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| Non-linear speedometer error [message #370652] |
Sat, 08 October 2022 18:37  |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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I recently changed my final drive from the OEM 3.07 to 3.42. Previously my speedometer read about 10% low. When my speedo read 50mph, my GPS read 55mph. I usually had the GPS turned ON, otherwise I just added 10% in my head.
I expected when I changed the final drive, the error would actually decrease and the speedo would be more accurate. Instead, when the GPS read 55, the speedo is reading 60+ (1.09x). The 1.11 change in the FD caused a 1.2 change in the speedo (was 5mph low, now 5mph high).
We just came back from the first trip with the new FD and I noticed something strange. Seems at 40mph, both the GPS and the speedo read the same. But at faster speeds, the speedo reads much further away as a percentage. I'm going 75mph by the speedo to get to 65mph on the GPS (1.15x).
I've never noticed this before as I am either aiming for 55mph or 65mph.
So it seems to me that a geared reducer will not fix this problem. I'll need to investigate this more as I was almost home before I noticed the 40=40mph thing.
Has anyone else noticed this. I think I'll need to correct it with stickers on the gauge, just like when we went metric back in the '70's here in Canada.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Non-linear speedometer error [message #370653 is a reply to message #370652] |
Sat, 08 October 2022 20:41  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Bruce,
I did a short stint with Chrysler Introl way back when. Up until that time I thought I could sort of count on normal speedometers to be close and sort of linear. That ended the day I got assigned to work the calibration stand.....
They are not linear devices, the are not accurate and they are not even very repeatable. Isn't that about what you just wrote??
The guts of an eddy current speedometer (or any similar device) is a magnet that gets spun by the mechanical input. That magnet is spinning inside a cup. That cup has a pivot, a spring and needle. The plan being that the field induced by the spinning magnet produces an eddy current in the cup and that drags the cup along to deflect the pointer.
To try to linearize the system, that cup is made of pedals almost like a flower. These can be bent into or out of the field to calibrate the system. As you can also appreciate, as the spinning element bearings wear, all bets are off. Oh, I forgot that the alnico magnets tend to loose strength with vibration and the cup (I have forgotten what that is actually called in the business) can develop residual magnetism of its very own...
My advice??
Get a cheap or used GPS to station on top of the instrument panel and use that. You should be able to set it for KPH when you are at home too.
Almost an post text: I just remembered that an associate put a different transmission in his truck and lost the speedo cable. He bought a GPS speedo that was cheaper than the cable to correct the issue. Look on Amazon there are a few.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Non-linear speedometer error [message #370656 is a reply to message #370652] |
Sat, 08 October 2022 22:29 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Bruce,
I made the exact same final drive conversion and experience the exact same result. I also thought it should have been linear, but it's not. I do use a dashmount GPS with the speed display. Now when I check my speed my eyes go directly to the GPS instead of the speedometer on the dash. I'm loving the 3.42 final drive more than enough to make the speedometer and accuracy's not an issue.
Take care and let me know if you find a solution to the speedometer. I always like having everything work as it should.
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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| Re: Non-linear speedometer error [message #370657 is a reply to message #370656] |
Sat, 08 October 2022 23:55 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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The What's Up Display MPH should be a linear proportion of the final drive ratio change, I think. You can record the vss pulses using datalogs from either the WUD or WinLog-Ebl and read them using Excel (it's a csv file).
You can start a WUD datalog at a mile marker and stop it at another and then look at the datalog to see how many pulses it recorded (it counts up to 256 pulses and starts over, so you have to add rollovers and leftover pulses. WinLog-EBL lets you insert markers in the datalog while under way to do the same thing and without disrupting the datalog.
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
[Updated on: Sun, 09 October 2022 00:06] Report message to a moderator |
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| Re: Non-linear speedometer error [message #370659 is a reply to message #370658] |
Sun, 09 October 2022 09:59 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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RF_Burns wrote on Sun, 09 October 2022 08:57BillV, I just need to find a place to mount my Windoze tablet and I could run both WUD and WinLog-EBL. Can you run both at the same time and play nice with the single USB connection?
TomK, I'm liking the 3.42 as well. It's a great feeling being able to accelerate up a hill! Yes, it bugs me when things are not working right, even if I have a work-around!
Sure can; you do have to exit WinLog-EBL to flash BINs, however. But otherwise you can run both, including running both datalogs. Easiest way to run both is to get a serial splitter cable and two serial/usb cables. It's also possible to run virtual usb software and share a single usb port.
