Hello
I have a 79 camaro with a 305 (TH350 tranny) and the stock 10 bolt rear . Right now it has the stock highway gears (2.41:1). I plan to switch to something to give me some better acceleration. The car is only used for short drives around town and rarely(if ever) sees the highway. I was thinkin I would gonuts with it and put something like 4.56 or 4.11 in the car. Would this be amistake to put these gears in? Also does anyone have an estimate of what a shop would charge me to change the gears? Ive heard that this isnt a job I should try without experience. Any input is apprecitated.Thanks

 

A decent shop will probably charge you about $3-450 for labor-setting the backlash and crush sleeve pressure isnt easy.You may want to seriously consider adding a posi unit if you are going to pay to tear apart the rear to add a set of gears. I rebuilt the rear in my 70 (have many posts on the subj. may want to take a look..)Id suggest Richmond gears and Auburn posi. If you wont go on the hiway w/the car, go ahead and go crazy with it. I had stock 2:73 gears andput it3:23's w/posi, But I drive to work on the hiway one or twice a week.

 

Hey, go nuts! Lower gears will really wake up that car. I have 4:10 in my 69 and am pushing over 4k rpm on the highway.I don't travel long on the highway either, but eventually I'm going with an overdrive trans. With a 350 trans, I feel a 3:73 would be a good all-around gear. If you give your tire diameter, I can tell you what your final hwy. rpm would be for different ratios. Or if you like to do math problems, I can tell you how to figure it.

 

Hey thanks for the input! My tire diameter is about 25 inches. I used to have the formula to calculate rpms from the gear ratio and tire size but i seem to have lost it. It would be great if i could see how your calculating it.

 

Working for a drive train shop, I've rebuilt a few rear ends. Unless you have more than a stock motor, I would recomend not going any lower than a 3.42. That will still leave you something on the top end, in case you need to traval more than 45 mph. You will also need to replace the carrier anyway cause a 2 series carrier will not support a 3 series gear set. Auburn makes one hell of a L/S, but, if you want something with a longer wear life and all steel construction, you should look into a Detroit true trac or a thorsen. They use helical gears for the L/S that lock the diff under torque load and offer a somewhat stronger case. It also alows you to upgrade to 31 spline axles. It would be as strong or stronger than a 12bolt.

 

Ive read that I could use the 3 series gears on a 2 series carrier if a spacer was used. Is this not a good idea? would it be better to go with purchasing a new carrier?

 

Never, ever, ever, under any circumstances should a ring gear spacer ever be used....Ever! I cannot stress that enough, they sacrifice to much strength and cuase more problems than they solve. The ring gear must run perfectly true to the pinion gear in order for the diff to live long. Also, anytime a ring gear is installed, the two mating surfaces (ring gear and carrier) must be "faced" with a facing stone to remove any high spots prior to assembly. Now, just to settal any arguments before they get started, I have installed gear sets from Ford Motorsports, Richmond, Youkon, Motive Gear, Spicer, GM, Precision, and various no name, overseas manufactured sets that were passed off as good quality gears, They must be faced to ensure a perfect fit. Anyone who's done this will know what I'm talking about. They get dinged during manufacture and must be trued up before installation. The carrier gets distorted around the bolt holes from the bolts being torqued this has to be removed also. I face all the carriers I touch and have found the same distortion on new ones as well as used. Our coustomers pay between $800-$2000 for an overhaul, depending on the severity of the damage and/or the type of work being done. For me, it has to be right the first time.

 

Let's assume you're going with a 3:73 gear, with your 25" tires, and we'll base it on a highway speed of 65 (if you like going that slow)!
The formula is: (65 mph x gear ratio) multiply that number by 336, then divide that number by the tire diameter.
65x3.73=242.45. 242.45x336=81463.2. 81463.2 divided by 25=3,258.53 rpm's.
Currently, your 2:41 gears should be giving you 2,105.38 rpm at 65 mph...quite a difference!
A 3:55 gear would give you 3,101.28 rpm at 65 mph.
Or, if you had26" tires with 3:73 gears, the rpm would be 3,133.2, not far different from a 3:55 with 25" tires. You can see that just changing your tire by one inch can make a noticeable difference.
Your trans has a final drive of 1.00 so nothing else gets factored in. But for those who have an overdrive trans, the percentage of overdrive has to bemultiplied by the rpm's you get from this formula.
For instance, a 700-R4 has a .70 final drive. So with 3:73 gears, wherethe T350 is making the engineturn 3,258.53 rpm's,the 700-R4 will make the engineturn 2,280.97 rpm's...almost 1,000 less!
I have 25.5" tires and 4:10 gears, turning 3,511.53 rpm, and it doesn't take much more to get to 4,000. At that point, I can hear my carbs making this very loud thirsty sucking sound. Now you see why I want to go with an O.D.! I really like the bottom end mine has, but I would like to be able to compensate for it at the top end.

 

Thanks alot for that formula! thats great! the input on the carrier is really helpful, this is the first time ive had anyone give me a straight answer! So trying to do all of this on a small budget what do you guys think would be the best parts(gears, carrier, etc...) for me to buy? Im really not looking for top of the line, best of the best stuff...The cars not worth enough to dump a lot of cash into the rear end! im just looking for some acceptable parts for an acceptable price...thanks