XM813 Underdrive Starter

[Shirehorse]

I recently decided to install an underdrive starter on my 1970 XM813 with a 1988 dated NHC-250 Cummins. I did not have any problems with the original Prestolite direct drive starter, so it was not out of necessity but rather boredom.

I obtained my Underdrive starter from SS Member 74M35A2, and it came promptly a few days later in a 30lb box, much to my FedEx driver's chagrin.



Upon first observations, they are not cheaply made, and fit n' finish are spot on, with no child labor mistakes on the outside of the case and no sharp machining mistakes to rip my body parts off. They're Bosch, made in the good ole' USA in the great state of Ohio. The starter pulls 50 amps less than the original direct drive unit. The unit has baffled drains in both the motor and gearbox housings. It's also very quiet, especially when compared to the giant Prestolite beast that comes in these trucks from Uncle Sam.

They are rated for twenty seconds of continuous cranking with a two minute cool down between crankings. They are also designed to last a guaranteed minimum of 40,000 cycles (That's ten years of usage, with multiple starts a day). They are available in both 12v and 24v.

One of the nice things about this starter that attracted me as well was the soft start feature. Basically, the motor and pinion slowly rotate as the solenoid engages them to help prevent misengagements. Per 74M35A2, a misengagement rate of 1-3% is expected to happen on medium and heavy duty starters due to large tooth sizes, but that I shouldn't experience any for at least 50,000 starts unless the ring gear has burrs on it.

So, after getting the required number of beverages for the task at hand, I set forth with my trusty 15/16 wrench and went about removing the two top studs of the old starter. Use a 3/4 wrench to remove the wires on the big studs, and a 3/8 wrench to get the little guys off. Mark which cables go to which studs for easy installation later on your new starter.


The bottom stud of the starter had an odd 5/8 12 point stud in it, which I guess is akin to a rim lock in the hood, in case some mope wants to run off with your eighty pounds of original direct drive starter. If he can get it out without assistance, he can keep it in my opinion. You'd need to have hands like Shiva to maneuver that thing out of there if you're short like me.



Forgive me, I didn't take any pictures of the installation of the new starter, as I figure you'd be bored and quit reading this thread if you had to look at pictures of each of the three studs. I will say this, put the top rear stud in first, as it will help hold the starter up and even in the pilot hole as you install the other two. Install your cables on each of the corresponding studs like they were on your old starter. I used T for Top, ST for Side Top, and R for Rear because I'm unimaginative.



And, I know this thread wouldn't be worth a hoot if I didn't have a video of the new starter in action. This is the first start of the day, 45 degree temperatures, with four 6TL batteries. It has a mean whine to it that I really enjoy, and almost sounds like a really quiet air starter. It DEFINITELY sounds a lot different than the original Prestolite. Available in HD for your viewing pleasure.

https://youtu.be/1N70wu-oqZc

All in all, great success! WORTH EVERY PENNY.

Number of Beers:

Three Dos Equis


Tools Needed:

15/16 Open Ended Wrench
3/4 Open Ended Wrench
5/8 12 point wrench
3/8 Socket and Ratchet
1/2 drive Extension
1/2 drive Ratchet
15/16 socket 1/2 drive
Rope to lift starter

Enjoy!

~Brian

 

[162tcat]

I can vouch for the quality, I have the same unit from the same source. Well worth the money, mine cranks over effortlessly even on the coldest mornings now.

 

[74M35A2]

Thanks guys, glad they work well for you. Your trucks look great. The starters weigh half the amount of the removed original starter, and about 1/3 savings on physical size. They will not necessarily crank faster at room temp, but they will in cold and hot (engine) conditions because of their consistency, developing their full rated output of 7.5kW all they way down to -40C. They will also pull 50 amps less than the removed starter due to efficiency increases of a decades newer design.

The connections are simply ground on the rear aluminum end cap (don't want to pull +600 amps through your engine bearings), battery+ on the solenoid large wire, and starter switch signal from the starter relay or PCB as the solenoid small wire. The starter typically includes an additional starter mounted relay which can be used to run a crank switch directly from the dash and not require any additional relays or PCB's. This can be utilized or removed as desired.

The starters are O ring sealed at the brush end cap, where the motor joins the nose cone, where the solenoid joins the nose cone, and the solenoid retaining screws. There is also a seal on the pinion shaft to prevent any water or dirt intrusion. They are water tight, as even during submersion, water will not enter the drains due to a sealed design. The armatures are computer balanced for smooth and quiet running at 20,000rpm.

Available in 12v and 24v for LDT/S, 6CTA8.3, and NHC-250. 3 year warranty.

 

[patracy]

Interesting. I wonder how well it'd perform in a two battery truck?

 

[74M35A2]

Less current draw, so will give longer available cranking time in any comparatively similar situation against the stock starter on a given battery set, whether 2, 4, or more batteries are used.

 

[Swamp Donkey]

You've had my ear on the alternators for a while...we'll be talking when it warms up. You're bending the other ear with these starters. Thank you for bringing a quality product to the table and more than anything, the tech support to go with it. Drudging through part numbers and cross references to see what fits can be more time consuming and labor intensive than replacing the part itself.

 

[74M35A2]

Yep yep. Actually, you hit the nail on the head. Because I can't buy directly from my company and re-sell (conflict of interest, I tried), I have to go through a distributor, so the prices are not total rock bottom. But, as you indicated, because I swim in this stuff, I know what it takes to apply a specific part number to a certain application. That is where the gain really is. A distributor or dealer is simply going to look in their book, see no listing for a 1972 M35A2 with a multi-fuel, and say "Sorry, we don't have anything.". Well, they do, if they really understand what they have vs what is required. Happy to give tech support on any, including original, or aftermarket not from me. Because this stuff is pricy, I don't even recommend doing it unless one needs to, through failure of their original, or needing to upgrade from add-on's, a desire to reduce batteries, etc.... It is great to bring the technology and reliability up by 40 years or so when doing though. From that perspective, I personally don't think it makes much sense to pay $350 for a 40 year old designed factory NOS starter. Look at any new 15L over-the-road truck, and see what they are using. It won't be a Presto from 1970. Reliability costs $ on these 1 million mile machines, and a single pound saved is one additional pound of cargo they can transport for more $.

 

[Swamp Donkey]

The alternator won't have a chance to fail before it's replaced. It's a time bomb I don't want in my truck. Too many modes of failure in one item for me.

I agree about prematurely replacing the starter though. But when it does go out...

 

[gimpyrobb]

Interesting. I wonder how well it'd perform in a two battery truck?

In addition of what he said, I have one going in my deuce this spring. Great product!!!

 

[74M35A2]

It looks like all the cool kids have them...

 

[gimpyrobb]

Well, except for that swampy jackass...

 

[Swamp Donkey]

Does this mean I can't party in the Yankee tent at the rally now? I got flares...

I hear this starter works upside down too. Will be a nice upgrade for you Chris, lol.

 

[gimpyrobb]

All are welcome to hang out at our tent!









Even the LD newbs.