67 sports sprint 289, C4. Factory. No tag. HOW can I MEASURE something on the rear to confirm that I have a 9 inch?? I want to put in traction lok rear, and need to know FOR SURE it's a 9 inch!!

 

Two quick ways. The bolts on the 8" can be turned with an extension on a ratchet and they go straight on, whereas the 9" has a bolt that you have to use a knuckle to get it off. Also, from 1967 on, the 9" had a hump in the middle of it for the ring gear to clear.



Here is some more information for ya.
http://www.maliburacing.com/ford_9_i..._nine_inch.htm

 

WOW! That was just what I needed. I defintely have the hump on mine. I'm going to get the "8.8 inch" 28 spline traction-lok rear from a seller on ebay. Supposed to be NEW ford product for about $215 Is this price reasonable? Will I need any other parts to do the job? (or have it done for me...)

 

??? The 8.8" is a totally different rearend. Installing one in a Mustang is involved
Is the length of the differential the same as yours?
Does it have spring perches?
Are they the right distance apart?
Will the yoke match up to your drive shaft?
What about brakes?
etc., etc.,

The right 8.8" can be put in a mustang but it's not a drop in deal.

 

You misunderstood. I'm just wanting to replace the standard diff with a traction-lok pumpkin. I will have it done by a pro who sets up rear ends for a living... I know better than to mess with adjusting gear lash and all that stuff!! So if I have a 9 inch rear, I should look for a 9 inch traction-lok? I thought "9 inch" was just a slang term for anything close in size... a hot rodder freind said the 8.8 inch traction-loc would fit in the 9 inch rear that's on the car, and I don't know enough to question this logic.

 

OK, I also thought you were wanting to put a complete 8.8 rear and axles on, and I was just wondering why you were asking about if you have a 9" or not. If your 9" is presently an open rear, you can upgrade that 9" to put in traction lock gears with clutches, etc. Have you researched enough to know that the 8.8 gears with the traction lock will work in the 9" rear? Is there any advantage the 8.8 traction lock offers that the 9" traction lock doesn't? I guess if your mechanic says it will work, then you have an obligation to post the resusts here so we old classic guys can have that info. Good luck to ya.

 

The 8.8 does not have a pumpkin, it has a rear plate. Maybe the traction lock unit would from a 8.8 will fit a 9", but I would be suprised.
Some good rear end reading
http://www.hotrod.com/techarticles/48618/

 

OK. I've figured out I have a 9 inch rear. I've also discovered that I can purchase a "Third Member" all set up in any gear ratio I want, with the posi unit installed. If I'm reading all this stuff correctly, all I need is to bolt this new unit in, fill the axle with the right lube and additive, and I'm back to driving with both wheels hooking up at lauch. Do I have this right? Sounds like this is the way to go - I'm either going to pay somebody to do the posi setup locally, or I can just buy it all ready to go with a 1 year guarantee. Sounds like the "ready to go" route is the way to go... no?

 

Just having the hump does not mean it's a 9:. Check the bolts as Soaring mentioned. That car did not come with a nine unless it had a big block or 289 HiPo. If it is a 9", it was swapped in somewhere along the line.

 

OK, now I'm really confused. the 10 bolts that hold the 3rd member in all seem to be straight in and easily accessible. The axle housings DON'T taper, and the axles are 28 spline and appear to be really robust. Here's a picture of the actual rear in the car. Hope this can help figure this out. I checked the ratio by turning the driveshaft, and it appears to be just under 3.00 - probably 2.79, 2.80 or 2.83. I've read all the links you guys gave, and none of them show MY rear exactly... I hope the picture will help.

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