Freeway Speed in a 3 Speed

[Laid_Out_50]

I'm running a TH400 and on the freeway I do 65 at about 2900rpms 3.73 gears on 27" tires. What are some options to help lower the rpms and still be about to do freeway speeds

[PDW HOTRODS]

Get an overdrive trans, gear vendors overdrive unit, or change rear end gears.

[Dan in Pasadena]

Cheapest is to get lower (higher numerically) rear end gears. Was about to post a link to Patricks Truck Parts until I realized you probably already have a newer rear end in it.

[Laid_Out_50]

I've been told to swap out the gears to 3.23 or lower

[mr48chev]

There are a number of charts on the net that you can input engine rpm, tire size and gear ratio to calculate what would work best.

I was going to say just up the rear tires size to something like 29.5 dia but after reading a couple of your other threads that is most likely out and you will have to do the rear gear thing, swap to an overdrive trans or spend 2500 bucks on a gear vendors od.
I'd think that swapping rear axles or rear gears is probably your simple option.

Play with this from Randy's ring and pinion and you can figure out what gear ratio would work best for what you want to do and the rpm you want to run down the freeway at. http://www.ringpinion.com/Calculators/Calc_RPM.aspx

[Russell Ashley]

Would a 700R4 bolt in? I think I'd be looking into that.

[Laid_Out_50]

No it wouldn't I'm running a Buick Nailhead engine that has a different bell housing pattern weird I know

So after finding a calculation online to figure out rpms with various r&p gears here's what I found

Gear Ratio x 336 (common member for auto trans with lock up converter 355 without) x Speed x Final Transmission Gear Ratio

Gear Ratio's at 70mph
3.55= 3092rpms
3.31=2883rpms
3.27=2848rpms
3.15=2744rpms
3.08=2683rpms
2.73=2378rpms

I was thinking 3.08 gears

[_Ogre]

i run a 3.27 gear and a 700r4, i don't have a tach but it feels like i'm idling at 55 mph

[dfrank]

I run a th350, 4.10 gears and 35in tires and get about 2800 rpm at 70mph

[Sethmark]

I'm running a 350 with a th350 and a 2.72 rear end ratio. I leave a LOT on the table performance wise, but I can roll at 75 at about 2300 rpm.

There's a balance to be had. I'd prefer to be a little closer to 3.23 myself.

[mr48chev]

If the Nailhead is close to stock the ideal setup would be to figure out what gear ratio would match up with the stock rear end and tire size of the car the engine came out of so you were geared out to match the donor car's rpm at road speed.

Most of the mid 50's early 60's Buicks were real road burners that the engines didn't work hard in until you got up over a hundred. I think you are right in the ballpark with 3.08 or 3.23 though.

[yossarian19]

Taller rear tires will help, too.
Note that if you change either the rear gears, the trans *or* the tire size, your speedo gets off calibration.
The best answer is going to be an OD trans. It's no coincidence that overdrive transmissions came into vogue with the Interstate Highway system.

[Keith Seymore]

Drive slower.

I try to hover around 60-60 mph when on the freeway and limit my freeway drives to something other than rush hour. I also find I enjoy traveling the secondary roads more than I do the superhighways, both because of the greenery and because the outside air seems cooler.

Relative to a trans swap with a Nailhead: you might see if there is an adapter commercially available. Sometimes they are a bit pricey but can enable some of these less common combinations.

http://www.transmissionadapters.com/Pricing.htm

I used one of these to put a TH400 in my '63 Grand Prix (...of course, now I wish I had done an overdrive trans of some sort).

K

[_Ogre]

Originally Posted by _Ogre

i run a 3.27 gear and a 700r4, i don't have a tach but it feels like i'm idling at 55 mph

just ran these numbers through a rpm/gear calulator with 3.27 gear, .70 4th gear and 28 inch tires
truk is idling at 55 mph, truk runs 1511 rpm; at 70 mph it is 1940 rpm and at 100 mph it is 2747 rpm
no wonder i get 20 mph cruising at 80 mph

[_Ogre]

Originally Posted by Keith Seymore

Drive slower.

silly man

[Keith Seymore]

Originally Posted by _Ogre

silly man

LOL.

Yah. Around here if you drive too slow you'll get run over.

K

[1project2many]

Homegrown / hotrodder method from the days of the Nailhead:

Install 2nd 3 spd trans backward and connect only 2/3 arm shift linkage. You'll have direct and OD with the OD equalling .59:1

Searches for brown-lipe, brownie, US gear, watson, Ranger, & laycock auxilliary transmissions will all produce interesting options.

Also, as mentioned early 3spd w/ OD trans is still available. This trans is not bulletproof... original wiring actually cut ignition momentarily during shift to prevent parts breakage.

[Highsider]

Originally Posted by 1project2many

Homegrown / hotrodder method from the days of the Nailhead:

Install 2nd 3 spd trans backward and connect only 2/3 arm shift linkage. You'll have direct and OD with the OD equalling .59:1

Searches for brown-lipe, brownie, US gear, watson, Ranger, & laycock auxilliary transmissions will all produce interesting options.

Also, as mentioned early 3spd w/ OD trans is still available. This trans is not bulletproof... original wiring actually cut ignition momentarily during shift to prevent parts breakage.

Wow. Several things here that I did not know, or had not thought about for over 40 years!

Thx.

[FirstNation]

Hey Dan in Pasedena- "Cheapest is to get lower (higher numerically) rear end gears." Help me out here, i'm confused- aren't lower rear end gears also lower numbers?

[sstock]

yeah, Dan got it backwards. To lower the rpms you need lower numerically number which are taller gears not shorter.

[_Ogre]

Originally Posted by sstock

yeah, Dan got it backwards. To lower the rpms you need lower numerically number which are taller gears not shorter.

nice first post, sstock

[OrrieG]

Originally Posted by Highsider

Wow. Several things here that I did not know, or had not thought about for over 40 years!

Thx.

I learned to drive in a 50 Willys Wagon with 3 speed OD trans, when shifting to OD you had to remember to clutch or it made interesting noises and my Grandmother beat me with her hat saying "Dammit Patrick you're going to break it and we will have to walk home".