I have an 84 Trans Am, with drum brakes. I found a guy with an 84 with factory?? disk brakes. He is unsure of the gear ratio but he thought it was original. My question is what's it worth? How would you tell what the ratio is without tearing it apart? Could it be factory from 84 or is it more than likely out of a different car? I can get it farely cheap, I think but would like to know more first.

very simple limited slip Diff... mark a line on the yoke.. mark a line on the rotor or axle hub. also make a reference mark on a stationary part matching the yoke & rotor turn the yoke smooth and continuously. count the turns of the yoke to return to your lines

I was just told that early third gen disks are junk and not even bother with it. Any truth to that?

Compared to what? Compared to newer, more expensive disk brakes or aftermarket, sure. Compared to drum brakes, no.

They said it wasn't better than the drums on the car now. I can get it farely cheap( I think) so I considered it a good upgrade. Is there anything else I have to change to make the rear end work with the disks?

If you all your questions will be answered without you having to wait for everyone to repeat what is already here 1000 times.

Sorry if I'm coming off as harsh, but people who ask the answer that already has been answered a 1000 times here on TGO really gets under my skin.

I absolutely hate the search function. It's flawed. Why search for an hour hoping to maybe find an answer when this forum is here for help from other people. So instead of being "harsh" as you put it don't say anything at all. Thanks anyway.

I was helping, Newbie. The answers you seek are here if you simply learn to correctly. Once you refine your searching terms, answers will come to you very smoothly.

I'm assuming I get the "newbie" moniker because of my low posts? The way I see it if you hvae nothing to contribute to the coversation, stay out of it. I have been a member here for 5 years longer than you. I don't spout off claiming to know anything when I shouldn't. I read research and help when I can. So instead of bitching about people that don't search move on and don't cause an arguement. Thank you and have a nice day.

Not that I owe you any explanation, but I have been here WAY longer than you (try the mid 90s) just that I have a new screen name.

I do have nice days when people are capable of finding stuff on their own & don't have to be spoon fed. Go play with your rice car. Obviously a 3rd gen is way beyond your abilities, since you can't even use a simple PC on a website! Unsubscribing so that I don't have to read your stuff anymore, like you did in that other thread on the low operating temp where you tried to call me out.

The EXACT reason I never post. Ignorant a-holes trying to be all high and mighty. I just wanted a couple questions answered quick and I get this crap.

i put factory discs from an '82 z with the rear disc option
onto my originally drum car-used the master cylinder
and proportioning valve from the donor.It is true the
calipers on the '88-earlier are kinda klutz and leak
prone,but if you get them set up right they do work ok
though i am not sure they are any more effective than
a drum setup in good condition.About half the reason i
did the swap was just for the "coolness"of having disc
rears

That's what I was thinking also, lol. Plus disk rears have to be more upgradeable than the drums. I can get the whole rear end for $100. I thought it's a deal so i mights have to make a trip a few hours away to do it.

Different proportioning valves for the brakes. Get the e-brake cables that go with the discs. Check the 8th digit of the VIN of the donor car, if possible. If it's "G", it could be 3.73:1 posi. If it's "H", it could be 3.23:1 posi, as my '84 T/A WS6 was built. Mine's a gov-lock. Don't buy without first popping the rear cover and checking it out for yourself. Don't even go if he won't commit in advance to letting you do so. Tooth counts are stamped into the perimeter of the ring gear. 11-41 is 3.73:1, 13-42 is 3.23:1

What gear do I want? I know very wide question but hey I'm new to gearing. I want more low end powerbut also decent gas mileage.

And there's the dilemma. If yours is a T5, then you'll wish for 3.73:1. But for a 700R-4, you can fix a soft launch by swapping the torque converter. The 3.23:1 is okay for all-around, and can allow MPG in the mid-20s. 3.73:1 is more for acceleration. But if you have a big nasty wild cam, you might do better MPG with the 3.73:1.

Right now it's all stock with the 700R4 but, I plan on building the original numbers matching 305 in the future. I wan to get around 300HP out of it. I think for a decent looking car that's used for dd and just general cruising 300 is more than enough for fun.

300 HP 305 is going to like 3.73:1 gears and a 2400-stall torque converter. Unless you do a stock rebuild plus nitrous, or mild boost. Then you could have the 300 HP with better MPG. In that case, a 3.23:1 axle and a 2000-stall would be good.

Did a quick search on your car and if it is a HO 305 you have the top of the line firebird from that year. 3.42's are standard and G92 option had a 3.73. you cant assume what the gear ratio is. counting tire and driveshaft revolution will get you in the ballpark but i would pull the covers no matter what. its not that hard. I tried the tire,driveshaft rev check and thought i had a 3.90. after buying it and taking it home i found out it was a 4.10. only way to see what its got is to remove the diff. cover and read the numbers. Also you never know what has happened to a rear end that has been around for almost 30 years. someone could have swapped gears, posi, etc....

Thanks for the info. I don't know how to look up all the info on my car. Like the original color codes, appearance package, rear end gearing, tranny, motor and those type of things

Id pull your cover off and see what you have first. After that you will know what ratio you might want to go to. Its like buying a 3.23 rear end and thinking u are getting a lower gear for acceleration when you already have a 3.73 which is better to begin with.

The main reason i want to do the swap is for the disks. The gears should be interchangeable, correct? I should be able to use whichever gears i want if the other rear end has different gearing

never hurts to pull the cover and change the oil. like most (mine included) probably has 30 year old oil in it. cost 15 bucks at advanced for gasket and two qaurts of 80w-90 gear oil. rtv gasket sealer also needed

Yeah, I planned on doing that before it hits the road.

Well, since the 3rd gen 10-bolt never got a 3.90, your estimate couldn't have been right anyways. And I suspect your estimate got the "just before" a full revolution confused with "just after", giving you 3.90 instead of 4.10.

I thought you were unsubscribing so you didnt have to read my stuff anymore???

true. I would see what kind of gears you have already in your car first. If its a low gear already like a 3.42 i would keep yours, theres a article on here on how to swap a fourth gen camaro disk brake setup(easily found at junkyards cheap)onto a third gen drum brake axles. there are far superior compared to earlier disks like your looking to get

Thanks, I'll look into that

I did Unsubscribe which means no more Email Notifications but that doesn't mean it doesn't show up as a New Post.

they sell 3.90 gears for third gen 10 bolts.

For what it's worth, I have an 83 with factory discs, I would rather have drums, the pedal is always low, they wont adjust even if you use the e brake, if I remove the calipers and adjust them, they dont last, I'm going to convert to pbr calipers and hope to be happy.

Let me know how that swap turns out

The PBR calipers are the way to go. They work great and look way better.

Are they a direct swap once you have the disc brake rear end?

Yes, but you'll need the correct backing plates and a few other things. You can see my swap at the end of the following link:

https://www.thirdgen.org/forums/tran...-10-bolts.html

JamesC

Yes, but it's not a direct R&R, you would still need an installation kit, and re-setting the pinion depth, preload, and backlash, plus crushing a new crush-sleeve. Side note: Motive gear offers a 3.9090909:1 gear set, dunno why they advertise it as 3.90 rather than 3.91

This is GREAT information!! I did not know the tooth counts to be this way marking these down and will inspect my rearend once I am able to pull the car out of my garage. Dont want that smell to get into my house haha!!