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3rd Member question
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60 Windsor
Posted 2014-12-10 9:04 PM (#464276)
Subject: 3rd Member question


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Posts: 41
25
Location: South Central PA
Hey guys, working on my 60 Windsor's differential and am seeking some advice. Was going to replace the wheel bearings since the seals were shot and pulled the 3rd member to reseal and noticed that the spider gear case is shot. The hole that the shaft goes through is blown out and no longer round.

After some research on the fl site, I believe that the 3rd member/axles were changed out from a 1959 Canadian donor (it has left/right hand wheel bolts not nuts, axles are 1 3/8" dia) and the 3rd member casing has a part number cast 1634983. I wanted to upgrade to a sure grip but am finding that they are difficult to locate. Is this 3rd member an early 742 and has anyone had any experience installing a truetrac diff in this early of a 3rd member or does someone have advice on what 3rd member/guts to put in? It has a 3.73:1 gear in it and I was going to change that to a 3.23. Also, should I change the axles to 1 1/2" and does anyone know offhand what size speedo pinion I would need? Looking at a parts book it says 19 tooth, I am running 235/75/15 tires on the rear but I'd like to confirm.

I'd like to keep this axle housing and not change out to a later model flange type.

Thanks!
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57chizler
Posted 2014-12-11 1:26 PM (#464358 - in reply to #464276)
Subject: RE: 3rd Member question



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Location: NorCal

The 1634985 is the earlier version of the 742. All 8 3/4" axles have the same 30 splines but the actual shaft diameter varies. Prior to '64 the open differential axles are longer than the Sure-Grip axles so when a Sure-Grip is installed the axles must be shortened 1/8".

When contemplating installing an aftermarket limited slip differential like the TrueTrac you have to take into account that the there is no thrust block in the center so the factory axle bearings won't work with them.
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60 Windsor
Posted 2014-12-11 9:30 PM (#464407 - in reply to #464358)
Subject: Re: 3rd Member question


Member

Posts: 41
25
Location: South Central PA
I called Cass at Dr Diff today and he said that the truetrac comes with a thrust block for 1964 and up rears but if I had another thrust block made the same thickness as the one that came out of the original diff using the truetrac thrust block dimensions I can use the old axles and tapered bearing/shim setup. Also if I go with that I have to get the 2" carrier bearings and it should fit. Sounds promising to say the least. I still might try and hunt down 1 1/2" axles, although I am not sure what the main difference is between Plymouth axles and Chrysler besides the inner seal ID.
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d500neil
Posted 2014-12-12 1:40 AM (#464421 - in reply to #464407)
Subject: Re: 3rd Member question



Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!

Posts: 19146
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Location: bishop, ca
Andy, FWIW, you should definitely appreciate that intended 3.23 gearset installation in your car.

I played around with a SureGrip 3.55 (off of an 80's pickup, IIRC) in my car and did NOT like the increased operational noise or the decreased
MPG (like around10+) or the limited amount of increased performance, over the OEM 3.36:1

I went Bonneville on my 'built' D500 and installed the mighty 2.76:1 ratio, but I wouldn't recommend that guy to anyone who
isn't prepared to smile on his car's preparation; stick with the 2.93:1(-maximum) ratio....like the IMP's use in them.

Installed the 742 carrier housing (for the 2.76 bad boy); bolted right in, with quiet smooth operation.


The rear-gear does not affect the engine music, at slow maneuvering speeds, so your neighbors will
know that your car's motor is still "packing".





Edited by d500neil 2014-12-12 11:43 AM
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60 Windsor
Posted 2014-12-12 10:24 PM (#464489 - in reply to #464421)
Subject: Re: 3rd Member question


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Posts: 41
25
Location: South Central PA
I'm going to break down the carrier this weekend and measure everything out just to be positive I have a 742 carrier then most likely order up the parts from Cass.

The SureGrip mpg theory explains a lot, I have a 77 dodge van keeping the Windsor company and it has one in it and I can't get more than 13 mpg out of that (318, 4 barrel). It sounds like the TrueTrac is the way to go, everything I've read on them is positive.

I hope the 3.23 gearset is a good one, the 3.73 is definitely too low of a gear, sounds like the motor wants to come eat me at 70mph (3500+rpm). I haven't done the calculations yet but 3.23 should be optimal for back road/highway running. right now I get an average 14mpg out of it.

