Ford 9 inch rear differential guru’s

[jamesroney]

I need some advice from the 9 inch crowd. I just bought this 31 spline helical limited slip differential. It does not have any ID marks, except for the “31 HT” stamped on the case. Anyone out there know who built this thing, and how do you take it apart?

It has no bolts, and the ring gear “hat” does not split. I can see the ends of a helical gear tooth in the window.

It it not a ford traction lock, or equa-Lok and does not look like a true-Trac. Doesn’t look like current production wave-Trac, or Torsen or Quaife.


I’m thinking that the case halves are somehow threaded together.
Any ideas welcome.

 

[Yeller]

That’s an interesting one. It’s a really beefy looking case. My assumption is pressed together opposite the ring gear side. Potentially making it nonservicable.

I first thought it was a Power Trax or a TORQ unit but that would be a negative.

 

[DirtDonk]

Spanner wrench in the holes?
Case halves threaded in the opposite direction of normally applied torque? As in forward, instead of reverse?
Specialized spanner pins that might push into something to release a spring loaded cog tooth?

In other words, I have no idea…

 

[ntsqd]

Sierra Mfg. used to sell their version of a Tru-Trac, which they called a "Gold-Track" or something like that. Theirs could be had with different bias' or sensitivity or whatever you want to call it. They only made it for the 9" and very specifically targeted the roundy racer market with it. What you have looks like what I remember one of those looking like.

Sierra also bought the LBS, that BCB used to sell on my suggestion, from Stewart Components, and made them up until they went out of biz.

 

[EPB72]

https://www.markwilliams.com/Catalog/pg31.pdf they show a gold trac but is 35 spline ...

 

[okie4570]

It does look pressed together.

 

[ntsqd]

The "DPI" in the MW part numbering stands for Dan Press Industries. I had it partly wrong when I said "Sierra" above. DPI was the last incarnation. Now it is Larson Racing Products. LRP does offer the Gold-Track, now called the "Platinum Track", in 28 and 31 spline, as well as 8", 8.8", and QC diffs.
https://www.larsenracingproducts.com/categories/differentials-parts.html?page=3

They also still show the LBS for sale too.

While researching this I stumbled onto an article about Dan Press: https://scvhistory.com/scvhistory/lw3312.htm Worth the read.

 

[jamesroney]

The "DPI" in the MW part numbering stands for Dan Press Industries. I had it partly wrong when I said "Sierra" above. DPI was the last incarnation. Now it is Larson Racing Products. LRP does offer the Gold-Track, now called the "Platinum Track", in 28 and 31 spline, as well as 8", 8.8", and QC diffs.
https://www.larsenracingproducts.com/categories/differentials-parts.html?page=3

They also still show the LBS for sale too.

While researching this I stumbled onto an article about Dan Press: https://scvhistory.com/scvhistory/lw3312.htm Worth the read.

We have a winner! @ntsqd thank you very much!

Dan Press Industries was purchased by Randy Larsen of Larsen Racing Products. LRP purchased DPI and Randy Larsen is still making race products in Petaluma, CA.

I called Randy Larsen today, and learned that the unit I have is an early "gold track" and was made in the 1990's and is a 31 spline "HT" or Half Tight preloaded helical worm driven limited slip differential. It is indeed assembled in three segments, and it is threaded together. The case halves are left-hand, and right-hand threaded. They are torqued at the factory to 700 lb-ft, and are intended to last a lifetime.

The unit has evolved and is now sold as the "platinum" with bolted case halves.

Thanks!!!

 

[jamesroney]

Spanner wrench in the holes?
Case halves threaded in the opposite direction of normally applied torque? As in forward, instead of reverse?
Specialized spanner pins that might push into something to release a spring loaded cog tooth?

In other words, I have no idea…

great guess! Spanner holes indeed, and left-right threaded case halves. LRP told me not to unscrew it...because there's no need.

 

[jamesroney]

The "DPI" in the MW part numbering stands for Dan Press Industries. I had it partly wrong when I said "Sierra" above. DPI was the last incarnation. Now it is Larson Racing Products. LRP does offer the Gold-Track, now called the "Platinum Track", in 28 and 31 spline, as well as 8", 8.8", and QC diffs.
https://www.larsenracingproducts.com/categories/differentials-parts.html?page=3

They also still show the LBS for sale too.

While researching this I stumbled onto an article about Dan Press: https://scvhistory.com/scvhistory/lw3312.htm Worth the read.

One of the sponsors listed in the article for Dan Press was Sierra Mold and Engineering. So you probably weren't really wrong...

 

[ntsqd]

You're welcome. About time some of my useless trivia wasn't so useless.

No, I just had the sequence wrong. DPI came after Sierra.

There used to be a Sierra Racing Products that came after JFZ racing products. JFZ made clones of the wilwood Dynalite calipers. The wilwood side of the story is that JFZ stole a master plate and had the wilwood logo replaced with their logo. I've long wondered if the two Sierras were actually the same company.

