Bus won't start, just clicks

[luvrbus]

Jump across the 2 large terminals on the solenoid and see if the starter spends freely and fast without a load,if not you may need to buy the starter from John 316.
You need to load test the batteries first as Derrick stated 13+ volts mean nothing when testing a battery. If you don't have a load tester AutoZone or O'Rileys will let you barrow one for free after you leave your first born for a deposit     

[kyle4501]

I had a similar issue. Ended up being a bad ground on the frame for one of the batteries. Looked perfect - until I took it apart & then I saw the hidden rust. I burned up 2 starters before I found the issue. It seemed random when the starter would drag/ not work.

BTW, the solenoid can pull in, but if the contacts are corroded, that corrosion will act as a resistor. . . .
I haven't done it in a long time, but you used to be able to take the solenoid apart to rotate the contacts to fresh . . . . cheap rebuild.

[windtrader]

Sure seems like batteries have lost cranking amps. You may see full volts but battery is not able to generate the amps needed to start the motor.

The batteries in the coach I just bought were pretty new and showed full voltage but did not crank the motor all the time. Got them checked at the store and they show very low CCA; I think around 300 instead of 1100. The engine starter/solenoid would click and sometimes try to kick it. With two new group 31, it is almost scary how fast it kicks over. Barely touch the button and whoosh it is going. Huge difference. Since it starts with a boost from a different battery, it is almost surely a battery issue.

Don

[sledhead]

I have 4 group 31 batteries on my cat and it takes all of that to start the big beast and this is at 12 volts

dave

[bobofthenorth]

Years ago I had my 8-92 load tested at Prevost Mira Loma.  They said the inrush current when starting was 1000+ amps.  That's a lot of power to draw out of two little group 31s.  My money is on just not enough lead.  Weight counts - particularly when the engine is hot.

[luvrbus]

Years ago I had my 8-92 load tested at Prevost Mira Loma.  They said the inrush current when starting was 1000+ amps.  That's a lot of power to draw out of two little group 31s.  My money is on just not enough lead.  Weight counts - particularly when the engine is hot.

Yep starter rebuilding outfits love the people using 2 group 31 for starting with the MT 42 or MT 50 on a Detroit 12 or 24V that is a 10 hp DC motor. 
If you are going to use the 2 group 31's at least buy the 39MT reduction starter it will save you some grief IMO you left turning people don't have much choice so use enough batteries

[Branderson]

I'm far from an expert but since it starts right up when it's getting jumped mean there's something wrong with the batteries? 

[windtrader]

A major reason going with two Group 31 (24v) on the 8v71 was the remark that the motor needs less start amp if the AC compressor is removed. The way it starts with the 31 indicates zero lack of cranking amps. Firing up now is like pulling a trigger - boom and it's running in 1/2 a second.

[luvrbus]

A major reason going with two Group 31 (24v) on the 8v71 was the remark that the motor needs less start amp if the AC compressor is removed. The way it starts with the 31 indicates zero lack of cranking amps. Firing up now is like pulling a trigger - boom and it's running in 1/2 a second.

You are in a warm area too try starting one without a pre heat of some type in 30 degree weather with 2 group 31 batteries Coachnet will be on the way,do you a test cut the fuel off and spin the engine and see how long the 31's will last 

[Iceni John]

I'm guessing that you don't have a way to temporarily connect your house batteries to the start batteries?   If you can do so, the start batteries' Reserve Capacity becomes less critical because you can supplement it with all the amp/hours of your house bank.   I use a pair of Blue Sea 9001 and 9002 switches to send house power on some 4/0 cables directly to the starter   -  my two Group 31s can then have about the same RC as two 8Ds.

You mention that your old cables were 2AWG.   Even for a 24V starter, is that enough?   I like to use the fattest cables I can to minimize voltage drop under load.   It's good to have some closed-end tinned copper lugs circumferentially crimped on, along with some good heatshrink, and if the cables look iffy just replace them;  4/0 is less than $4 a foot.

John

[Lin]

Regardless of the systemic improvements that can be recommended, the fact is that the bus has started fine before and now it does not.  The first step is to load test the batteries, if they are great then it's on to the starter.  As Clifford said, the big auto parts chains will either loan you a load tester or do it for you.  The batteries do not even have be removed.  You could also use a hydrometer to test the cells looking for a bad one-- bad cell bad battery, but even if all the cells check out, it is the load test that is definitive.

[akroyaleagle]

I tried the Group 31s on my 8V92 and they just wouldn't cut it. They were new.
Back to the 2 8Ds, no problems.
I quit buying the Sams/Walmart 8Ds and use NAPA now. They last a lot longer.

The jumper to me is a dead give-away that the batteries don't have enough oomph.

[Scott & Heather]

Thank you so much for the great info guys. I haven't load tested the batts yet so I'll get a tester or just take them in. I'm hoping I haven't trashed my starter. It starts every single time when I jump it so I'm feeling like the starter is ok for now (famous last words I know). I am going to have the batts load tested and then go from there. Likely I need 8D's. I always thought two group 31's wasn't enough. I don't have a house battery bank yet so jumping those in isn't an option


Sent from my iPhone using Tapatalk Pro

[fortyniner]

I had a lot of trouble with 12v 8v71. The PO installed two new 8D with all new cables including grounds but it cranked very slow. Turns out the
starter brush holders were tilted due to overheating. With new brush holders and brushes it cranked ok. Then I converted it to 24v.
Now I giggle every time I hit the starter. 

-Tom P.

[luvrbus]

Makes no difference to a Detroit what is used for starting hydraulic,air,12v or 24v all they need is the 60 rpm per Detroit and it comes to life in warm weather and if you have enough batteries they will in cold weather too