Dwolsieffer

Okay so over the past 5 years ive slowly been working on my car. im just 20 but my grandpa who is helping me has rebuilt some classics. however, we found that our rearend doesnt match the car.

we found a perfect body 1985 firebird and we already had a 350 chevy so we bought it. the car has a 350 chevy like i said and a rebuilt 700r4 transmission. we think there is a short gear in the rearend because it had a 4cylder in it. Its fast, but off the line it has no get up and also reavs high??

My question is what is the best rearend to match my motor and tranny? heres another question, is the 700R4 one of the better transmissions to match a 350 chevy? the motors been completely rebuilt, mild cam and the works. like i said im 20 so moneys hard to come by =] but i want everything to match up right.

customblackbird

iTrader: (15)

u got alot goin on there... we cant give u our opinions without the specs on your motor and the rear u have. obviously its a 3rd gen rear but we dont kno your gear ratio... the 4cly prob had the 2.73 open diff. depending on the specs of the motor your gona want more gear. did u install EFI? cam duration? heads specs? intake specs? etc.

im pretty sure you dont have posi so your gona 1.) rebuild what you got by replacing the stock stuff with taller gears... prob 3.73ish and a posi and prob 28spline axles if u dnt have them which you prob wont if its the 85 rear. this is gona run u a bit of coin and your still gona be stuck with the strength of the stock 7.5" ring gear. but you should be fine as long as ur not running more than 400hp at the wheels, if you upgraded to a eaton posi, and 28spline axles. figure 400-500$ for the posi, 200$ for the gears, 300$ for the axles, and prob 100$ for the install kit. i would also throw on a support girdle for extra strength. thats about 160$. add it up and u still have to pay for someone to install it or do it yourself if your grandpa knows how to.

or you could just fork over MUCHO $$ and get a bolt in housing 12bolt/9" for your car. you wont be able to break them prob ever and they run about 2700-3000$ ready to bolt in.

again we need more specs on the engine. prob gona want to run 3.73s in the rear but you be better with 3.42s or so if you want better MPG. but if its a rever and you want more off the line you could step it up to 4.10s. most stick around the 3.73 range. i went with 3.55 in my ford 8.8.

on the cheap prob will have to get the gears 200$ or so... and install kit for about 100$ and new fluid etc and have someone install it and call it a day. but your rear wont be any stronger than it is and you wont have a posi which will increase traction dramatically and allow more acceleration

Dwolsieffer

yea, i know it cost money to rebuild but ive done it "cheaper" the first time around and realised it all will have to be the best eventually!!!

well i wanted to say its not a daily driver its just a weekend diver/TOY so while speed is good i dont need to be running 10s lol!!! and mpg doesnt really matter i have a 4 barrel carb and strait back exhaust so im getting maybe 13 mpg...cant get much worse


another thing is what do you mean by specs bc i can tell you everything about my motor and really the tranny i have seriously done all the work myself on this car, shes my baby!!! let me know what i need so i can get it running the way she should

customblackbird

iTrader: (15)

believe me 13mpg can get alot worse. figure u get 13mpg with the 2.73 rear gear that u have... now imagine that with 3.73 or 4.10s haha thats gona bring it down to like 8mpg. and around town its gona be alot worse.... 3.73/4.10s with the 3.08 first gear in the 700r4 will cause u to pull some serious RPMs in the city/town driving. it will be alot more fun dont get me wrong but expect to be throwin alot more out on gas.

my 86TA with a 305tpi has 2.73s in the rear and on the highway at like 70-75mph im only doing like 1800rpms... on my 87 formula 350 with 3.27s i was doing 2400-2500 rpms at 70-75. both had lock up converters and 700r4s.

when i say specs i need to kno things like they heads your using, stock aftermarket? any porting? intake? is it a single plane/dual plane... company? cam.... i need duration and lift numbers. other things to look at are your trans. u said a rebuilt 700r4... does that mean a stock rebuild? u using a shift kit? upgraded corvette servos? boost valves? any upgrades to the trans or just a stock rebuild? what converter are you running? whats the stall on the converter?

i can tell you that if your gona be changing out the rear gears for something around 3.73 your should definitly be changing out the tq converter. rear gears are gona affect your RPM range and so will the tq converter, miss match these and you can lose all driveabilty. if your going with a 3.73 your stall should prob be in the range of 2400-2800rpm.... but this can be wrong since i dont kno your engine specs.

