fix'n a speedo problem

[scott]

i've got the ususal, reads nice up to about 30 mph the after that ya gotta kind of take an average reading as the needle bounces all over a 15 mph range. and it pretty inaccurate too. i've an 88 w/ 16" wheels wearing 285/75s. recently calculated using highway mile markers that when my truck says it's gone 76 miles it's really gone 100.

i just bought a 109 dash unit because i need a fuel gauge. if i swap the speedos will i get a more accurately reading? didn't the 109s come with 16" wheels?

[I Leak Oil]

It's the diameter of the tire that matters not the wheel itself. 285/75 is a bigger tire than stock so your speedometer will be off.

[scott]

yes i know it's tire diameter. but if lr used a larger rim on the 109s wouldn't they have used tires with a greater overall diameter and made adjustments to the speedo or the gear in the tranny? so the question is what was the stock tire diameter on a 109, on an 88 and if different were the speedos alter or was it the cable drive gear in the tranny? are 109 and 88 speedos the same?

[I Leak Oil]

I think the speedometer is what is different. I assume the 109 had the larger tires so would make sense that the 109 speeometer would cut down on the amount of error but not eliminate it. A 285/75 tire is still large enough that you won't be that much closer with it though. Find one of those on line gear calculators and run the numbers for the different size tires.

[KevinNY]

The problem is a dry or worn speedo cable. Regrease or replace it. 88 or 109 are the same.

[pisten-bully]

You know about Nisonger Instruments?
http://www.nisonger.com/

[scott]

You know about Nisonger Instruments?
http://www.nisonger.com/

yea, know of 'em. but aren't they for those folks that are so attached to ever part of their roves that they would spend almost as much on a rebuild as they would a new part?

[SafeAirOne]

Chart comparing the stock size tires for a 15" rim (or close to it) to commonly used 16" tire sizes. I used this (http://www.1010tires.com/TireSizeCalculator.asp?action=submit&reset=yes) tire size calculator/comparitor.


STOCK 15" TIRE SIZE: 205 75 R15 OVERALL DIAMETER: 27.10" CIRCUMFERENCE: 85.13" ACTUAL SPEED: 60mph

COMPARISON TIRE #1: 7.50X 16 OVERALL DIAMETER: 31.64" CIRCUMFERENCE: 99.39" INDICATED SPEED 51.3mph DIFFERENCE: 16.76% low

COMPARISON TIRE #2: 235 85 R16 OVERALL DIAMETER: 31.72" CIRCUMFERENCE: 99.65" INDICATED SPEED 51.2mph DIFFERENCE: 17.05% low

COMPARISON TIRE #3: 285 75 R16 OVERALL DIAMETER: 32.83" CIRCUMFERENCE: 103.1" INDICATED SPEED 49.5mph DIFFERENCE: 21.15% low

[I Leak Oil]

COMPARISON TIRE #3: 285 75 R16 OVERALL DIAMETER: 32.83" CIRCUMFERENCE: 103.1" INDICATED SPEED 49.5mph DIFFERENCE: 21.15% low

There you go. That 21.15% is pretty close to the 76 mile vs. 100 mile discrepancy you are seeing.

[pisten-bully]

aren't they for those folks that are so attached to ever part of their roves that they would spend almost as much on a rebuild as they would a new part?
No.

[scott]

No.

our host sells new speedos for just over $300. i wonder what those guys charge to rebuild and recalibrate. i'd guess it'd be up there close to it. a friend had his willy's speedo rebuilt at a local speedo shop and it he found out afterwards that he could have bought a new one for almos the same ammount

[pisten-bully]

I like recycling. In '97 they rebuilt mine and set it up for 16", cost me $80.50 (can't believe I still have the invoice!) Figure inflation, but they were good folks there and did it in a timely fashion.

And aren't replacement speedos discontinued items?

[scott]

I like recycling. In '97 they rebuilt mine and set it up for 16", cost me $80.50 (can't believe I still have the invoice!) Figure inflation, but they were good folks there and did it in a timely fashion.

And aren't replacement speedos discontinued items?

rn sells the series iii speedos which will work and have a trip meter so you can tell how far you've one before breaking down. recycling is good. $80 ain't bad but i got the 109 dash for $40 and i just wanted the fuel gauge but it comes with a speedo, water temp (elec) gauge, the test plugs and a couple of toggle switches. i hope the fuel gauge at least works

[badvibes]

a friend had his willy's speedo rebuilt at a local speedo shop and it he found out afterwards that he could have bought a new one for almos the same ammount

Actually less. I think H paid close to $100 to have his speedo re-done and a replacement speedo was @ $80 if I remember right. The shop in Alb has a $75 base charge and then adds parts from there. On a side note H said the guy told him it's a dying field, with all the digital/electronic stuff used on more modern vehicles there is less and less call for old school mechanical gauges.

Jeff