Electrical problem help!!
Thread Starter
Instructor
Joined: Jan 2011
Posts: 102
Likes: 1
From: St. Jacob IL
Electrical problem help!!
So I have been having my engine and transmission (th350) rebuilt. I took the transmission in because I thought it had some water in the pan and asked the transmission shop to check it out. They called me back today and said there wasn't any water but the transmission itself is basically bombed. Apart from the clutches and seals being worn out (usual stuff) they told me I have a bad ground in the car. The pump was destroyed because of weld spots on the inside of the pump 
The guy I talked to said he has been rebuilding transmissions for roughly 40 years and that this happens on Chevys when a ground strap comes loose and grounds to the frame. The charge tries to find its way to ground and finds it in the transmission. As the pump spins it arcs with the charged casing and creates weld spots on the rotor. It also burns the seals out. My question is how do I find the loose ground? Are there any that are especially common culprits, or, where are the ground points on these cars? The battery was holding a charge fine when it was running. The only thing I can think of is that I had a plug wire melt and arc to the engine block. Could that arcing have been what caused the weld spots in the pump?
The guy I talked to said he has been rebuilding transmissions for roughly 40 years and that this happens on Chevys when a ground strap comes loose and grounds to the frame. The charge tries to find its way to ground and finds it in the transmission. As the pump spins it arcs with the charged casing and creates weld spots on the rotor. It also burns the seals out. My question is how do I find the loose ground? Are there any that are especially common culprits, or, where are the ground points on these cars? The battery was holding a charge fine when it was running. The only thing I can think of is that I had a plug wire melt and arc to the engine block. Could that arcing have been what caused the weld spots in the pump?
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,481
From: Southbound
Cruise-In II Veteran
Do you have the assembly instruction manual (AIM)? The AIM shows all the factory grounding points.
First hunch is to check #1 body mount on the driver's side. There should be a ground strap from the mount to the frame.
First hunch is to check #1 body mount on the driver's side. There should be a ground strap from the mount to the frame.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
The only ground I can think of that is supposed to carry the kind of current that can do that is the main engine ground on the passenger side motor mount. It grounds the engine and starter to the frame. Mine was cooked on both my 77 and the 81.
Check all of them, alternator harness ground, starter harness.
Check all of them, alternator harness ground, starter harness.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 102
Likes: 1
From: St. Jacob IL
Thanks guys. A couple of years ago I was driving it and blew the oil pump. While I was replacing the pump I had to detach some sort of electrical ground that was attached to the side of the motor at the diptstick mount. When I reinstalled the dipstick I put that ground strap sandwiched between the dipstick and engine block. I'm thinking maybe that was the engine ground and I did not connect it properly? I talked to two of my friends (one has built a '67 Chevelle and a '73 Nova, the other has an '85 K10) and neither of them have heard of anything like welding the inside of a transmission that way. I will definitely check my AIM and go over the grounding points. I just think it's odd that my battery and charging system worked correctly if I had that big of a ground issue on the car...
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Thanks guys. A couple of years ago I was driving it and blew the oil pump. While I was replacing the pump I had to detach some sort of electrical ground that was attached to the side of the motor at the diptstick mount. When I reinstalled the dipstick I put that ground strap sandwiched between the dipstick and engine block. I'm thinking maybe that was the engine ground and I did not connect it properly? I talked to two of my friends (one has built a '67 Chevelle and a '73 Nova, the other has an '85 K10) and neither of them have heard of anything like welding the inside of a transmission that way. I will definitely check my AIM and go over the grounding points. I just think it's odd that my battery and charging system worked correctly if I had that big of a ground issue on the car...
Thread Starter
Instructor
Joined: Jan 2011
Posts: 102
Likes: 1
From: St. Jacob IL
Well I am supposed to pick the transmission up this afternoon. I think I will ask to see the old pump so I can see what he is talking about. If I can take the old pump with me I will post some pictures if that would be helpful.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Thread Starter
Instructor
Joined: Jan 2011
Posts: 102
Likes: 1
From: St. Jacob IL
I actually don't have the AC system on the car. It was disconnected when I got the car and so after I got the motor out I took the rest of the system (except for the heater box) out of the car. The engine bay wiring when I got the car was kind of scary. The tach cable was disconnected and the plastic connector was melted. The hood lamp is zip tied up inside one of the fenders and has the bulb removed. The AC harness was totally disconnected, as was the electric, choke, manifold heater, etc. I am 100% going restomod on the car because I don't really think it is worth the effort to take it back to stock. My plan is to check the ground points I have and reconnect any that I can find that are not there. I have toyed with ripping everything out and point to point wiring the electrical system. For my mental redesign all I need it the engine electrical system, blower/heater system, the gauges, the lights and the radio. I don't use the cigarette lighter, the convenience lights, the rear defroster, AC, etc.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 102
Likes: 1
From: St. Jacob IL
Got a suggestion to run an extra ground wire from the starter to the frame, and one more from the alternator bracket to the frame. Seems like a good idea to try since it's simple. Do I risk hurting anything by doing this?
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
One ground or a hundred grounds, makes no difference as long as one of them is big enough.