are you gona be running any nitrous? turbos? superchargers?
just post everything youve done to the engine and trans and how u want to drive it

customblackbird

iTrader: (15)

believe me 13mpg can get alot worse. figure u get 13mpg with the 2.73 rear gear that u have... now imagine that with 3.73 or 4.10s haha thats gona bring it down to like 8mpg. and around town its gona be alot worse.... 3.73/4.10s with the 3.08 first gear in the 700r4 will cause u to pull some serious RPMs in the city/town driving. it will be alot more fun dont get me wrong but expect to be throwin alot more out on gas.

my 86TA with a 305tpi has 2.73s in the rear and on the highway at like 70-75mph im only doing like 1800rpms... on my 87 formula 350 with 3.27s i was doing 2400-2500 rpms at 70-75. both had lock up converters and 700r4s.

when i say specs i need to kno things like they heads your using, stock aftermarket? any porting? intake? is it a single plane/dual plane... company? cam.... i need duration and lift numbers. other things to look at are your trans. u said a rebuilt 700r4... does that mean a stock rebuild? u using a shift kit? upgraded corvette servos? boost valves? any upgrades to the trans or just a stock rebuild? what converter are you running? whats the stall on the converter?

i can tell you that if your gona be changing out the rear gears for something around 3.73 your should definitly be changing out the tq converter. rear gears are gona affect your RPM range and so will the tq converter, miss match these and you can lose all driveabilty. if your going with a 3.73 your stall should prob be in the range of 2400-2800rpm.... but this can be wrong since i dont kno your engine specs.

are you gona be running any nitrous? turbos? superchargers?
just post everything youve done to the engine and trans and how u want to drive it

Dwolsieffer

ill have to go through most of my stuff lol, i didnt know you would need that specific.

Would i be better off just going to the junk yard and getting a 12bolt and rebuilding my own? or just buying one somewhere?

customblackbird

iTrader: (15)

the engine, trans, and rear end are interconnected.... with one of them "off" or outa wack it can totally negate the potential of the rest. they are the three things that need to be matched to achieve optimum performance for the type of driving you want.

notice how most race cars run high reving engines... so all there power is in the upper ranges, hence why they run really high stall converters and really tall rear gears. 4.56 etc are normal on a drag car. a street car will not want a 4000-5000 stall converter and 4.56 rear gears.... u would have to floor it at every street light just to move and gas mileage would suffer tremendously... really theres no "all" around setup... its a compomise with everything, best u can do is set it up for the driving u intend.

really we need cam specs, head specs, intake specs. then we need trans specs... tq converter stall, trans upgrades. then we need to kno what you plan to do with the car. and if your deciding to keep the stock rear and build it up or throw in an aftermarket bolt in rear.

good luck getting a 12bolt from the junk yard. none will fit the 3rd/4th gen firebird/camaro... bc we have a tq arm setup rear suspension. all 12 bolts have a 4link with upper control arms cast into the rear housing. there are ways around this if you have decent fabrication skills. (which im in the proccess of doing for my ford 8.8 swap) basically the ford 8.8 is just like a 12bolt... same housing etc same cast in upper control arms. i had to fab up my own tq arm mount and swap everything over to the ford 8.8 from my stock housing. but if you want strength and you got some money saved... i would def just get a MOSER bolt in rear or a strange 12bolt or 9".

first one top left
http://www.moserengineering.com/Page...ous-ford9.html

or the 12bolt complete packages run from 2700-3000$ but u wont be able to break them. bottom right
http://www.moserengineering.com/Page...s-moser12.html

you can buy just the housings or u can get the complete setup already together and ready to bolt in.

you need to figure out the total cost to rebuild your stocker for a stock setup, a total rebuilt aftermarket setup(handle 400rwhp) or get a aftermarket. figure out what ur planning to make (ever) with the car and decide wat fits our budget and goals.

Dwolsieffer

will any used 12" just bolt right up or will i have to do a bunch of work???

i guess what i am saying is rebuilding a rear end will probably be cheaper...so what rear end could i possibly start looking for at the junk yard and i can swap gears and everything in my garage!!

big gear head

The ONLY rear ends that will bolt into this car are the 7.5 10 bolt and 9 bolt Borg Warner from 3rd and 4th gen Camaros and Firebirds. All other rear ends require major modifications to work with the torque arm suspension in these cars. The after market Moser and Strange 12 bolt rear ends will bolt in, but start at $2220.

You can build the rear end that you have for around $1000 to $1200 with all new parts. This will include a new Eaton Posi, 28 spline Moser axles, new gears and a good installation kit. Labor is another $200 to $400, depending on where you take it. This will give you a pretty strong rear end, IF it is assembled right.

I usually recommend a 3.42 gear with the 700R4 transmission because of the 3.06 first gear. This combination will be like having a 4.10 with a TH350 transmission in first gear, but work like a 2.73 in high gear because of the overdrive.

