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7.25 rear end

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65-coupe
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Posts: 378
Joined: Sat Aug 13, 2011 10:43 pm
Location: Lakeland Fl

7.25 rear end

Post #1 by 65-coupe » Wed Sep 14, 2011 10:06 pm

How much HP can a my original 7.25 rear end handle. I plan on change to a alum head and intake from classic inlines and a new cam. Just want to make sure I can keep what I have. I do have a second 7.25 rear end in really good shape.
1965 Mustang coupe, SPI Orange with custom TMI interior, 250 DUI, CI alum head ported, 274/274 110 Clay Smith cam, 1.65 roller rockers, Holley 390 4bbl, Lokar pedals and throttle calbe. Street or track front coilovers suspension, CI headers stainless with Jet-Hot ceramic coating, CI Stainless 2" impostor dual exhaust, 17x8 Coys C-67 wheels,

CZLN6
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Re: 7.25 rear end

Post #2 by CZLN6 » Tue Sep 27, 2011 10:04 am

Howdy 65-coupe:

The 7.25" rear-ends are fairly robust for their small size and light weight. And they were changed and upgraded over their manufacturing life time. '65 and later units were better than earlier ones. The critical abuse is not the amount of HP up front, but the way it is applied to the differential. I don't recall ever seeing an hp rating for this rear-end. The critical abuse is most likely dead stop burnouts with wider, sticky rubber. The typical demise of the 7.25" rears is a slow and increasingly noisy one. They will start to hum, then growl and eventually let go at the least opportune time. pinion bearings and differential gears are more likely to go then the axle bearings. You can help it live by making sure the gear lube in it is fresh and up to the proper level. Also avoid burnouts. Since you have two units, go ahead and use them up. Once your new engine is in place it may be time to step up to an 8" then let the abuse begin.

Adios, David
co-author of the Falcon Performance Handbook
http://www.falcon6handbook.com/

MPGmustang
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Joined: Fri Jan 09, 2009 10:23 pm
Location: Chandler AZ

Re: 7.25 rear end

Post #3 by MPGmustang » Tue Sep 27, 2011 12:19 pm

I agree with the rear axel hum'n... my is (good thing I found a 4 lug 8 inch :D ) the proper level of fluid helps alot, my pinion is leaking but I suspect from the 60+ dyno pulls I've ran to tune and try different things.

I think they can handle quite a bit before total catastrophe, mine is only showing some failure in the pinion except the axel bearing I spun a few years back. and I'm pushing 136hp to the tires... maybe more if I replaced it...

for now, blow up the 7's it's a cheaper learning curve than an 8 inch, but I doubt the 8 will blow up behind our sixes... unless forced :twisted:

anyways, IMHO, build the car from the gound up, then go for the power plant, you don't want to tear back into it once it's going
65mustang-SOLD-200ci-t5-scarebird disks-vintage air ac-264/274 110 cam-mav 8inch 3.8 open-350cfm-CI headers
66 Bronco-SOLD-i6 170 - rust bucket never ran...
75 bronco-SOLD-v8 c4 dana 20 33's and disk brakes, locker front/rear.

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65-coupe
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Posts: 378
Joined: Sat Aug 13, 2011 10:43 pm
Location: Lakeland Fl

Re: 7.25 rear end

Post #4 by 65-coupe » Tue Sep 27, 2011 4:37 pm

Thanks alot for the info. I have been torn between changing to five lug with an 8" rear or staying 4 and use the two I have and get a maverick 8" four lug later. I have a 8" that is about 1" short from a 65 falcon that was redone with a 289 and 8" rear end. I do need to rebuild the rear end from the Falcon. They guy bought another one when it went bad. I would rather stay 4 lug getting ready to upgrade to power disc so I need to make my mind up.
1965 Mustang coupe, SPI Orange with custom TMI interior, 250 DUI, CI alum head ported, 274/274 110 Clay Smith cam, 1.65 roller rockers, Holley 390 4bbl, Lokar pedals and throttle calbe. Street or track front coilovers suspension, CI headers stainless with Jet-Hot ceramic coating, CI Stainless 2" impostor dual exhaust, 17x8 Coys C-67 wheels,

MPGmustang
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Posts: 1610
Joined: Fri Jan 09, 2009 10:23 pm
Location: Chandler AZ

Re: 7.25 rear end

Post #5 by MPGmustang » Fri Oct 07, 2011 6:41 pm

personally, I would go 5 lug if you already got the rear end, there are scores of granadas in the junk yards that have great disk brakes, they cost the same as scarebirds conversion, except the added cost that you can finally get those 15inch rims you love.
65mustang-SOLD-200ci-t5-scarebird disks-vintage air ac-264/274 110 cam-mav 8inch 3.8 open-350cfm-CI headers
66 Bronco-SOLD-i6 170 - rust bucket never ran...
75 bronco-SOLD-v8 c4 dana 20 33's and disk brakes, locker front/rear.

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