[koz5614]

My 1965 Tempest 2 door post is back on the road and I can't wait for spring cruising. I currently have a 12 bolt 3.73 rear that was set up by Mr. Gaydosh several years ago. I'd like suggestions if I can run a numerically lower gear for a little better highway manners. Most trips I take in the car are under 25 miles, but I'd like to go to Carlisle PA this year, and that's about 150 miles from my house. Here is my combo: 440 Stroker, Demon 825, and solid roller 268/275 @ .050", .604/.607 w/ 1.5 rockers. Trans is a T400 w/ B&M 3000 stall. Just seeing if I can put in something to drop those rpms down a little, but still rip it up stoplight to stoplight. Thank you very much.

[LeighP]

I prefer something between 3.08 and 3.42....I had 3.7 gears in the back of my 4 speed camaro and didn't like how buzzy the car was on a trip.

[Johnny406]

The 3.31's are a nice multi-purpose gear, that's what is in my 12 bolt.

[Tim john]

Perhaps leave it alone and slip in an O.D. transmission for highway use ? The fifth gear would bring down your RPM's significantly and raise your fuel milage.

Tim john---

[PontiacMatt72]

I'm running a 3.42 gear in my 12 bolt with TH400... (can see my setup in signature).

but... i haven't really had a chance to get a good feel for it, as I have been chasing a driveline vibration since getting it all put together (last summer). Believe I finally got it figured out tho.

for more of a cruiser, i'd go with 3.08. partial strip time, i'd go with 3.42.

[koz5614]

My dream is to go retro and find a Hone O Drive unit - Not gonna happen. Gear Vendors or an OD transmission are too much $ for me, so the gearing is the way to go. I was steering towards 3.331s, but have had no luck finding any. If I am unsuccessful in my search, I will go ith 3.42s. Thanks for all your suggestions.

[mrennie]

12 bolt 3.31 gears are available new from Tom's Differentials. He has them made specially for him by US Gear in batches of a couple hundred at a time.

I spoke with him just before Christmas when I was ordering a new R&P set and some other parts and decided to go with the 3.42 gears, but at that time he did have many sets of the 3.31 in stock.

Price is a bit higher due to the custom production runs, and I think they are around $250 a set.

HTH!!

http://www.tomsdifferentials.com/catalog.asp?pg=1

[PontiacMatt72]

I wanted 3.31's but couldn't find any at the time I built my rear... Honestly, I'd go with the 3.31's, if the extra cost wouldn't be a huge issue.

[koz5614]

mrennie: You sir, are the MAN! I just called Tom's Differentials and they have 3.31s in stock. Now I just have to find out if I have a 3 Series Carrier. Thanks again!

[BVR421]

put some big tires on?
actually before you throw $$$ at the gears, it would make sense to use one of the many online calculators to see the effect of a 26" tire and a 29" tire etc vs a gear swap

[74Grandville]

My vote is tranny (permanent) or tires (temporary).

looks like you have a pretty healthy engine that may need the gear.

[Matt Meaney]

i had a b&m holeshot 3000 convertor many years ago behind a mild 455 with 3.55 gears 255/70/15 tires. never liked it. it always felt like it was slipping. even lite throttle would push the rpm's up. i was worried that it would overheat the trans fluid when driving on the highway, even with the extra cooler. didn't have it in very long, ended up the a GM 13". something to consider when choosing cruising rpm.

imo, keep the gear (i think the motor will like it) and go with a tall tire.

[Tim Corcoran]

Dump the B&M converter, go with a Continental 10 same stall as you have now.

Tim C

[mrennie]

Originally Posted by koz5614

mrennie: You sir, are the MAN! I just called Tom's Differentials and they have 3.31s in stock. Now I just have to find out if I have a 3 Series Carrier. Thanks again!

No problemo!

Glad to help. The 3.31's at Tom's seem to be a best kept secret, as I also frequent some other A-body forums and have read many posts from guys that say they can't find any. As soon as I found out they were available I have spread the word as required!!

[02Hawk]

If you go lower than 3.55 you will have to change the posi unit also

[Pontirag]

yea carrier is different when you go that low and posie's are very hard to find

[mrennie]

We are talking 12 bolt, and the 3 series carrier is good for 3.08-3.73 IIRC. (Up to 4.88 with aftermarket gears).

[HWYSTR455]

Originally Posted by BVR421

put some big tires on?
actually before you throw $$$ at the gears, it would make sense to use one of the many online calculators to see the effect of a 26" tire and a 29" tire etc vs a gear swap

What he said. Going from a 3.73 to a 3.31 is only going to drop it about 400 RPM, not enough to really give you any improvement you're looking for. You would have to go to like a 3.08, and that would adversely affect your out of the hole performance, AND take you out of the optimum RPM operating range for your cam. Stall helps make up for some of that, but not enough IMO. Try to remember factors used for cam selection, since changing any of those factors means your cam isn't optimum. Do you want to change gears and a cam?

http://www.differentials.com/calc.html

Your best bet is an OD trans.

Gears are available from 3.08 - 4.88 for 3-series carriers, fyi.

.

[Schoust]

Anyone know of a dealer to get the Conte converter and a good street strip rebuild kit for the Turbo 400 trans??

[b-man]

I'd go with 3.42s and cruise to the track on a set of 28" tall tires, then swap for a set of 26" tall slicks to drop the effective gear ratio for racing. Your cam has a lot of duration, it may not be all that happy with the 3.31 gears and the 3.42 may be marginal in that respect.

Seriously consider a better 10" tight converter from Continental to drop your highway revs even further and increase track performance at the same time.