rearend gears

[kirk98]

I've got a 98 Firebird, completely stock except I added a K&N air filter, nothing big. My differential is very SLIGHTLY leaking, but its still there. Since I've got to have a new seal (I've been told thats all I'll need) put in, I figured why not maybe change my gears while everything will be opened up. I'm assuming I have 3.23 gears (since I have a 5 speed), how would 3.42 work for me? This is my daily driver, but I would like to have a fast car, you guys know how it is :D What I'm looking for is faster acceleration, not top end. If I have 3.42 gears installed, would I rev high in 5th gear while cruising at say...55 mph? or even 45? Thanks for any and all comments/suggestions/help. I'm still very new with cars, and I'm still learning. I find it very interesting how cars/engines work...thanks again everybody.

-kirk

[BLLDOGG]

well, you can look at the codes inside your door and compare to the list of codes in the Tech. database. if your going to open it up and do all that work, put in LSD too. i would recomend 3.73s if your not worried about anytop end stuff. it will give you some pretty good take off power and no, you rpms will not be up high, around 2K like usually i believe

[FunkZ]

I just changed from 3.23 to 3.42 ratio. It will throw your speedometer off by appx. 5.5% - so cruising down the highway at an indicated 75mph will actually be closer to 70. You'll be taching 130 more rpm at that speed.

<edited for math>

[ September 28, 2004, 08:50 PM: Message edited by: FunkZ ]

[BLLDOGG]

yeah, that is one thing i forgot to mention, you'll have to fix your speedo

[93camaro_zzz]

and another thing is that taking the rea diff cover off isnt exactly "opening up the rear end". it's not hard at all to do that. I would definetly suggest gears, but you dont have to do them, just because you took off the rear diff cover. Good luck. ;)

[MustangEater8251]

Alwasy keep on the lookout for a deal on a used v8 rear end..

As for 3.23-3.42s, I felt it was wortht eh gain on my 3.4L especially for 4 wheels disc and lsd I got with a v8 rear end swap.

[FunkZ]

Depends on where it's leaking. Replacing a cover gasket is simple enough for anyone who can change motor oil. GM rears always seem to have some seepage around the pinion seal, so unless it's actually dripping out I wouldn't be too concerned about it. If the pinion seal does need to be replaced you're right, it would be an excellant time to change gear ratio.

As in Mustang Eater's case (and mine too) it was a better idea to simply swap rear ends since we upgraded from drum to disc, got posi and a gear change all in one swipe. But if your '98 has low miles and already has the disc's, it's a tougher decision.

[kirk98]

thanks for all the help guys! My Firebird already has disc brakes all way around, and only has 47,000 miles. I thought that taking off the diff cover was "opening the rearend up". A friend of mine told me to get the pinion seal checked. So I guess all I'll do for now it just get everything checked out and replace the seal (and/or anything that needs fixed). I'll change gears later. All I really need to do for now is get things like this fixed before winter sets in. Hmm, what else.....OH- by adding 3.42 or 3.73 gears, how much would my gas mileage change? Would highway travel be bad with 3.73? I ask because I like to go to Baltimore to visit family once a month or so, and its 60 miles (almost all highway). And another small question- what exactly is LSD? Thanks for helping me out and being patient, its appreciated.

-Kirk

[FunkZ]

LSD is limited slip differential. It's a carrier that transfers power to both rear wheels rather than just the one with the least amount of traction.

[ September 28, 2004, 08:51 PM: Message edited by: FunkZ ]

[mjparme]

but it seems to be in the 10-15% range. So cruising down the highway at an indicated 75mph will actually be closer to 65.

Be careful about giving information about this since it could result in someone getting a ticket if they convert wrong.

3.23->3.42 would result in your speedo being off by 5.5%. It would show you going 5.5% faster than you are.

3.08->3.42 is 9.9%.

When going from a numerically lower gear to a nummerically higher gear

(1 - (startGear / endGear))) * 100) = percentage

I have a program that shows speedo speed and then actual speed for any gear ratio change. However, it uses JSP and Java Servlets and I don't have a J2EE hosting solution.

Maybe I should write it using Java Swing.

[FunkZ]

Thanks for keeping me honest MJ, you're right I hadn't done the math so I went back and did some calculations and posted the correct information.

Here's a page with a bunch of calculators for stuff like this.

[mjparme]

OH- by adding 3.42 or 3.73 gears, how much would my gas mileage change?

I went from 3.08 gears to 3.42 and didn't notice any fuel mileage difference. Technically there should be since you will turn a slightly higher rpm at any given speed but it is only 200 rpm or so more, I wasn't able to quantify a difference in mileage.

Plus if you add a cat-back or CAI (cold air induction) you will probably make that gas mileage back up.

http://www.howstuffworks.com is a great resource for any subject. They have a very good automotive articles. About anything you want to know you can find there:

http://auto.howstuffworks.com/differential.htm

[rallysportman1997]

Ok you sound exactly like me. First off dont have anything done in my opinion. All F-bodies rear ends leak. Dont worry about it unless if it is leaking excessivly. Mine was leaking and i had the seal replace and converted my 3.23 to a 3.42. After that my car was never the same. Once you rip apart those rear ends they are very touchy and you have to be perfect to get it to not make a winding noise after its been torn apart. There is a slight winding noise now and it bugs me but its put back together fine and it runs fine. Just makes noise. Also I found this out after the fact but if you have a manual your 3.23s are better for you car than the 3.42s. Automatics benefit from the 3.42s not the 3.23s. So i would leave it alone if i were you. I wish i did.

[rallysportman1997]

Also I forgot. When i went for a 3.23 to a 3.42 my speedo is changed by approximently 4mph. if im doing 74 im really doing 70. And im thinking about going back to my 3.23s. Check out the information provided on this website. I believe its under the tech section were they talk about the gears. Personally with a car with no modes i think your 3.23s will work the best for your car. just my 2 cents.

[kirk98]

After putting gears in, how do you recalibrate the speedometer? Also, is putting gears in considered a lot of work? Like- is this gonna take the garage a long time to do, are they gonna have to take a lot of stuff apart to put them in? In other words: am I looking at spending a lot of money?

-Kirk