HUGE speedo error AND experience with Jacobs speedo on EBay? (or N. Hlywd, Palo Alto)

[Russ in VA]

My speedo/odo has two problems:

1-the usual broken gear = no odo (about a month ago)
2-before this happened and ever since I bought the car ... the speedo and odo read about 80% of actual ... that is the speedo says 60 mph when I'm going 75 (or 80 when going 100, ect.) and the odo shows only 8/10ths for every mile traveled

Any ideas what could cause #2? Is it just a speedo that REALLY needs to be calibrated? A guy I talked to at a local speedo shop suggested that it might be the sending unit since it's both the odo and speedo. Is there a unit screwed into the side of the tranny somewhere that I can replace?

I plan to borrow a friends speedo (that would be you David if you are reading) and see if the error goes away as a test.

Currently there is a speedo on EBay that might turn out to be a bargain.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2438664423
(I hope I won't get into a bidding war with any fellow Pelicanites now that I've tipped my hand!)

Anyone have any experience with these guys (Jacobs Speedo)? I emailed them and the quickly responded (they said they WOULD set the odo to match my current reading at N/C).

Should I just bite the bullit and send mine to North Hollywood? In a recent Pano article it said that Palo Alto Speedo was the former N. Hollywood, but they BOTH advertise in the mag so what's the deal there?

TIA,

Russ

[Tim Walsh]

Russ,
What size tires are on your car? They can make a big difference when it comes to the speedometer reading. Is it the stock size?

[Russ in VA]

Tim,

Good thought, but the tires were stock when I did the calibration I quoted. Incidentally, I calibrated with a stop watch, a steady throttle foot, and the mile markers on a long road trip. Then I confirmed my results using my wife, some walky talkies, and her late model car. The stop watch was much more patient with my efforts than my wife.

I HAVE since changed from the stock 205/60/15's to 225/50/15's which has made the speedo a little less inacurate but not much. Doing the math will show that tire diameter (proportional to circumference) went from a stock dia of 24.69 to a new smaller dia of 23.86 which is only a 3.35% change or about 2.5 mph at 70. So now I only have a 17% error. To explain my HUGE problem, I'd have to have HUGE tires on the car (275/75/15's would about do it)

On a similar thought, I also don't think the ring and pinion have been changed since the rpms at any given (true) speed match the little chart in the owners manual (you've got to LOVE an owners manual that gives you a speed in gears chart and a listed top speed!). Again, a change to the ring an pinion to explain this problem would have to be a big change AND would have had to be what most of us would call in the wrong direction (top speed gears for a car with big power, not acceleration gears for a stock engined car).

One thing I did think of, is could the original owner have put some kind of device in the car to do this on purpose to keep the miles on the odo down? Anyone ever heard of such a thing? I know there is a similar electronic device that can be installed when you do a gear change to correct your readings (I've heard of this being done on Mustangs, don't know if it applies to Porsches).

[n8marx]

Russ,

My '86 was off by just about the same percentage. I checked it against a GPS unit and found my speedo read 24% high, all with stock tire sizes and no change to ring and pinion. North Hollywood Speedometer calibrated it and cleaned it up for me for $90. Total turn around 4 days from take out to put in.

[Russ in VA]

Nate,

Thanks for the input. Good to hear that an error this large can be fixed by a simple calibration. Also thanks for the refferal on N. Hollywood!

Anyone have experience with Palo Alto or Jacobs?

[racea911]

The worst company I dealt with in the entire restoration of my car was North Hollywood Speedometer. The absolute worst, from the length of time they said it would take to repair, to the length it actually took, to their inablilty to write down a credit card number correctly adding more delay to my order, to their inablilty to write down an address correctly and shipping the item to an address that does not even exist adding even more time to track my gauges down.

I don't normally throw companies under the bus like this, but my experience with them totally sucked. I would be more inclined to walk into the dealer and pay full retail for a new gauge than to send anything else to No Hollywood Speedometer. To top it all off, my speedometer only worked correctly for 1600 miles. I will send it to someone else, ANYONE else to have it repaired.

The worst, ever. They were good on my first 911 I restored, but this last one? In the words of Janet Jackson, "What have you done for me lately?".

[jbryant]

Russ,

Try this site www.odometergears.com

[RoninLB]

Speedometer Adjustment for tire size?

Speedometer Error. Need some help

[Jdub]

Try www.speedometer.com.

John