Stumped!!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

JAB'70 · 03-19-2009, 08:46 AM

On my '70 c10 I've had one bolt holding the alternator bracket break off in the block (3) times. I can't figure out why it's doing it. My alternator is mounted on the driver's side with (2) bolts holding the bracket in place, the one on the right is the culprit. See photo...Any answers?

71swb4x4 · 03-19-2009, 08:53 AM

Are you running a long water pump? It looks like you have the alternator brackets spaced away from the head an inch or more. That is going to put a lot of stress on the bolts that hold it to the head. If it's a long water pump I would go back to a short water pump. If it's the pulleys that are forcing you to space it out then get a pulley that will let you put the alternator back where it belongs.

**LockDoc** · 03-19-2009, 09:06 AM

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I would buy some grade 8 bolts and replace all of those.

LockDoc

Andy4639 · 03-19-2009, 09:20 AM

Everything is in balance right? If you have that brace spaced as mention above then that is also going to make it do this. I would suggest a grade 8 also as above. If everything is good then I would say it was just cheap bolting.
I run the same bracket and have never had a problem.

JAB'70 · 03-19-2009, 11:42 AM

I running 1" spacers, the bolts are grade 8, everything is aligned. I'm running (1) single belt. I'm sure it's the result of unneeded tension.
And I'm running with a short water pump.

mrein3 · 03-19-2009, 12:38 PM

I had this very same problem. That same bolt would snap off at the worst time. I tried everything above, grade 8 bolts, spacers, nothing worked. Finally one day I had the hood up and while on high idle the alternator and brackets were dancing like they had a bee in its pants.

It turns out my pulleys were all mismatched. Certain rpms would cause a bad harmonic that really had stuff moving under there.

My solution was to get a matching set of crank and alternator pulleys off of an unmolested truck. That was some time ago and I've never had a problem since.

Surf the parts board and see if anybody is parting out a truck that didn't have some backyard 'mechanic' matching up pulleys that shouldn't have been.

71swb4x4 · 03-19-2009, 01:04 PM

You should not have to have those 1" spacers. The cast iron bracket should mount right to the head.
I think your problem is the 1" spacers as well as incorrect pulleys.

The good thing is that it's all an easy fix.

JAB'70 · 03-19-2009, 02:20 PM

Okay, sounds logical to me. I surf to see if I can find a matching set of pulleys.

The 1" spacer was there when I bought the truck back in 2007 (it ran but had been abused by the backyardigan) I've put alot of work into it (body and engine) however I didn't see a need to take out the spacers (besides it would've caused belt mis-alignment) until this broken bolt issue came along.

Thanks for the info, this forum is a gets thumbs up from.

03-19-2009, 08:46 AM	#1
JAB'70 Registered User Join Date: May 2007 Location: South Carolina Posts: 54	Stumped!!! On my '70 c10 I've had one bolt holding the alternator bracket break off in the block (3) times. I can't figure out why it's doing it. My alternator is mounted on the driver's side with (2) bolts holding the bracket in place, the one on the right is the culprit. See photo...Any answers? Last edited by JAB'70; 03-26-2010 at 10:57 AM.

03-19-2009, 08:53 AM	#2
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: Stumped!!! Are you running a long water pump? It looks like you have the alternator brackets spaced away from the head an inch or more. That is going to put a lot of stress on the bolts that hold it to the head. If it's a long water pump I would go back to a short water pump. If it's the pulleys that are forcing you to space it out then get a pulley that will let you put the alternator back where it belongs. __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

03-19-2009, 09:06 AM	#3
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,773	Re: Stumped!!! - I would buy some grade 8 bolts and replace all of those. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

03-19-2009, 09:20 AM	#4
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Stumped!!! Everything is in balance right? If you have that brace spaced as mention above then that is also going to make it do this. I would suggest a grade 8 also as above. If everything is good then I would say it was just cheap bolting. I run the same bracket and have never had a problem. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. Last edited by Andy4639; 03-19-2009 at 09:21 AM.

03-19-2009, 11:42 AM	#5
JAB'70 Registered User Join Date: May 2007 Location: South Carolina Posts: 54	Re: Stumped!!! I running 1" spacers, the bolts are grade 8, everything is aligned. I'm running (1) single belt. I'm sure it's the result of unneeded tension. And I'm running with a short water pump. Last edited by JAB'70; 03-19-2009 at 11:43 AM.

03-19-2009, 12:38 PM	#6
mrein3 Registered User Join Date: Feb 2000 Location: Center City, MN, USA Posts: 3,254	Re: Stumped!!! I had this very same problem. That same bolt would snap off at the worst time. I tried everything above, grade 8 bolts, spacers, nothing worked. Finally one day I had the hood up and while on high idle the alternator and brackets were dancing like they had a bee in its pants. It turns out my pulleys were all mismatched. Certain rpms would cause a bad harmonic that really had stuff moving under there. My solution was to get a matching set of crank and alternator pulleys off of an unmolested truck. That was some time ago and I've never had a problem since. Surf the parts board and see if anybody is parting out a truck that didn't have some backyard 'mechanic' matching up pulleys that shouldn't have been. __________________ '70 cab, '71 chassis, 383, TH350, NP205. '71 Malibu convertible '72 Malibu hard top Center City, MN

03-19-2009, 01:04 PM	#7
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: Stumped!!! You should not have to have those 1" spacers. The cast iron bracket should mount right to the head. I think your problem is the 1" spacers as well as incorrect pulleys. The good thing is that it's all an easy fix. __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.

03-19-2009, 02:20 PM	#8
JAB'70 Registered User Join Date: May 2007 Location: South Carolina Posts: 54	Re: Stumped!!! Okay, sounds logical to me. I surf to see if I can find a matching set of pulleys. The 1" spacer was there when I bought the truck back in 2007 (it ran but had been abused by the backyardigan) I've put alot of work into it (body and engine) however I didn't see a need to take out the spacers (besides it would've caused belt mis-alignment) until this broken bolt issue came along. Thanks for the info, this forum is a gets thumbs up from.



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