auto trans gear idea

[Cummins Cowboy]

many people say auto transmissions started to go down hill in realiability when the overdrive was added to it. We all know how bullet proof the 727 is. so instead of using overdrive to drop the RPM in final gear, Why not make first gear an underdrive and gear the rearend so that its a 1:1, in 4th gear. since most autos spend so little time in first gear and almost all the time in 4th.

 

[supeerman4422]

i think toyota had a 2 speed rear end that was used as overdrive? someone correct me if im wrong



-Tom

 

[PGreenleaf]

many people say auto transmissions started to go down hill in realiability when the overdrive was added to it. We all know how bullet proof the 727 is. so instead of using overdrive to drop the RPM in final gear, Why not make first gear an underdrive and gear the rearend so that its a 1:1, in 4th gear. since most autos spend so little time in first gear and almost all the time in 4th.

Because that wouldnt do what your thinking. 1to1 ratio means 1 turn of input shaft on trans gets you 1 turn of the output shaft on trans. In out 48re 3rd is 1:1 and changing the rear end ratio does't make 4th a 1:1 ratio. You still got the weak spot in the trans. It would however take a lot of load off the trans, by putting a 4. 56 gear in , but then you mess up empty driveing.

All you have to do to accomplish your goal is lock out 4th and run 3rd steady.

However the new 48re is quite capable of towing in 4th or overdrive all day providing it doesnt hunt gears. Oo.

 

[Moose Truck]

727

CCB; Dude, I had an Auto 1st gen, a '89 to be exact. True, the 727 was bulletproof and it did go over 250K on 4 oil changes and band adjustments, but driving a truck with a 3:08 rear would net you 76 MPH against the govenor. Also it didn't have a lock-up Torque Converter, so you have no TC shudder, but it would loose speed going up hills. :{ All in all next time make it a Stick for this Moose



Moose00

 

[y-knot]

Think about what you just said??? You are trying to combine the transmission with the rear end gear, and you are not thinking about overall gearing.

Most transmissions (47 & 48RE) have about a 3. 42-1 first gear, a 2. 73-1 second gear and a 1-1 third gear. The newer tranys have a overdrive which is about . 79-1 (21% overdrive). The ratio in the transmission, is a relationship between input rpm (from the engine) and output rpm (leaving the transmission), it has nothing to do with the rear gear, but it does effect the overall gear (the overall gear takes into account all rpm effecting devices, transmission, transfer case, and rear end gear).



If you were in first gear (3. 42) with the TC locked and had a rear end gear of 4. 11, the overall gear would be 14. 06-1. Or the engine would spin over 14. 06 times for every full turn of the rear end, a pretty slow go. If you were to drop the transfer case into 4 low (2. 71), with the same scenario, the ratio would go to 38. 10-1. The engine would now spin over 38. 10 times for every full revolution of the rear end, an even slower go.



If you can see the above and how it works, then you would be able to see that what you proposed would never work.

The overdrive unit on the transmissions in question are suspect, they have to live in a very intense atmosphere. They see maximum torque and maximum load, and have to survive. Unfortunately they do fail, usually while towing or hauling a very large load. But then again they see the highest demand of all the gear sets. The engine is running in the rpm range where it makes it's largest amount of torque, and the torque converter is locked up, which throws all the load on the OD gear set. If something has to give, it will be the band that holds it into OD, which is what always happens. We abuse this band and after some time if refuses to hold, viva the shudder then slip syndrome.

For what it's worth, heat plays a very big part in how long a transmissions life will be. The use of a auxiliary transmission fluid cooler is a very wise investment.

 

[Cummins Cowboy]

I think you guys are missing what I am saying, lets imagine a stock 727, now move all 3 of the standard ratios in the trans up except keep 3rd 1:1. now add a 4th speed, but make this one any other than 4th. so what I am saying is 4th would now be 1:1 and the extra gear would be in the lower gears of the trans. now keep the rear end get real high say 2. 78 or 3. 08 or so now you have a truck that turns the same rpm and operates the same as what we have now, its just that the overdrive or extra gear is placed sooner in the gearing

 

[Hoefler]

It would work! By going to a 3. 08 or 2. 73 ring and pinion, you would be able to have your final drive in the transmission be a 1 to 1 ratio. This would also keep the heat down in the transmission since you would be locking the crank shaft to the drive shaft and every thing in the transmission would be spinning with no load and no wear except to the bearings. Any time you multiply your torque either up or down, you will generate heat, and excessive heat usually leads to oil breaking down and ultimately catastrophic failure of the transmission.

 

[Cummins Cowboy]

exactly!!!!someone gets it, lets design and build the transmission from the ground up as a 4 speed or 5speed whatever, not a 3 speed with an overdrive as an add on or band aid. and make the trans with a 1:1 top gear and the rear low geared like 2:78 or 3:08

 

[cerberusiam]

It would work just fine, and make any truck it was in totally worthless for anything other than a car or grocery getter. If you want that and diesel by a VW TDI.



The reason for the gear ratios at 3. 73 and 4. 10 is the mechanical advantage gained when towing heavy loads. This mecahnical allows a transmission the size of the current ones to do the job. Without the advantage of the lower gear ratios you would have to super size the trans to get it to handle the load and do the leveraging. THAT would be cost ineffective.



Sorry guys, its a zero sum game. You take it away some where you put it back some where.

 

[Cummins Cowboy]

what is the difference between the transmission or the rear end doing the gearing?? my proposal in effect moves the overdrive gear speed out to the rearend instead of the trannie. the engine would still turn at the same RPMs in each gear, so how could this not do exactly the same work as our current set up

 

[raychem]

Aisin Warner 6 speed around the corner and they make very good units used in heavy equipment.

