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How To Calibrate A Speedometer

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Gary Lewis

Re: How To Calibrate A Speedometer

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I'm not sure I want to do that. I say that because I have one problem and one minor issue with the speedo. The problem is that it is off ~5 MPH while the odometer is accurate. At present the thing reads essentially what it is supposed to read with the shaft speed I'm giving it, so I think it is essentially calibrated correctly. So I think I need to adjust it to read another 5 MPH higher and give that a try.

The issue is that it bounces or wavers a bit. I think that is probably due to two things - a worn speedo cable and a worn input bearing. I'm replacing the speedo cable so will take away that source of error, but I'm thinking the biggest cause of the bouncing is the input bearing. And while they could replace that, I'm not sure it is worth it.

I hope to get the new cable installation as well as the wiring from the t-case mounted VSS to the early harness done today. That leaves adjusting the speedo and then reinstalling the gauges. The plan is to get that done tomorrow morning and then take it out for a spin when I send the brake stuff to John/Machspeed.

After that I'll know a lot more about what may need to be done to get the speedo "right".

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

grumpin

Re: How To Calibrate A Speedometer

In reply to this post by 85lebaront2

Wow! Interesting! I did not know that.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

85lebaront2

Re: How To Calibrate A Speedometer

Administrator

In reply to this post by Gary Lewis

How about swapping the input bearing housing with another better one?

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Gary Lewis

Re: How To Calibrate A Speedometer

Administrator

I thought about that, but the are two different housings - with and without trip odometer. I only have three of those with trip odometers - Big Blue's, Dad's, and the NOS one. I think I'll put a different face plate on the NOS one to make the MPH marks be primary and KPH secondary, and use it in Dad's truck. So I could use the one from Dad's truck in Big Blue. However, I'd then need to paint the needle to match the others. And I'd want to swap or reset the odometer.

So for now I think I'll just bump the speed up 5 MPH. And I did lube the bearings. So maybe it'll be better.

Btw, the tester arrived today. Thanks!

Gary, AKA "Gary fellow": Profile

85lebaront2

Re: How To Calibrate A Speedometer

Administrator

Damn, a Sunday delivery? We're lucky to get any packages on a Saturday, although our carrier surprised us yesterday. He had some prescription meds for me that needed a signature so rather then have it stuck until Monday he drove the van to the house and brought all our mail to us.

I am sure that a number of us will be waiting with bated (or should it be baited) breath to here the end results. BTW, have you considered the possibility the vacuum and vent valves might be sticking?

Bill AKA "LOBO" Profile

Gary Lewis

Re: How To Calibrate A Speedometer

Administrator

Yes, I'm anxious to see how this works out. And while this is the wrong thread, I'll respond to your question/statement here anyway.

I'm very sure the problem isn't vent valves. Of the components in the speed control system I've made these changes or tests:

Servo & Valves: I've had three different servos on with essentially no change

Throttle Cables: I've had three different cables on from the servo to the throttle (they are removable) and have had no change. However, all the adjustments to the throttle have been as directed by the FSM, so the next time out if the problem isn't fixed I'll try David's suggestion and put a bit of slack in it.

Amplifier: Two different ones, and the only difference was the one that picked up ~6 MPH when you hit Set/Accel, and I discovered how to fix that so am still running that one.

Speed Sensors: Two different sensors on the end of the speedo cable, and soon to be a transfer-case mounted one that bypasses the speedo cable

Speedo Cables: Have pulled and lubed both cables with no change, but am now replacing the two cables with a new one-piece unit.

Vacuum: Have tried several different restrictions between the vacuum valves and the servo, and while that has made the back and forth on the throttle less bad, it hasn't fixed it. In addition I added a vacuum reservoir between the engine and the servo, with little if any change.

Wiring: Using a DVM I've check out ALL of the wiring associated with the speed control, twisting/turning/pulling on it to see if I could get it to fail. NADA. Everything checked out.

But now, with your tester, I'll check again. Not sure if that'll be before I take it for a spin tomorrow or not, but I will certainly test the system. And I'll compare your tester to Scott's. If, as expected, yours works and his doesn't, and assuming he doesn't get his money back from the seller, I'll do as you suggested and merge the two and Scott will have a good tester in a good case.

Gary, AKA "Gary fellow": Profile

BigBrother-84

Re: How To Calibrate A Speedometer

In reply to this post by Gary Lewis

Gary Lewis wrote

And as I was gathering them I realized that I have a NOS one, as shown below.

Gary, what did you do with that Km/h + trip speedometer?

You installed it, mixed it with a mph facade, or still in its box?

Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.

Gary Lewis

Re: How To Calibrate A Speedometer

Administrator

I think it is still in its box.

Gary, AKA "Gary fellow": Profile

BigBrother-84

Re: How To Calibrate A Speedometer

Email sent.

Jeff / 1984 F350 Crew Cab 4x4/5.8L w351 4V/ T18/ D50 4.10 front/ 8' bed.
Restored 2019-2022.
Nicknamed «Big Brother 1984», due to its soooo-looong shape & nod to George Orwell's 1984 famous novel.

Gary Lewis

Re: How To Calibrate A Speedometer

Administrator

Reply sent. I'll need to go see if I still have it, but should later today.

Gary, AKA "Gary fellow": Profile

myrl883

Re: How To Calibrate A Speedometer

In reply to this post by Gary Lewis

Thanks Gary! This is going to come in handy. I always wondered how to do it, because on my old '85 F150, the speedo was about 3mph off at 60, but the odometer was dead accurate between mileposts.

Ford Parts Monkey since 1985
1981 F100 Flareside - Black, 302-4V Roller/AOD
1986 F150 Flareside - Medium Fire Red 302/AOD
1989 F150 Standard Cab 4x4 - Dk Shadow Blue 302/AOD
1993 F350 4x4 Crew Cab - 7.3 IDI/ZF-5
I think it's a sickness...