Mumbles

iTrader: (5)

Hey there...
I'm just looking for some advice on installing a ring and pinion in my '99 Firebird Formula.
First off, I've asked around with some friends about what gear ratio I want. With the six speed, my factory gears are 3.42. I've been told I wouldn't notice enough of a difference with a 3.73, but at the same time a 4.10 or 4.11 may be a little steep for my taste. I've seen a couple of sites that offer a 3.91 from Motive Gear, but Motive's website doesn't have any info for this ratio, so I'm wondering if these other sites aren't mistaken. I have also found a few sites that offer a 3.91 option if I purchase a Moser 12 Bolt. But this option is inconsistent between sites and a 12 Bolt isn't exactly in the budget at the moment.
Second, I am wanting to perform the installation myself. I've never removed a rear unit, so I'm not really sure what I'm getting into. I've heard if the lash(?) or teeth alignment aren't correct it can destroy my rear end. Obviously not what I'm looking for. I've searched youtube.com for an installation video with no luck. Any advice would be greatly appreciated. Sorry about the novel. Thanks...

SSCamaro2000

Ive been around when some diff were taken apart, but never a new gear install when it had to be shimmed. To set the lash there are shims that move the ring gear closer or further away from the pinion. To test it i have seen some sort of paste or paint used to ensure a good tooth pattern. To do it right is a tedious process, i would look for a book or something that might help. I think this info is pretty accurate, but if im wrong im sure ill be corrected. The install is not impossible but take your time and you should be alright, good luck.

Mumbles

iTrader: (5)

Thanks.

ksk1980

iTrader: (33)

wrong forum but word of advice save yourself alot of money in the long run and have a professional do it . what may look right might not be (backlash and all sorta stuff to look out for ) . im sure you can figure it out w/ a manual but why take the chance of wasting your $$ and have it done correctly the 1st time . unless you wanna sound like a jet coming in for a landing everytime you let off the gas pedal(excessive whine from incorrect setup). gears run about $150-$210. and i had mine installed for $150 . so IMHO $300 i well worth not dealing w/ the headache

oh and by the way 4.10's are awsome w/ a 6 speed you'll love them.

g/l either way

BlackWS666

iTrader: (31)

There are a few good write-up here on the site. I agree with the above post about having it done, but at the same time, how are you supposed to learn if you dont try it. And if your like me I like working on my own car. Try to find some one who has done it before(successfully) and have them walk you threw it. The only hard part is getting the lash right, you need a special caliper. And yes 4.10's are awesome.

Mumbles

iTrader: (5)

Yeah I realize I posted on the wrong forum. I'm a bit novice when it comes to the site. Anyways, I do appreciate all the advice. I have considered having it done professionally, but only as a last resort. I'm in the research phase of the project and until I know for sure its NOT something I want to tackle, the plan is to do it myself. Also any professional at some point had to do it for the first time as well. Its just a matter of learning how. 4.10's huh? How low is your 1st gear? I don't want to be shifting at 10-15mph. I've also heard you could be wrapping 4th gear pretty tight by the end of the 1/4mi. Plus I'm one of those guys who just likes to be a little different than everyone else. I'm not ruling out a 4.10, I just thought a 3.91 would be a happy medium between that and 3.73. I found a book on amazon.com called: Differentials: Identification, Restoration and Repair by Jim Allen. Anybody familiar with it? Thanks...

BlackWS666

iTrader: (31)

with 4.10's you will top out around 125-130 with a 28" tire. As far as first gear goes. I would say I got it up to about 35ish, or so. Its fine, dont think about it just do it. I promise you will like it.

DVS99TRANS

iTrader: (7)

http://www.f-body.org/gears/Here is the gear calculator
This will give you the info your looking for. i would recommend getting the gears installed at a shop. You will mess it up the first time and if your on a budget, your wasting money and will have to get it done again. Just some words of advice because been there done that. 4.10s are the way to go though, they aren't as bad as you think they are.

madmax_mfp

iTrader: (1)

I have 3.91's and wish I had 4.10's since the m6 has a deep 6th gear owerdrive.

I agree with both of your posts, but to properly setup rear end gears, you will need a few tools. A pinion depth tool along with the dial indicator and torque wrenchs (in/lb. and ft/lb.) among other tools and shims that can be quite expensive. If you plan on doing many rearend setups (for yourself or charge people to do theirs) than by all means learn it and do it, otherwise the one time charge is a better way to go. Now you can spend your time and money on learning something that you will use more than just once or twice. Good luck with what you choose.

LtTransAm91

iTrader: (4)

I have a 3.73 gear ratio in my 97 trans am and i noticed the difference but having driven it for a while I kinda wish I would've went with the 4.10. in 6th with a 3.73 at 60mph im at about 1500rpm and the only time i use 6th is on highways or interstate. the only thing really hard about installing is shimming...if its not just right it wont last very long at all. good luck!

Mumbles

iTrader: (5)

I've been digging around the site alot lately. I've been thru a number of threads and the general opinion seems to be that even if you plan to make only some moderate power level changes you WILL eventually break your 10 bolt. Damn, huh. That doesn't mean I have given up on changing my gears. It simply means I have yet another decision to make concerning them. Do I spend the money and learn from it or do I save the money and put it toward the inevitable? This isn't a question I expect anyone to answer. The research for this project has lead me here and I guess I just want to let you all know where I'm at at this time. Thank you for all your advice. 4.10 it shall be, but in what rear end remains to be seen. Thanks again...

TA-Swede

iTrader: (4)

Motive makes 3.91 gears for the stock 10bolt. I had them, so I should know.

"Someone" also makes 3.91s for a Moser 12bolt. I have them, so I should know.

I also wanted 3.91 as a "happy medium" between 3.73 and 4.10s.

Be aware though. 3.91 is a tricky ratio, so most of them are noisier than 3.73s or 4.10s.

Edit: Yea, don't I wish the stocker was a 10"... 10bolt it is..

Cobra Kid

We did the 8.5 10 bolt on my son's Nova and it wasnt that hard! If you have mechanical experience you can do it. Special tools needed- torque wrench, die grinder , press , dial indicator. You could have the old bearings pressed off at a shop and then the inside clearanced for slip fit to test new shim pack. You should replace all bearings since you have it apart , but if you have good bearings and they dont get damaged you could reuse them. Used gears are almost as good as new and you can get them for half price or less (these dont wear like other parts). The 2 things you need to be conciuos of are backlash and gear mesh pattern. New gears (or old ) should get new ring gear bolts. You can get a video on how to from Richmond gear. We added a used posi , used 3.73's and new Timpkin bearing s and seals for $450.00.

ksk1980

iTrader: (33)

^^^ agreed on the new ring gear bolts . i sheared off two from the ring gear (with stock 3.42gears after installing a dual friction Centerforce clutch and flywheel ) . i thought i ran over something at first then about 100' farther i felt a jump come from the rear end,so i pulled over. Low and behold i had a trail of grease following me. what had happened was when the two heads rung off they dropped down and were picked up by the ring gear . the ring gear drug them up the stock diff. cover and ripped about 3/4" hole from the bottom to the top of the cover. they had to drag my car up on a rollback because a bolt head was lodged inbetween the ring and pinion. all this happened w/ stock gears that had never been messed w/ so if your going w/ 4.10 which is a thicker ring gear(heavier) i'd go w/ some ARP bolts . thats what i did and no problem to this day. I'm not all that easy on the 10 bolt rear either .