding credability to this speedo adjusting/weekend wrench style.......Ron

[laddsc]

I am trying it too. I have nothing to lose since I am off so far with no apparent reason. All the "itty bitty's" make me nervous but oh well, it is only money if I screw it up, right?

[RoninLB]

Ted...I don't believe adjusting the trim pot affected the odometer setting..I tried testing on the "measured mile" on big roads and couldn't see any difference...and whoever succeeds at adjusting the speedo please post your results..........Ron

[laddsc]

I agree with Ron. My speedo is 9-10 mph off and the odometer was right on with mileage markers on the road over a 5 mile length. They don't seem to be connected, much to my relief since my 83 SC only had 78k when I purchased it a year and a half ago and I now drive it daily.

[Cordts]

Can you adjust cable driven speedos on a early car..