what gears 3.73 or 3.90?

**JDCAMARO99** · 03-11-2015, 07:24 AM

Guys, I have a 6 speed with all bolt-ons. I have a friend who has a set of 3.73's and 3.90's he's letting me choose from. I can have either one. I think they are both made by motive. Which would be good for the M6? I hear the 3.90's tend to whine due to how they are cut at the factory. But, I also heard that as long as you have a good mechanic to install ,they should no whine. I also hear horror stories of having too small of a pinion gear that it chips the gears up on the 7.5" 10 bolt......and not to go too small. But for free, I'm gonna take one of them I suppose. Is there much of a difference from my stock 3.42's to 3.73's? And, are motives a good gear? Any help would be greatly appreciated.

**Whamhammer** · 03-12-2015, 02:26 PM

With the 3.73's, you will have an 8 percent shorter gear, with 3.90's its 12 percent shorter than the 3.42's. If its free parts and labor, longevity of the gears assumed the same, it really comes down to what kind of area you will drive, the 3.90s will not be as highway friendly as the 3.73's, but if most of your mods benefit the higher rpm band, the 3.90's will benefit more.

If the labor wast free (did t notice if you said that), andyour making some good power, the 7.5 will give out in a matter of when, not if, and that money might be better spent towards abetter rear that you have your pick of gears anyways.

**theorangeguy** · 03-12-2015, 04:21 PM

3.90's and dont look back...the MPG difference with a 6 speed on the highway is very minimal. Like less than 1 or 2 MPG's. You will enjoy driving your car around town a lot more with a 3.90 as well.

**JDCAMARO99** · 03-12-2015, 05:51 PM

I'll have to pay for labor. Kind of bummed i gotta get the speedo calibrated too. Everyone in my area wants an arm and a leg to calibrate it. I'm really wanting to throw the 3.90's in there. I do worry about the rear going out, but i guess i'll worry about that when it comes. Speaking of which, do you guys know what usually breaks in the 10 bolt? is it usually the pinion gear that fails? ring gear? everything? lol.
And the only reason i was thinking of the 3.73's were for traction purposes. My bud has 4.10's in his six speed and can't keep the tires from spinning. I kind of figured the 3.73 would be a decent jump and not enough to get me squirly I don't currently have any traction issues with my nitto's. I just got them in the fall. They seem to stick pretty good. The 3.90's just call out though.
Thanks for the feedback guys. I love this site. Can't get any info you need on here!!!!

**ASh302** · 03-13-2015, 07:40 AM

IMO I would say 3.73s, best all around gear for street/highway/drag
but if the car is mainly more drag, then the 3.90s will be better.
I think no matter what gear you go with if they do not get installed good then the whine will be there
I have built moser 9in with 3.73 gears and 31spline and get a little whine from it, but just normal from what Moser said, but its all good

ASh

**67CamaroRSSS** · 03-13-2015, 02:32 PM

I've not had any luck with Motive gears but maybe that's just me. Had 2 sets of 3.73's. 1st set whined like a whore who hadn't gotten paid and the 2nd set broke a couple of teeth off of the ring gear. 3rd set of 3.73's were Richmond. No whine but it welded the pinion bearing to the pinion shaft, burned the seal and leaked like a sieve. I was mostly racing the car at the time (see sig).

The Motive's were set up by one place; the Richmond's by another place.

I'ts now back to stock with a set of used 3.23's and it works just fine.

Also, recalibrating for gear ratio can be done with most hand held programmers (they aren't much good for anything else though). You merely have to be able to access the PCM through the ALDL and change the ratio. Simple as that. If they're charging you very much they're ripping you off.

I'm also another fan of not sticking any $$$ into the spindly 4 cylinder rear end (originally used in Chevy Vega's, Monza's and the like) they stuck us with. Trust me, I've spent enough to have bought a 12 bolt at this point...

