norcalitwin26

I have a 1975 dodge D100 with a 318 4 speed manuel tranny with a granny gear. My truck tops out at 55mph what to change to a 4 speed auto tranny whats the best route to go to get more mph and best tranny to switch to I know I might have to change my rearend gears also. Help plz im a newbie to the mopar world.

TVLynn

Your best bet would be to just replace the trans with a conventional 5 or 6 speed trans without the low gear. If you need an auto ? A TF518 would do the job

norcalitwin26

Thanks for the input, which vehicles came with that tranny that would bolt up.

440roadrunner

!!WHOA!!! !!! STOP the presses!!!! !!!!Step away from the shift lever!!!!


What do you mean "My truck tops out at 55mph"

Are you talking about WHAT GEAR is this in? Now I KNOW that if you really do have a "granny gear" in your "tranny"

STOP.......no your truck does not have a



It might have a 3 speed, a 4 speed, a gearbox, a transmission, but I digress


So once again, you are talking about FOURTH gear that the truck "tops out" at 55?

Or LOW gear?

Now if you are talking about LOW gear, you truck cannot possibly have a "granny gear."

But if you are talking about FOURTH gear, either there is

A.......something wrong with the engine

B.....you have incredibly small diameter tires

C....or you have very very low (high numerical) axle gears

RacerHog

Hahahahahahaaha..... 440roadrunner..... Really!!!! Tim Curry.lol
Thats funny as Chit rite there !!!!!!!!!!! I spit beer all over my Screen !!!

norcalitwin26

I have a 4 speed manuel transmission. When im in fourth my truck tops out at 55mph the motor is good nothing wrong, tranny shifts great. Im guessing that its my gears in my rear end not sure what gearing I have, havent taken cover off to count the splines. I know its a 9 1/4 rear end 12 bolt. Like I said im new to mopar and any help with it would be appreciated. Its a stock 1975 D100 the only things changed was intake manifold to a 4bbl and a 600cfm carb. And an electronic fuel pump.

norcalitwin26

I have a 4 speed manuel transmission. When im in fourth my truck tops out at 55mph the motor is good nothing wrong, tranny shifts great. Im guessing that its my gears in my rear end not sure what gearing I have, havent taken cover off to count the splines. I know its a 9 1/4 rear end 12 bolt. Like I said im new to mopar and any help with it would be appreciated. Its a stock 1975 D100 the only things changed was intake manifold to a 4bbl and a 600cfm carb. And an electronic fuel pump.

Mr.4spd

Perhaps someone swapped in a SM465? 4th is still 1:1 though. So when you say it tops out @ 55 do you mean you're on the rev limiter? Put the rear on jack stands, and rotate the tires one revolution by hand, count the driveshaft revolutions and voilà...there's your rear end ratio.

norcalitwin26

Thanks ill have to check my casting number on my transmission to find if it was changed over. When I say it tops out at 55-60mph I mean as im driving it thats as much as I can push it, it does not push past that. Ill be checking my rwar end gear ration later today.

DonNene74

then give Manuel his transmission Back.... or do you mean Manual?.....

Sorry for being a grammar **** ...... anyway.


I had the same granny transmission , and I replace it with a 727 Torque flight on my 1970 D100 318 V8. I am completely satisfied with the change. I also had a 904A... but 727 is better in my opinion.

440roadrunner

OK, here's the deal. There are basically TWO major types of manual transmissions in Dodge pickups

One was the "car type" transmissions, AKA A-833 4 speeds, and I don't believe yours would have one, unless it was the overdrive version or unless someone swapped one in

Conventional A833 4 speed

http://www.precisionpontiac.net/imag...nkage_A833.jpg

IF YOU HAVE an overdrive type (this has external shifting rods like a 4 speed) make certain it is going into 3rd and 4th gear properly. The 3 / 4 shift lever on the front of the transmission should point DOWN if it's an overdrive gearbox.

The other type would be what most of us call an honest to goodness "truck" transmission ALL truck transmissions have the shifter coming out the top center of the gearbox, and all shift linkage is internal.

NOW

If you have ..............

someone put a passenger type A833 4 speed 4th gear

or if you have an A833 type OVERDRIVE 4 speed that is in 3rd gear

or if you have a "granny" "truck" 4 speed in 4th gear

or if you have a conventional old-school Torqueflite automatic in High gear (3rd)

THIS AMOUNTS to all the same thing. That is, the shaft coming back out of the output of the transmission rotates at ENGINE CRANK speed when in "high" gear

This means that if you DO actually have a 4 speed and are actually in 4th gear, that changing transmissions to another type will get you NOWwhere

HOW TO????

EASY

Figure out "what you got."

Get the TIRE SIZE. Google online for your tire size and find out the outside diameter of the tire

Figure out the rear gear ratio Jack up one tire, with the other safely blocked. Put the gearbox into neutral, and make certain the parking brake is released. TRY to turn that tire. if you CAN mark or notice the driveshaft, and count driveshaft turns while turning the tire TWO exact turns. Your driveshaft will turn 'whatever' the rear ration is, that is if you have 4.10 rear, the shaft will turn just over 4 turns

IF YOU cannot turn the tire, you have LIMITED SLIP rear gear of some sort. Now, you'll have to jack up BOTH rear tires. Now, turn either wheel and make sure the other wheel "follows," that is, turns "with" the first. Again watch the driveshaft, and turn the wheel ONE full turn while counting the shaft. Again, the shaft will give you the ratio

NOW take your tire size, and your rear gear ratio, and plug it into one of the hundreds? thousands of online gear / speed calculators and see how this works out.

Some OTHER random commentss.......................................

How do you know your speedo is correct? CHECK it. Use your GPS, I know you have one. If not, borrow one from a friend. many "smart" phones have GPS function. Determine vehicle speed

You say "tops out." How do you know at what RPM the engine is turning? Do you have a tach? You didn't say. All you have said is "tops out." Maybe the engine has a problem and is starting to miss at higher RPM

Get or borrow a tach.

You need to know the following:

Actual engine speed, actual engine RPM, rear tire size, and rear gear ratio. With those you can figure out

"Wut ah gots"

hckrphil

Now that is a "sweet transvestite"... hahaha