How Fast am I going?

[Shadowman]

Over the weekend we took a trip South. I was so excited to see the difference the new Banks system had on maintaining my speed and getting up over some of the mountain passes.

Things were going great, the coach was running like a champ, as we were getting through a construction zone I looked down to check my speed and I was doing 90 MPH. Out of instinct, I took my foot off the pedal and watched the speedometer back down to 70, however, I noticed everyone passing me liike I was standing still, so I sped up a little and within a snap of a finger I went from 70 to 95 MPH, I had the needle buried.  Knowing something was not right I backed off again and the needle on the speedometer went crazy, bouncing from  95 to 50 and back up again. Luckily I had my GPS and was able to use that as my speedometer for the rest of the trip.

So can anyone tell me what I should be looking for? I pulled the dash when we got to camp, thinking I can shoot some WD40 down the cable and free it up a bit, but I looked and NO CABLE and do you know how hard it is to put WD40 down a wire?  I obviously have an electrical issue. I know the wealth of knowledge here is tremendous, so before I start making appts at the auto shop, I thought I would check here first.  I'm sure it's a bad modul somewhere, but is it on the transmission or engine.  Also, the speedometer tended to act more as a tach, cause as the RPMS went up, so did the speed? 

Any assistance anyone can provide would be greatly appreciated. My coach is a 1995 Coachmen with a 454 on a P30 Chasis? If more info is needed I can provide.

Thanks as always for all your help.

 

[Dan Walters]

I had that same thing happen to me on my 1998 Allegro MH.  The problem with the speedometer was a bad chassis battery.  My speedometer is electronic and the bad battery caused it to display erroneous readings.  It would register 15 MPH when I was sitting still and peg out at 95 MPH when I was only going about 50 MPH.  When I replaced the chassis battery, that cured the speedometer problems.  In one of your other posts, it sounded like you were having battery troubles and that could be your problem with this as well.

Dan

 

[John From Detroit]

There are a couple of different types of speedometers, Today many companies use electronic as, well, it's easier to install,  Older ones use cables.

If yours uses a cable you can try lubrication but once it starts binding, replacement of the cable is the approved repair, note, approved means you might get by with lubrication.

Or, just buy a GPS, it comes with a built in speedometer as a bonus, and it is very, very, very accurate in the speedometer mode

Do get the one on the dash fixed though

 

[Karl]

Question: Are you experiencing any other electrical problems/anomalies - like the headlights getting brighter with higher engine speed, then going dimmer at idle? Tune your radio to AM, but not on a station. Hear any high-pitched, whiney noises that change with engine speed?

 

[Shadowman]

Thanks guys for the replies. Yes the speedometer is electronic.

Dan, I hope you hit the nail on the head. Your right I am having battery problems. Took the alternator out and took it to Checker they confirmed that it was bad, so I'm replacing it tomorrow (they gave me the wrong one tonight).  So, hopefully I can cure both problems with one shot. I did buy a new Speedometer sensor that goes in the tranny, but based on your feedback I'm going to hold off and see if it was the battery. If so I can take it back and spend that $20 on something else.

Thanks again for all the help, I can always count on the quality of experience here. I'll let you know what I find out.

 

[Karl]

Over the years, I can count on one finger the number of times I've heard that the Hall-effect sensor has gone bad. ;D

 

[summerwinds48]

My MH is a 1994, P30 Chev. Itasca.  Had lots of experience with fixing the electronic speedometer problem on my rig.  First problem was noticed when the speedometer started zooming to 90 when I was only going 45.  The odometer was also double timing.  The worst part was that my engine would idle down when the speedometer hit 95 and I was going 47.  Very frustrating, not being able to go faster than 47. 

Rather than spend hundreds of dollars at a speedometer shop (they would start with the whole dash module and go backwards), I researched everywhere online, and found that it could be the speed sensor on the rear of the transmission.  There are two down there, one for the speed output and the other is ABS.  Replaced them both, but didn't solve the problem.  The old units were causing intermittent speed readings after about 10 miles, but the new one was consistently showing 90 mph right from the start.

Well, I read the P30 manuel and found that an electronic buffer existed between the sensor and the engine computer.  Located the buffer, a small white plastic box under the dash.  It's an integrated circuit that divides the sensor signal to the correct pulse then sends a signal on to the computer module.  It's an electronic version of the gears on  cable systems.  The correct operation of this system is important because the transmission shifting relies on the speed signal for shifting, and torque control.  If disconnected, the transmission won't shift out of first gear.

Found part numbers on the module, and called Delco.  They referred me to an aftermarket company located in Tampa for that part, called Technicar.  It's actually a GM owned company.  The part was $70, and easy to install.  Only two connectors, a mounting screw, and it's done.  The battery should have been disconnected and reconnected when ready to start up for a test drive, to reset the computer.  Wahoo!  It worked, and my speed/odometer was right on the mark, according to my Garmin gps and no more shutting down at 47 mph.

Hope this information helps someone out there with a P30 chevy MH.
Deen