Speedo jumping

[chicken bones]

I know this has been a topic many time before but could not find my problem. So my truck is 1994 F 250 4x4 IDI factory Turbo 7.3 with auto Transmission. I have recently rebuilt POSM and replaced VSS sensor.The problem is when I start truck all is good , as soon as I touch the brake the speedo jumps around.It does not jump at all when moving only when stopped and foot on the brake.I was wondering if my trailer plug or trailer brake controller could have anything to do with this?

 

[Thewespaul]

Just had a thread on this, try lubricating the cable

 

[chicken bones]

I have no speedometer cable ?

 

[david85]

1992 and up don't have a spinning cable. It all comes off the ABS/VSS sensor on the rear differential. Bad trailer wiring and tail light harness have been known to cause problems on those later years of IDI trucks though (particularly those with E4OD automatic trans). Maybe try double checking your tail light grounds at the rear frame of the truck.

 

[Thewespaul]

Ah that’s right! As said check your lights, it affects the tranny through magic I can’t explain. Many members have reported that led lights can cause issues as well.

 

[chicken bones]

Thanks,I shall check the tail light ground and trailer plug while I'am at it.I have had the high cab mounted brake light mess with my E40D Transmission shifting before.Crazy how a light bulb can mess with your Transmission.

 

[snicklas]

The E4OD TECA passes a very low current signal through the brake light circuit. Not 100% sure why, but I know the brake lights being activated causes the torque converter to unlock (the hazards do this also, which lights the same filament in the bulb). The TECA is looking for this current, which is also affected by the resistance or lack of resistance from the bulbs. This is why a bad bulb, or LED bulbs can affect the transmission. I’ve even read people having the LED bulbs illuminated all the time because of the control current, which can be enough to light the low draw of an LED, but not a standard incondesent bulb.......

 

[chicken bones]

Bulbs are the first thing I check when the Transmission starts acting up. 390,000 KM on the original Transmission, change the fluids maybe 3 times that's it.Last service they told me it needed a rebuild because there was some fileings on the plug, that was 100,000 KM ago,still running strong.Wonder how many people have rebuilt their Transmission because of a brake light bulb .