Possessed Speedometer

[jhenegh]

How are the Brakes and Speedometer related?

1994 F250 in my signature:

My speedometer will randomly jump right up to 10MPH sometimes when at a stop or shifting from P to R or D (also when stopped). IT ONLY DOES IT WHEN THE BRAKES ARE APPLIED. Functions fine once the wheels are rolling again.

Speed sensor in rear axle is new Raybestos 10 days ago. Replaced due to these observations.

Thanks for any ideas!

 

[slim072590]

Subscribing to this.. my speedo bounces about 20 mph difference above 30 mph (30-50mph).. the damn thing is real bad, haha

good luck, lol

 

[jhenegh]

Brake pedal and Speedometer interaction!?

Lets try this:

http://www.youtube.com/watch?v=_GcgwNSMfUc

So in that video you can see the needle going up to 10 mph and back down. Every time is went up is when I'd hit the brakes. When I let off, it returns back to 0. Truck never moved the whole time.

 

[OLDBULL8]

THIS VIDEO IS UNAVAILABLE. Take the lens cap off.

 

[franklin2]

Subscribing to this.. my speedo bounces about 20 mph difference above 30 mph (30-50mph).. the damn thing is real bad, haha

good luck, lol

Are you waiting for some advice on your 87? If so, it's a different animal. It has a mechanical speedo with a cable that spins inside a flexible tube. The OP has a electronic speedo.

To the original poster, I would check the battery voltage at idle. Low voltage can cause cluster problems.

 

[jhenegh]

Video seems to be working through both Oilburners and Youtube...

The speedometer only does this when the brakes are applied. How are they connected?

 

[OLDBULL8]

Does the speedo stay at 10 if you hold the brakes on. Check the wiring around the brake peddle under the dash, might have a bare wire and just making contact momentarilley.

 

[slim072590]

Well what do you know, haha..
damn thing surprises me every day, lol

Sent from my C811 4G using Tapatalk

 

[jhenegh]

Does the speedo stay at 10 if you hold the brakes on. Check the wiring around the brake peddle under the dash, might have a bare wire and just making contact momentarilley.

Yep. Hold the brakes on it stays at 10. It doesn't always do it, but it was being very consistent that night when I took the video

 

[icanfixall]

I'm betting somehow there is a grounding issue. But please for heavens sake.. turn off the left blinker.. Thats enough to drive me nuts. Whats worse is to see some fool driving down the freeway with their hazard lits flashing going 70 mph or faster. Seen that so many times and other drivers are afraid to pass them. Never an officer round when you need one..

 

[franklin2]

Yep. Hold the brakes on it stays at 10. It doesn't always do it, but it was being very consistent that night when I took the video

With it in neutral, hold the brake down with your left foot so the speedo fails. Then take your right foot and rev the engine. If it still is failing, then that will blow my theory out of the water.

 

[jhenegh]

I'm betting somehow there is a grounding issue. But please for heavens sake.. turn off the left blinker.. Thats enough to drive me nuts. :

Haha I took that video stiiting at an intersection about to turn left. I was the middle of the night wiith nobody else out on the road while I was out snowplowing so I waited through a light cycle while I shot the video since it was consistently reproducing the issue.

I'll check under dash wiring for chafed wires etc. Any idea where the dash ground is?