Thread: Gears

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I`m going to look at a gear set today, waited long enough to convert to a 9 inch, the guy has two third members 3.00 and a 3.25, both tracton lock 31 spline, question is don`t think I would notice any appreciable differance between the two would I, already have a `58 inch big bearing housing from a bronco, got one left side 31 spline axle, still need to buy the right, also looking for crown vicky disc set up. Things take time when your a penny pincher,

They dont call me a penny pincher, they say iam cheap. I dont care tho, if your ever going to finish i think you have to pinch every penny.

Sometimes I would rather figure out how to make something work than spend alot of money for a bolt on. The difference between R&R (Remove and Rebuild vs Remove and Replace).

Yes, you will notice a difference between the 3.0 and 3.25. You really have to look at your engine/tranny combination to select your rear ratio. Are you running an overdrive tranny, and if so what is your final drive ratio? Where does your power band come in for your engine? If I were selecting between the two ratios with no other input I would pick the 3.25's but would be looking to go even higher numbers if I had a good OD ratio and tall tires.

I would also go the 3:25s. Back in the day, 3:70s were an okay all-around street gear... but 4:11s or 4:56 would give so much more "dig". :-)

It would also depend if you want to trade away performance, for mileage. Either way I would not run a real tall tire, or it won't be much like a "hot rod".

Roger and Hotrod I`m running a 406, smblk, mild cam, turbo 350.....only because I didnot want to cutup the frame to bad installing a 700 4r, right now its got an eight inch ( second third member in it, heavy foot does that ) with 325 gears with a 29 tall tire.

OK - with 29" tires and a 3.25 (dang few of them as OEM's) will give you an effective ratio of about a 3.00 set of gears. A set of 3.00 gears with those 29" tires will give you about a 2.75 prairie (dog) ratio. I have 9''/3.25's in my roadster and hope to change back to the original 3.70's with my (also) 29" tires come spring as that 5.0L needs a little help. If it was me, probably not be in a hurry to swap out an 8" for that 9" - find a 250 cid Granada with 3.40s or 3.55s and you will be right in the right rpm range (also some Pinto wagons had an 8" diff with the same ratios). I never killed a decent ratio 8", tho I tried - often

I was told to look for a `67 third member carrier, supposedly stronger, having more ouside ribbing and a little thicker area around the pinion support, but I have never seen one as of yet, but I have been looking...

I think your right about the 3.73's being the best all around street gear, Hotrodpaint.
I've run all three of those gears on the street back in the day.
Like you said if your not running a Overdrive trany 3.73's work great.
To me the 4.11 and the 4.56 were a little to much especialy if you had to get on the inter state at all, which I did from time to time. I do like the Dana 60 rear ends though,
I've been told they don't drag as much as the 9 inch rear ends.
but thats just me. Kurt
Kurt

With the 3.25's, 29" tall tire and the Turbo350 1:1 final drive you will be turning 2636rpm at 70mph. Running 3.00's only drops you to 2433rpm. Switch to the 700R4 with it's 0.696:1 final drive and you get 1835rpm at 70mph with 3.25's, or 1693rpm (too low) with 3.00's.

i have 4:11 18.50x 31 tires and a 700r and 70 is about 2100 if i remember right and my car only weighs 2000 pounds and 350 hp

Originally Posted by bobby6319

i have 4:11 18.50x 31 tires and a 700r and 70 is about 2100 if i remember right and my car only weighs 2000 pounds and 350 hp

Calculates out to 2170, but tire inflation affects tire diameter, too. The taller tires really make a difference!!

I suggest the 3.25 ratio. Will give you a hair more "dig" out of the hole. With Overdrive you can even go steeper in your choices. Just my two cents.
Don Jr

Ok so as life would have it this is the same third member I have under the coupe, who would of thought that I got lucky, but need to replace the pinion seal its starting to leak. Thinking that while its out put a traction lok in it. Need to look for new K-frame mods to see what it will take to put in a 700 4r, any particular year 700 r I should look for, and what is the differance from a 4L80, I know the E is electronic....

Look for a '86 or newer 700. The early ones were somewhat fragile. A 4L80 is similar to a TH400 stength and sizewise. These are great transmissions but you have to cough up about $700 for a controller.