TennesseeIroc-Z

iTrader: (7)

Ok- before I even start.

I am FULLY aware of the limitations of the 7.5 10 bolt rear. However, I do NOT have an extra $1500 for a 9" or $2K+ for a 12 bolt or S60.....so I have to just make do with what I can. I'm sure most of you can relate.

I'm not building a drag car, I'm building a hot street car that might have 400hp.

My question for anyone who knows:

Most people on the ole inter webs say to stay away from the higher gear ratios because one of the (many) weak links is too many ring gear teeth. But when I look at aftermarket ring sets, there is some contridicting info going by that standard.
Ex:

Ratio /Ring-Pinion teeth

273. - 41-15
308. - 40-13
323. - 42-13
342. - 41-12
373. - 41-11
390. - 43-11
410. - 41-10
456. - 41-9

So, by ring gear teeth, the 308 ratio would be the strongest*. Accordingly, the 390 looks the weakest because it has the most teeth. Correct? But it looks to me that the 410 ratio is not necessarily a poor choice...

I'm sure the different ratios have a different pitch to them, meaning a 41 tooth 273 is not the same as a 41 tooth 456. Is that a contributing weak link factor?

Can anyone shed some light?

I want to run a 410 ratio, but don't want to make my diff any weaker by doing so.

AlkyIROC

It won't make a lot of difference what ratio you pick for a 7.5" diff. If you put enough power to the diff, the teeth will still fail. Your best bet would be the 2.73 ratio since that has the lowest torque multiplication. Lower torque means less stress on the parts.

If you build a much higher than stock HP engine, don't expect the driveline that's designed for stock power to survive. It's a package deal.

sofakingdom

iTrader: (1)

The problem isn't how few teeth are on the ring; it's how few are on the pinion.

Since "number of teeth" is only PART of the whole concept of "ratio", it would be worthwhile to consider the OTHER PART of "ratio"; arguably, the more important part.

And that would be, DIAMETER.

The ratio of the diameter of the ring to the diameter of the pinion is the same as the ratio of the tooth count. I.e., a 3.08 ring gear is about 3.08 times as large as its pinion, a 3.73 ring is about 3.73 times as large as its pinion, etc. BUT... since the ring gear is always the same dia (7½" give or take, in this rear) then as ratio INCREASES, pinion diameter DECREASES.

Now think back to what you know about torque multiplication. Torque = lbs × feet. Feet being, the radius (half the diameter) of the thing that's being twisted. Meaning, if you have a constant amount of torque, (namely, whatever the engine in question produces after the gear reduction and whatnot in the transmission) then as the pinion radius DECREASES, then pounds of force on the teeth INCREASE.

Meaning, if you wan to compare a 4.10 gear to say a 2.73, the 4.10 puts right at 1½ times as much force (4.10/2.73) on the teeth, as the 2.73.

The problem with "more" teeth can be, if there are "more", then each one is smaller; meaning, the amount of metal connecting it to the body of the gear, is also smaller.

But none of that is how you go about picking a gear, anyway. You pick the one that puts the engine in the desired RPM range (usually, the range between max torque and max HP) as much of the time as possible; then you accept what comes with the metallurgy.

vortec350s10

If you keep slicks/drag radials off of your car, I don't think you'll have an issue no matter how much power you have. The most torque the rear end will ever see is the most traction you'll ever have. The only exception I can think of is shocking the diff with a transbrake or doing a high rpm clutch dump. Like the other guys are saying, gear it for what you want, don't let it become a strength factor.

big gear head

Yea, smaller pinion equals weaker gear. A 2.73 is much stronger than a 4.56.

TennesseeIroc-Z

iTrader: (7)

This is why you have to ask questions.

There is so much mis-information out there it's ridiculous. I couldn't for the life of me understand why ring gear teeth count made a difference, when all the gear ratios have close to the same.

If you search around for "7.5 10 bolt strength", many times it will come up that "don't go with too low a gear ratio because the ring gear is weaker due to having more teeth", or "373 is as low as I'd go cause more teeth is weaker"...it's the same amount of teeth for 273, 342, 373, 410, 456...on the ring.

