Doug T B42X Posted June 29 Share Posted June 29 I have a B42 that won't start without a jump. This started about two months ago. Once started, I'm reading about 12.5 volts on battery, which is only two years old. I did remove the negative cable from the battery and she kept running (this truck is positive ground). I got this truck about five years ago and have not rebuilt anything electrical. The brake lights stopped working about a year ago, but that's another story. Maybe it's not - the wiring is not too good. You can see from the picture that the coil wire looks to be in bad shape. Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted June 29 Share Posted June 29 Check your ground connections on the truck Most vehicles have more than one Unbolt, clean back to bare metal, bolt back on The generating system is working or the truck would stop when you disconnect the battery 12.5 volts would hardly charge a 12 volt battery Paul Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 Never a good idea to disconnect a battery on a running engine. Yeah, I know you've done for years, and "not had a problem" but one day you will. Generators don't put out much at idle so your voltage reading doesn't mean much. "Doesn't start without a jump" doesn't say much, does it crank but not fire, does in not crank? I see the battery ground side goes to the frame, this is a common problem and a cheap way out that many mfg used. Run the ground to the highest amp draw item on the truck (starter motor) and ground the frame from there. If the starter is grounded through the case than run the ground to the mounting bolt. If the starter has a ground stud, run the ground there. It cost a bit more in wire, but eliminates many problems. Often there is a braided strap that grounds the engine to the frame, and it degrades over time and doesn't allow the current through. Frame and body need to be bonded to the engine with ground straps. 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted June 29 Share Posted June 29 1 hour ago, Geoff Weeks said: Never a good idea to disconnect a battery on a running engine. Yeah, I know you've done for years, and "not had a problem" but one day you will. Generators don't put out much at idle so your voltage reading doesn't mean much. "Doesn't start without a jump" doesn't say much, does it crank but not fire, does in not crank? I see the battery ground side goes to the frame, this is a common problem and a cheap way out that many mfg used. Run the ground to the highest amp draw item on the truck (starter motor) and ground the frame from there. If the starter is grounded through the case than run the ground to the mounting bolt. If the starter has a ground stud, run the ground there. It cost a bit more in wire, but eliminates many problems. Often there is a braided strap that grounds the engine to the frame, and it degrades over time and doesn't allow the current through. Frame and body need to be bonded to the engine with ground straps. got that one covered 100%. changed many of the braided ground straps . Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 It why my 6 volt truck will start when sitting in below 0 weather. heavy cable to the starter case and the hot feed. Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted June 29 Author Share Posted June 29 Thank you all for your help. I will work on it today and report back. When starting without jump box, it makes a very brief cranking noise, then nothing. 7 hours ago, mrsmackpaul said: Check your ground connections on the truck Most vehicles have more than one Unbolt, clean back to bare metal, bolt back on The generating system is working or the truck would stop when you disconnect the battery 12.5 volts would hardly charge a 12 volt battery Paul Thanks I'll do that. Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted June 29 Author Share Posted June 29 53 minutes ago, mechohaulic said: got that one covered 100%. changed many of the braided ground straps . Without jump starting it just makes a noise like it is trying to crank, but then dies. Regarding the grounding to the starter, do you mean to run the battery ground to the same ground terminal that the starter uses? I'll check for the frame - body - engine grounding straps. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 No, if the starter only has one copper bolt coming out of the motor, then the starter motor is internally grounded to the case. For those, run your ground cable from the battery to one of the mounting bolts of the starter motor to the bell housing. If that is too difficult you can run to the transmission case. Many more modern starters have a 2nd copper bolt (stud) sticking out the back of the starter that needs a ground connected. (IE Delco MT 40's etc) Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted June 29 Author Share Posted June 29 Thanks I'll check. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 Starter with external (two stud) grounding Quote Link to comment Share on other sites More sharing options...
mowerman Posted June 29 Share Posted June 29 I hadda 48 Plymouth deluxe back in the 70s 6 V system and that engine used to turnover so slow and the cold it didn’t even look like it was going to fire, but it would… wish I had it now ha ha bob Quote Link to comment Share on other sites More sharing options...
