From my perspective, I have noticed a vast wealth of knowledge and skill that frequents this website. Just wonderin if anyone can answer: 1. How much, or at least what general magnitude, of power does a mechanical speedometer require (or rob), in the doing of its duty? Would it be for example, equivalent to .01 or .1 miles per gallon? 2. I noticed that semi frequently, someone has a hangup regarding the T5 transmission they want to couple to their hotrod. That hangup is the existence of the mechanical speedometer. I presume this is so they can run the original or retro gauges that help make a traditional rod, a traditional rod? I believe it was late 1989 that Borg Warner went to the electonic impulse (digital, I think), type speedometer facility. Numerous times I have seen ads wanting the earlier type, which makes me think there are probably plenty of the later type, and that the earlier are relatively rare. Am I correct to say that the change was made for better accuracy, cheaper costs, dependability, and maybe (see question 1), a lighter load in the power department? 3. Why not cross a machinist and an electonics engineer, and throw in a a little venture capital & build a prototype adaptor from a small simple DC motor, with the output shaft being the female of a mechanical speedometer cable? I believe a primitive PLC (Programmable logic controller)could be used to calibrate and regulate the ouput speed for the speedometer? Anybody? Device might be used for other apps, as well. Then any T5 should serve the purpose?
Already been done. http://www.summitracing.com/parts/TCI-377300/ I have used these and they work fine. Kinda pricey but you can adjust the output for pretty much total accuracy for using an old cable driven speedo with an electronic transmission speedo output. As for the fuel economy, it isn't anything that can be measured. More of a reason for the change from the OEM was for reliability and they can make it more accurate with a simple calibration change in the electronics and not have to tool up a bunch of different gears.
Like Bad Banana said it's already been done. You can also go the other way from mechanical sender on the transmission to electronic like this one. http://www.summitracing.com/parts/DAK-SEN-01-1/
I think you need to add a few more zeros after the decimal I'm of the opinion that getting a half century old mechanical speedometer to work properly is one of the better challenges of playing with old cars, and I wouldn't want to give it up. Then again, I detest 5 speed transmissions, they make me think of hondacars.
1. I'd never thought that parasitic loss of a mechanical speedometer would be a topic of discussion and I certainly wouldn't think of it in miles per gallon. You're talking about something that you can spin with your fingers, for goodness sake. How many horsepower per finger? 2. The trend in automotive engineering has been to eliminate mechanical connections of all kinds and replace them with electronics. Two of my OT cars don't even have throttle cables or linkages anymore, never mind speedometer cables. 3. You'll go broke in a New York second.
what i'd like to see is an adapter that would combine a GPS with a little motor to drive a mechanical speedo. like a cable-X box or TCI controler that takes it's signal from a GPS instead of the trans.
I have been running an Abbot engineering cable-X for three years on a t-5 and it works great. http://www.abbott-tach.com/cablex.htm
Just get a GPS speedometer. One was awarded best new product at the 2011 SEMA show. No wiring required. Just mount it in the dash and it works and is always accurate no matter what axle ratio, tire size etc.. I think Autometer makes it. If you google "gps speedometer" a shitload of them come up. It is just a matter of time until someone makes them with whatever gauge face you want or converts your original to GPS operation.
I don't really know what the parasitic loss for a speedo is. I would imagine that it is negligible. Look at it this way, the reason that professional racers went to electric tachs was not to overcome a loss in power. In fact some pros still run mechanical tachs and these guys are dealing with .001 of a second in the quarter mile. If the parqasitic loss were a problem they would not be running them. There is no reason to overthink this or even rationalize a decision like what kind of speedo to run (or wear for that matter). If you want to run an electric speedo run one just because you want to. I mean hell this is a car that you are going to toodle around in right? it needs to make you happy while you are toodleing around in it. Life goes on.
i thought about that, but i like my stock 55 chevy speedo and with a GPS hookup to the stock speedo you wouldn't have to re calibrate every time you change tire sizes, gear ratios, or transmissions. and you wouldn't have to have another speedo hanging around.
I know what you mean, I have to add the little SW adapter when I swap gears in my 55. Swapping the rearend gears is still a hell of a lot more work than adding the adapter box, though.
Who gives a crap about the speedometer just DRIVE your car and be proud you can. The speedometer in my 50 merc don't work and I don't care!!!
i DO drive the shit out of it. i'm past just being proud that i can drive it and i want to make it BETTER now. when you drive your car on road trips it is REAL nice to know how fast you're going. 50's cars don't adapt to after market/extra speedos as well as older cars.(without looking like a streetrod!)
Well actually I do care but can't find an original speedo that works ... so the wife got me a gps thingie and it gets me close on speed therefore I don't care! Besides being stock as a clock I don't get much more that a wave and a smile from the cops anyway.
Scotty, I know I'm replying to a 4+ YO thread, but you request has been granted! I patented Classic Speed (http://www.classicautoinnovations.com/) last year after 3 years of development, and we just started shipping units. I invented this device to do exactly what you described - to keep the original mechanical speedometer in place and always have it read accurately no matter what modifications are made to the car. Not wanting this to be shameless pitch, just wanting to let you know you were not alone in wanting this. Thanks! Brian
WOW, impressive! i'm going to have to re-think the electric speedo i bought. cheaper than a cable X box too. how well does the "line of site to the sky" mounting of the GPS work with the old car nearly vertical windshields? could it be mounted to the rear window?
Thanks so much Scotty! It was an incredible amount of non-trivial work, but I'm very happy with the end result. Not sure what you mean about the windshield.... the antenna is magnetic and has a very long (5m) cable so it can be mounted just about anywhere there is visibility of the sky. In my MGB, I have it on the dashboard tucked up against the bottom of the windshield. Some people tucked it behind the bumper face, others have had great results tucking behind the grille. Feel free to ping me through our website. I don't want to hijack this post to be a commercial...
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