I understand the concept, and understand the small diameter ring, and understand the ratio how a lower gear ratio puts more torque to the axles compared to higher ratios and all that jazz.

This is the first I've heard of gear ratios being weaker because not "enough" teeth on the pinion. I'm not doubting it, it's just that I've not heard it. Makes sense tho, your actually increasing the torque multiplicity but at the same time taking away more tooth area to do so by using less teeth (area).

410 is what I want but wanted to understand this whole " less is more" B.S. Regarding ring gear teeth.

Thanks

sofakingdom

iTrader: (1)

I don't think you understand yet.

The ring is NOT "small" in some ratios compared to others. All of them are THE EXACT SAME SIZE: 7½", more or less.

Only THE PINION size changes.

The reason a higher gear ratio is weaker, is NOT "not enough teeth on the pinion"; it's because the gear part of the pinion is SMALLER, therefore the pinion shaft has more leverage on the teeth, therefore it loads them more heavily. Just like, a 12" ratchet loads the palm of your hand more heavily when you put 35 ft-lbs on it, than a 36" breaker bar loads your palm at the same torque.

But that's not how you choose a gear, anyway. You select a gear ratio that makes the car perform its best, and you accept whatever "weakness" comes with it. It's a non-issue.

eseibel67

I've always wanted to know why lower gear ratios compromise longevity.

Three thumbs up to sofa for a wonderfully clear explanation. Thanks!

big gear head

Yea, good job sofa.

AlkyIROC

For street driving, it doesn't really matter what ratio you install. 4.10 gears will get you moving a lot quicker than 3.08 gears will however if you use a 700R4 tranny with it's deep first gear, you don't need a deep gear in the diff. If driven on the highway, fuel mileage will suffer even with an OD if a deep diff gear is used.

For dragstrip use, gear selection depends on a lot of factors. Based on the engine's powerband, converter stall speed and tire size, the best gear ratio will have the engine maxed out to peak rpm at or just before the finish line in high gear (not OD). Change any of the factors and the gear selection changes. Something simple like a different converter stall speed will change the required gear ratio to maintain peak performance.

Since you don't plan on dragstrip use then pick a suitable street gear. Typically good street gear ratios are in the 3.08 to 3.73 range when using a 26" tall tire. If you go to a 28" tall tire then 4.10 could be used.

No matter what ratio you pick, start saving for a better diff because the 10 bolt will not last forever unless you granny drive it. It could last for years or could fail next week.

TennesseeIroc-Z

iTrader: (7)

I understand completely. I'm not a complete idiot, believe it or not. "Smaller" compared to a 9 inch, smaller compared to an 8 inch, 12 bolt, Dana 44, just about every other differential that's made with a v8 has a larger ring gear than a 7.5 10 bolt.

My original question/comment was asking why all the mis-information about a "taller" or higher numerically gear ratio supposedly weaker due to more teeth on the ring gear. The ring gears have basically the same amount of teeth, which made no sense.

Of course the ring gear is the same diameter.

And, no, I know that's not how one should pick a ring gear. I asked why I've ran cross numerous posts regarding the number of ring gear teeth being one of the numerous weak links. I know the 10 bolts limitations. I also know my budget. I have to make it work. This is my hobby car, for summer fun. My T5 will blow before my 10 bolt will, or they'll both blow together. As long as I don't clutch dump, or speed shift, I plan on cruising just fine.

A 4.10 ratio will be ideal for me, as I don't like the gear spread in its current form, mainly from 3-4-5th gear spread. This will tighten this up quite a bit, and when/if that T56 falls in my lap, I will be geared more appropriately for it.

sofakingdom

iTrader: (1)

Glad to see you're learning.

I appreciate the humble, grateful attitude. I look forward to helping you out further someday.

TennesseeIroc-Z

iTrader: (7)

I apologize. I did not mean to be such a smart*ss. I didn't realize how that sounded until after I sat back a minute and digested the posts.

