Mustangs of Illinois

i currently have a 3.0-1 rear end and plan on changing it to a 3.55-1 ratio. To keep my speedometer reading correctly what is necessary ?

Mustangdemon67

All you need to do is pop out the Speedo cable from the transmission tail shaft housing and you 'll see a plastic gear on the end of the cable. There's a retaining ring that holds it on. Replace that gear with the proper one for your tires size / gear ratio. If you Google Speedo gear calculator, you can enter some info and it'll tell you what tooth count gear you need for your cable. off the top of my head I THINK you 'll need the black 20 tooth gear. Find that calculator online though and you 'll be set.

creaky

This video shows how to calculate which gear is needed.

http://www.cjponyparts.com/speedomet...sion/p/HW1290/

bop11

You need to match the gear on the end of the speedo cable with the one on the tail shaft. You can't change only one. To change the one on the tail shaft you need to drop the drive shaft (4nuts on universal joint at rear) and pull it out. Then remove shift linkage from tail shaft housing, remove housing (4 bolts up front). You may have to drop the exhaust to do this in some cases. The drive gear on the tail shaft is held on by a C-ring and there is a ball bearing that goes into a hole in the shaft that actually drives the gear. Don't lose the ball. You need the drive and driven gear set, a new ball if you lost the old one, a gasket set for the front of the housing and while you have it off you might want to replace the bushing and the seal at the back of the housing. at least do the seal. Replacement is the reverse of taking it out.
Oh, I forgot drain the transmission oil first and replace it after. This is easiest done on a lift and would cost about $250 from a shop plus about $30 for parts. Takes a good shop 2 hours.

69mach1377

^ I don't think all that is needed. He may just need a plastic gear with one more or less teeth on it than what it has now.

Starfury

You're both right. At the end of the day, it depends on the ratio needed. You need to take a look at both to see what colors (and therefore teeth count) gears you currently have, then see if you can achieve the desired ratio with just a speedo gear change. If you can't, you'll need to change the output shaft gear as well.

I don't believe there's a wide enough selection of either gear in our case to cause any mesh problems between gears, but you may check with a drivetrain specialist shop (or a place like David Kees) to make sure.

bop11

I see Mustangbarn has available a whole series of drive and driven gears as do many other suppliers. and different driven gears can be used with the a single drive gear.

Mustangs of Illinois

The second link, will work great !
I can get the color of the driven gear, look it up on the chart to see which drive gear it would be. Then figure out which driven gear I need


Thanks, that is exactly what I needed !

Chances are it is a 18t and I need a 20 t