Starter solenoid

[Chopper Scott]

I replaced my starter last fall because it was jumping in and out as if the solenoid wasn't holding it engaged. As to advise gleaned here I checked the cables out and cleaned them even though they were fine. I broke down and replaced the starter and the 2 batteries and all was fine for a few starts. Then it started doing the same thing as the previous starter and set of batteries. It wasn't long and the starter would not even engage. Just a click. I shorted the solenoid directly and nada, just a click. I could short the main posts and the starter would spin but not engage. So now starter # 2 or 3 depending on who you ask! It worked fine for awhile but once again it jumps in and out just as the other 2 before it. This is getting old and I am sure others have had the same joy as I have. It's my MCI 7, 24 volt, 8V71 with an Allison 740. I really could use some advise. Thanks all

[luvrbus]

Scott, I preach this to choir all the time low voltage will kill parts of the Delco starter are you using 2 8D's or 2 group 31 batteries ? you diffidently have a voltage problem some where move the batteries from the front closer to the engine if you still have the batteries up front that was a good screw up MCI did putting batteries 30 ft from the starter

good luck

[JohnEd]

There is a absolute MIN VOLTAGE ALLOWABLE for that starter.  Somewhere in your +12/24 volt line OR THE GROUND LINE there is resistanvce.  Eating starters is the symptom.  Get you "new" starter and install it.  Might want to have the shop make sure it is actually bad without you "telling them" it is cause you know what they say about the customer....right?  Install the working starter, new or your after verification.  Hit the start and measure the voltage ACROSS the starter....that is to say from the plus term to the ground terminal OR THE STARTER FRAME/CASE.

You might have onne of those rare problems that needs the naster but if you got 90% of the bat voltage at the starter you have gone as far as you can go.  By the way....I am being confusing with this.  Measure your bat voltage at the lead bat terminal, not a bolt or clamp or connection.  Measure across the bat from each term.  MEASURE WHILE CRANKING. 

Those starters are spendy.  You must be bored with changing them out by now as the novelty of that experience wears rapidly.

John


Pardon me for yelling but I know what those starters cost unless you know the shop owner

[bobofthenorth]

Buy a 39MT series starter.  That won't completely excuse you from having adequate cables but it will cover up for some deficiencies.  I've got two runs of 4/0 cable on the positive side, two runs of 4/0 to ground and 2 ground straps at the engine and my 8-92 was still chewing up 42 series starters and spitting them out like so much multi-grade oil.  Six years later I could likely still be on the same 39 series except that I chickened out last winter and bought me a spare - just in case.  Mine's a 12 volt system which only made matters worse.

I've been told that you can find bad connections with an IR temp gun.  I've never done it but the theory is that you pull a heavy load (starting IOW), maybe even a couple of sequential starts and then immediately shoot all the connection points.  Might work??

[jjrbus]

Old posts that helped me


Here are few steps to diagnoses starter & solenoid & bendix & relay before solenoid & NC (normal close) fuel pressure switch problem: Please use an analog meter only...so you can watch needle to be steady or erratically like a loose connection or dirty relay's points for diagnostic reason. Alligator clip on both test leads to get a good sable connection. Set meter range at 30 volt DC or the next higher scale.

Before the tests, the batteries should be at 80% or higher state of charge for diagnostic checks but not cranking voltage test unless full state of charge.

I attached a wiring circuit with numbers which label each test points.

A) NC fuel pressure switch:
1) Hook + test lead to #7 and – test lead to #8...while cranking, it should read 0 voltage until it starts.. If it erratically or full battery voltage before engine run...bad pressure switch. Hook up + test lead to #8 and – test lead to chassis GRD... it should read 0 voltage until it starts. If it erratically or full battery voltage before engine run...poor ground wire or connection.
2) If fuel pressure is higher then 8 psi @ cranking speed...checks for restricted return fuel line flow. It will cause the starter to shut down automatically.

B) Starter switch relay before solenoid:
1) Hook up analog meter + test lead to #6 and – test lead to chassis ground...it should be at battery voltage while cranking. Otherwise if it erratically meter movement....bad starter button switch or wire connection.
2) Hookup analog meter to solenoid coil post (#5) (it the same + from battery post) with + lead and – lead to (#4) pressure switch. Watch voltage meter for steady cranking voltage reading while hold down the start switch...if it 0 voltage while cranking is good. If it does erratically while using either front or rear starter switch mean bad wire connection to or in the relay or bad relay points.