But I do have one more question, as far as metallurgy is concerned, I'm seeing two different ways this goes.

With a pinion gear that has more teeth, the gear set is weaker because there are more teeth and the pinion diameter is smaller to accommodate more teeth...

With a pinion gear that has less teeth, the gear set is weaker because of the increase of torque multiplicity but all the while having less teeth (area) to distribute the load...

Doesn't make sense? Or...does it? I guess it's just weak period.

big gear head

A pinion gear with more teeth is larger. They don't make the teeth smaller to fit the pinion head, they make the pinion head larger to accept more teeth of the same size. A 2.73 gear has a much larger pinion head than a 4.11. The 2.73 will be stronger than the 4.11because the pinion head is larger, more tooth contact area and less torque multiplication.

Ron U.S.M.C.

The 3.42 gear ratio works well for me with the Eaton posi and 700r4.

First gear pulls nice and hard from the line when quickly stepping on the throttle. It will bark the tires from first to second and chirp them from second to third.

I can even do the same from 30mph when I let off of the throttle then mash it to the floor. It will kick down and bark the tires when it up shifts.

That ratio is perfect when combined with the Corvette servo. in the 700r4.
Heres the build. =
https://www.thirdgen.org/forums/tran...de-photos.html

TennesseeIroc-Z

iTrader: (7)

Man, I wish there was a shop around here (east/mid Tennessee) that did respectable rearend work.

I'm trying to make a list of tools I'll need to "properly" do a rear-end rebuild, and I can easily spend more than $500 on just tools.

Granted, some of the tools I could probably just need anyways, I.e. A good press, inch lb torque wrench, dial indicator...that kind of stuff can be used for multiple things.

To do all the shimming I Really want one of those Yukon bearing puller tools. Would make pinion bearing pulling a lot easier. But there not cheap, and kind of a special tool...

I can probably make a case spreader out of parts laying around. So that's a no biggie.

I guess what scares me most is to bite the bullet, purchase the right tools for the job, and in the end have wasted money on tools on an in properly setup rear. I'm fairly mechanically inclined, not afraid of turning a wrench, etc. but with this rear already a weak link an improperly setup gear would just amplify the weak traits of the 7.5.

From what I have researched, a "properly" set up rearend can last a while, whereas an improperly set up rear will most definitely grenade in the near future. Especially since I'm using a manual trans.

It would be nice to just be able to spend a couple hundred and have it set up properly by an experienced rear end mechanic. I hate being my own guinea pig...spending $500 on tools and then finding out that I should've put that .005 shim on the other side after my gear broke makes me worry...

big gear head

You don't need the bearing puller or a case spreader. I have built hundreds of rear ends without the case spreader and I use a bearing separator in my press to install and remove the pinion bearing. I do have the bearing puller, but I only use it for removing the differential bearings. Also DO NOT waste any money on a pinion depth tool.

92RS_Ttop

iTrader: (3)

I changed my 3.42 gears to 3.73 using just a shop press, bearing separator, dial indicator, and inch-pound torque wrench. All purchased from Harbor Freight, except the torque wrench which I got cheap on Ebay. I had less than $200 in tools, and not even that really as the shop press was a gift, so more like $50-60.

First time I has ever done it, and haven't had any problems in the last 7500 miles since. I had lots of help from members on here, mostly BGH and sofa.

AlkyIROC

To set the pinion shim depth, you buy another pinion bearing. By whatever means possible, you enlarge the center hole of the bearing so that it slips onto the pinion without needing to be pressed on. You can then easily take it on and off as you play with the pinion shims. Once the proper depth is determined, put on a new pinion bearing and keep the modified one for the next time you change gears.

TennesseeIroc-Z

iTrader: (7)

So that big fancy bearing puller from yukon gear isn't necessary?

It looks like a nice unit, I actually found a similar unit on TomsBronco parts.com

http://www.tomsbroncoparts.com/produ...ller-minor-kit

For "only" $219, which compared to the Yukon deal is not a bad price.