 

[BHanna]

A friend of mine had an old chevy pickup with a 4-speed, high rear-end gears, and L-1-2-3 on the shifter knob instead of 1-2-3-4. This is the same idea I guess.



Seems like 6 of one and a half-dozen of the other to me.

 

[cerberusiam]

what is the difference between the transmission or the rear end doing the gearing?? my proposal in effect moves the overdrive gear speed out to the rearend instead of the trannie. the engine would still turn at the same RPMs in each gear, so how could this not do exactly the same work as our current set up

The reason for the gear ratios at 3. 73 and 4. 10 is the mechanical advantage gained when towing heavy loads. This mecahnical advantage allows a transmission the size of the current ones to do the job. Without the advantage of the lower gear ratios you would have to super size the trans to get it to handle the load and do the leveraging. THAT would be cost ineffective.

As I said it will work, but, you CAN NOT do what you suggest with the existing pieces without changing the characteristics of the truck. These trucks are made to haul heavy loads not run empty. Your idea takes away one of the major capabilities.

 

[Cummins Cowboy]

As I said it will work, but, you CAN NOT do what you suggest with the existing pieces without changing the characteristics of the truck. These trucks are made to haul heavy loads not run empty. Your idea takes away one of the major capabilities.

so what you are saying is a truck with 3. 08 gears and no overdrive can't possibly pull as much as a truck with 4. 10''s with a . 73 over drive. the final gear in the 4. 10 truck would be 2. 99, this is a higher gear than the 3. 08, it doesn't matter if the final gear comes from the trans or the rearend. what matters is keeping the motor in the right spot in the powerband, you can do this in the trans or the rear, This is the concept we get by having 4lo in our transfer cases. some think lower gears in the rear end helps the truck pull more total weight, not so, this just mearly speeds the engine up a little more so it is turning faster to pull the load and usually in a more powerful area of the powerband, The same thing can be done gearing the transmission differently, hence shifting down to 5th on a 6speed

 

[cerberusiam]

so what you are saying is a truck with 3. 08 gears and no overdrive can't possibly pull as much as a truck with 4. 10''s with a . 73 over drive

Given a 5. 9 ISBe , a 48RE, and AAM rear end that is exactly right. Oh, you may tow the same weight but not as easily or anywhere near as long before the components break from stress. You can circumvent the laws of physics on paper but not in application. Additionally, keeping the engine at the same rpm will much harder with a higher rear end gear and will untimately use more fuel to do so.



Think of it as a lever and fulcrum with the lever being engine/trans and the fulcrum being the rear end. Starting out with the fulcrum close to the load to be moved it takes x force to move the load. As the fulcrum moves away from the load it takes increasing force to move the load. At some point the fulcrum will no take the force needed to move the load and will need to be larger. As I said, without upsizing the engine/trans unit you run into diminishing returns and will break components.



All your ideas look great on paper, but, try them in an actual application first. I guarantee there is a large difference towing a 20k load between a 3 speed/3. 08's and 4 speed/4. 10's.

 

[KennethS]

Mine has 1234 and angle gear

Back in the old days they use to use that a lot some call it Georgia overdrive. Have you heard any other names. Tha Ausie call it Angle gear. :-laf

 

[Moose Truck]

CCB; Dude, I had an Auto 1st gen, a '89 to be exact. True, the 727 was bulletproof and it did go over 250K on 4 oil changes and band adjustments, but driving a truck with a 3:08 rear would net you 76 MPH against the govenor. Also it didn't have a lock-up Torque Converter, so you have no TC shudder, but it would loose speed going up hills. :{ All in all next time make it a Stick for this Moose



Moose00

As I have said in the above post; 3. 08's: Been there done that, I will keep 3. 55's and an OD

 

[betterthanstock]

many people say auto transmissions started to go down hill in realiability when the overdrive was added to it. We all know how bullet proof the 727 is. so instead of using overdrive to drop the RPM in final gear, Why not make first gear an underdrive and gear the rearend so that its a 1:1, in 4th gear. since most autos spend so little time in first gear and almost all the time in 4th.

That's how the big rigs are geared. Most do not have O/D. For our trucks, the O/D would still be good for going empty 80 mph, so there's no need to get rid of it. Just make the rear end low, like 2. 70, then tow in direct drive, and cruise empty at 80 mph at 1700 rpm in O/D.

The only downside is that it would need driveshafts about 40% bigger, and the same for the transfer case to handle the extra torque (the o/d reduces the engine torque, and multiplies rpm)

 

[Hoefler]

Think about it, if you go back in history, all the trucks, from 2-ton to over the road trucks all ran direct drive final ratio in the transmission. It wasn't till the late 70s that they started to experiment with over drives. The 2-tons like the F750s, the C60s, and the D600s all had direct transmissions. Most 2-tons had 2 speed rear ends for the low gearing needs, but still had a direct final gear. This goes on to the late 80s early 90s. Even in the over the road trucks, overdrives didn't become common place till the early to mid 80s. If you look into the trucks that do the real grunt work, you will find that they to still top out in a direct ratio in the top gear in the main transmission and often in the auxiliary transmission as well. If over drive was needed, you find it in the auxiliary, not the main box, and seldom used.

 

[cerberusiam]

Back in the old days they use to use that a lot some call it Georgia overdrive. Have you heard any other names. Tha Ausie call it Angle gear. :-laf

I can't speak to angle gear, but "georgia overdrive" is neutral on a down hill run. :-laf





Some are missing the point here. He is advocating a 1:1 ratio in OD with a higher speed rear end to get the rpm's down. This moves the load from the rear end to the transmission.



Remember when top fuel cars used to run 2 gears instead of direct drive? When the innovators started using direct drive several crew chiefs responded with "if we tried a direct drive the crank would be on the ground with our setup". Some times it still is.