Changing open diff to limited slip / trac lok - needed parts / kits

[timachone]

I have originally a 9" rear with a 3.50 gear and open differential and want to change to a limited slip diff when I am overhauling the rear axle.

Therefore I have the Ford Performance Parts Traction-Lok Differential M-4204-F28A laying on the shelf since 6 years. 

Besides new axle bearings/seals, which parts / parts kit do I need? Concerning the change from open to limited slip there are longer bolts needed 

https://www.yukongear.com/productdetails.aspx?ProdID=8495

Concerning the differential and its dimensions I came to these kits: 

https://www.rockauto.com/de/moreinfo.php?pk=3903966&cc=1132995&jsn=1041&jsn=1041

https://www.rockauto.com/de/moreinfo.php?pk=3903777&cc=1132995&jsn=1042&jsn=1042

http://www.usastandardgear.com/productdetails.aspx?ProdID=9638

http://www.usastandardgear.com/productdetails.aspx?ProdID=9639

When I tinker with this topic I came across words like "setting preload", "shimming", "crush sleeve" etc. 

For this procedure I read this procedure 

https://www.diyford.com/mustangs-disassmble-rear-axle-rebuild-assembly/ 

Concerning the change with the already pre-assembled Limited Slip differential and reading the above mentioned text and others: am I right that I do not have to go that deep into the differential other than I have to rebuilt an old one? Do I "only" have to slap on new bearings and seals, set lash on the gears and that's it? Therefore some of the parts of these kits aren't needed? 

Perhaps one of you folks could enlighten this dark area of my knowledge...  :thumb:

 

[droptop73]

Hi Tim, sorry, I didn't look through all the links. 

It's not quite that simple but almost. You will need a press to remove and install the large bearing on the pinion. Are you replacing the gearset? If so pinion depth is important, start with the shims that were originally installed and work from there. You will need a new crush sleeve as this helps control the preload on the pinion bearings. I added a Yukon gear trac lok and needed to grind a little bit off the boss for the pinion support bearing for clearance. It just needs to clear. The 9" ford is much simpler than other types for gear set-up. Wishing you the best, take your time. BTW, I picked up the gearset, trac lok and install kit from Quick Performance, nice parts and very good service. 

 

[timachone]

Hi Tim, sorry, I didn't look through all the links. 

It's not quite that simple but almost. You will need a press to remove and install the large bearing on the pinion. Are you replacing the gearset? If so pinion depth is important, start with the shims that were originally installed and work from there. You will need a new crush sleeve as this helps control the preload on the pinion bearings. I added a Yukon gear trac lok and needed to grind a little bit off the boss for the pinion support bearing for clearance. It just needs to clear. The 9" ford is much simpler than other types for gear set-up. Wishing you the best, take your time. BTW, I picked up the gearset, trac lok and install kit from Quick Performance, nice parts and very good service. 

Jeff, thank you for your support! 

No, I am not willing to replace the gearset. I like it as is, 3.50 gears original, love that snap and will tolerate the somewhat high rpm (3.000 on 60 mp/h). 

I have an 9" rear with open diff and 3.50 gears. This is what I have on the shelf, a new Ford Trac Loc assembly 

As using the original gearset (if condition ok'ish) and the whole new trac lok assembly from above and looking at this picture of a typical rebuild kit from USA Standard Gear

http://www.usastandardgear.com/images/products/zkf9a.jpg

I only have to use the new bearings, seals, o-ring, pinion nut for the yoke and the longer bolts for the trac lok assembly, right? The new bearings will go to the new trac lok assembly and the old pinion gear or its original pinion support from the third member. The 5-hole-shims for the pinion support and the shims or crush sleeve for the preload on the pinion I do not need, if using original pinion gear, am I right there? 

 

[Don C]

You must use the new crush sleeve, they are not reusable. The exception would be if you use a solid spacer, then you have to adjust it with shims. 

As to using new pinion carrier shims, it will depend on how close to original the new bearings are, as to whether you can just reuse the shims. You will find out when you check the pattern on the ring gear. You will still need to set the clearances, backlash,  and preloads. You'll need a beam or dial inch-pound torque wrench. 

 

[Stanglover]

Well, I know nothing of rebuilding the rear end, that's why I paid a specialist. I switched to a Traction Loc from open as well, but kept the 3.25:1 gears. I sometimes wish I'd sprung for a 3.50:1 set, but I was spending enough as it was. 