mowerman Posted June 29 Share Posted June 29 Good luck, bud and yes, we have all taken battery cables off with the engine running and no, I do not think it’s a good idea. I don’t know why I just don’t…. Bob Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 17 minutes ago, mowerman said: Good luck, bud and yes, we have all taken battery cables off with the engine running and no, I do not think it’s a good idea. I don’t know why I just don’t…. Bob It can send a large voltage spike into the electrical system. Anything with an alternator and/or electronics can be damaged. It is a bad practice, and someday you'll pay the price of doing it. I've seen it blow headlight bulbs, when someone did it with them on, a 12 volt headlight will take 24 volt for a few seconds, this spike must have been over 50 volts. 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted June 29 Share Posted June 29 also keep in mind; the braided ground strap is a duel purpose item. not only for ground but also it is made of the braided material to act as a weak link in system should a problem arise. it will melt in half intentionally when major short happens. 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted June 29 Share Posted June 29 2 hours ago, Geoff Weeks said: It can send a large voltage spike into the electrical system. Anything with an alternator and/or electronics can be damaged. It is a bad practice, and someday you'll pay the price of doing it. I've seen it blow headlight bulbs, when someone did it with them on, a 12 volt headlight will take 24 volt for a few seconds, this spike must have been over 50 volts. similar to having TV on during lightning storm and house or near by tree is struck. current will follow through house and take-out plugged-in appliances. 1 Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 29 Share Posted June 29 22 minutes ago, mechohaulic said: also keep in mind; the braided ground strap is a duel purpose item. not only for ground but also it is made of the braided material to act as a weak link in system should a problem arise. it will melt in half intentionally when major short happens. Ahh, not so much, no way to fuse something like a starter motor. It is very close to a dead short with the rotor not turning. The battery would have to be capable of supplying far more current than a starter motor could draw with a locked rotor. Any resistance in the braided cable goes to reducing the power from the battery to the starter, not a good thing. It is braided to make it as flexible as possible. In rush current can exceed 1000 amps on a medium starter and over 2000 on a big one. Starters are a short term load, so if they heat the cable a little, it can survive, no way those cables are going to survive a continuous load of 300 or more amps, so how do you fuse something that can take 8x-10x the current? You don't! Running battery cable to the engine just means running more copper, after all the "hot" side is already run direct to the starter solenoid, so if it can handle the engine moving around the ground side can also. 1 Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted June 30 Share Posted June 30 21 hours ago, Geoff Weeks said: Never a good idea to disconnect a battery on a running engine. Yeah, I know you've done for years, and "not had a problem" but one day you will. With the greatest of respect I'm gunna call this urban myth No difference to pulling jumper leads off a vehicle with a flat battery once you've jump started it I'm sure you have heard plenty of stories and had blown tail lights but Im calling this as myth It just makes sense at all If you were disconnecting a coil on a huge solenoid (a inductive load) I would say it's possible But not a battery as they are a capacitive load and as such would absorb any spike in voltage not creat a spike This goes against the basic electrical theory we operate the entire world on Anyway, carry on everyone and I'll go back to painting the house Paul Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 30 Share Posted June 30 when you pull the jumpers off a dead battery, you still have the battery to help clamp the voltage. It acts as a big capacitor and quells the spike. Carry on doing it, if you like, I have seen the results. BTW battery cut-off and dual battery switches (the good ones anyway) have a kill circuit to cut the field to the alternator before it breaks the circuit to the battery. If it is such a myth, why did Cole Hearsee and the rest go through the trouble? It is especially bad with alternator charging system, because they can produce more at lower RPM. Some heavy alternators can be had with "load dump" regulators designed to clamp the voltage quick enough to prevent damage, but most do not have this feature. Less of a problem with generators as they produce less at low rpm, however the vibrating point type regulators used with them are slower to react and have a lower ability to clamp the voltage and prevent spikes. Load dump - Wikipedia Not an urban myth! Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 30 Share Posted June 30 (edited) 21 hours ago, Geoff Weeks said: It can send a large voltage spike into the electrical system. Anything with an alternator and/or electronics can be damaged. It is a bad practice, and someday you'll pay the price of doing it. I've seen it blow headlight bulbs, when someone did it with them on, a 12 volt headlight will take 24 volt for a few seconds, this spike must have been over 50 volts. Turns out I was way wrong about 50 volts! When I was looking for a short-sweet link on the subject, and found the Wiki page, I also came across a SAE "white paper" on the subject for automotive load dump, they recorded an short duration voltage spike of over 200 volts (202 to be exact) and calculated momentary current of close to 50 amps. That is like a momentary connection to 200 volt mains! Older vehicles with generators, esp cars or farm tractors with generators in the 30 amp range, yeah, you can get away with in most cases, no electronics to be damaged, the spike will be low if the engine is at idle. Add a Pertroix to replace points, and you are rolling the dice. Anything with an alternator, and you are asking for big trouble, at an ECU (computer) and you could be looking at damage that exceeds the vehicles worth. You can look it up yourself, do a search for "load dump" and read some of the papers on the subject. It is just bad practices and asking for trouble. P.S. a quick and dirty test you can do on the side of the road, is hold a piece of steel (Key ring, but not keys, as they are mostly brass) near the rear bearing on an alternator or near a pole shoe screw on the side of a generator, and if it is drawn to it, you know the field is active and the regulator and generator are likely working. Edited June 30 by Geoff Weeks Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted June 30 Author Share Posted June 30 Thank you all for your suggestions. I appreciate the benefit of your combined knowledge. Yesterday and today, I cleaned and tightened: battery terminals, starter ground and braided ground to frame, put new commutator cover on starter, cleaned terminals on generator, tightened belts on generator. It is still reading between 12.5 and 13.0 volts at the battery, and 12.5 volts at the generator. The biggest change is that it does not need to be jump started. Starts immediately again after running, after going to dinner last night, and again this afternoon. That's great. But still at 12.5 - 13.0 volts. Two questions: what about getting generator rebuilt? (I would also change twin belts) and Thursday I would like to take her to the parade, about three miles from my house, 1 hour waiting, 1 hour parade, three miles back? Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted June 30 Share Posted June 30 If you have voltage at the generator with the engine running, (shouldn't be any when the engine isn't running) then the generator doesn't likely need to be rebuilt. I see the cover is off your regulator, has someone tried to adjust it? They are adjustable but it isn't easy to, it involves setting the current as well as the voltage, each takes a separate procedure. wouldn't be a bad idea to put some oil in the oil cups on the generator and starter. Generators will not produce much if at all at idle, so you need to run the engine 1500-1800 when checking the voltage, same for current. Regulator needs to be grounded, as it is mounted in rubber grommets, it does look like there is a ground wire on it, where it goes isn't clear. Generators are very well made, and if not abused, will still work fine after 80 year or more. I have two that old that still work fine. If the generator works when the engine speed is raised, then no problem taking to the parade, if it doesn't and you have a buddy with some jumper cables that can give you a charge if needed, that would work also. Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted July 1 Author Share Posted July 1 Thanks for your reply. I took the cover off the regulator to check it, but that procedure looks too ambitious for me, so I'll button it up. I'll make sure the oil cups on generator and starter get some oil. I have a jump box and will keep some jumper cables handy, my brother will be there with his 79 LaFrance so that should be all right. I'll run the engine up to 1500-1800 tomorrow but I think I should be all right. Thanks again. Quote Link to comment Share on other sites More sharing options...
BOBWhite Posted July 1 Share Posted July 1 Remember not too much oil in the generator/starter cups! I use 3-in-One Oil in my stuff with generators and only lubricate them annually. As stated there isn't much to go wrong with these generators. I think I've posted this video here before but it explains the generator/regulator better than anything I've seen: 1 Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted July 4 Author Share Posted July 4 Thanks BOBWhite, I'll bear that in mind. Interesting to learn that the tests should be made with the generator regulator cover ON, not off. I'll admit I didn't make all the tests that Steve in the film did, but I am going to replace the generator regulator and hope for the best. I also noticed they didn't cover polarizing a replacement generator regulator, although that was not really the subject. Doug Quote Link to comment Share on other sites More sharing options...
Doug T B42X Posted July 4 Author Share Posted July 4 Just now, Doug T B42X said: Thanks BOBWhite, I'll bear that in mind. Interesting to learn that the tests should be made with the generator regulator cover ON, not off. I'll admit I didn't make all the tests that Steve in the film did, but I am going to replace the generator regulator and hope for the best. I also noticed they didn't cover polarizing a replacement generator regulator, although that was not really the subject. Doug 1 minute ago, Doug T B42X said: I did clean the contacts and terminals and checked all were tight, but still have 12.5 volts at the battery. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.