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
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| Re: Non-linear speedometer error [message #370660 is a reply to message #370652] |
Sun, 09 October 2022 10:26 |
boybach
Messages: 566
Registered: December 2020
Location: Vancouver Island
Karma: 4
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Senior Member |
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RF_Burns wrote on Sat, 08 October 2022 16:37just like when we went metric back in the '70's here in Canada.
As an aside -this was one of my first jobs in the graphics industry, designing speedo overlays when we went to Kph LOL
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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| Re: Non-linear speedometer error [message #370661 is a reply to message #370652] |
Sun, 09 October 2022 11:09 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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The standard is 1000 spedo cable revolutions per mile. First you have to get that correct. Once that is correct, then the odo will be correct. And spedo errors are then in the head calibration. There used to be speedometer shops. My friend worked at Henry the speedometer man in Oak Park IL. They fixed such things, installed aftermarket cruise and add-on knee knocker underdash AC as you did in the 70s. With a correctly working speedo, I don’t think there is a spot on add-on gear corrector box ratio that fixes 3.07-3.42 swap. Cinnabar did my 3.42 and added the in line box and mine is off a bit too. Maybe reads 3 high at 70? I have not noticed a nonlinear issue though. I will have to experiment next time coach is out.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Non-linear speedometer error [message #370663 is a reply to message #370652] |
Sun, 09 October 2022 15:23 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Senior Member |
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It a shame it is not a simple spedo gear replacement. When I changed my tires on my 1977 CJ5 I just change speedo gear to a different color and all was well.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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| Re: Non-linear speedometer error [message #370664 is a reply to message #370652] |
Sun, 09 October 2022 17:40 |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Larry,
That would be one solution due to the non-linear markings. I could figure out what speed to label where on the dial, then print a new dial to stick over the OEM dial. I'd likely make a big mess of it though.
Tom,
There are (used to be) different gears available, but alas, no longer available. I don't think it would fix it because the faster the speed, the more the speedo is out.
John,
There is a speedo place about 2 miles from me. I stopped in there and the 30 something guy looked at me like I had two heads. He knew nothing about gears or reducers. They only work on stuff later than 2000 and mostly on used pickups being exported to the USA... changing them from kms to MPH. I thought that was kinda strange since every vehicle I've had since the early 2000's was electronic and KMs or Miles was a menu selection. The lot was always full of late model GM and Ford pickups with no plates on them.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Non-linear speedometer error [message #370665 is a reply to message #370664] |
Sun, 09 October 2022 18:52 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Senior Member |
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Quote:Tom,
There are (used to be) different gears available, but alas, no longer available. I don't think it would fix it because the faster the speed, the more the speedo is out.
Bruce,
I agree. I will be greatful to just have the the GPS and the WUD speed indicators.
I just received the Dakota Digital VSS that Randy recommended and will install it this Saturday. Hopefully from there I can program the Pulses and be off to the races. Im sure I have a little more learning to do and will also place a couple dots on the original speedo.
Take care,
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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| Re: Non-linear speedometer error [message #370666 is a reply to message #370664] |
Sun, 09 October 2022 19:56 |
boybach
Messages: 566
Registered: December 2020
Location: Vancouver Island
Karma: 4
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Senior Member |
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RF_Burns wrote on Sun, 09 October 2022 15:40Larry,
That would be one solution due to the non-linear markings. I could figure out what speed to label where on the dial, then print a new dial to stick over the OEM dial. I'd likely make a big mess of it though.
Well if I was to attempt it, I'd get some transparent, pressure sensitive [non-adhesive] vinyl and cut out a circular piece to fit over the speedo. Taking a drive with the gps on, I'd mark the vinyl at the various increments with a permanent marker then remove the vinyl and scan it into something like Coreldraw! then make a "pretty" copy using the vinyl scan as a template.
If you have a way to print onto an adhesive substrate, all well and good. If not, find someone with a Cricut or take the file to your local sign shop and have them output a couple on to the vinyl of your choice ...but heck, that's just what I'd do!
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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| Re: Non-linear speedometer error [message #370670 is a reply to message #370652] |
Mon, 10 October 2022 08:14 |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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TomK,
The EBL has a VSS-Pulse per mile parameter (6th entry from the top in TunerPro) that you can adjust to set the WUD speedometer. I had adjusted that parameter to match GPS speed long ago, so I just multiplied that number by 1.114 and came up with 2224.44. It seems to be close to GPS, but I'll need to test it when the dog is not with me. Dog and laptop are not compatible in the same space beside me!. Also check the setting of the VSS filter. It smooths the speed reading. I noticed several years ago that my engine would randomly cut-out. I then noticed the WUD speedo was jumping up by 40-50kms. Turns out it was the Over-Speed parameter causing the engine to cut-out. My VSS sensor had a noisy reed switch causing extra pulses. Replacing the reed switch fixed it. RandyV then told me about the VSS-Filter, so I raised it to 75.
