[Josue]

It's so cheap that, if anything, I can run it for a season or 2, then decide if the 3.08's are perfect, or when I need a beefier rear end, if I want to go with a 3.23 or 3.42. Trial and error!

[68400BIRD]

Pull your rear end out and put it in under his car so it's still a roller. Then, you will not have to wait.
I'm running 3.55's in a 12 bolt with a Yukon posi carrier.
I'm also looking at adding a Gear Vendors OD down the road. It revs a little higher than I would like going down the freeway.
It must be that I'm getting older but I had 3.73's in my last car and the rpm's did not bother me in the least. But, that was twenty years ago.

[JLMounce]

Originally Posted by 68400BIRD

Pull your rear end out and put it in under his car so it's still a roller. Then, you will not have to wait.
I'm running 3.55's in a 12 bolt with a Yukon posi carrier.
I'm also looking at adding a Gear Vendors OD down the road. It revs a little higher than I would like going down the freeway.
It must be that I'm getting older but I had 3.73's in my last car and the rpm's did not bother me in the least. But, that was twenty years ago.

This is a good idea.

On the gear ratio, it's all in what you're doing. If you're on the highway a lot, you're not going to want steep gears.

I always like to point out that a 3.55 and 3.90 axle ratio were available from the factory on these cars. Spinning them that much isn't going to hurt an engine in good repair, but you'll suck down a lot more fuel and make more heat on the highway with them.

[Josue]

Good points!

And really, with the lack of nice days we get here in NE Ohio, the days I DO get to drive it will likely just be back and forth to work, or to the store real quick or something. I'm not going to get out on the highway with it and drive off into the sunset each night just because. haha

I just want it to have decent highway manners and not god awful MPG, so I could drive it wherever if I wanted to. My wife's family is an hour and 20 away from us, random car shows all over NE Ohio, etc. When we finally DO get nice weather, we have to really take advantage of it!

[Josue]

Can anyone point me in the direction of what's needed to recalibrate the speedometer after a gear change?

[b-man]

Here's the one I've always used:http://www.tciauto.com/tc/speedometer-gear-calculator

[Josue]

How does that chart/site work then? You have to calculate what part you need to fix your speedo?

I've never looked into this before, but I imagined it'd be as simple as "I have so and so trans, with so and so gear...here's the part you need". Unless that's what the website is doing, just in a way that's really confusing. haha

[b-man]

The only thing you really need to determine is the number of teeth on the speedo DRIVE gear inside the trans. Pop the DRIVEN gear holder out, look inside the hole and figure out how many teeth are on the DRIVE gear.

Once you have that number, simply input your rear tire diameter and rear gear ratio.

The calculator will tell you which speedo DRIVEN gear you need to buy.

[Josue]

Originally Posted by b-man

...Pop the DRIVEN gear holder out, look inside the hole and figure out how many teeth are on the DRIVE gear.

Driven gear holder is where the speedo cable goes into the trans then? Pop it out, look in the hole, and there'll be a little gear in there?

Sorry, I've never done anything like this before!

[b-man]

Yes, remove the holder that the speedo cable attaches to.

You'll see the drive gear in there. Figure out a way to mark one of the teeth, then count the teeth. You can turn the driveshaft slowly (a helper needed?) with the trans in neutral and count the gear teeth, rear wheels off the ground, front wheels both blocked front and rear so the car doesn't roll.

Use jackstands under the rear axle tubes.

[Josue]

Sounds simple enough!

And with me wanting to do the 200R4 swap, this can be checked before the trans gets installed...

[Josue]

Alright....wound up scoring a good deal on a TH350 to use for the time being. I was going to put a higher torque converter just to have better drivability for the rest of the season, but it was brought to my attention that a TH350 is a direct swap, would give me more pep on the bottom end with the 2.52 1st, no loss on the top end because the final drive is the same as the PG, and they're so plentiful, it'd be almost the same cost as a new converter for this powerglide! Found a built TH350 with a 2600 converter locally (guy from the boards coincidentally) for $300!

I'll be getting the 8.2 10 bolt from my neighbor soon, and I was trying to figure out this driven gear thing I need for the speedo calibration....

I have 19 teeth in the TH350, a white gear. The driven gear is orange/pink...35 teeth. I plug in 19 teeth, 3.08 ratio, on 26 inch tires...and it says "gear not available" in the link above. I went to another site, and they said..." Simply multiply the rear axle gear ratio by the speedometer drive gear, divide that by the tire diameter and multiply this by 20.2 (a constant)."

So...3.08 times 19 = 58.52. Divided by 26 = 2.25 (rounded). Times 20.2 = 45.47 (rounded) Did I do that right? Looks like a 45 tooth gear is the highest available? At least through Classic...

http://www.classicindustries.com/pro...s/9775187.html

[Squidward]

http://www.tciauto.com/tc/speedometer-gear-calculator/

There is a note under the calculator for TH350's that there are two speedo gear housings depending on number of teeth.

With a 19 tooth drive gear, the closest you can get for a 3.08 with 26" tire diameter would be a 45 tooth. You would have to get a smaller drive gear to get a lower tooth count on the driven gear.

Did your new tranny come with a driven gear? What color/teeth count?

[Josue]

Yea, it's the 35 tooth orange/pink gear.

Is that how this works then? Doing these calculations just gets you "close" to where you need to be? Or if I went down a few teeth on the drive gear, in order to get a lower count driven gear, would that be a more accurate speedometer reading?

[Squidward]

Yup, gotta get lower. But according to the calculator, you would need a 14-15 drive gear to work with that 35, but such an animal I don't think exists. Looks like the break occurs at 10 and 17. I don't think your housing would support 45 teeth driven gear.

If you got a new housing, either new or used, for a 40-45 tooth driven gear, BOP TH350 specific, then you could keep your 19 tooth drive gear. The tooth range is embossed on the housing, with numbers 40 through 45.

Like this:
http://www.summitracing.com/parts/tci-880023/overview/

Or, maybe a package deal from these dudes:
http://www.ebay.com/itm/45-tooth-700...-/161782427650

[Josue]

15 tooth BOP TH350 drive gear?

http://www.amazon.com/La-Speedometer.../dp/B00P8BL2KI

Looks like that will be much cheaper than getting a whole new driven gear housing, which would be clutch in keeping the budget down. The least amount of money I have into all this, the better, since it's just a temporary setup anyway.

[Squidward]

Ya, give those dudes a call, since they would know their biz. They could give all the answers.

Didn't know there was a 15 tooth. Yeah, if that's available and fits a BOP TH350, then it's a much simpler/cheaper option!

[Josue]

Score!

How is it pulling that tail shaft out? Will a bunch of parts come springing out all over the place like a snake in a can? Will I get a trans fluid bath if I do it while the trans is in the car?

By the calculations, my speedometer will be off with this trans and my current 2.56 gears anyway, so maybe I'll put this 15 tooth drive gear in before installing the trans. Unless that will make me run 15+mph off or something. hahaha

[68400BIRD]

Pulling the tail shaft is real simple. I always put a drain pan under the rear of the transmission to catch any fluid that might come out. Remove the four bolts, look for the big O-ring gasket and replace your gears.

[Josue]

Gotcha. It looks easily accessible from under the car, I'll just hold off until I get the rear end....whenever that may be. My neighbor is taking a lot longer to get his car done and get me the rear end than I'd like. lol For the price though, I can wait however long it takes!