i currently have a 9 bolt w/ 2.77 gears in it. are there any other gears i can put in w/o switching over to a series 3 carrier. Basically whats the highest ratio it will hold??

If you have a 2.77 Borg Warner 9-bolt, and want 3.27 or higher you will have to get a 3 series carrier.

i know....im just wondering if there are any higher gears i can put in it w/o switching it over. maybe 3.08s????

hmmm, I dont think so. Read threw the thread below, there is alot of info about the 9-bolt rear. Maybe you will find it in there.




https://www.thirdgen.org/forums/show...hreadid=239666

I have 3.73s using my 2 series carrier. I bought my gears from DTS. If I remember right, they are in Michigan. I think that's the lowest gear you can use with a 2 series carrier though.

In a 9 bolt?

I have a used 9 bolt 3 series posi with a 3.27 gear for sale in the classified boards.

https://www.thirdgen.org/forums/parts-sale-2006/352964-9-bolt-rear-sale.html

Hi 5.7tpiroc,

I looked at this on my 1986 Trans Am (with 9 Bolt Borg Warner 78 2.77 ratio) last year.

The BW78 for the 2.77 ratio has a unique case and unique differential centre than the 3.08 upwards ratios. It actually uses BW75 internals for the LSD centre, and ring & pinion. The 2.77 ratio has a deeper bore where the pinion gear fits in the case, and an offset differential assembly to suit the larger 2.77 pinion gear. I have verified with the engineering, and spare parts departments from Borg Warner Australia.

Note: BW78 part numbers start with 0578-?????, while BW75 part numbers start with 0575-?????.

You have 2 options for the 2.77 ratio BW78:
1. Replace the complete differential housing and assembly with a 3.08 ratio upwards BW78 assembly from a wreckers, or on eBay. Hopefully you can get the ratio you want for the right price. 3.27 ratios are the most common I've seen on eBay.
2. R&R your 2 series centre and 2.77 ring and pinion, with a 3 series BW75 LSD unit and matching ring and pinion gears. The BW75 centre from a VN to VS Holden Commodore, or most EAII to EF Ford Falcon, will fit your 2.77 housing. Similarly the ring & pinion from a VN to VS Holden Commodore, or most EAII to EF Ford Falcon, will fit this BW75 centre. The most common BW75 ratio is 3.08, with some 3.23 ratios available in some Ford Falcons. The problem here is that the BW75 LSD centre is very popular in AU for Commodore or Falcon owners looking to upgrade to LSD will also want this centre. The ring & pinion will also need a spacer on the pinion shaft of approximately 7mm to fill in the space of the 2.77 housings deeper pinion bore.

I would recommend Option 1 if you live in the USA, and option 2 if you live in Australia.

I did Option 2 on my 86 Trans Am. It cost me AU$200 for a used BW75 LSD centre, AU$60 for a used 3.08 BW75 ring & pinion, AU$180 for a BW78 complete rebuild kit with wheel bearings and seals, AU$250 for mechanic friend to make the 7mm spacer and rebuild the differential assembly, and AU$50 for 2L of Castrol LSD Synthetic Differential Fluid.

All up, it cost me about AU$740 to go from 2.77 to 3.08 ratio.

In reality it cost me about AU$260 more than I was already going to spend as my differential needed a rebuild as the gears we already noisy from wear on the ring & pinion.

The difference between 2.77 and 3.08 ratios is like night and day. The 2.77 ratio used to lug the motor a lot. The 3.08 gearing is perfect for a mix of stop and go city traffic and highway work.

Cheers,
Andrew

ive got a 9bplt 3.08 posi w/ disc brakes but im probably going to sell it. i thought the 2.77 and 308 were same carrier!?

I have read this in numerous threads as well. I have a 9-bolt with drum brakes and no posi, and it has a 3.08 gear ratio. I have always thought the process of finding better gears would be difficult since I would have to change over to a 3 series carrier.

vortec57L, are you absolutely sure that the 3.08s use the same carrier as the numerically higher gear ratios? After some thought, I decided that gears would be too steep in price for me to change them out, especially since there are plenty more "bang-for-the-buck" mods I can do to the car at this point. However, if what you are saying is correct, I might make it a point to pick up some 3.45s if I happen to come across them.

Thanks for the info.

personaly i think that the 9bolt is just to expensive on parts if i had one with better gears already id probably be singing a diffrent tune but i dont and i think the posi will have to be rebuilt mabey but still im gona sell mine and look around for a better rear w/ lower gears posi and disc brakes probably a 4thgen rear.