C) Solenoid:
Hookup analog volt meter with + test lead to + post (#1) of solenoid and – test lead to starter's + post (#2). Watch for meter goes to 0 voltage while cranking...that is good. But if it erratically...bad connection either in solenoid's contact switch or starter's brushes or wire connection. Take it to repair shop for further testing or replace both solenoid & starter motor with warranties.

D) Bendix Drive:
1) Wrinnninnnn noise (spinning) mean over run clutch is slipping, mean a bad bendix drive.
2) Very loud gear clashing before fully engage...either worn gear's teeth    or    starter is spinning before fully engage...solenoid connecting link is out of adjustment or worn out. Replace both solenoid & starter motor with warranties.

E) Starter Motor:
Hookup analog or digital volt meter to solenoid's + post (#1) and the – lead to engine's ground. Watch for voltage dropping at the beginning & during cranking.  If the voltage is below 18v with a fully charged 24v system and growling noise mean starter bearing is worn out to cause armature to rub on field poles. Replace both solenoid & starter motor with warranties. If no growling noise...check power source for weak & "hot" (high resistance) connection of both the + positive & - negative. While cranking with fuel shut off, it should never have more then .5 volt drop between #1 and starting battery's + post. Same way with grounding between engine to battery – post of no more then .5 drop. Under size wire or cable will cause greater voltage drop as well old cable with a few broken strands from too much vibrating and/or corroding.


Whatever you do about getting parts replacement, always take the old one with you to the store same or newer version.

FWIW

Sojourn for Christ, Jerry




Title: Re: Bus starting problem
Post by: Sojourner on August 09, 2008, 11:45:52 PM
Thank you...JohnEd.
Sorry....perhaps I have not made my self clear on this subject. I am not a shop manual writer and not good in grammar but trying my best to get a step by step diagnostic in writing...while I am too far from being there to solve the problem.

You're not the only one are confuse about my diagnostic check step from my earlier post.  And...I still see more posts after my reply, which they are suggesting whatever it could be. My profession has been diagnostic work in electrical, plumbing, old internal combustion engine (ICE), transmission, front wheel alignment, with/without posi-track rear end, air & hydraulic brake system. Most of it was my everyday job making a living since 1953 to 1970. I am not updated now since computer equips cars & trucks came out and am not perfect by all means.

What I am saying that most diagnostic can be done in must quicker time and replace only the problem's part or parts or repair. Just follow the diagnostic steps.

Need to clarify this diagnostic step by step check points via using analog voltage meter to pin point problems....It is not all about resistant load in electrical system. Read on!
The following tests is using an analog volt meter is not to measure voltage but to see what the contact's points condition are or wiring connections are like, by watching the needle movement for either erratically or steady while under load or cranking.

About erratic voltage meter reading...dirty or worn relay contact points from either the starter solenoid relay (before solenoid) or solenoid's high current contact point (heavy duty relay). In other words, a partial contact or arcing points will cause a guarantee voltage meter to read erratically. If it good contacts...it will read a steady and low resistant voltage of less then .5 volt as per manufacture spec. (in general terms).

About measuring voltage....digital volt meter is much more accurate then analog version but cannot tell if how much of how high or big it is erratically if any.

On the other hand, you can use a cheap portable AM radio at about 1300 hertz with no station tune in. Hold radio near by starter or relay or whatever needs to check for arcing points/contacts or loose connection. It will sound cracking or scratching if it arcing or moving a loosen connection.
You can use AM radio to locate loaded or switch "ON" AC wiring in wall via listing for the humming "60 cycle sine wave" sound.

Also you can tell if you have shorted or open alternator's diode by listening for high whining sound. Bad diode will sound growling and very hot alternator.

My hearing aid set on "telephone" mode will do the same as AM radio...cracking sound.

    HTH   JIm

[JohnEd]

I've been told that you can find bad connections with an IR temp gun.  I've never done it but the theory is that you pull a heavy load (starting IOW), maybe even a couple of sequential starts and then immediately shoot all the connection points.  Might work??

