Help with GM starter/relay problem

John Z · July 25, 2011, 11:00:39 AM

My 4104 burned up the starter about a wk ago in Bemidji. It started the bus, but the motor kept running. By the time i discovered this and managed to disconnect start battery, the old starter was shot. Rebuilt it, put new solenoid on. Reinstall and same problem. Starter motor still runs after engine starts. So to get home, i found the wire running from relay to solenoid. I basically just used this to connect to 12v when i wanted to start the bus.

It appears, but i sure dont know for sure, that perhaps some phantom voltage is tricking the relay into trying to start when it shouldn't.

Question - am i going to cause harm to anything but going around the relay to start the engine? I am basically going from 12v to a switch, which goes direct to the solenoid.

fe2_o3 · July 25, 2011, 06:31:18 PM

Or the relay is stuck on...If you disconnect the power to the relay, does it relax or does it stay on? Is there power to the relay all the time, or only when the master is on?..Cable

Barn Owl · July 25, 2011, 08:47:28 PM

Not sure on the 4104, but on the 4106 the OEM relay in the back compartment de-energizes the alternator (Am I using the correct term?), so the starter is not burdened with any extra loads.

Barn Owl · July 25, 2011, 08:51:16 PM

Be sure to check your start toggle switch for failure. They can go bad, and cause weird intermittent problems similar to what you are having. Part of the process of elimination.

pvcces · July 25, 2011, 09:58:35 PM

Laryn, I don't think that the relay you mentioned is there to prevent a load on the engine while cranking. I don't think that the engine cranks fast enough to put out any power, even if it was energized. The alternator should require revving the engine in order to energize it.

It prevents the air conditioning and heating systems from running if the alternator IS NOT producing power, and it prevents the starter from cranking if the alternator IS producing power. The batteries would not last long if there was no alternator output, and it would be hard on the starter to engage it while the engine was running.

Since the failure of this relay circuit can cause such serious problems, I generally call it the safety relay. Picture hitting the starter button when you want to put the transmission into reverse. On our coach, the buttons are the same.

For what it's worth.

Tom Caffrey

roadrunnertex · July 26, 2011, 06:55:26 AM

I had the same problem with a PD-4104 that I use to own years ago.
The starter relay would stick closed and the starter motor would keep running.
I replaced the starter relay and it solved the problem.
FYI the reverse relay next to the starter relay is interchangleable with the start relay.
jlv

luvrbus · July 26, 2011, 07:22:15 AM

Most of the time you will find low voltage and cranking amps are the problem with a the delco 39 and 42 starters hanging up those old starters will last a lifetime if amps and voltage is right but that is hard to do sometime on a GM

good luck

Just Dallas · July 26, 2011, 07:43:04 AM

Look for a bad ground from the battery to the bulkhead, the bulkhead to the engine, the engine to the starter.
In the meantime, there are probably either 2 or 4 screws holding the contact end of your start solenoid in place.
Remove the end plate and look at all the contacts. Even if they look good, sand them down and try to see if you can get good contact again.
a stuck starter is normally caused by low voltage caused by a bad ground or by a corroded terminal on the battery.

bevans6 · July 26, 2011, 07:45:35 AM

if the start relay fails to disengage, doesn't the pinion stay engaged? I was thinking that in this case, the pinion came back but the motor continued to run. I had that failure last year, straight forward solenoid failure. Engine started, pinion kicked back but the starter motor continued to run.

Brian

Busted Knuckle · July 26, 2011, 08:13:05 AM

I agree with Clifford & Dallas both on this. Everytime I've seen one burn up it was because of low voltage. (with one exception we had one MCI with the Ford ign. switch that hung up and left the solenoid engaged.)

Brian you got lucky. And sounds like your issue was just that a solenoid failure and not a low voltage issue which more than likely would have cost you a burnt up starter.

BK

John Z · July 26, 2011, 11:26:06 AM

Thanks for the input. Today i wired in a relay of my own, between the feed from the starter button and the wire that goes to the solenoid. It appears to be working. I want to track down what my relay is doing. BTW, i put in a new oem relay last fall. The book shows a feed from bat term on reverse relay; a feed from starter cut out switch in engine compartment; the feed to solenoid; the feed from start button, and one that i cannot figure out yet.

I have replaced the start button although the old one seemed ok.

With my current new relay wired in, am i ok to use the bus as it is, providing it charges when running? Anything else i should chk for?

Just have a gut feeling a phantom voltage leak or some such thing is causing the original relay to screw up.

bevans6 · July 26, 2011, 11:30:33 AM

"Brian you got lucky. And sounds like your issue was just that a solenoid failure and not a low voltage issue which more than likely would have cost you a burnt up starter.":

your hint that it's a bad solenoid is if giving it a serious hit with a 20 oz ball pien hammer fixes it, it was probably a stuck solenoid...

Brian

gus · July 27, 2011, 11:22:14 AM

This relay (Not the starter solenoid- two different things) is infamous for failing.

I see no reason it can't be replaced by a generic cube relay, I've done this with the other original relays with no problems, including the engine-run relay.

The start switch replacement idea is good also, my original failed. My experience is that toggle switches (Original equipment on a 4104) last longer than push buttons.

Two more places to check are the terminal posts at the driver and rear electrical panels. These terminals are VERY bad to corrode including the wires or up to an inch from the terminal ends. I replaced a bunch of these.

zubzub · July 28, 2011, 01:13:18 AM

I'm with Gus on this, the old relays in the back compartment are pretty much done by now (mine anyhow)....actually all the relays in an old 4104. They are nice old little black boxes but every one I have checked, while still operational, has had "phantom" voltages etc going through it, sometimes as much as 2V trickling through the relay when the relay is not energized... I guess the windings/insulation is grounding out or something. I have been replacing them with cube relays as I go, but this thread reminds me I should just replace them all ASAP.
Good work on finding the problem and wiring around it. Alligator clip jumpers are my best friends with my old bus.

gus · July 28, 2011, 08:21:36 PM

Zub,

I found that a lot of those phantom voltages were caused by the old blue rectifiers in the original alarm system being wired around which allows a bunch of current flow the wrong direction,

It is just about impossible to correct this once it is done so most have been removed from the system. Too bad too because some of those alarms could be put to good use.