RPM clueless

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rdb

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Can anyone tell me what slant 6 RPM @ 60 mph is in top gear with

3/tree manual
4/floor manual
3 pb auto

thanks
Bob B
still pondering transmissions
 
The top gear ratios in all 3 trannies is 1:1. So with a given rear axle ratio, they will run at the same RPM's. (The auto RPM's will be a bit higher due to slippage in the TC...)

You need to have the rear axle ratio and the tire size to figure this out.
 
The final drive ratio will determine the rpm. The includes size of tires, and rear end ratio. All variables remaining the same, the three transmissions (assuming high gear is 1:1) will all have close to the same rpm.
 
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nm9stheham said:
The top gear ratios in all 3 trannies is 1:1. So with a given rear axle ratio, they will run at the same RPM's. (The auto RPM's will be a bit higher due to slippage in the TC...) You need to have the rear axle ratio and the tire size to figure this out.
Click to expand...

So the 4 speed just divides a set range into smaller divisions....no real advantage over 3 speed, at least as far as lower rpms @ high speed.

Were there many 4/floor paired up w the slant?
 
Uh..........................Uh..............Uh.............................Uh.......................

1:1? What happens if the OP has an OVERDRIVE 4 speed?

There are plenty of online calculators. Google speed gear rpm calculator

You need to know the transmission final ratio, 1:1 in a conventional 4 speed, "point something" if you have an OD that is .73. Don't know if they are all the same for the OD ratio

So you need the above, you need the tire size, and the rear axle ratio. Easy way to determine that is look for a "tag" on the rear axle. BUT THE GEARING MAY have been changed!!!!!!!!

So jack up one rear wheel. Block the front tires, put the transmission in neutral, and release the parking brake. See if you can turn the tire. If you can, watch the driveshaft and turn the tire exactly TWO turns. Count the driveshaft turns. If you have a 2.63, etc ratio, the shaft will turn 2 1/2 turns plus a bit. If you have a 3.23, it will turn 3 and very close to 1/4 turn, etc, etc

IF with the above conditions you CAN NOT turn the wheel, it means you have some form of limited slip AKA "Sure Grip" registered branded copyrighted business trademark of the "we used to be Chrysler Corp now Fiat"

So NOW you must jack up BOTH rear wheels. This time, turn one wheel, and the other should "follow" exactly ONE turn Again, count shaft turns for the rear ratio

HOW DO YOU KNOW if you have a conventional 4 speed or an OD (overdrive)? EASY Stick your head under the car on the driver side so you can see the shift linkage on the side of the gearbox. LOOK AT the front shift lever. If it points up, you have a 4 speed, 1:1 ratio. If the lever points DOWNwards you have an OD gearbox. This is a B/ E body box. The front lever is DOWN, means OD

index.php
 
RMS has an RPM calculator that offers the choice of many transmissions.
 
rdb said:
So the 4 speed just divides a set range into smaller divisions....no real advantage over 3 speed, at least as far' as lower rpms @ high speed. Were there many 4/floor paired up w the slant?
Click to expand...
Yes, the 1:1 is by far the most common Mopar 4 speed. Buuut, as 67Dart273 sez, you can possibly find an overdrive 4 speed. Some of these were used in the slant 6 Feather Dusters and Dart Lites in '76 (and maybe '75?). I owned a Dart Lite and ran it to about 250k miles; it really and truly would get about 28-29 mpg on the interstate. But part of that good mileage was a very low rear axle ratio. (2.76 or 3.0 I think....) I recall these looked different than the 4spd OD pictured but certianly can't swear to that anymore. (But the AL box looks right...)
 
nm9stheham said:
I recall these looked different than the 4spd OD pictured but certianly can't swear to that anymore. (But the AL box looks right...)
Click to expand...

I know of no visual way to tell an OD from a 4 speed externally, other than the shifter. If it's out of a car, IE used parts, it's even possible someone wrongly flipped the lever upside down.

Only way I know of EASILY telling on a used piece is to put it into OD or "3rd gear" as if it's a 4 speed, that is, rotate the front shaft CLOCKWISE

Then rotate the input shaft one turn, and watch the output

Less than 1 turn means a 4 speed, more than one turn means an OD
 
BTW, Del, do the 4 speeds you are talking about have 3 regular forward gears with the 4th gear being overdrive? That was what my Dart Lite had and I am just not familiar with other 4 speed OD Mopar trannies, so am curious.
 
OK, sounds like the same box.....been 25-30 years since I pulled the one for a clutch change!
 
nm9stheham said:
BTW, Del, do the 4 speeds you are talking about have 3 regular forward gears with the 4th gear being overdrive? That was what my Dart Lite had and I am just not familiar with other 4 speed OD Mopar trannies, so am curious.
Click to expand...

"Sort of." What you FUNCTIONALLY call 4th from the driver's seat is OD

But the reason the front shift lever is upside down is what (Ford) and Mopar did was to re--gear the box so that the "formerly known as 3rd gear" is now an OD gear

So in "4 speed" parlance, when you shift the OD box, you are actually shifting 1 - 2 - 4- 3 in order to get 1 - 2 - 3 - 4

When these came out, they were good and bad. Many people did not stop to think, with pickups and vans, or even HP cars, that the "geared" OD is somewhat weaker than the old "4th" straight through, and you used to see a fair amount of these in pickups or vans that would not stay in gear, LOL
 
OK, as I recall in the Dart Lite, you shifted 1-2-3-4 in the normal H pattern. 4th OD was down and to the right.....but that is as I recall it.
 
nm9stheham said:
OK, as I recall in the Dart Lite, you shifted 1-2-3-4 in the normal H pattern. 4th OD was down and to the right.....but that is as I recall it.
Click to expand...

No, not what I meant. The SHIFTER was moved by the driver 1234 just like a 4 speed. Looked the same, shifted the same. But the front LINKAGE arm was reversed so that the actual transmission gears shifted 1243. 3, then, was re-geared into an OD gear.
 
Ah I see...... what a clever way to sneak an OD gear into there in the 3rd gear position. Someone was a'thinkin' ! I wonder if they had to do anything to the bearing on the nose of the main shaft, since the main shaft would be spinning the 'wrong' way inside of the input gear in OD....

Wonder if the OP is still hanging in here, lol.
 
The mainshaft / input shaft issue is no different than any other "non straight through" gear, that is, the two are turning at different speeds. First gear is about the worst situation, as you can have very high input speed and very low output shaft.

Or winding the engine up in neutral LOL
 
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