Speedometer Question

[Frog2Spider]

My speedometer only goes up to 85 mph. The car will go much faster than that, but I've been reluctant to take it past 85 for fear of breaking the instrument.
Does anyone have any first hand knowledge of what I could expect if I did?

Thanks,
Dave

[donm]

Lots of room here for a funny response but seriously nothing will happen. I've had my 85mph speedo pinned to the point where i figure I'm doing about 95.

[aevansgatech]

You may go back in time to 1981..

[aj81spider]

In my state you transition from a speeding ticket to reckless driving and end up arrested.

[DieselSpider]

In my state you transition from a speeding ticket to reckless driving and end up arrested.

Depending on the posted speed limit you could just about instantly morph into a pedestrian or end up pedaling a bicycle for the next few years.

[stuartrubin]

Doesn't the speedometer work through eddy currents generated by spinning magnets? There is no mechanical linkage between the spinning cable and the dial itself. I would think that pegging the speedo would not hurt anything. (You might, theoretically, be generating a little heat from the "unused" power transferred through the magnetic fields.)

[Frog2Spider]

Here in Washington state, the posted I-5 speed limit it 80 mph on most of the north south corridor, however, to stay up with traffic, one needs to be doing 85 - 90. The alternative is to do 65, behind a caravan of 18 wheelers.

So, with that said, I appreciate the informative replies to my question.

Dave.

[RRoller123]

I have buried the 85 speedo on mine a couple of times with no consequences. Obviously there is some sort of protective mechanism inside it. 100 mph+ will get you locked up here in MA. But speeds on 495 and 90 typically are in the 80's all day long.

[Frog2Spider]

I have buried the 85 speedo on mine a couple of times with no consequences. Obviously there is some sort of protective mechanism inside it. 100 mph+ will get you locked up here in MA. But speeds on 495 and 90 typically are in the 80's all day long.

We have referred to I-5 as the Autobaum of the US. Sometimes you'!! see a Trouper with a car pulled over, but I think Washington has bigger fish to fry, and a limited amount of 'heat' to cook with, if you know what I mean.

The speed limit is technically 70 mph, but they have been talking about raising it to 80 for so long, that it 'goes without saying' (or in this case without posting) The only posted speed signs I ever remember seeing from Vancouver to Seattle are those slow downs through Fife, Oympia and coming into Seattle, which people often exnore also.

A friend of mine was clocked at 102 mph and stopped. The trouper liked his car and gave him a ticket for 'exceeding the posted speed limit'! I was stopped once, quite a while ago, for doing 90+ on my motorcycle. The trouper who stopped me, checked me out, and told me to slow it down, at bit.

Rule of thumb here is to follow traffic. If it's moving at 80, do 80. 90 do 90. Also 'time and place' and the use of common sense, plays big. I'm knocking on wood here, but after 40 years of driving, I've only had 2 - 3 speeding tickets, and they were all over 25 years ago, and all when I lived in Canada.

Drive safe, but have fun!
Dave.

[micbrody]

Speedo cable is connected to a rotating shaft in speedometer. At the end of this shaft, is a bar with a magnet. This magnet spins inside of a magnetically sensitive metal drum that can turn, but is opposed by force of a spring loaded hair spring. The needle is attached to a shaft that is fixed to the other side of metal drum, the needle is affixed to end of shaft.
So when speedo cable spins, it spins the magnet inside of the metal drum. The metal drum "feels" the magnetic force and tries to rotate in the rotational direction of the spinning magnet. It only could go so far because of opposing hair spring force. So the greater the speed, the faster the magnet spins; the more the metal drum rotates; the more the fixed needle moves.

http://www.howacarworks.com/illustratio ... peedometer

Above is a general photo of this. I did unassemble ; clean; and re-assemble the fiat speedometer. Really works the same exact way. I have some photos; just not easy to put on this website.


Bottom line: it will not hurt speedometer to go past it's pegged upper limit

[Frog2Spider]

Thanks micbrody!

Dave

[PhillySpider]

If you add a 1.21 jigawatt battery....

[klweimer]

And a flux capacitor!

[Frog2Spider]

And a flux capacitor!

[DieselSpider]

Still by the book even when a 10% deviation is forgiven the max allowable in a 70 mph zone is only 77 mph. Washington State officially holds to a 70 mph max top speed on its interstates for cars and 60 for trucks so that is what the insurance and courts will be holding to in an accident judgment. Too bad enforcement has allowed scofflaws to get away with pushing the limit for so long that its become an expected allowance. We really need uniform enforcement across the country and people who are willing to obey the law even when there is a perceived low risk of being called to task for their disobedience. Sad commentary of the mindset(ethics) of drivers frequenting I5 if there are that many pushing things past 85 to make it the norm. Even if the posted was 80 the max tolerance lever should only be 85 to 88.

Regardless of the prevailing speed of traffic being pushed up by scofflaws and limits of your speedometer one has to be mindful that tire speed ratings are only for a 10 minute sprint and not a sustained speed. Truck tires for instance have a 75 mph max speed rating which means that they must be able to carry their rated load when the ambient temperature is 70 (maybe 75) degrees for 10 minutes at 75 mph before overheating. As tires age and wear or are patched the max safe speed declines. You really should not push even a 120 mph rated tire to a constant 90+ mph especially during the summer months.

The speedometer should not be harmed by moderate pegging but can get jammed up and require disassembly, cleaning and lubricating when pushed to extremes which it has not seen in a number of years. After mine was converted to diesel the speedometer was not connected for a number of years until the previous owner got it and while he found a cable to connect the Isuzu MSG5 transmission to the speedometer and had it working for a while its now stuck at 5 mph. I use a Garmin GPS as a speedometer now and have yet to vet out whats wrong with the 140 mph unit in the dash. I am under the impression that the connection at the speedometer was not as good a match as he believed it to be. A 1978 model year vehicle registered in Florida is odometer exempt so having the factory speedometer/odometer working is not much of an issue as long as you have some form or speedometer in the vehicle.