Automatic vs. Manual Transmission

A common question prospective diesel buyers have is whether they should choose a manual or automatic transmission. Obviously, an automatic transmission wins in convenience - step on the throttle and let the transmission do the thinking for you. However, a manual transmission does have many benefits. First, the stick shift is likely to live longer. The clutch will need replacement eventually, but this is a minor expense compared to the cost of rebuilding or purchasing a new automatic trans. There are fewer parts to wear out, very little maintenance is required, and the design of a manual trans is much simpler mechanically. Additionally, the stick shift has a lower first gear which can be beneficial in getting heavy loads moving. You can also use a manual trans to help slow down or maintain the speed of a vehicle by downshifting and letting the engine slow down the truck, often preventing your brakes from overheating. This can prove much more efficient than the engine braking systems equipped on automatic trucks (though they perform adequately). The most beneficial advantage of a manual transmission is that there is less parasitic loss (power that is used in rotating the transmission that is not transmitted to the tires) and thus improved efficiency and often better fuel economy.

It should be noted that automatic transmissions use torque converters, which allow for dynamic gear ratios (ratios that change based on the amount of slippage in the torque converter). Additionally, today's automatic transmissions are capable of handling much more torque input than manual transmissions. For this reason, GM and Ford have completely phased out the manual option for their new trucks. Dodge still offers a 6 speed manual behind the Cummins, but you'll be limited to 610 lb-ft of torque, as the 800 lb-ft version of the Cummins is only available with an automatic transmission.

 

So which is better, the manual or automatic transmission behind a diesel? Cummins owners seem to prefer manual transmissions. Chrysler didn't build a dedicated diesel transmission until the 68RE, and the Cummins diesel has a reputation of tearing autos apart prematurely. While not known for reliability or durability, they still get the job done. In many cases, the Cummins was offered with higher output in manual transmission trucks than auto equipped. However, if you're in the market for a new 6.7L Cummins, know that the manual version will have 190 lb-ft of torque less than the automatic version. With Power Stroke and Duramax owners, it depends more on driver preference and use of the truck. Ford has historically offered automatic transmissions with reputations of long life and dependability, and GM's Allison 1000 shares a similar reputation of reliability. For daily driving and recreational light to medium towing, the automatic transmission is likely a better choice. It's convenient and equally capable. However, if your truck is a dedicated tow rig or work truck, the manual transmission may have some benefits in store if you don't mind the inconvenience. Of course, driver preference is the most important component of this decision. If you prefer one over the other, go with your gut. It is highly unlikely that you will be disappointed with your decision.

 

Ford Automatic vs. Manual transmission:

 

Ford TorqShift Ford 6 speed manual

Transmission:

Ford 5R110 TorqShift 5 speed auto

ZF 6-speed manual

Max Input Torque:

1100 lb-ft

650 lb-ft

Speeds:

5

6

1st:

3.11 : 1

5.79 : 1

2nd:

2.20 : 1

3.30 : 1

3rd:

1.54 : 1

2.10 : 1

4th:

1.00 : 1

1.31 : 1

5th:

0.71 : 1

1.00 : 1

6th:

N/A

0.72 : 1

Transmission Weight:

300 - 350 lbs

230 lbs

 

GMC/Chevrolet Automatic vs. Manual Transmission:

 

Allison 1000 automatic

Ford 6 speed manual

Transmission:

Allison 1000 6 speed auto

ZF 6 speed manual

Max Input Torque:

600 lb-ft in 2009, approx. 775 lb-ft 2011

650 lb-ft

Speeds:

6 speed

6 speed

1st:

3.10 : 1

5.79 : 1

2nd:

1.81 : 1

3.30 : 1

3rd:

1.41 : 1

2.10 : 1

4th:

1.00 : 1

1.31 : 1

5th:

0.71 : 1

1.00 : 1

6th:

0.61 : 1

0.72 : 1

Transmission Weight:

330 lbs

230 lbs

 

Dodge Automatic vs. Manual Transmission:

 

48RE automatic transmission

NV5600 manual

Transmission:

48RE 4 speed auto

New Venture NV5600 6 speed manual

Max Input Torque:

N/A, Chrysler strength designation 8 of 10

550 lb-ft

Speeds:

4 speed

6 speed

1st:

2.45 : 1

5.63 : 1

2nd:

1.45 : 1

3.38 : 1

3rd:

1.00 : 1

2.04 : 1

4th:

0.69 : 1

1.39 : 1

5th:

N/A

1.00 : 1

6th:

N/A

0.73 : 1

Transmission Weight:

N/A

360 lbs

 

You may also be interested in the following articles:

Allison vs. TorqShift

Allison vs. 68RFE

4R100 vs. 47RE