Why am I posting? one thing my "guy" told me was to use new 3/8 fine thread smooth flange nuts and new copper crush washers and torque in stages up to 45 ft/lbs. Oddly, he was out of stock on the crush washers, so I had to get my own to finish up the install which was no problem as I was repainting the axle. 

 

[timachone]

Thank you Don and Geoff  :thumb:

From your words I assume that I am quite right with such a kit mentioned above, a buddy with a press and some rear axle skills, muscles and a few hours of focused work  :classic_cool:

That should do the job  :wrench:

 

[Bentworker]

Just to echo what Don said.  If reusing gears you should measure backlash and check pattern with marking compound BEFORE you take it apart.  Providing the used pattern looks good you want to try to copy it.  If it looks bad you may want to consider new gears instead (as the gears may be worn). You will need an inch pound dial or beam style torque wrench to set bearing preload.  Marking compound to check pattern.  Dial indicator and base to check backlash.  Press and assortment of bushings to install bearings.  Have fun and take your time.

This video is the best I have found to show what pinion depth and backlash do to pattern.

 

[droptop73]

Great explanation! 

 

[timachone]

1 hour ago, Bentworker said:

Just to echo what Don said.  If reusing gears you should measure backlash and check pattern with marking compound BEFORE you take it apart.  Providing the used pattern looks good you want to try to copy it.  If it looks bad you may want to consider new gears instead (as the gears may be worn). You will need an inch pound dial or beam style torque wrench to set bearing preload.  Marking compound to check pattern.  Dial indicator and base to check backlash.  Press and assortment of bushings to install bearings.  Have fun and take your time.

This video is the best I have found to show what pinion depth and backlash do to pattern.

Thank you  :thumb:

 

[Doug's 73 Mach1]

If your 3:50 ratio was original, you may have 31 spline axles vs. 28 spline typically used with 3:25 ratios and under.  Make sure your traction lock assembly has the correct number of splines to match your axles.   

 

[timachone]

If your 3:50 ratio was original, you may have 31 spline axles vs. 28 spline typically used with 3:25 ratios and under.  Make sure your traction lock assembly has the correct number of splines to match your axles.   

Thanks for the hint  :thumb:  

As I could see from the outside the axles have the typical 28-spline look with the center oval on them, I don't think I have a 31-spline rearend although it is a 351C 4V with 4-speed and 3.50 gears, all original: 

http://www.metropartsmarket.com/rearend/Axle_28_Spline.jpg

I never heard of a 31-spline 1973 Mustang though. My TracLok is a 28-spline. If all else fails I have a pair of good 28-spline axles laying around - they fit the TracLok-assembly very well. So if I unexpectedly have a 31-spline I could change it  :thumb:

 

[Doug's 73 Mach1]

Sounds like you should be in good shape with 28 spline axles one way or the other.  According to Ford's 1973 car facts organizer, 3:50 ratio rear ends should have 31 spline axles and a "cast nodular iron" center section.  The center section casting would have a large raised letter "N" cast in it above the pinion bearing housing if it is made of cast nodular iron (more commonly known as "ductile iron" in the foundry industry).  According to the "Mustang and Cougar Tag book" by Kevin Marti, the 1973 3:50 ratio differential tag should have the code WES-AK2 for non locking or WFD-F3 for locking (same for 1972 models). 

When you put new differential gear oil in, it needs to made for locking (limited slip) rear ends.  I think most differential oils these days are that way.  However, back in the early 70s, a special additive (friction modifier) was required for Traction Locks so their clutch plates would work properly.  Another thing you may want to do is change your speedometer gear at the trans end of the speedometer cable to compensate for the rear end ratio change so your speedometer will read correctly.  Your trans output shaft (and drive shaft) will turn slower with 3:25 gears than with 3:50 gears making the speedometer read slower than you are actually driving if you don't change the speedo gear (assuming the rear tire outside diameter is as originally equipped).    

Good luck with it.  I too have an original 73 Mach 1 4 speed, I converted from 3:25 open over to 3:50 locking and switched to 31 spline and the nodular case.      

