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Author Topic: 7.25 to 8.25 swap questions  (Read 858 times)

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80 Lebaron Coupe

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Re: 7.25 to 8.25 swap questions
« Reply #15 on: August 06, 2017, 10:22:24 »

The 7 1/4 is to weak to wast time and money on
X2!
If you ever had one apart, you would see how dinky the parts are inside.
8.25 at a minimum for anything with some power.
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HunterB

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Re: 7.25 to 8.25 swap questions
« Reply #16 on: August 12, 2017, 20:44:41 »

I just noticed something weird on my current rear axel. It looks like there is a bolt hole peaking out from behind the diff cover, that can't be right? And I cleaned up the tag on cover good enough to read it and says 2.7 but the numbers are backwards? Also I highly doubt it has 2.7 gears but who knows. Heres some pics
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Derekb

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Re: 7.25 to 8.25 swap questions
« Reply #17 on: August 13, 2017, 06:44:21 »

How to check your gear ratio
https://youtu.be/fB0jrucjlxg


Are your axle tube the same size all the way or do they neck down to a smaller size by the center
« Last Edit: August 13, 2017, 06:50:52 by Derekb »
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DobaMark

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Re: 7.25 to 8.25 swap questions
« Reply #18 on: August 13, 2017, 14:53:17 »

That odd bolt hole is normal.
You could have 2.7 gears, it was a common gear for slant cars and the rear axle could have already been replaced once since I assume you have a V8.
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HunterB

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Re: 7.25 to 8.25 swap questions
« Reply #19 on: August 16, 2017, 12:30:43 »

Just checked and turns out it is 2.7. Yes the axle tubes neck down to a smaller size next to the pumpkin so it's definitely a 7.25 diff.
I'm glad I checked it though because I filled it up with gas last night, and when I jacked it up today I noticed it has a small fuel leak on the drivers side. Looks like I'm replacing a gas tank now too.
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Barkfin

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Re: 7.25 to 8.25 swap questions
« Reply #20 on: August 17, 2017, 09:58:44 »

I got a set of 39/11 (3.55:1) gear/pinion for a 7.25" for $60 brand new! (NOS?) Actually $100 mailed to Canada.
I guess these are not popular parts ha ha  :biggrin:

It occurred to me old Blue never goes much above 2,000 rpm and is pretty much timid as a kitten, despite loud headers etc.

Anyway since I have 2.26:1 right now, I guess I need to get a larger carrier case due to "carrier break".

https://www.ringpinion.com/TechnicalHelp/contentframe.aspx?filepath=%7e%2fcontent%2fparts%2fcarriers%2f%2fcommon+carrier+breaks.inc

Question, where to find such a carrier? Is this a chance to upgrade to Suregrip?
I don't really know much about differentials, or where to get such parts and what they're worth.

(I know the general perception is that 7.25" unit is weak, however I never abuse a car with 'neutral bombs' or burnouts or stomping the gas over railroad tracks / potholes. I'm the guy gurgling along at 50 km/hr in construction zones while everybody else goes sailing by  :roll: so I'm gonna chance it.)
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IronBrick

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Re: 7.25 to 8.25 swap questions
« Reply #21 on: August 17, 2017, 10:46:30 »

I got a set of 39/11 (3.55:1) gear/pinion for a 7.25" for $60 brand new! (NOS?) Actually $100 mailed to Canada.
I guess these are not popular parts ha ha  :biggrin:

It occurred to me old Blue never goes much above 2,000 rpm and is pretty much timid as a kitten, despite loud headers etc.

Anyway since I have 2.26:1 right now, I guess I need to get a larger carrier case due to "carrier break".

https://www.ringpinion.com/TechnicalHelp/contentframe.aspx?filepath=%7e%2fcontent%2fparts%2fcarriers%2f%2fcommon+carrier+breaks.inc

Question, where to find such a carrier? Is this a chance to upgrade to Suregrip?
I don't really know much about differentials, or where to get such parts and what they're worth.

(I know the general perception is that 7.25" unit is weak, however I never abuse a car with 'neutral bombs' or burnouts or stomping the gas over railroad tracks / potholes. I'm the guy gurgling along at 50 km/hr in construction zones while everybody else goes sailing by  :roll: so I'm gonna chance it.)

I owned a Fifth Ave with a "weak" 7.25 that I drove to hell and back for 6 years. Towed with it, drove it like I stole it, raced, etc. Yeah maybe they're weak if you're doing 1/4 mile runs with slicks but honestly I never had an issue. If you're a highway cruiser you're fine, but that being said I wouldn't spend money on that axle.

For me a 2.76 or 2.92 would be the ideal gear ratio since I do highway cruising.
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Derekb

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Re: 7.25 to 8.25 swap questions
« Reply #22 on: August 18, 2017, 07:38:40 »

I got a set of 39/11 (3.55:1) gear/pinion for a 7.25" for $60 brand new! (NOS?) Actually $100 mailed to Canada.
I guess these are not popular parts ha ha  :biggrin:

It occurred to me old Blue never goes much above 2,000 rpm and is pretty much timid as a kitten, despite loud headers etc.

Anyway since I have 2.26:1 right now, I guess I need to get a larger carrier case due to "carrier break".

https://www.ringpinion.com/TechnicalHelp/contentframe.aspx?filepath=%7e%2fcontent%2fparts%2fcarriers%2f%2fcommon+carrier+breaks.inc

Question, where to find such a carrier? Is this a chance to upgrade to Suregrip?
I don't really know much about differentials, or where to get such parts and what they're worth.

(I know the general perception is that 7.25" unit is weak, however I never abuse a car with 'neutral bombs' or burnouts or stomping the gas over railroad tracks / potholes. I'm the guy gurgling along at 50 km/hr in construction zones while everybody else goes sailing by  :roll: so I'm gonna chance it.)
Yes a sure grip is a carrier but you will have to get one for that 7.25 the later ones for the dakota will not work they added splines to the axles to make it stronger. With that gear ratio you will be putting a lot more power threw a known to be weak rear keep a number for a rollback on ya it will be just a matter of time
« Last Edit: August 18, 2017, 07:39:57 by Derekb »
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MarkM

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Re: 7.25 to 8.25 swap questions
« Reply #23 on: August 18, 2017, 10:06:50 »

You're pissing into the wind with this, trust me.  Just find a Ford 8.8 or 9" with 4.5x5 bolt pattern, maybe with disc if you want, put new bearings in it and shorten if needed.  You'll be money ahead.
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Derekb

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Re: 7.25 to 8.25 swap questions
« Reply #24 on: August 19, 2017, 08:01:01 »

You're pissing into the wind with this, trust me.  Just find a Ford 8.8 or 9" with 4.5x5 bolt pattern, maybe with disc if you want, put new bearings in it and shorten if needed.  You'll be money ahead.
Pem racing sells a very nice 58 inch ford 9 at a good price if anyone is interested I used there 57 inch kit very happy with the quality
« Last Edit: August 19, 2017, 08:02:37 by Derekb »
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HunterB

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Re: 7.25 to 8.25 swap questions
« Reply #25 on: August 19, 2017, 11:14:52 »

Thanks for all the replies. I think I'm still going to have to find a factory 8.25 because I can't weld or fabricate anything really. I'd also rather have a chrysler rear end, putting a ford diff under a mopar just seems wrong to me.
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Derekb

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Re: 7.25 to 8.25 swap questions
« Reply #26 on: August 19, 2017, 11:28:09 »

, putting a ford diff under a mopar just seems wrong to me.


If you think that's bad my brakes are chrysler Chevy and ford
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