My Daily Drive is an 84 B II 2.8 V6 Auto. I think the Auto is a C5. Recently my speedometer did the "Exorcist". When I accelerate to 10 Kph the Speedo jumps to 50, at 30 Kph Speedo reads 80, at 70 Kph the Speedo is reading 120 anything over that is registered as maximum. I checked the cable & connections, checked the Tranny fluid level; which was about a litre low, but a clean strawberry red and free of odor. I added 1 Litre of ESP-M2C166-H Oil that my dipstick specified as the only oil to add, but it didn't fix the speedo problem. It did however change the colour to amber and it now smells like burned toast. I realize that I have probably put an improper oil into this tranny but, it was the exact spec on the dipstick.
Is it possible to flush the tranny and replace the fluiid? what is the correct fluid? Who let the Ford Engineers out of their asylum long enough to design multiple tranny failures? (Answer= ACCOUNTANTS).
Going by the "Ford Transmission Spotter's Guide" I have the dreaded C5 Tranny, could being a litre low on fluid hoop my speedo? Similar to an air or vapor lock? Like having the drive spline & gear cavitate because of lack of liquid in the drive chamber?
The Truck and tranny are running great! No shifting problems, no noise & no heat. Just the busted Speedo.
What should I do besides buy a new truck?
JK

 

Usually on older models, before speed sensors, the speedo cable was gear driven. If the gear is broken or missing teeth it can give erratic readings. If the cable itself is not well lubricated, the speedo can jump. If the cable is broken, it might jump or cause really weird readings, or none at all.

It is also possible that the speedo itself has problems. The internal gears my be broken or slipping on their shafts. Or maybe the magnet inside the speedo has gotten weak or out of alignment. You can sometimes fix these problems by yourself , but getting the calibration correct is trial and error. I am not sure it is legal to mess with the insides of your speedo, I have done it long ago since I was Po, and needed a fix cheap. So you my be better of taking he speedo to a speedo shop.

As far as the tranny goes, burnt smell is not good. I would quickly drop the pan, inspect for problems and fluch the torque converter and cooler and then refil with fresh fluid per specification in your manual. I do not know what type of fluid you have nor the type called out on the dipstick so make sure you know what is correct for your tranny.

Good Luck,

Jim Henderson

 

Thanks, I'll have the Tranny serviced this week and check the gears @ that end and the cable. If it isn't that I'll get another Speedo from Ford.