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Using a 742 pinion in a 741 case via slight modification
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1960desotoman
Posted 2021-01-10 1:17 PM (#607583)
Subject: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.

I am looking for a 2.94 or 2.76 rear end for an early 741 differential case (casting number 1820657) and all I can find are 742 case ring and pinion sets in that particular ratio. As I understand the 741s have a 1-3/8" pinion stem and the 742s have a 1-3/4" pinion stem. My brother has a machine shop, so I'm wondering if a 742 pinion stem could be machined down to 1-3/8" and fit in a 741 case. Both are 10 spline and I believe the splines are the same size between the 741s and the 742s. 

p.s. if anyone knows where I could find a 741, 10 spline, 2.94 or 2.76 ratio ring and pinion for less than $300 that would be ideal.

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57chizler
Posted 2021-01-10 4:43 PM (#607585 - in reply to #607583)
Subject: RE: Using a 742 pinion in a 741 case via slight modification



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https://www.ebay.ca/itm/NOS-Mopar-2070296-RING-GEAR-PINION-2-93-1-57...
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1960desotoman
Posted 2021-01-10 4:56 PM (#607586 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.
Hmm. Well now I feel silly. I suppose I was using the wrong key words. Thanks!
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Powerflite
Posted 2021-01-10 8:22 PM (#607592 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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When I recommended you to get 2.76 gears, I didn't mean to purchase just the gears. I meant to purchase the whole third member (used) all together and swap it out. Another option is to swap out the entire rear end with one from a '65-'69 C-Body. I'm not sure from the description here, but maybe this one is a C-body rear end? They are a direct replacement. The only thing you have to do is to maybe move the brake hose mount position or use a longer hose on it.

https://denver.craigslist.org/pts/d/denver-mopar-axle/7247567857.htm...

If the perch spacing is 46", then it is likely a C-body axle. If it is 44", it is a B-body.

Edited by Powerflite 2021-01-10 8:24 PM
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1960desotoman
Posted 2021-01-10 8:45 PM (#607596 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.
Is it necessary to replace the whole third member?
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Powerflite
Posted 2021-01-10 10:17 PM (#607599 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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You can replace just the gears with 2.93 as Chizler showed, but it is a lot more expensive and the labor to do it isn't cheap either. A used full third member will likely cost you $100.
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NM Desoto
Posted 2021-01-10 11:31 PM (#607600 - in reply to #607583)
Subject: RE: Using a 742 pinion in a 741 case via slight modification


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I've got a 741 case with 2.94 gears and a 742 case with 2.76. Neither are limited slip. The 741 has been in inside storage for
several years,but will need a good cleaning. The 742 is still in the car.
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1960desotoman
Posted 2021-01-11 3:21 AM (#607606 - in reply to #607599)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.

Powerflite - 2021-01-10 8:17 PM You can replace just the gears with 2.93 as Chizler showed, but it is a lot more expensive and the labor to do it isn't cheap either. A used full third member will likely cost you $100.

 

After reading through the rear axle section in my service manual, I see what you mean. Unfortunately I have been having difficulty finding one that cheap, but I've got time to find one. Thanks for the input!

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1960desotoman
Posted 2021-01-11 3:22 AM (#607607 - in reply to #607600)
Subject: RE: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.

NM Desoto - 2021-01-10 9:31 PM I've got a 741 case with 2.94 gears and a 742 case with 2.76. Neither are limited slip. The 741 has been in inside storage for several years,but will need a good cleaning. The 742 is still in the car.

 

Either one of those for sale perchance? 



Edited by 1960desotoman 2021-01-11 3:42 AM
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57chizler
Posted 2021-01-11 12:45 PM (#607615 - in reply to #607607)
Subject: RE: Using a 742 pinion in a 741 case via slight modification



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If your car doesn't currently have Sure-Grip, swapping in any '64 or later third member or one with Sure-Grip will require shortening your axle shafts 1/8". This is because the internal thrust block is wider in those.
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1960desotoman
Posted 2021-01-11 12:50 PM (#607616 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



Member

Posts: 23

Location: Estes Park, CO.
Ok. Just this morning I purchased a '66 plymouth rear end with 2.94 gears. Were all post 64' rear ends sure grip or was it an option? My current rear end is not a sure grip.
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1960desotoman
Posted 2021-01-11 12:51 PM (#607617 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.
<p>Ok. Just this morning I purchased a '66 plymouth rear end with 2.94 gears. It appears to be a non-sure grip model unfortunately. My current rear end is not a sure grip.</p>

Edited by 1960desotoman 2021-01-11 12:53 PM
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Powerflite
Posted 2021-01-11 12:52 PM (#607618 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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No, it was always an option. What model of '66 Plymouth did it come from? What are the dimensions on it?

Edited by Powerflite 2021-01-11 12:53 PM
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1960desotoman
Posted 2021-01-11 12:54 PM (#607619 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



Member

Posts: 23

Location: Estes Park, CO.
It came from a Plymouth Fury. It is a 741 case, the same as my current rear end.
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Powerflite
Posted 2021-01-11 12:55 PM (#607620 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Perfect. C-body, so it should bolt right in as a direct replacement, other than the hose issue that I stated before.
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1960desotoman
Posted 2021-01-11 12:57 PM (#607621 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



Member

Posts: 23

Location: Estes Park, CO.
Great! That's what I assumed.
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NM Desoto
Posted 2021-01-11 8:00 PM (#607634 - in reply to #607607)
Subject: RE: Using a 742 pinion in a 741 case via slight modification


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They are both available, but it appears that you have found one locally. let me know if there are any changes.
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1960desotoman
Posted 2021-01-11 8:35 PM (#607637 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Posts: 23

Location: Estes Park, CO.
Ok, I'll keep it in mind.
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RICKYMOPAR
Posted 2021-02-22 8:50 AM (#609153 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Ian, Wish I had seen this thread earlier, may be able to help. A little over an hour away. Broomfield 80021
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1960desotoman
Posted 2021-02-22 11:45 AM (#609157 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



Member

Posts: 23

Location: Estes Park, CO.
I'm glad to find another Mopar enthusiast nearby! I bought a 2.92 third member and I'm just procrastinating on putting it in at this point. Do you have a DeSoto?
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RICKYMOPAR
Posted 2021-02-22 4:54 PM (#609166 - in reply to #607583)
Subject: Re: Using a 742 pinion in a 741 case via slight modification



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Ian, not at this time, I have owned DeSoto's in the past ..Just sold my perfect 58 steering wheel to another member Not for too much. I formerly owned 2, 57 Firedome 2DHT and 3, 58 Explorer wagons, one was a two door.

Edited by RICKYMOPAR 2021-02-22 4:59 PM
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