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My HUD display for my 94 SSEi gives me two different speeds...at 35 on the dash, I show around 38 on the HUD, and it climbs from there. My question is, which friggen one do I believe? At 70, the difference is almost 8 MPH, definately enough to get a ticket with. Any information would be greatly appreciated.

My Cutlasses with HUD did that too...Very weird.

I read an artical once reveiwing the SSEi, it said that there was a differeance in the HUD to the speedo, it said there testing showed the HUD to be the correct one...



however this doesn't mean thats the case for your car..

do you have a GPS devide to compare to? or one of those permanent speed signs?

The HUD is less likely to be wrong. It reads the signal and displays it electronically, very few things that can be thrown off there. The speedo, OTOH, has mechanical elements than can be thrown off after years of bouncing over rough roads, or could even be assembled wrong in the first place.
Go with the HUD reading.

If you really feel paranoid, find a radar trailer and buzz it. (Make sure it's not a ticket camera, first, obviously...) Go with whichever is closer to the trailer's display.

The HUD can't be more than 1-2mph off at 65mph by the way it works. That signal is coming from the reluctor wheel which is part of the differential. It counts pulses per mile and displays them in their pure form.

The speedo is electro-mechanical. It has loss, as well as drag.

jstpsntym on the old forum had a very good procedure for calibrating the two that he shared with amy_lynn:


1. Speed up the car until you reach a speed that shows the HUD faster than the speedo.
2. Roll down your window.
3. Reach around in front of the windshield (you need long arms for this or some help through the sunroof), and grab the green numbers floating in front of the car.
4. Hold onto the numbers until the speedo catches up with the HUD, then let go of the HUD numbers.

This works better when it's not raining. The hud numbers get really slippery and hard to hold onto when they're wet (my own little personal observation).

Seriously, the HUD is correct, the speedo typically lags behind, especially during quick accelleration.

willwren wrote:

jstpsntym on the old forum had a very good procedure for calibrating the two that he shared with amy_lynn:


1. Speed up the car until you reach a speed that shows the HUD faster than the speedo.
2. Roll down your window.
3. Reach around in front of the windshield (you need long arms for this or some help through the sunroof), and grab the green numbers floating in front of the car.
4. Hold onto the numbers until the speedo catches up with the HUD, then let go of the HUD numbers.

This works better when it's not raining. The hud numbers get really slippery and hard to hold onto when they're wet (my own little personal observation).

Could I add a HUD to my non-HUD'd car by following the above procedure? I could just borrow someone's car that has one, and steal it.

TenGHz wrote:Could I add a HUD to my non-HUD'd car by following the above procedure? I could just borrow someone's car that has one, and steal it.

ROTFLMAO

The Hud will be electronically correct given the sensors and wiring is fine. But unless you have the exact height tires that the factory equipped, it may be off.

i would go with whatever one is higher then the other, then you know your either doing the right speed limit or below it

I think I recall reading a TSB about the difference between the HUD and the speedo.

mine are pretty close, but i can tell the HUD is faster to respond, due to facts stated above. I would trust the HUD, esp if it is higher, b/c then you are doing the speed limit or under, as stated above

willwren wrote:The HUD can't be more than 1-2mph off at 65mph by the way it works. That signal is coming from the reluctor wheel which is part of the differential. It counts pulses per mile and displays them in their pure form.

The speedo is electro-mechanical. It has loss, as well as drag.

jstpsntym on the old forum had a very good procedure for calibrating the two that he shared with amy_lynn:


1. Speed up the car until you reach a speed that shows the HUD faster than the speedo.
2. Roll down your window.
3. Reach around in front of the windshield (you need long arms for this or some help through the sunroof), and grab the green numbers floating in front of the car.
4. Hold onto the numbers until the speedo catches up with the HUD, then let go of the HUD numbers.

This works better when it's not raining. The hud numbers get really slippery and hard to hold onto when they're wet (my own little personal observation).

Seriously, the HUD is correct, the speedo typically lags behind, especially during quick accelleration.

*dang*, those are slippery little buggers!!! Will have to try again another time when sleet is not hitting me in the face.

Tried again, this time I got them. Only ran over one nun, two dogs and three cats, and I think a VW bug, but I have a problem, so now what do I do when the little green numbers come off in my hand, Bill?

Seriously though, thank you all for the help. I was always going with the HUD because it does read faster, just to be safe, but I thought I would find out from the *ahem* experts. to you!

Of course, if you want to sort-of "test" how accurate either is, you could find a stretch of roadway, set the cruise control to 60 MPH (according to the HUD or the speedo), and then using a stopwatch or other timing device, see how long it takes you to get from one mile marker to the next. In theory, if the mile markes are accurately placed, at exactly 60 MPH, it should take you 60 seconds between mile markers. Even if they are not totally accurate, it is probably close enough to tell you whether the HUD or Speedo is the more accurate of the two.

My hands are usually too slippery with grease to grab the green digits floating in the air in front of the car. Besides, they get angry when molested like that, start picketting the dashboard, flicking bugs at your back, etc.

Meanwhile, back in the real world....

I used to do the measured mile/stopwatch thing. Now I'm just lazy and use a hand-held GPS. Find a stretch of road, set cruise control, then compare the GPS velocity to the speedometer. If both are off, you can alter the multipliers in the ECM to correct the electric speedometer to match actual speed.

Differences in speedo's

NICE title BTW

Doesn't anyone else see the humor?

not till you mentioned it O.o

ROTFLMAO, now i see it, i don't have that dirty of a mind, geez