83z28camaro

you have a problem if off the line you have no get up and revs high. low gears make for quick accel and high rpms. high gears make for slow accel and low rpms.

Dwolsieffer

would you reccomend rebuilding it ourselves or having it professionally done??

is it extreamly dificult?

83z28camaro

There not to bad if you take your time. If you have a service manual that will help. The most important thing to do is mark the carrier bearing caps for the side they come off of. And make sure you have a good pattern on the gears before you drive it.

big gear head

You must know how to set the pinion depth, bearing preload and backlash to get the correct contact pattern. You must know how to read the contact pattern so that you will know what adjustments need to be made to the pinion depth. This is precision work and requires a few special tools.

Dwolsieffer

would a 4th gen Z28 rearend do the trick??

customblackbird

iTrader: (15)

yes a 4th gen is essentially the same but are about 2" wider on each side a total of 4" wider than the 3rd gens rears... this will cause your wheels to stick out 2" more on each side. 4th gen wheels would fix this issue (if u dont like how they look or they rub on the rear quarters)

seems like if i was you i would have someone rebuild it for u. u can do most of the work and save alil cash but overall the pinon depth/backlash etc needs to be very very accurate. special tools are a must. i just rebuilt a ford 8.8 for my car. i rebuilt the posi with carbon fiber friction plates, cleaned it all out, attached the new ring gear to the posi etc. assembled it but i didnt have all the SPECIAL tools needed to set pinon depth. took it to a friend who set it up for 125$ plus 36$ for new seals and i gave him 10$ for helping me out. he had every tool needed (owns machine shop etc) and it took him 11 times to set it correct. he had to dissasemble it 11 times and using shims to get it correct. its well worth the 160-170$ i paid. and its set up right.

if you decide to go with the 4th gen rear your still stuck wit the tiny ring/pinon gear. these rears wont handle 400rwhp for a long time. id say if your not making more than 400hp at the motor then rebuild a stock 3rd gen or 4th gen rear... anything over 400hp at the motor and its gona wear on the rear fast. not to mention if u get slicks or any decent traction, u can kiss it gbye

Dwolsieffer

would a ten bolt limited slip im guessing 3.23 gears be good?

or should i get taller gears?

Dwolsieffer

okay, im back with another idea. could i just rebuild/get it rebuilt a 2002 Z28 rear end? if i replace all the interior gears with what i wanted could it hold up to or around 450 hp?

big gear head

As long as you don't get good raction. It's still a 7.5 rear end and not very strong. If you are really making 450 HP then the rear end will probably break with good traction. You will need to step up to a stronger rear end, which means more money.

customblackbird

iTrader: (15)

i agree with gear head.

a 7.5 aka 10bolt from a 3rd gen and 4th gen are no different internally... except earlier 3rd gens had 26spline axles. 4th gens came with 28 splines. otherwise the 4th gens are not stronger... and they are 2" wider each side. by rebuild do u mean.... eaton posi? support girdle, gears, ARP bearing cap studs, moser 28spline axles and a good installation kit? and set up by a professional?

if so the rear should handle 400rwhp which is over 450 crank hp... but as stated your still running the small ring and pinon which is the weak link... good traction like a sticky track and slicks and it wont live long. street tires and not so great traction and you should be ok as long as u stay below 400rwhp.

if you plan on hitting the track with slicks dnt even bother with the 3rd/4th gen rear...

Phil Parrish

does anyone no if a turbo 3 speed trans. will be compatiable for rearend n my67 firebird and with 307..............its original eng. is 230 c.i. o.h.c. in line 6 not sure the gear n rear no the ratio in first is 1.52to 1.,,..2nd 1.52 to 1 ,,,,,3rd is 1 to 1

big gear head

You would probably get better answers to your 1st gen F body questions here
http://www.camaros.net/forums/forumdisplay.php?f=27
I know it says Team Camaro, but it is for all 1st gen F body cars. It would also be better to start a new thread instead of posting in one that is 4 years old.

As for your Firebird, you need to give more information about the gear ratio in the rear end, what you want to do with the car, some information on what you have in the 307, what transmission was in it with the 230...

I'm guessing that the 3 speed is a TH350? It will work with most rear ends, but there is a lot of things that need to be considered. The stall speed of the converter needs to be matched to the cam, engine size and rear end ratio. There are also modifications that can be made to the valve body that will improve shift quality and at what RPM and speed it shifts gears. If you are going to use a stock 307 then a stock TH350 with a stock converter should work fine. As for the rear end, that's a completely different subject