Momma Mia! What a question!
I went back into my statistics to check the mean time between failure rates (MTBF). This shows the number of days between unscheduled shoppings and excludes planned maintenance and the traction motor bolt problems (more on that below).
In rank order from best to not the best, the performance is
#1 C30-7 Series 3600
#2 B39-8
#3 C30-7 Series 5000
I excluded the GP units and the lone B23-7 from the figures.
Now, comparing the C30-7 units to the B39-8 units, let’s look and the differences and similarities, from cab to radiators.
Control Cab
-Same air brakes and controls on both
Electrical Control Cabinet
-C30-7 units have relays and solid state “dash 7” controls, few engine sensors
-B39-8 units have three computers: CAB, AUX and EXE, plus several engine sensors
The B39-8 computers can cause a failure with only a minor glitch (a technical term!). These can be sent to GE for repairs which can cost over $5000 each, but some small defects have been repaired by MMA’s own staff at the cost of a few dollars.
Compared to the 3000, the system in that unit is better than the system in the B39-8 units. This is a mater of improvements as technology becomes better. To compare and contrast what Randy Stahl has shown me, the advantage over the B39-8 system is that it can be fine tuned in several areas of performance using a lap top computer to adjust among other function, locomotive adhesion.
If I had unlimited funds, my personal preference would be to install GE Bright Star on all of the units. We used this system on the GE fleet in Estonia and they pulled anything we put behind them.
Alternators and Engines
-C30-7 units have 16 cylinder 7FDL engines, rated at 3000 horsepower with GTA 11 alternators
-B39-8 units have 16 cylinder 7FDL engines, rated at 3900 horsepower (the staff at Derby reprogrammed the computers to reduce the horsepower for better fuel economy) and as I recall GMG 186A1 alternators
Reliability and rated performance is equal between the models
Radiator Cabinets
The radiator systems are very similar between the two models. GE operates as a dry system as compared to the EMD wet system. The GE units have no water in the radiators until there is a need to cool the water. At that point, GE uses a water diverter to send the water to the radiators. Once cooled, the water is diverted out of the radiators. This is why the GE units have no radiator shutters and similar vintage EMD models do.
With the GE dry system, clogged radiators can retain water even after the cooling water is diverted away from the radiators. This pooling of water can freeze in cold weather, causing winter radiator leakage. MMA has been diligent in cleaning their radiator interiors to prevent this.
-C30-7 units have engine (shaft) driven air compressors and engine (shaft) driven cooling fans – The compressors run fine, but MMA has had a few failures on the right angle drive mechanism for the cooling fan. The Derby staff has rebuilt more than a few of these.
-B39-8 units have electric (motor) driven air compressors and electric (motor) driven cooling fans – The compressor control contactors allow for two speeds, and these have on occasion failed, causing the motor and compressor to operate continuously, with the end result being a compressor motor failure. This requires sending out the motor for repair, and I know MMA has had a significant number of this type of failure. I do not recall any significant number of radiator cooling fan motors.
Traction Motors
The C30-7 units came with a mixture of GE 752E8 and 752AF traction motors. The B39-8 units came with GE 752AG traction motors.
The 752AG has a lighter frame than the 752AF. This causes traction motor case flexing and can cause open circuits and grounds in the field coils. Long ago, MMA made the decision to standardize on the 752AF as much as is possible.
As for the broken traction motor bolts, this has occurred between both of the models of locomotives. The bolts that are used to secure the traction motor gear case to the traction motor are what fail. This is caused by rough track. These failures occur during the winter freeze of the track structure. The section crews are working hard to eliminate the poor track so as to eliminate these failures. MMA was told by the NBSR that they too have the same problem on their EMD units and that they reduce track speeds in the winter to reduce these types of failures.
Interestingly enough, we had poor track issues in Estonia. But the GE’s there damaged the traction motor armature bearings and not the gear case bolts. The solution in Estonia was to replace the traction motor armature roller bearing, using a bearing with a one piece roller cage as compared to he original two piece cage. MMA 5017 has a specially designed Timken bearing on her #5 traction motor for testing. Derby Shop Manager Steve Johnston had the staff paint this motor orange to differentiate it as a test motor.
Now, after that long winded answer, you can draw your own conclusions. The facts are that these are good units, and the crew at Derby does a good job of keeping them running. As an example, the daily availability of the fleet on average has been increasing month to month this year.
TNT
