Diff help!

I just dropped the 302 swap into my 70 Maverick! I have only driven it around the parking lot because it is open headers until this weekend when I can get the exhause fabbed up. My question is about the rear end. Did all the Mavericks with I6's come with a small (approx. 7.7in.) rear end? And if so, how long will this rear end hold up under the new 302's power?

Is it a must to add on a 9in. rear end, or will a 8.8 be good enough. I am wanting to go 5 lug, but am a bit lost when it comes to rears

Thanks in advance!!

 

I don't know much about the smallest Mav rears.
However my gut says it won't last long.
I6 Mavs were also equipped with 8" rears.
The early ones are small bearing/4 lugs, later the all went 5 lug/8" rears. I think 74 and later all had 5 lug/8".
An 8" is not a very tough rear, but it can handle a mild 302/C4 combo.
If you run a radical 302, stall converter, or manual tranny, you are better off with a 9".
8.8" rears can be made to fit with lots of work, but they are heavy and not quite as strong as a 9". Not as strong as an 8" IMO if they still have c-clips.
Dave

 

i have heard a lot of people running into the 12's with a 8inch rear end without problems.... and using a posi with 411 gears... so yes... 8 inch will work fine up to about 350-400 HP.. once you get in that range of 350-400 i would highly suggest a 9inch... but thats getting down into the 10's yeah, at those speeds, 9inch is a smart investment

i have a 170 mav that has 4 lug axles (not sure of its a 8", but it doenst have a rear cover so i am failry certain its an 8") and i did the 302 swap and i have been hard on my car... launching, burnouts, etc... and it has held up fine so far...i have an 8" with 5 lugs in my backyard waiting for the funds... and i wil posi that one... although my friend wants me to weld the spider gears so its a cheap posi for now, and then when that lets go , go get a posi to put in it... i am not so sure i want to do that...

 

It depends on how much power your 302 is putting out, the rearend gears your running, & maybe how you drive it. Maybe the type of trans. you use but I'n not sure on that one. I have a 302/C4 combo with 3.55 gears & Auburn posi., 2500 stall but I might be around 275 - 300hp. It works fine for now. I have the factory 8 inch.

 

I run an 8" with a powertrax unit, 4.11's, 3000 stall, funny gas and sticky tires, no problems.

 

The 7.5 rear was only in the very early 70 Mavericks. It is left over from the Falcons and will not hold up to any power. Funny thing though, Ford Motorsports carries a trac-loc carrier for the 7.5 but not for the 8. Go figure.

 

I ran the 7.5 with the first transplant. I had no money to upgrade and the car was a 2 barrel with a rv cam. Lasted a few months of my attempts at smoking the tires before the spider gear climbed outside the case! Made quite a mess...

 

I never had any kind of luck with 8" rears.
I guess I am the minority though.
Dave

 

IF it's an 8" (no cover on the rear, dropout center section) it will put up with a LOT of abuse. Dad and I ran one for years with only one failure. Only reason I went to a 9" was due to gear selection.

If it's a 7.5, you'll be surprised how much punishment they will take. They won't last forever, but they do hold up quite well considering their bad reputation. Kind of like fishing; some folks can catch 40 lb trout on 4 lb line, others can't catch small crappie on 20 lb line.

 

Yeah, that pisses me off too!

 

Thanks for all the info guys, I'll double check to make sure what the rear is EXACTLY.

 

I have a 8" with 4.11's. I run 12.40's on funny gas with slicks and have had only one failure and it was my own fault. However with my new 408 I will be going to a 9".

 

This thread is 3 years old. But I do agree, 408 needs a 9".

 

My guess would be for the '79 to '85ish Mustangs that used a 7.5

 

the small diff with a cover in the mav is actuly a 7.25. the 7.5 came around in the 80s. it replaced the 8". it was used and still is used in mustangs, and rangers.