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Topic: Delco MT42 Starter (Read 802 times) previous topic - next topic

Delco MT42 Starter

Over the 6 years enjoying this 2001 320, the only nagging issue that had been bothering me was the slow engine crank speed rpm, so I always used the boost contactor and finally got fed up, so first had the starter checked & new brushes, holders insulators, bearings & Bendix. The original starter was not hurt nor show much wear.  Same slow cranking, so I made up a 5' cable using 2/0, proper 1/2" & 3/8" ends, all crimped, soldered then the heat shrink. The cranking improvement is large,  now the cranking is identical rpm with or without the boost.
Two years ago I added an extra 2/0 ground bond battery to frame, that improved a noticeable amount.
Six months ago I rebuilt the battery terminal assembly on frame near the batteries, new studs/mounts, nuts With no improvement?
Would been nice if Foretravel had ran heavier cables.

Dave M

Re: Delco MT42 Starter

Reply #1 –
Bigger cables do the trick. GM put aluminum cables on Corvettes for a couple of years back in the 70's. Easy to get that "too much advance" sound when cranking. With a diesel, faster cranking means a lot faster starting. The old 6 volt systems had to use really large cables to get the juice to the starter. I converted a VW truck to 12V but left the 6 volt starter in place. Really spun the engine and never burned out.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Delco MT42 Starter

Reply #2 –
Over lunch (awhile back) was discussing the MT42 with a friend that rebuilds starters. 
Unless it goes underwater or lives in anything that gets used under normal conditions, upgrading and/or maintaining the battery harness to insure proper current, is the main issue.
As for the MT42.. it's an anvil of a starter and will last a long time.
Current draw was on the low side of spec for my Cummins.
I had the same starter in a class 8 for a million plus miles without issue. pc
S/W Houston 95" U320C SE/40' 
Build #4778  Cummins M11
Repairs & Covered RV Parking (BAO)
PPL is close..

Re: Delco MT42 Starter

Reply #3 –
Dave a number of us have upgraded the ground and wiring.  It makes a huge difference and I can crank the same speed like you with or without the boost on. 
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Delco MT42 Starter

Reply #4 –
As mentioned, it was a nagging thing.  So when I find both free time and ambition at the same time, I will find the issue, am guessing it is the cable between battery and the frame mounted connection stud, as when the boost is closed, it cranks fine from the frame connection stud, both the engine batteries and house batteries feed the same cable to the starter.
So looks like the weak link is the origional connection/cable batteries to frame mounted stud junction.  Will have a good look see one day.
If I could watch the meter and hit the starter, it would be real quick and simple to check.
FWIW

Re: Delco MT42 Starter

Reply #5 –
That junction box that the cable runs thru is the culprit.
it is a black box that splits the power and the start batteries run thru it to the starter.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Delco MT42 Starter

Reply #6 –
Dave M, a couple of years ago I had the slow crank going on, among other things the cables that tie the batteries together had a large voltage drop on both of them, as well as some bad ends on other cables. Like you say the old meter tells the tale. One of these days I'll have all new ones made up, or just run some additional 2/0 cables to the starter. All of the cables that had big voltage drops looked very good. 


Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Delco MT42 Starter

Reply #7 –
Three battery harness is available, $120 a set plus freight. pc
Looks just like OEM btw.
S/W Houston 95" U320C SE/40' 
Build #4778  Cummins M11
Repairs & Covered RV Parking (BAO)
PPL is close..

Re: Delco MT42 Starter

Reply #8 –
I think it is much better to use heavy duty 'military' battery terminals and two separate short pair of cables, instead of replacing the OEM cables with similar cables.
NAPA AUTO PARTS - Home nals-Top-Mount-Official-Military-Post-Terminal/_/R-NW_728223_0282494479

We carry spare terminals to replace a single problematic ones, instead of scrapping the whole cable string.

Also easy to connect extra cables with the horizontal bolt. We used these battery terminals to connect three start batteries together with homemade bus bars, but I think that cables are just as good and may have advantages over bus bars.

We also use these terminals on house battery posts. Positive and negative have different part numbers.

To improve current flow, putting one long bolt through a terminal connects all cables to one battery negative and all positive cables to the 'last' battery in the parallel chain.