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Offline Jays74

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Rear end highway gears
« on: November 09, 2019, 09:00:51 PM »
Hello everyone
I got a stock 74 pinto 2.3 , 4 speed
I would like to cruise the car on highways / freeways 75/80 comfortably
My question is what rear end gears can I put in that will allow me to get those speeds
I've done this before on a 74 Datsun 620 many years ago and it worked well but not sure from what car I can add this from on my 74 pinto
Any help is greatly appreciated
Thanks , jay

Offline Wittsend

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Re: Rear end highway gears
« Reply #1 on: November 10, 2019, 12:00:13 AM »
Wow, where can you legally drive 75-80, maybe Wyoming or Montana?

The Pinto used two different rear ends. If you look from behind the car and the center area is a roundish oval it it a 8". If you can see bolts for a cover plate it is a 6-3/4."  Somewhere on the rear end there should be a tag attached with one of the bolts. Note, on the 8" the bolt is actually a stud and they are on the front side of the rear end. You need to find that and see what gears you have. Sometimes the actual number is express and sometimes they state the ring and pinion teeth numbers and you need to divide.  If you can post a picture I'm sure there are those here who can help you.

It will probably be hard to find gears for the 6-3/4" rear end. The 8" is still popular and offers a decent selection. This link http://www.mustangii.org/decoder/axle/ will show you the ratios that were commonly available. It is a Mustang II site but they used the same rear ends.

Aside from the difficulties of 6-3/4" gear availability is just the overall concept that you "don't get something for nothing."  What you might gain in a higher speed you will lose initial acceleration. And even at a higher speed you are fighting wind resistance etc. Anyone who has ever ridden a 10 speed bike in the wrong gear will understand that the problem.  It is just my opinion but the best ratios (mileage and then overall driving) for a  Pinto are either the 3:18 in the 6-3/4" rear or a 3.25 in an 8". But the 3:25 was very rare from Ford and likely only an aftermarket item.

Please understand that the rear end ratio, the transmission ratios and the tire size all work hand in hand.  It is actually possible to change the rear ratio and the tire size and wind up right back where you started. A switch to a 5 speed (overdrive) will lower your RPM's as well going to a taller tire (to some degree). It is basically how many engine revolutions to any specific MPH.  There are calculators all over the internet that you plug those three variables in and get the comparative numbers.  You should do that with the ratios you have and get a baseline number.  Then change things and see what the differences are.

My real world experience is with a Turbo Coupe engine (more than twice the HP of a stock Pinto) and a 5 speed. I found that 3:00 gears were horrible for street driving. I could never find a right gear for the speed limits (25, 35, 45 etc.). I went to a 3:40 gear and that all went away. The 5 speed allows for 2,600 RPM at the LEGAL 65 MPH limit.

If you have 6-3/4" rear end you are probably looking at replacing the whole thing (from a junk yard) with gear limitations. It would then be best to go with an 8".  If you already have a 8" it is probably near $500 to buy the gears and set them up. But remember what you gain as lower RPM's you lose acceleration and there is a limit to engine power as to just how low you can drop the RPM and not bog even at speed.

Offline Jays74

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Re: Rear end highway gears
« Reply #2 on: November 10, 2019, 04:27:45 AM »
Thanks Wittsend !
Very good info ! Definitely gotta find out what rear end ratio I got on mine and go from their .
I know the swap will help out alot just needed to be pointed in the right direction :)
Thanks again !

Offline pinto_one

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Re: Rear end highway gears
« Reply #3 on: November 11, 2019, 05:54:45 PM »
Well if you got a 8 inch rear end I have some New 3:40 gears in the box , figure a far price would be $120 , I brought then for my 76 but later decided to use 3.55



76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline LongTimeFordMan

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Re: Rear end highway gears
« Reply #4 on: November 11, 2019, 11:11:57 PM »
I have a 73 wagon with 14" tires and rims and 3.40 rear gears so i think the overall ratio would be a bit lower probably equal to maybe 3.30 or so

And I agree that 3.40 is a pretty much ideal.ratio which is why most of the stock factory 4 speed  pintos with the 6 3/4 had that ratio.

With that ratio i cruise at 70 mph at 3000 rpm and i can also CRUISE (Not accellerate) around town as slow as 40 mph in 4th at about 1800 rpm and 30 mph at 1500 so i can usually just start out doing the 1st, 2nd 4th shift and eliminate 3 rd around town.

But I also have an adjustable cam pulley and have advanced the cam timing to about 7 degrees advance to get  better low end torque so my engine starts developing power aboit 2400 rpm vs the 3000 for stock cam timing.

Of course when i need power i shift 1st at 5500 rpm at 30, 2nd at 5000 at 50 and usr 3rd to get to 65 in the fwy before settling into 4th.

But as mentioned above, a car set up to  cruise at low rpm on the fwy will loose driveability around town

If you go too high with rear gears ie 3.18 or 3.25 you will be using 2nd and  3rd gear around town a lot.

Also be aware that pintos tend to develop max torque at 3000 and peak power at 5500 so thay were intended to rev. And many stock engines dont develop power below.3000 rpm

With the stock cam timing setup you may need to use more throttle to get the engine to pull the car at 2600 vs at 3000 so your mileage may not improve and you will need to.downshift more  on hills or to.accellerate which also defeats the purpose.
Red 1973 pinto wagon DD, SoCal desert car, Factory 4 speed, 3.40 gears, Stock engine, 14" rims and tires, 60 K original miles

Offline pinto_one

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Re: Rear end highway gears
« Reply #5 on: November 12, 2019, 07:26:03 AM »
I tried diffrent gear ratios over the years to find the sweet spot , my early pintos with the 2.0 4speed and 3.55 gears I felt that there was a need for a 5th gear on the hwy ,  my pinto has the V-6 built up for torque and a A4LD overdrive trans , I have 15 wheels with 205 /60 /15s ,  and a posa unit with 3.55 gears , in over drive my rpm is 2500 at 70 mph , 2200 rpm its 60 mph and touching 30 mpg ,  it has TBI fuel injection , a 2.9 crank out of a bronco ii , and long tube headers  , comp cam ,  I pull a small camper with it that when full up is 2400 lbs , I do not pull in over drive , but in drive only the the converter locked uped ,  yep around 3000 rpm a tad below 65 mph , it pull hills like a truck ,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0