Matt,
Thanks for your info on calibration. Since the error percentage seems to increase with speed, I was thinking maybe the needle spring has weaken. Or maybe bearing, or 45 years of dust accumulation has increased a slight bit of physical drag. This past summer the needle would jump up in speed. I found the cable was not tight at the transmission, but seemed to turn freely. I didn't notice it "jumping" on this trip. Could be just things are worn and dragging.
Larry,
I plan to do some tests with Paula recording the data. Your plan seems a viable way to keep the old speedo, however I'm not sure I'm good enough at graphics to pull that off. I'm an electronics guy so I could replace the mechanical guts with a stepper motor.
I don't really want to replace the speedo with a new one because I'll loose the PRNDL indicator. Non of the replacement speedos I've seen have that.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Non-linear speedometer error [message #370674 is a reply to message #370652] |
Tue, 11 October 2022 08:37 |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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So Paula and I went out for some tests yesterday afternoon. With a second set of eyes, it would seem the error is not as bad.
First, I'm in Canada so we are with 96% of the world that uses Metric. My coach is a 1977, so it has Km/Hr markings, but they are not accurate. So I made a chart using MPH from the speedometer and EBL's What's Up Display (WUD). I have my GPS set to KM/Hr so I put all the readings into a spreadsheet and had it convert the measurements, then give me the error factor compared to the GPS speed.
I drove to the indicated speeds on the speedometer and then Paula recorded the indicated speeds from the GPS and the WUD.
The change from 3.07 to 3.42 is a factor of 1.114 or 0.898 depending on which way you are looking at it.
So it appears that a gear reduction to 0.90 will put the Speedometer just about right on in the 55MPH (about 90Kmh) and above range which is hyway driving. The inaccurate Km/hr markings were taking me down a rabbit hole!
My WUD is reading a tad high, which I can fix in the EBL parameters for the Vehicle Speed Sensor (VSS).
First Pass (cMPH and cKPH are calculated MPH and KPH in the spreadsheet)
Speedo MPH |Speedo error factor | GPS (KPH) | GPS (cMPH)| EBL (MPH) | EBL (cKPH) | EBL error factor
15 1.08 26 16.2 17 27.4 1.05
25 0.97 39 24.2 25 40.2 1.03
35 0.94 53 32.9 33 53.1 1.00
45 0.93 67 41.6 43 69.2 1.03
55 0.90 80 49.7 52 83.7 1.05
65 0.89 93 57.8 63 101.4 1.09
Second pass
15 1.04 25 15.5 17 27.4 1.09
25 0.94 38 23.6 26 41.8 1.10
35 0.94 53 32.9 33 53.1 1.00
45 0.94 68 42.3 43 69.2 1.02
55 0.90 80 49.7 52 83.7 1.05
65 0.90 94 58.4 63 101.4 1.08
70 0.90 101 62.8 65 104.6 1.04
75 0.89 108 67.1 69 111.0 1.03
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Non-linear speedometer error [message #370678 is a reply to message #370652] |
Tue, 11 October 2022 12:10 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Senior Member |
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Bruce,
That information is great. Starting Thursday I will be installing my VSS and then the SGI-100BT Signal Interface Unit. After that I will be working on the connections and speed odometer adjustment. I will definitely be utilizing your data.
Thank you for providing the information.
Take care and have a great day,
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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| Re: Non-linear speedometer error [message #370681 is a reply to message #370680] |
Tue, 11 October 2022 15:12 |
Bill Van Vlack
Messages: 419
Registered: September 2015
Location: Guemes Island, Washington
Karma: 14
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Senior Member |
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Quote:For the EBL, there is a parameter you can change in the BIN to adjust the What's Up Display's speedometer and mileage without needing the SGI-1000
I bought the SGI-100BT based on my EBL research on the GMCMI-EFI board. I guess I didn't need it. I was probably misled by early posts for the EBL before the adjustable ppm change was made. (DRAC, etc.) I'm using the SEN-01-4160 VSS sensor.
But I'm set up to add a Rostra cruise control if I ever decide to go that way.
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid November 2015.
[Updated on: Tue, 11 October 2022 15:55] Report message to a moderator |
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