[jiffy53]

69 XR7 351w 4v FMX. Can I convert the stock rear end to posi-traction? If so, is there a kit available? Or is it better to just buy a posi rear end?

As I have stated before, I'm not an experienced mechanic, but I'll try anything once, I'm willing to learn, and not afraid to ask dumb questions!

Thanks.

Jeff

 

[dfwcatsclub]

Yes you can convert. A new posi is available from several sources. You would have to tear down the existing "pumpkin" (gears+differential) and put the posi in.
It might be simpler to buy a complete pumpkin from a reliable source.

To do it yourself requires a quite a few steps and a lot of tools. And of course a shop manual.

 

[Bad69cat]

rear gears are kinda tough to set them up properly and not very forgiving if you don't. Shouldn't be to hard to find another setup reasonable - just know what gear ratio you want and start hunting. I have seen quite a few pop up on CL as of late.

 

[jiffy53]

Thanks guys. Sometimes there is a fine line between being brave enough to try something new, and being stupid enough to do something beyond your own skill level! I'll start shopping for a posi rear end.

Jeff

 

[wonderwrench]

Thanks guys. Sometimes there is a fine line between being brave enough to try something new, and being stupid enough to do something beyond your own skill level! I'll start shopping for a posi rear end.

Jeff

+100, Diff setup is an art. I have been in the automotive field for over 30 years and many claim to have the skill to properly set one up but few get it right. Most drive line shops are a fail.
Years ago I found an old guy that built pulling and monster truck drive lines. He rebuilt the diff in my fathers 63 Fairlane wagon. The result was totally silent under all conditions which is near impossible in a wagon as they have little or no sound deadening and act like a speaker. I need to pull the diff out of my 67 standard as it has gear whine under light loading between 30 and 40 mph. It had this problem since new and the dealer went though the diff under warranty. Still made noise afterward. I would guess the old guy is no longer with us so I have no clue where to go. Note if you are going to be pounding on your car I'd go with a Detroit locker. A limited slip diff will fail at some point. Might take a few years depending but I have seen limited slip diff's burn up in a single weekend at the strip.

Bill

 

[cj750]

I'll second the Detroit Locker suggestion. I've had one for several years in my '69; it works as advertised and has been totally reliable. Be aware that with no clutches to soften things, you can sometimes feel and hear the locker working as you back up or go around corners. Its not really harsh or noisy, but something to be aware of. Likewise, the car will handle a bit differently, since the inside rear wheel no longer slows down when negotiating corners (the outside wheel has to speed up, to provide differential action.) Again, not really a problem, just something to get used to.
BTW, "positraction" and "posi" are GM words. The generic terms are "limited slip" or "locking differential." "Traction-lok" is Ford speak for the same thing.
Lastly, NASCAR teams sometimes sell their used Detroit Lockers (as well as 9" ring and pinion gears) on eBay at reasonable prices. They're usually 31-spline units though, and its also important to get one with the correct bearing size for your housing. But if you do your homework, you might find a bargain.

 

[wonderwrench]

I'll second the Detroit Locker suggestion. I've had one for several years in my '69; it works as advertised and has been totally reliable. Be aware that with no clutches to soften things, you can sometimes feel and hear the locker working as you back up or go around corners. Its not really harsh or noisy, but something to be aware of. Likewise, the car will handle a bit differently, since the inside rear wheel no longer slows down when negotiating corners (the outside wheel has to speed up, to provide differential action.) Again, not really a problem, just something to get used to.
BTW, "positraction" and "posi" are GM words. The generic terms are "limited slip" or "locking differential." "Traction-lok" is Ford speak for the same thing.
Lastly, NASCAR teams sometimes sell their used Detroit Lockers (as well as 9" ring and pinion gears) on eBay at reasonable prices. They're usually 31-spline units though, and its also important to get one with the correct bearing size for your housing. But if you do your homework, you might find a bargain.

Cant leave out MOPARS SureGrip!

Bill