Does anyone know if a 19 tooth speedo pinion will get me close on speed readings? It has a 17 tooth in it now and that is way off, I have a feeling the original rear was a 2.93. Who knows where that went or why it was changed out...

Thanks for all the assistance.
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57chizler
Posted 2014-12-13 1:51 PM (#464539 - in reply to #464489)
Subject: Re: 3rd Member question



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Location: NorCal

Your tires are almost 29" in diameter, with your existing 3.73 gear you're turning closer to 3100 at 70 mph, as you guessed, the speedo is reading high because your existing 17-tooth pinion is wrong for that combo...should be a 21-tooth.

If you change to 3.23 gears an 18-tooth pinion is what you'll need and you'll be turning under 2700 at 70 mph..
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60 Windsor
Posted 2014-12-13 6:07 PM (#464565 - in reply to #464539)
Subject: Re: 3rd Member question


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Posts: 41
25
Location: South Central PA
I pulled it apart, unfortunately it has a 1 3/8" pinion in it so that case number 1634983 is an early 741 case. The reason it gave out was the locating pin sheared and caused the spider gears to go wild. Most likely because it was for a 6 cylinder lighter car. The ring and pinion have date codes of 1/57 on them.

Back to the drawing board, in search of a 742 case...
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58coupe
Posted 2014-12-13 10:18 PM (#464575 - in reply to #464276)
Subject: Re: 3rd Member question



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60 Windsor, here's a little more info for you. The 741 with the 1 3/8" pinion was not just an early axle, it was used for many years and is stronger than you think. My 58 Fury used one. The 6 cyl. cars used an 8 1/4" axle that is not interchangeable and is definitely weaker. The big cars Chrysler, Desoto, and Imp. used the 742 axle with the 1 3/4" pinion as well as the limited slip starting in 58. Unless you are building a race car or a high horsepower stroker, any of the 8 3/4" diffs. should be strong enough IMHO.
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57chizler
Posted 2014-12-14 5:25 PM (#464634 - in reply to #464565)
Subject: Re: 3rd Member question



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Location: NorCal
60 Windsor - 2014-12-13 3:07 PM

I pulled it apart, unfortunately it has a 1 3/8" pinion in it so that case number 1634983 is an early 741 case.


Hmmm. The early 1 3/8" stem casting number should be 1820657 but, regardless, the small stem is plenty strong unless you're running a lot of power. Sixties Top Fuel dragsters ran the small stem (they didn't know the difference).
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60 Windsor
Posted 2014-12-14 10:19 PM (#464656 - in reply to #464634)
Subject: Re: 3rd Member question


Member

Posts: 41
25
Location: South Central PA
I'm not opposed to reusing the case, it's not that easy to find the ratio I'd like in the 1 3/8" size. The 3.73 provides a lot of torque and the gearset isn't in bad shape but I'd rather have a little more economy. If I could find a 3.23 or at worst a 2.93 with the 741 case that doesn't cost a small fortune I'd probably reuse it. I'm going to make some phone calls and see what I can dig up, if anyone knows of a place to get a new gearset or knows where a used one is sitting on a shelf please let me know. Thanks for all the help!
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d500neil
Posted 2014-12-14 11:30 PM (#464657 - in reply to #464656)
Subject: Re: 3rd Member question



Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!

Posts: 19146
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Location: bishop, ca
As all well know, those 3rd embers weigh a 'ton' and are difficult to package, for shipping.

A good (partial) container is a HD nylon milk carton-carrier.

Two of them can be wired together, to hold a 3rd member inside their cavity-enclosure...for truck or even Greyhound shipping.

There are swap meets, like Spring Fling & Fall Fling, in L.A., that routinely have 3rd members laid out onto the grassy field for purchase.


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jimntempe
Posted 2014-12-15 8:54 PM (#464780 - in reply to #464276)
Subject: Re: 3rd Member question



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I bought a ford 9" third member and the guy shipped it in a 5 gallon paint can.
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d500neil
Posted 2014-12-16 3:09 AM (#464802 - in reply to #464780)
Subject: Re: 3rd Member question



Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!

Posts: 19146
5000500050002000200010025
Location: bishop, ca
Isn't that really messy?

Latex, huh?


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60 dart
Posted 2014-12-16 3:50 AM (#464805 - in reply to #464276)
Subject: Re: 3rd Member question



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anything past 3.55 you aint gonna like . 3.23 is a nice get it goin gear . less gear your gonna get better fuel mileage but a suregrip is a real good choice in any size ----------------------------later
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