40MT to 39MT starter

[TomC]

On my truck, I had Delco 40MT 24v starter that required a series/parallel switch since the truck is on 12v (of which trucks are still 12v today). I wanted to both get rid of the series/parallel switch and convert to straight 12v. Since my 4 batteries were 10 years old and one of them blew up when I tried starting, I thought it time to change to 12v 39MT gear reduction starter. The only requirement was to make sure the pinion gear was the same-in this case a 11 tooth.
First I had to figure out the wiring of the series/parallel switch. There are numerous wiring diagrams on line and once I had one, it became relatively easy. I eliminated numerous wires in the battery box including the series/parallel switch. There were two wires-one coming from the ignition switch, then another going to the starter. I grouped both together on a push button with the push button powered by the batteries-so now I have a starter button in the battery box.
As to actually switching the starters-the 40MT is a beast at 58lbs (now called 42MT). The 39MT is about 31lbs. I checked directly with Delco about changing the battery cables, but they said the old cables should work just fine since the new starter is more efficient. So I just cleaned the cables and reused them. Installed the starter, hooked up the battery cables to only 3 batteries and it worked perfectly! Now I have an extra battery to service my generator!
Unfortunately, the 39MT is only made in clockwise rotation, so those (like me) that have a V drive will still have to keep with the 42MT.
I love working on commercial vehicles. With this starter, it doesn't matter whether you have a Cummins, Detroit, Caterpillar, Mack, Volvo, etc engine-as long as you have a SAE #1 flywheel housing with 11 tooth starter pinion, then the starter works! Too bad cars are not that way. How many hundreds of different starters are made for the different models of cars?
Next time you change your starter-go to the 39MT, very easy switch.

[CrabbyMilton]

That's an interesting post Tom.
The direct drive starter is going the way of the square wheel and 8 track. One would think that there would be a counter drive version by any starter builder.
One other thing about a gear reduction starter is that they give off a nice sound as well.
I used to get such a kick out of my grandparents '65 PLYMOUTH FURY when they would start it.
So we can thank CHRYSLER for helping to pioneer that starter in 1962.

[TomC]

Luckily, the 39MT doesn't sound like the early Chrysler products. While it is higher pitches, it is a pleasant starter sound.

[CrabbyMilton]

Yeah those early versions had that sound combination of a crow and Curley.
I wonder why it took GM and FORD so long to switch over though.

[chessie4905]

They didn't  want consumers to think their cars sounded like Chryslers when started. It was a crappy cheap sound. Chrysler should have spent a couple more bucks per starter to make them quiet or quieter.