Bob,

Delete the "might".  It certainly will work.  Voltage drops tell you how bad that joint really is but if there is heat you have work to do rtegardless.  Also, heat checks can't eval the wires and joints you can't see....only electrical tests of the entire circuit will do that.  If I had the hard starting or my voltmeter said I had low volts at the starter I would shoot what I could see with the gun cause it is quick.  Good point!

thanks,

John

[FloridaCliff]

Scott,

#1, make sure the batteries are fully charged and afterwards verify the full charge with a load tester before attempting to start.

You may have a parasitic load that is drawing them down slowly.  We can get into that after you charge and test them.

Cliff

[Chopper Scott]

I have 2 4d batteries that I replaced the 8d's with. Similar results either way. I'll try the ir gun and see if that helps me find any bad spots. I also thought about hooking 2 smaller 12 volt batteries closer to the starter and seeing if that is the case. Jerry's post has me thinking also. Rear start and front start are all the same and I can easily bypass the fuel switch but I doubt it's that. But the start relay.... I'll know more this weekend. thanks everybody...

[jjrbus]

If it is the fuel switch it will not start! I was having a fuel switch issue at the same time as a starter problem and of course battery problems!!  I took the battery's back three times before one failed a load test!!

That is when I learned that you cannot fully charge a battery and then load test it!
                                               HTH   JIm

[luvrbus]

Scott, the 42 mt Delco starter like you should have on the 8v71 has what is called a OCP (over crank protection)  if the re-builder did not by pass it in the process that said if not enough voltage is at the starter they disengage so it won't burn the starter up or the solenoid will hang up.
That is a bad setup MCI uses Eagles may have rust problems but not starter problems lol


good luck

[Chopper Scott]

Thanks Cliff. I'm always amazed at the knowledge you have with these ole girls.

[buswarrior]

Be aware that reputable coach re-builders routinely pull all new battery cables through the coach from battery box to the engine room.

Mine, on an MC8, are some mess up behind where the coach toilet tank belongs, middle of the cable is burst out in the creeping green plague, far from any connection.

On a set of 6 year old seated Prevost, the fleet found the cables turning to powder in under the heat shrink at the cable ends.

Check the voltages as noted, fails? then the whole lot is suspect.

Another thing to add to the long list of gotta dooze...

happy coaching!
buswarrior

[Chopper Scott]

Ok guys. Here's what I think is causing my issues. As many know the main power switch for killing all power on the bus is not the easiest to get to on my 7. It seems my problems always occured when it was cold even with the motor plugged in and warm and  with chargers on the batteries. When it gets real cold the switch is hard to turn and I have came to the conclusion that I wasn't getting it turned far enough. Something for my 2 do list is take a look at how it's made and see if I can make it work properly. Hope that helps someone else maybe have similar issues. 

[mikewarmblood]

This is worrying me,  I have a starter problem with my Flx. I was in desperate need to move the bus and I had bad batteries. I had my F250 a charger hooked up to the batteries. I barely got the engine to turn over and it was about to take off then I hear a sizzle sound and then all I get is a relay click.  I know some starters have a link from the solonoid to the motor.. Or is that my wishful thinking??? I remember another time I had a bad ground and tried to start the bus and there was a link looking thing and it was getting red hot.    Could that be a "fusable link" to protect the starter from idiots like me?? thanks Mike.

[Lin]

As suggested sometimes with MCI's it is that the batteries are too far from the starter.  Although having the batteries closer has to be a good thing, and many say their problems were solved by moving the batteries, I would suggest that that might not be the entire story.  When my engine was reinstalled after the tranny switch, Don was concerned with the cable that went from the junction on the engine compartment wall to the starter, so he bypassed it and used a new cable.  The old cable went into the frame rail and came out by the starter after only a couple of feet.  Later, I decided to pull that old cable out.  When I did, I found that it was stripped bare at places inside the rail.  This is 45 years of chaffing we are talking about.  Hence, I would suggest the possibility that the original cables could be compromised just about anywhere that you can not see them.  In an MCI that's a lot of distance.  Therefore, moving the batteries solves the problem for two reasons.  One is that less cable is less resistance.  The other is that you inadvertently bypass bad cable and replace it with good stuff.

I am not saying that you have to move the batts, but rather that there could be cable issues.  Anyway, I would strongly recommend checking or bypassing that last piece of cable that dips into the rail and any others you find that do the same thing.