nba1341

Hello I am trying to figure out what this line coming from the transmissions purpose is and why it connects to this black plastic triangle piece which is leaking from its screw on connects drops at a time. I tried tightening it but I thing I might need to get a new black piece but don't even know what it is? It comes out the side of the tranny then goes up through the firewall right under the brake booster and from there I am not sure where it goes.

Any help here are some pictures.

Jonk67

Pretty sure that's your speedometer cable but that black triangular box looks like a converter? not sure how to call it but it corrects the speedometer for changes of rear tire heights or non factory speedometers. Is your speedometer a factory one?

If the rear gears were changed, rear tires are much taller, etc. they may have installed it to get the speedo to read more correctly. Most people just change out the plastic gear at the end of the cable but maybe the changes were more drastic than standard gears could correct for.

It shouldn't be leaking unless it somehow uses trans fluid to lubricate, it'd have to creep up the cable to that converter though.

Give some more background > stock speedo?, rear gears, tire size? Maybe you can replace the whole shebang with a stock speedo cable and correct gear.
Jon

tx65coupe

I bet its the speedometer cable.

tx65coupe

I guess Jonk beat me to it.

JMD

That is often the problem when working around a problem instead of working through it.

Someone put the ratio converter in line to calibrate the speedo, with a little research and some math, putting the right gears in the tranny would eliminate the whole mess, and the parts will likely be a LOT cheaper than the converter.

Oh, there should be an o-ring around the shaft of the plastic gear to keep the tranny fluid from wicking up the cable, you can probably fix the leak by replacing the o-ring.

Gun Jam

Yeah it takes what...2 minutes to swap the gear

I guess an issue could arise if the rearend changed enough that the speedo drive gear could not longer be mated with a proper tooth count driven gear.

nba1341

I had my rear end gears changed to 3:80 years ago. They changed the gear in the speedometer gauge itself (that little plastic color gear). So would i be able to get the correct speed without that little box and just a different tooth gear? Also why would the speedo cable have fluid coming out of it anyways how does it work?

I dont have to change my speedo drive gear do I? Thats in the transmission (in tailshaft?) itself isnt it?

When it comes to transmissions this is new to me sorry for the stupidity.

Jonk67

As JMD said you may be able to just change the speedo cable gear, yes it's in the trans tail but easy to remove, just one screw clamping it in and a C clip takes it off. Also as JMD noted the fluid is probably from trans fluid wicking up the inner cable to the converter and leaking through a dried out/split o-ring.

You have 2 choices, replace the o-ring and leave it as is and see if that fixes it or first do some math with your 3.80:1 gear and whatever tooth gear is driving your speedo gear (from reading C4's could have 7,8 or 9 tooth drive gear) and tire diameter.

Here's a calc. to figure out the gear you need (one of many) http://www.tciauto.com/Products/Tech...eedo_gears.asp
From looking at the chart near the bottom here:
http://www.tciauto.com/Products/Comp...gears.asp#ford

If you go this route I'd try a 21 tooth and see how close you get and if it's still off step up to a 23 tooth, however there is a footnote on the 23 >
"1 This is a retrofit gear to allow the speedometer to function with 3.73 and 4.10 rear end gears. Since the gear tooth pitch is slightly different than OE, the service life of this gear is limited to less than 25,000 miles."

Jon

2+2GT

Not gonna happen. The C4 drive gear is machined into the shaft itself.