4.10 vs 4.11 - yes, they are different

[acammer]

Hey guys. I know it - I'm the guys always talking gears and poking his head into every conversation about them. Well, it's time to go even deeper. I wanted to share something I've observed, and see how it sets with some of you guys as we think about our 4.10 vs 4.11 gear options. If you don't like some good technical discuss, I'll try to summarize at the end.

So, first some ground work - what's the general difference. It's simple - 4.10s have 41 ring gear teeth, and 10 pinion teeth. 4.11s have 37 ring gear teeth, and 9 pinion teeth. Both use the exact same diameter ring gear, so the count (and size) of the teeth is what's changing here. I never gave it much thought, but I saw something that got me thinking about this and what implications it has for our cars.

First, in a general sense, from what I've found if from a strength perspective is that you want to run LESS pinion teeth, and have larger overall teeth. If you look at "pro" gear rear ends for race applications, they are all 37/9 arrangement for 4.11's. All the race specific (or HD offroad) gear sets in varying ratios keep the tooth count down nice and low, some using only 7 pinion teeth in certain ratios. Some would debate that more teeth spreading the load more evenly is stronger. I disagree with that theory, the design of these race gears ( which prioritize strength over all else) clearly points to the idea that bigger teeth > more teeth.

When we start talking specific to our application we find that 4.10 gears for the Gen 5 Camaro are almost exclusively a 41/10 arrangement (Motive, US Gear, Nitro). The only exception to that which I've found (currently in production) is the Yukon, which is a true 4.11, 37/9.

There is one other very notable exception, and that is the now out of production Richmond 4.10/4.11. Originally, Richmond made a 4.10 (41/10) ratio for the Camaro's. After many broken pairs they revised their gear to use a stronger material, and went to a 4.11 (37/9), and advertised that as a stronger setup. I think the damage had been done to their reputation at that point in the Gen5 Camaro world, so I don't know how many of those 4.11's actually made it out into the world. But, the telling thing there is that to gain strength they didn't just change materials, they went to a 4.11 (37/9) arrangement.

Further down the rabbit hole, we are starting to see that Motive is now making gears for the Chevy SS/Caprice/G8 differential. These use the same 8.6/218mm ring gear size as the gen5 Camaro, but have a slightly difference pinion shaft size, so it has to be a different gear set. What's really interesting is that Motive went with a 4.11 (37/9) instead of a 4.10 (41/10) for that differential. Why would they do this, especially if they have a ring gear mold for a 41 tooth 218mm GM IRS already. Maybe they aren't the same, but it still begs a very interesting question - why go to the 37/9 when the 41/10 was originally chosen for the Camaro?

I don't know, but I have to think it's lessons learned with 41/10 sets. Richmond and Motive (for the SS/Caprice/G8 carrier) both made significant changes to use a 37/9 when they redesigned things. It's definitely interesting to consider. I wasn't aware of these differences until very recently, and I'll bet some of you weren't either. Maybe we can get some interesting conversation going here.

In my personal experience, I've had Richmond 4.10s, Motive 4.10s, and now Yukon 4.11s. I pulled 5 ring gear teeth of the Richmonds. The Motives never broke, but were AWFUL noisy after I drove home from a race with a failed crush collar and no pinion preload - not the gears fault IMO and they still made passes after the fix, but were loud. The Yukon's put up with a good amount of abuse, going many passes in the 1.6-1.7x range, and dealing with some wheel hop on occasions. Eventually, I cracked a single ring gear tooth at the base of the drive side under some violent wheel hop - sort of a weird failure. Also of an interesting note - this car has NEVER broken an OEM axle - although I did replace one once when doing one of these diffs as it was getting a little sloppy. It's got Yukon gears in it again - hoping for a better life from this set.

*** EDIT - see dialogue below. SummitRacing incorrectly lists the G8/SS/Caprice ring gear as an 8.6" 218mm - it's 8.3" and unrelated ***

[NEstyle]

How did the crush collar fail? Was it defective or something?

[Bo White]

G8 is 8.3" ring gear

[NEstyle]

Originally Posted by Bo White

G8 is 8.3" ring gear

And PPVs and SS sedans should also the same. We all put 218mm Camaro rears in them (I have a PPV).

[Bo White]

Gears or whole diffs?

[NEstyle]

Whole diffs. They are completely different (way beefier housing and supposedly larger diameter gears as you mentioned) yet bolt right in.

[Bo White]

Right. Was just making sure on your info.

[Bo White]

Why I posted was what the reason for the 37 ring gear for the G8 is because of the 8.3 diameter. 41 would be harder to do.

[acammer]

Well, that makes more sense. Summit lists the G8/SS/Caprice ring gears as 218mm 8.6" stuff - so I was drawing some conclusions (incorrectly) from that. I looked it up directly on Motive's site, and sure enough, it's an 8.3" (gross!). Thanks for the clarification.

Still begs the question - why did Richmond go to a 37/9? Obviously, they thought it would be stronger. In practice, the Motive's seem to have the best reputation with their 41/10 - maybe that's superior metallurgy. Interesting stuff anyways.

[Bo White]

No problem bud. Thats what forums are for. If you want to get misinformation and arguments then go to FB lol

[oldman14ss]

well now. let me add to the mix. with the many unknowns out there let me add some : were the gears 5 cut or 2 cut? what was the metallurgy of the material 4320 or 8620. I think I got those numbers right. lets add face hobbing in there also. I did a little gazing when I was shopping for gears and it snowballed. I went to metallurgy sheets etc . the one thing I found was to get the gears already polished from the factory. less break in tighter tollerances, quieter. 5 cut has a taper where 2 cut has no taper from toe to heal. straight cut gears. that might have an influence on failure. pure speculation on my part. the oldman...........

[oldman14ss]

I think your crush collar fail was due to the pinion nut not staked or not staked well and it came lose, or the wrong pinion preload was had.

[NEstyle]

Originally Posted by oldman14ss

well now. let me add to the mix. with the many unknowns out there let me add some : were the gears 5 cut or 2 cut? what was the metallurgy of the material 4320 or 8620. I think I got those numbers right. lets add face hobbing in there also. I did a little gazing when I was shopping for gears and it snowballed. I went to metallurgy sheets etc . the one thing I found was to get the gears already polished from the factory. less break in tighter tollerances, quieter. 5 cut has a taper where 2 cut has no taper from toe to heal. straight cut gears. that might have an influence on failure. pure speculation on my part. the oldman...........

Two cut gears are face hobbed. Good point about strength, though. Two cut gears are supposed to be weaker than 5 cut gears due to the reduced contact patch. Can you even buy 5 cut gears for these rears?

[rich2342]

So, What is the concensus on best gears. 4.11 with the 9 tooth/37 ring or the 4.10 with 10/41 ring?

Looking for quiet and reliable of course..