OT - 8" 3rd member compatibility

[sargentrs]

Need some advice guys. My daily driver is a '64 Fairlane 500 with an 8" rear end. Pinion bearings bad and can't afford a full rebuild right now and not comfortable with my skills to rebuild it right. Having trouble finding any Fairlane rear ends out there but finding quite a few 1st gen Mustang parts. Is the 8" Mustang 3rd member the same as for my Fairlane? Any and all input is greatly appreciated!

[ultraranger]

An 8-inch 3rd member is much like a 9-inch 3rd member in that any 8-inch 3rd member will fit any 8-inch rear end housing.

Any 9-inch 3rd member (car or truck) will fit any 9-inch housing, so long as the axle gear splines of the 3rd member match the splines of the axles --9-inch could have either 28 or 31-splines. 8-inch only came with 28-spline axles.

In the case of an 8-inch, it's best to stay away from '62-'66 3rd members. Beginning in '67 ('67-'80), Ford revised the 8-inch 3rd member to have more ribbing on the face of the casting (structurally stronger than '62-'66 castings). These were the C7OW castings.

The 8-inch rear end was a passenger car rear end and as such, there generally weren't many low ratios in them. The primary ratios you will find in them will be 2.79, 2.80 and 3.00:1. There was a 3.50 and a 3.80:1 ratio available in them but, those are few and far between.

If you can find a Mustang II or Pinto, some of them came with a 3.40 or 3.55:1 8-inch ratio, if you were looking for something a little lower geared.

[Ranchero50]

Ditto, should be a direct swap with any other 8" rear.

[sargentrs]

I haven't check the tag to see what the original gear ratio is but I believe it's in the lower range, like 2.73 or maybe the 2.78 that ultraranger referred to. While I wouldn't mind going up a 3.25 or even 3.50, right now I just need a chunk to get back on the road. Being my DD, and a 4 door, with the LoPo 289 and Cruise-o-Matic 3 speed auto, she's not exactly a burnout queen. Here's a pic. I've only had her 6 months but it's a great car. Thanks for the info, guys!

[Ranchero50]

I like the 2.73's in my '68 fastback. It gets 20+mpg with a stock 289/c4 combo. I have 3.50's in the ranchero with a traction lock and it's held up to that duty. I used to have some 4.10's floating around from a Mustang 2 but I think they are gone.

[sargentrs]

I believe mine are the 2.73's, Jamie. They're perfectly fine for what I use her for, which is a work car and occasional trip up town. She's not going to win any drag races and she's actually pretty peppy. I've had her cruising the highway at 80mph and she didn't even stutter. I don't believe I need anything more than 3.25 and 4.10's definitely way out of the ball park. I've located a rebuilt rear end in Sharpsburg with 3.00's and have another line on one with 3.25's up in Blue Ridge. Both in the $200 or less range. Thanks for all the help guys!

[ultraranger]

2.73 is a much later Ford 7.5" or 8.8" rear end ratio (non-removable 3rd member). I had 2.73s in the 8.8" rear ends in both my '89 and '90 model 5.0L Mustang GTs.

If you have an 8-inch rear end and it has a 2-point-seven-anything ratio, it will be a 2.79, which is what ratio my '68 Mustang originally had in it before I replaced the rear end with a 9-inch.

With the 3rd member out of the housing, the quickest way to know what ratio you have is to count the ring gear teeth and the pinion gear teeth. Divide the number of ring gear teeth by the number of pinion gear teeth and you'll have your gear ratio.

A 2.79 ratio will have 39 ring gear teeth and 14 pinion gear teeth.

[sargentrs]

Thanks for the info, Steve! When I get it out I'll check and see for sure.

[PetesPonies]

2.80s and 3.00s were very popular in Mustangs and such.

[sargentrs]

Thanks Pete!

[sargentrs]

Not having much luck finding anything in "plug n play" condition. Either going to have to spend the money or try to rebuild it myself. I'd really like to go ahead and get this Quick Performance unit with 3.25 gears http://www.quickperformance.com/Ford-8- ... _p_39.html Also found this (supposedly) NOS unit on EvilBoy http://www.ebay.com/itm/FORD-8-Rear-End ... Tw&vxp=mtr I feel confident in my ability to disassemble and reassemble my original, it's just the setting up of the gears and shimming that I'm unsure of. It's not really something I'd feel good about as in "I think I can get it right". As a friend of mine said it's an "expensive thought" About $250 in parts and rebuild it myself, the $400 Ebay unit or the $600 Quick Performance unit? What do you think, guys? I need to make a decision this weekend.

[PetesPonies]

If you go to the Mustang sites, forums, you should find plenty of people who took out their 2.80s and 3.00s and they are sitting around the garage. That being said, a 3.25 is a good choice.

[sargentrs]

Thanks for the advice, Pete!

[PetesPonies]

http://forums.vintage-mustang.com/

[sargentrs]

Thanks for the link, Pete!