 

[Stanglover]

Doug made a good point on the friction modifier (and other things) needed for the Traction-Loc diff. I was able to get Ford friction modifier from my local Ford dealership. They actually had it behind the counter. As for gear oil, both my gear box rebuilder and rear axle rebuilder, recommended Valvoline 80-90 gear oil. It's as thick as molasses, so warm the bottles in hot water first. I'm not exactly sure how much I used to fill to the bottom of the plug hole, but it's about 2 to 2 1/2 bottles.

 

[timachone]

Looked for the axle tag in the meantime and saw this: 

WES-AK    3DA

3.50    9   9645

That would be correct for a 9" inch for 71-73 Mustangs or 72/73 Cougars, 3.50 gears without Limited Slip (otherwhise there would be a "L" between 3 and 50 instead the point), 28-spline, from 1th week April 1973. 

Am I right there? 

So according to the tag and that it would be original and nothing changed I have the original axle (my car was built in April 1973) with 3.50 gears but no LS and 28 spline. 

Time will tell... 

Concerning oil the 80W-90 seems right. If the oil would have the Ford specification M2C-104-A for Limited Slip differentials you would not need any additional friction modifier. This would only be needed if you use normal gear oil for non-LS-applications. The special LS-oils have this addition already mixed in  :thumb:

 

[Stanglover]

Looked for the axle tag in the meantime and saw this: 



WES-AK    3DA

3.50    9   9645

That would be correct for a 9" inch for 71-73 Mustangs or 72/73 Cougars, 3.50 gears without Limited Slip (otherwhise there would be a "L" between 3 and 50 instead the point), 28-spline, from 1th week April 1973. 

Am I right there? 

So according to the tag and that it would be original and nothing changed I have the original axle (my car was built in April 1973) with 3.50 gears but no LS and 28 spline. 

Time will tell... 

Concerning oil the 80W-90 seems right. If the oil would have the Ford specification M2C-104-A for Limited Slip differentials you would not need any additional friction modifier. This would only be needed if you use normal gear oil for non-LS-applications. The special LS-oils have this addition already mixed in  :thumb:

First from the Marti Tag book. under 73's your axle does not exist, not that the book is "totally" correct. The book shows 3.50 Code A WES-AK2 and would be used on both manual and auto trans. However WES-AK is listed for the 71 429 with a 3.50 code A. For 72, it's the same as 73. That's as far as the book shows. 

As for the diff oil, I believe you're right. I happen to use the regular 80W90. By the way, IF you do use the Ford friction modifier, a warning, It stinks to high heaven, so don't get it on your hands or clothes. Also add it first, then the oil, but I suspect you already know that.

All the best with it.

 

[timachone]

Geoff, 

I had not the Marti on hand because of my truck days I had this: 

http://www.fordification.com/tech/rearends_ford06.htm

I don't know where they have their informations from but since today they made sense. It would be not the first time Marti had its gaps in history... According to the truck chart it makes more sense to me concerning my axle than it would be a 429 one from '71. But who knows - it would be only clear when I open the axle the next 2-3 weeks... Thank you for your support  :thumb:  

Concerning rear oils I think we both are good with it! Original there was a SAE 90 in the rear with Ford specification M2C-105-A (open diff) or M2C-104-A (LS). Today we take better a good 80W-90 with LS-specification. 

And... I know, rear gear oil stinks to hell, especially when it's done  :classic_tongue:

 

[Stanglover]

Geoff, 

I had not the Marti on hand because of my truck days I had this: 

http://www.fordification.com/tech/rearends_ford06.htm

I don't know where they have their informations from but since today they made sense. It would be not the first time Marti had its gaps in history... According to the truck chart it makes more sense to me concerning my axle than it would be a 429 one from '71. But who knows - it would be only clear when I open the axle the next 2-3 weeks... Thank you for your support  :thumb:  

Concerning rear oils I think we both are good with it! Original there was a SAE 90 in the rear with Ford specification M2C-105-A (open diff) or M2C-104-A (LS). Today we take better a good 80W-90 with LS-specification. 

And... I know, rear gear oil stinks to hell, especially when it's done  :classic_tongue:

Hi Tim That's an interesting chart. I think you're right, Marti only has part of the information. I have not checked www.Mustangtek.com for rear axle, but I'll look later. it may clear things up. Regardless, it should be a 3.50 open diff. 

Talking of stinky oil, did you read my previous post "Stinky Rear End"? When I did mine, there was a strong stink for many day after, but although I did have a small leak off one axle seal, the real culprit was the vent tube. The axle leak has since stopped. It was very minor anyway.