You guys just use a bearing splitter to pull the pinion off in a press- I wondered if that actually worked or not....

I just bought a dial indicator set on fleabay for $30 bucks. Next up is a inch-lb torque wrench.

Harbor Freight has a 12 ton press on sale for $150, so I'll do that in a couple weeks.

I want to do it for the satisfaction of being able to do it. I've learned how to set up valve springs, I'm in the process of learning to rebuild (overhaul) my pickups NV4500, hopefully I can do a rearend tool.

There's lots of good info here on TGO to go by, I just don't wanna f-it up.

TennesseeIroc-Z

iTrader: (7)

This is the most awesome helpful thing I've ever heard. Thanks.

So, a different bearing won't have a different thickness or alter the shim length?

So, if I didn't purchase the fancy-pants bearing puller, how would I go about pulling the side carrier bearings? Does the bearing splitter work here too?

92RS_Ttop

iTrader: (3)

The pinion bearings are all the same. The shims are to align the pinion properly in the housing. As long as you keep the same pinion and housing, you can swap bearings with no problem. I would make sure the bearings are from the same manufacturer though, just to be safe.

To take the old carrier bearings off, I cut the retainer with tin snips. Then used a dremel with a cutoff wheel to carefully cut almost all the way through the bearing shell. Then a couple whacks with a hammer and cold chisel and they came right apart.

That 12ton press is the one I bought. Just check the post on the bottom of where the jack sits. It was bent pretty good on the first press I bought. They let me exchange it though.

big gear head

You mean the axle bearings? You can borrow a tool from Auto Zone to remove them. It's a big slide hammer with hooks on the end to grab the bearing.

The Yukon bearing puller is a great tool if you are going to do this a lot. I bought one from the original manufacturer many years ago. Yukon bought the business a few years after I bought mine. I have pulled hundreds of bearings with it and it works great. If you are just going to do one rear end then it's not worth it.

I have measured pinion bearings and found as much as .004 difference in the thickness. If you choose to do this then be sure to do another pattern check after you install the real pinion bearing. You might be surprised to find that the pattern moved after changing bearings. I always use the same bearing for all trial assemblies that will be used for the final assembly. It only takes a minute to press it off and on again.

Marc 85Z28

iTrader: (3)

This might help visualize things a little better:



For reference: the tiny 4.10 pinion head is the same diameter as the pinion bearing.

The pinion gear shears teeth due to case distortion. It's more common on the smaller pinions due to the smaller contact patch, and that they're typically used in setups that shock the driveline violently causing the housing to move around. I've never seen a 2.73 or 3.23 gearset fail, and that includes a few 9 second cars that have seen 1.4x 60' times.

TennesseeIroc-Z

iTrader: (7)

Cool picture Marc. That's what I needed to see. Really puts it in perspective. Man that 410 pinion is small.....a 456 probably just looks like a straight shaft...

I have a slide for the axle bearings, but I was actually referring to the carrier bearings. I think tho that they can be pulled off with a standard gear puller.

big gear head

Those bearings are hard to get off without the right tool. I used several methods to remove them before getting the bearing puller that I have now. One easy way to remove them is to cut the cage off and get all of the rollers off. Then use a MIG welder and run a HOT bead all the way around the inner race. This will loosen the press fit and you can usually knock them off with a hammer and chisel. Just be careful not to damage the bearing journal.

TennesseeIroc-Z

iTrader: (7)

That doesn't sound like fun at all Big Gear Head.

I may just save up for that $219 tool, and then I'll have it when my rear breaks again...

big gear head

Or you could pull bearings for all of your friends.

TennesseeIroc-Z

iTrader: (7)

Me likes that idea.

Thanks for the help All.

Jeremy85

Ok, are fewer larger teeth stronger than engaging multiple smaller teeth at once? 2.14:1 is a 21 tooth pinion, and I think a 45 tooth ring, I think 2.29 is 48/21, so that should be stronger, no?