I'm about to get into swapping the 3.27 for a 3.70. I see some old threads on here linking to old parts places. Are kits still available for these? In particular the cone clutches.

 

9 BOLT Parts

And junk yards/used parts.

 

I emailed 9 Bolt. Hope they're still around. Website says 2007-2024. I'm leery of getting parts like that from a yard. Probably just as worn out as mine will likely be.

 

I would call Hawks and see what they might have available. I know they have https://www.hawksmotorsports.com/com...tallation-kit/ and they have gear kits too. https://www.hawksmotorsports.com/87-...nd-pinion-set/

 

That's where I'm getting the gear from. I just don't want to end up hooping myself once I'm in there and find I need parts no longer available.

 

I copied a couple other guys on here and put a Torsen unit in my 9 bolt with 3.70 gears. was basically as straight forward as any other rear end rebuild and gets rid of the pricey Australian cone mumbo jumbo

 

And works FAR better than any clutch type posi ever dreamed of.

I just recently put a True-Trac (similar design to the Torsen) in one of my other vehicles. Even got a chance to test it out in the snow here lately. ASTOUNDING how much better it works than ANY clutch device I've EVER had. Which is ... quite a few, over the last half-century or so.

 

That's interesting. Is this a bolt in mod and do you fellas have any links to this? I've never heard of it.

 

Yes.

​​​​​​​There's several whole threads in this forum about it.

 

Thanks @TylerSteez and @sofakingdom I've gone down the rabbit hole and figured out this whole torson setup and have been emailing back and forth with Supa and now have a good setup planned and priced. My question is this: would there be any reason not to go with the 3.73 over the 3.70. They have that gear set. It's for a Ford/Holden setup but I've been assured it fits our **** ends. It's a lot lighter on the wallet than USD and I can save on having to ship from different places. I know 3.73 over 3.70 is probably not noticeable but it certainly is financially. Wondering what your thoughts are on that setup.

 

No noticeable difference between those ratios at all.

I think I just went with the 3.70 because it is a native ratio to the 9 bolt and the 3.73 ratio didn't even cross my mind when ordering parts for a 9 bolt. If Supa says it fits and costs less money then I don't see a reason not to go with a 3.73

 

I'm sure you've seen these by now but I think these were the two main threads I used to gather info when building mine. Never hurts to keep usefully threads linked in relevant posts.

https://www.thirdgen.org/forums/tran...installed.html

https://www.thirdgen.org/forums/tran...rg-warner.html

 

Yes I have and that's exactly what's been steering me in this direction in addition to yours and sofas recommendations. There's absolutely nothing over here parts wise for these rears. I knew they were Aus rears from the get go but had no idea how much was available for them once you start looking outside. This is the gear set:

https://supafspares.supplies/product/gear-set-m78-3-73-ratio-holden-ford/

 

There's really no parts in the United States for them either I believe.

The Torsen retrofit really saved the future of the 9 Bolt housings in my opinion. Before it was either swap in the slightly weaker 10 bolt or fork over the cash for a 9", 12 bolt, or the 8.8 rear that Hawks is doing.

 

I bought the cones, spider gears, ring/pinion and bearings from 9-bolt.com in Australia years ago. Can't really get anything other than a 3.70 ring/pinion and bearings here in the US. The cones were new, but had a slightly different design that required some machining of the original carrier for them to fit correctly.

While it worked out just fine, if I were to do it today, I would do the Torsen carrier instead.

 

Interesting...

At different times, other people have reported the exact opposite; namely, that all they could find, was the 3.73, butt NOT the 3.70. I guess that sort of thing must vary according to what suppliers are out there at any given moment.

There never were many factory 3.70 ones to begin with. AFAIK the only stock application that got those was 85 Firebird w L69 & T-5, of which there were no more than a few hundred made.

For whyever, the 9-bolt gears generally have fewer teeth than the 10-bolt, in any given ratio range. Fewer teeth tend to be slightly noisier, butt also slightly stronger, so there's always a tradeoff, in the real world. So where the 10-bolt has a 2.73 ratio available (15 & 41), the 9-bolt has 2.77 (13 & 36); 10-bolt 3.23 (13 & 42) vs 9-bolt 3.27 (11 & 36); 10-bolt 3.42 (12 & 41), 9-bolt 3.45 (11 & 38); 10-bolt 3.73 (11 & 41) vs 9-bolt 3.70 (10 & 37). I think, butt I'm not sure (I've only heard it mentioned once or twice), that there was also a 3.08 9-bolt; a 10-bolt 3.08 is 13 & 40, butt if it exists, I'm guessing a 3.08 9-bolt would probably have been 12 & 37. None of those are "identical", butt they're all so close, that IRL it makes essentially no noticeable difference.

Note that in every case, at least one of the tooth counts is a prime number. That's so that every ring tooth contacts every pinion tooth an equal number of times over its life, and any given ring tooth contacts any pinion tooth only one time in a complete "cycle" of tooth matings, with those contacts spread out over as many gear rotations as possible. Specifically, a pinion tooth only contacts the same ring tooth in the number of pinion revolutions equal to the ring tooth count (for 3.70 for example, a pinion tooth comes up against the same ring tooth every 37 pinion revolutions), and the ring teeth likewise against the pinion teeth (every 10 ring revolutions in that ratio).

I personally have no clue why the aftermarket 3.7x 9-bolt gears were 3.73 instead of the stock 3.70, except maybe, that the 3.73 is a nominally more "perfect" ratio, with both tooth counts prime. I also have no clue who actually MADE the 3.73s, butt I'm pretty sure it wasn't B-W of Oz themselves.

 

When I rebuilt mine 10 years ago, the only aftermarket gear set I could find was 3.70, made by Motive Gear. That was fine since it was the ratio I wanted anyway. I just checked on Summit Racing and it's still available and also still the only gearset available for the BW rear. When talking to Glenn from 9-Bolt.com back then, he could get some OEM gearsets in other ratios there in Australia and ship them here.

 

Motive makes the 3.70. Torqueline out of Oz makes the 3.73 that's listed for the M78 Holden/Ford.

https://supafspares.supplies/product...o-holden-ford/

 

I'm going with this setup. Where can I find axle bearings & seals for 89 GTA 7.75?
OK, I found axle parts at Ratech!

https://supafspares.supplies/product/diff-kit-m78-crown-wheel-3-73-ratio-and-torquelock-holden-ford-28-spline-axle/

https://www.strangeengineering.net/product/9-blt-7-75-installation-kit-iroc-only.html/

https://www.ratechmfg.com/gmaxlebear.htm

 

I bought mine from Napa about 10 years ago. Not sure if they still carry them, but here are the part numbers.

Wheel Bearings PGB PBR9

Left Seal NOS16491

Right Seal NOS16542

 

The bearings are eeeeezzzzy: they're a Set 9, or A9, or whatever any given vendor chooses to call ... set #9. It's a typical wheel or trailer bearing set. I guess PGB chooses to call it PBR9. You can get them from practically any bearing mfr though.

The seals AFAIK are the same on both sides except that they have the little grooves to direct the fluid inward as the axle rotates, so the grooves run the opposite way. Exactly the same except different. So, unlike practically all other rear ends, which don't use those grooves, there's 2 different part #s for the 9-bolt ones.

 

Very Expensive Swap! $900+ for lsd & 3.73 gears from supa f series. Then import tariff of 200.00. Ratech parts 280.00. T/A girdle with studs 280.00.