**pajeff02** · 03-13-2015, 03:37 PM

Mother Jupiter. If you were closer to us, I'd update your tune for the price of the HP tuners credit.

We went with 3.73's in our A4 car and they work great. Honestly, could have went just a bit deeper and been happy too.

**JDCAMARO99** · 03-13-2015, 08:44 PM

Thanks for all the good info gentlemen. Appreciate the feedback. Got a shop down the road to do the swap for $200. The cheapest place I found to calibrate my speedo was $100. Stuff adds up. Didnt want to dump too much into the 10 bolt, but why not try out some free gears. Hopefully either set can drop me a tenth or two. I've been wanting to hit mid 12's. Almost there.

**ASh302** · 03-13-2015, 09:13 PM

When my stock one went out, broken teeth on the gears is what happen, they wanted almost half the money as a built one to rebuild the stock one, I was like NOPE, lol but I was also blessed with being able to get a built one, I understand budget and dealt with it for years.
Traction is all in the driver and how they drive their rides, understanding how ones ride acts helps big time and your probably right on that tires do help big time, and all of it comes together to get your times down. The tires that are on mine right now, just suck to be honest, they spin too easy, which is going to drive me crazy the first time I go drag to find out times, which is next month, but it will be fun
It does add up, that is why I believe it is important to budget ones self for sure and do some research on what parts one is adding, I've had my fair share of bad direction and could still make that mistake if not careful, but we live and learn.

ASh

**pajeff02** · 03-14-2015, 04:23 AM

It is very doable -- our engine is still all stock and she goes 12.4's in good air. She started out running 13.3's or 13.4's when we made the first track outing back in '09.

**JDCAMARO99** · 03-14-2015, 06:33 AM

Great info man. I feel I know my car pretty well. I think ill try the 3.90s out. Why not you know!

**JDCAMARO99** · 03-14-2015, 06:35 AM

Originally Posted by pajeff02

It is very doable -- our engine is still all stock and she goes 12.4's in good air. She started out running 13.3's or 13.4's when we made the first track outing back in '09.

Wow....thats pretty incredible. These motors are no joke! Id be happy with that time. Until I do hit it and want more. Lol

**ASh302** · 03-14-2015, 07:33 AM

Originally Posted by JDCAMARO99

Great info man. I feel I know my car pretty well. I think ill try the 3.90s out. Why not you know!

Think about a pro driver and non pro driver and give them the same car and it is amazing how much quicker the pro driver is with the same car. That is what I was getting out about the gears and traction. I could take my T/A to the track and run a time and then a pro driver takes mine and runs a lot faster.

ASh

- - - Updated - - -

also sounds like you really want the 3.90s just go with them and call it a day

ASh

**pajeff02** · 03-14-2015, 08:19 AM

Originally Posted by JDCAMARO99

Wow....thats pretty incredible. These motors are no joke! Id be happy with that time. Until I do hit it and want more. Lol

I have done everything I can at this point without touching the engine. I will need a cam to dip into the 11's.

**JDCAMARO99** · 03-15-2015, 06:57 AM

U guys have any recommendations on gear weight and oil? I hear royal purple is the way to go. Is this a good oil to use?

**Firebirdjones** · 03-15-2015, 08:14 AM

In that little 7.5?? I'd put the thickest oil you can find in that thing to give it some cusion for the shock load you're about to put it through

**pajeff02** · 03-15-2015, 03:41 PM

Not a fan of R.P. for anything. A good heavy weight dino-style gear oil would work just fine.

Here's a good read with some comparison charts: http://www.lastgreatroadtrip.com/wp-...comparison.pdf

**JDCAMARO99** · 03-16-2015, 04:32 AM

Originally Posted by pajeff02

Not a fan of R.P. for anything. A good heavy weight dino-style gear oil would work just fine.

Here's a good read with some comparison charts: http://www.lastgreatroadtrip.com/wp-...comparison.pdf

Nice guide man. Thank you.