 

[okie4570]

We have a winner! @ntsqd thank you very much!

Dan Press Industries was purchased by Randy Larsen of Larsen Racing Products. LRP purchased DPI and Randy Larsen is still making race products in Petaluma, CA.

I called Randy Larsen today, and learned that the unit I have is an early "gold track" and was made in the 1990's and is a 31 spline "HT" or Half Tight preloaded helical worm driven limited slip differential. It is indeed assembled in three segments, and it is threaded together. The case halves are left-hand, and right-hand threaded. They are torqued at the factory to 700 lb-ft, and are intended to last a lifetime.

The unit has evolved and is now sold as the "platinum" with bolted case halves.

Thanks!!!

700ft/lbs is impressive on something like that!

 

[serial car restorer]

They also still show the LBS for sale too.

LBS is interesting. I recall a similar product available way back in the late '70s and '80s. I think it was called something like SafetyBrakes or Safe-T-Braker. It was a buffer of some sort to cushion brake pressure spikes, and was apparently popular on race cars (and street bikes) prior to the advent of true ABS. I hadn't heard of anything like that in a long time.

 

[toddz69]

You're welcome. About time some of my useless trivia wasn't so useless.

No, I just had the sequence wrong. DPI came after Sierra.

There used to be a Sierra Racing Products that came after JFZ racing products. JFZ made clones of the wilwood Dynalite calipers. The wilwood side of the story is that JFZ stole a master plate and had the wilwood logo replaced with their logo. I've long wondered if the two Sierras were actually the same company.

That's the Sierra I was thinking of - and didn't know if they were still around or not. I was trying to figure out the lineage/story on JFZ discs (they were popular on off road racing trucks years ago) and found Sierra was now making them.

I still have my LBS that I bought years ago from BCBroncos too - I can't remember if mine was mfg by Stewart or DPI. I ran it for awhile back in the day (I think) when I ran Lincoln Continental Mark V calipers on the rear of my truck - far too much caliper for the EB, as I later learned as I learned more about brake bias/caliper sizing etc.

Todd Z.

 

[markw]

James, I thought those looked familiar. I have the Larson Racing Products diff in my race Bronco. It’s worked perfectly through several races.
Mark


Sent from my iPhone using Tapatalk

 

[Oldtimer]

LRP told me not to unscrew it...because there's no need.

But inquiring minds need want to know what's inside

 

[ntsqd]

Fix it till it's broke.

In just a couple of year's use I've become a stout advocate of the Tru-Trac. If the Gold-Trak and Platinum-Trak's are stronger and closer to the original design, then that's even better. I'm blanking on the name of the fellow who originally designed this type of differential. argh! Vernon Gleasman isn't the name that I'm remembering, but his Gleason Mfg was the first to really make the design available. A worm gear can turn a spur gear, but a spur gear cannot turn a worm gear. How that is employed to make a limited slip differential is the magic. https://members.rennlist.com/951_racerx/PS84Gleason.html

Ah-ha! Weismann is the name that I'm remembering: https://www.weismann.net/

 

[jamesroney]

Fix it till it's broke.

In just a couple of year's use I've become a stout advocate of the Tru-Trac. If the Gold-Trak and Platinum-Trak's are stronger and closer to the original design, then that's even better. I'm blanking on the name of the fellow who originally designed this type of differential. argh! Vernon Gleasman isn't the name that I'm remembering, but his Gleason Mfg was the first to really make the design available. A worm gear can turn a spur gear, but a spur gear cannot turn a worm gear. How that is employed to make a limited slip differential is the magic. https://members.rennlist.com/951_racerx/PS84Gleason.html

Ah-ha! Weismann is the name that I'm remembering: https://www.weismann.net/

Weismann is the inventor of the double sprague ratchet locker. It is covered in the 1964 US patent 3,283,611. I'll attach a pic. It functions very much like a "no-spin" ratchet locker.

Gleasman did rely on the worm gear / spur gear combination in the original Gleason-Torsen...but the current generation Torsen 2 is a more standard helical gear configuration. As I recall, Gleasman sold to Zexel of Japan in 1990 who then sold to Bosch Automotive in 2000 and finally Toyoda Machine Works in 2003. That TMW group merged with Koyo of Japan in 2006 and became JTekt. So JTekt-Torsen operates as a subsidiary of JTekt North America.

I'll try to do some research on who pioneered the true trac configuration.

 

[jamesroney]

So it looks like the pioneering work on the truetrac comes from the 1966 US patent 3,292,456 Spin Limiting differential. The inventor is Oliver Saari, and it is/was assigned to Illinois Tool Works. There is a relationship between Illinois Tool Works, and Dyneer, and of course TracTech, and the parent company Eaton. So the ITW / Dyneer / Detroit / TracTech / Eaton "TrueTrac" patent is long since expired. The patent shows a spur gear configuration, but the helical gear configuration is in the claims.