mholm Posted September 7, 2015 Share Posted September 7, 2015 Hey all, new to site. Picked up a '62 Mack B85 Fire Truck a few months ago and have been learning as I go. Has been running pretty well but had a starting issue that has snowballed. Rebuilt the starter and was good for a couple weeks but now rectifier is smoking and alternator test off battery wasn't promising lowering V from 12.6 to 10.2. Do I need to replace rectifier? Rebuild alternator? Any advice would be much appreciated. Thanks Quote Link to comment Share on other sites More sharing options...
Gmerrill0516 Posted September 8, 2015 Share Posted September 8, 2015 When I powered up the 49 LS85 I put the battery in it with a negative ground and I was making stuff hot...I figured out my error and installed the battery with positive ground and everything worked properly...I'm not sure that is your issue, but it sounds the same...someone else will know better than I. I'd verify which way it should be before doing anything else. Quote Link to comment Share on other sites More sharing options...
mholm Posted September 8, 2015 Author Share Posted September 8, 2015 Crap, positive ground has to be correct. Just put new batteries in and I had cables off and old batteries out but I swore positves were hooked up to ground after following cables to the frame... I'll swap and see what alternators doing. That leads me back to starter issue then. Truck wasn't turning over, pulled starter and worked on a bench test with 12v, put starter back in and started without issue. I thought maybe that had to do with cables possibly being reversed but I guess that wasn't it. Again, any advice fir a rookie greatly appreciated Quote Link to comment Share on other sites More sharing options...
41chevy Posted September 8, 2015 Share Posted September 8, 2015 Starters like old generators can be polarized for a negative or positive ground system. They are an electric motor. Bench run it with a positive ground set up and it should be fine. If the grounds were reversed the Rectifier bridge could be toast. Some where I have the test values for the entire charging system. Paul Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
mholm Posted September 18, 2015 Author Share Posted September 18, 2015 Rectifier lighting up the engine bay with sparks like it's the 4th of July. Anyone know where I can get a new one or if/how to repair? Quote Link to comment Share on other sites More sharing options...
MrCat Posted September 18, 2015 Share Posted September 18, 2015 Rectifiers were discontinued back in the 70's. I converted many of those to Leece Neville or Motorola integral alternators. I think they are called Load Handler now. You will just need a pos and neg cable. IIRC you will need a new pulley also, the original had tapered shaft. Quote Mike PacittoChelmsford Mass Link to comment Share on other sites More sharing options...
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