Building my first 9-bolt rear. New 3.73 Yukon gears. Set the backlash to .009.

I tried using the original shim thickness on the pinion (.020) and took the pattern (photo attached). The pinion looked too far away to me, so I went with a thicker .030 shim. This looked too close, so I went with a .025 (photo attached). To my less-than-expert eye, it still looks too close.

Can some of the experts here give me their opinion of the pattern with the .020 and .025 shims? I really appreciate it.

Matt

 

I wanted to add that while I think the pattern looks better with the thicker shim, I was wondering why there is a clear line in the marking compound at the flank of the gear teeth. It's making it hard to see the full pattern at the flank. Did I use a bit too much compound?

Thanks for your help!

 

I think you did fine, but here is another guide ; http://www.precisiongear.com/pgtechpatterns.htm also, what does Yukon recommend for a backlash setting for your gear?

 

Yukon recommends .006 to .010 backlash for my gearset. I achieved .009, which I think is fine. The pattern is nice and centered on the geartooth, so I think the backlash is fine.

I'm more concerned with the pinion depth at this point. Using the thicker shim lowered the pattern away from the crown of the tooth, but I am concerned about what I am seeing (and not seeing) near the root of the tooth. It looks like the pattern ends abruptly around the root of the tooth. There is still more tooth surface below the pattern, but the flat edge on the pattern has me concerned.

Any idea on what I need to do to get a clearer pattern?

 

You of coarse don't want it too deep, but by shimming only .001-.002 will make a difference. Just depends on how fussy you want to get. Me personally, I would try to tighten your backlash by a couple of thousands, and repattern it.

 

What's the benefit of reducing the backlash when it is in the acceptable range? Will it improve my pattern or something? I've heard that setting the backlash on the low side can improve the strength, but can also result in some gear noise.

BTW, thanks for the help.

 

With a 3.70 you may still get some whine, i have some in mine that's not too noticable, just the nature of a high gear ratio sometimes. As for backlash, if you move it say down to .007 or .008, you may center the pattern from toe to heel a little better and also drop a little more into the root. All you can do is experiment and see, If you don't like it, then put it back to where you had it.

 

I went with the Yukon 3.73 gears in part because of their reputation for quality and because I've read that some of the other 3.70 gears on the market (i.e. Motive) tend to be noisier. I really wanted a new gearset and unfortunately you can't get anything other than a 3.70/3.73 ratio new for a 9-bolt, as you probably already know.

I see what you're saying about centering the pattern from heel to toe better. I'll adjust the backlash and see how I like it.

Thanks red rock, I really appreciate your help!

 

You are in the range of passing for sure. If you plan on racing or applying more power, I would myself shoot for about 7 or 8 on backlash so it's more centered. More Contact. Trying to remember which direction, but the pinion depth could be tweaked a little less deeper as well by about 1. Meaning the teeth mess farther out, so its center there as well on the thicker part of the tooth. I mean really you are fine. Depends on the power and stress you are applying to it. Also I'm not sure if a 9inch rear has solid spacers rather than crush sleeve, if they do, trash those crappy crush sleeves. It's a little more work but worth it in the long run. I’d like to kick the person in the side of the head that decided on saving money and using those d#mn crush sleeves.

 

8UpAFord, I see your points about getting more contact on the gear teeth. I thought my pattern looked a little "light on contact" too. I'm going to reduce the backlash a bit and re-check my pinion depth.

Thanks!

 

Take pics and reposted them again. It's always nice to have a third eye. and now just reply to my post "vette with 3:54 gears" I need some advice

 

OK, I decreased the backlash to .008 and put a .022 shim behind the pinion. The pattern looks as good as I can get it (see attached photos). I'm going to run with this setup and see how it goes.

Thanks for your help guys.

 

Mullery, That looks great. Just don't be alarmed if you have a little whine, sometimes thats the nature of a 3.70+ gear ratio. Also make sure you break it in EASY for about 500 miles.

 

I can handle a little whine, as long as it isn't too much. I've reviewed the break-in procedure and I'll be sure to follow it. I should get it back on the car in the next couple of weeks (I'm too busy to finish quickly). I still have to do the final assembly with the pinion, get some new bearings and seals pressed onto the axles and paint the housing with POR-15.

I'll post with the final results once it's all done.

Thanks red rock.

 

If it makes you feel any better, that pattern looks a little better than mine (richmond 4.10) and it hasn't made any noise (that I can hear over the exhaust) in the 60 miles I've put on it.

 

Kerplunk318, actually that does make me feel a little better.

I think the jury is still out somewhat on the amount of noise to expect from this gear set. Some say the higher ratios make more noise, some say the 3.73:1 is quiet as long as it is setup properly. I guess I will find out soon...

BTW, I just ordered a solid pinion spacer kit. I like the idea that I can disassemble, swap gears, re-shim the pinion, etc. without having to keep crushing a new sleeve each time. The cost was minimal and the extra assembly time is not a problem for me.

Thanks for your post.

 

yeah dude thats money. And the crush sleeve is crap (trash it), for strength a soild spacers is a good investment. Dealerships used that crap on the assemby line to save time and slap units togther, I've had to make my own spaces, if they don't sell them.
You won't have a whine eirther. As long as it's setup correctly. I've never broke in gears lol too, eirther they work prefect or not... I mean don't drive it 500 miles on your first trip maybe... Some people say they need to heat and cool down within cylces, but whatever, doesnt hurt I guess.

 

thats looks good. My 3.70s didnt wine in an old TA I had.

 

Your contact pattern looks just about perfect to me. If you do end up with any whining, it'd probably be due to the quality of the gears and not due to your pattern. It's also good that you took the advice of using a solid spacer. I've never used a crush sleeve on a new setup, except for one rear I set up for a friend of mine. He insisted on doing it just like stock and using a crush sleeve, even though I tried my best to talk him into a solid spacer! Lol. I think you'll be happy with a .007-.008 backlash as well. .009 is acceptable, but I like to set them on the tighter side of the range. When everything wears in, you'll have less slop than if you started with .009 when it's all new and tight. All my setups have been quiet and tight using a starting backlash of .006-.007. Yukon should end up being a good choice of gearset. I'm pretty sure they "pre-lap" their gears, which will help them run quiet. All those cheap, overseas gearsets aren't factory lapped and are made with inferior quality steel, so they're almost guaranteed to be noisy no matter how perfect you set them up. Motive used to be good gears, but I heard they were bought out by the Chinese not too long ago, so I'd avoid them nowadays. I installed a set of Motives in my 69 Camaro 12 bolt a few years back, and that was before they were bought out, and they set up great.

 

Is she singin'? Mine started to make a little noise around 60mph and light throttle. Probably has around 150 miles on it now