Bolt Size 🔩

Dezimade

Apprentice
Sep 22, 2021
58
8
Boston Ma.
Good day ! Lower bolt ,A/C Compressor
Curious 🤨 of the size.

As this may be a simple fix ! tossing belts ! Just noticed …… there is no bolt!

59C9446B-F966-4996-955D-D76E350D604B.jpeg
 

airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,668
113
hard to say. Could be standard or metric. GM did some goofy things back in the day
 
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Dezimade

Apprentice
Thread starter
Sep 22, 2021
58
8
Boston Ma.
If I knew the size I could get both!
 

ssn696

Living in the Past
Supporting Member
Jul 19, 2009
5,366
113
Permanent Temporary
Does it bolt into any of the bosses and tapped holes seen here? If so, it's a 3/8-16.
0B260651-AC23-4C8E-8465-B55F749A2A60.jpeg
Hard to see from your photos. If it is bracket to bracket, that's where GM often slipped in metrics. M8 or M10.
 
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Dezimade

Apprentice
Thread starter
Sep 22, 2021
58
8
Boston Ma.
You don't have a random bucket of bolts laying around to test fit a thread pitch?
Actually I was informed by my buddy. That he’s has the original. Never put it in.

Don’t ask .
 
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CopperNick

Royal Smart Person
Supporting Member
Feb 20, 2018
2,084
113
Canada
'79 'Bu Classic Coupe? Original 305 mill? or?? TH350 t-mission? All this being the case then 3/ths NC thread is what most of the bosses were drilled and tapped to. If you check your alternator, you will find the lower mount with the long bolt uses a 3/8ths as do the two shorties that thread into the water pump. The pump itself is held down by 4 of those 3/8ths bolts as is the power steering pump brackets so the chance of there being an odd duck bolt are possible but not probable. The picture, however does raise the possibility that not only is the bolt missing but that there might have been a spacer between that bracket and the mounting hole which is also MIA.



Nick
 
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Dezimade

Apprentice
Thread starter
Sep 22, 2021
58
8
Boston Ma.
'79 'Bu Classic Coupe? Original 305 mill? or?? TH350 t-mission? All this being the case then 3/ths NC thread is what most of the bosses were drilled and tapped to. If you check your alternator, you will find the lower mount with the long bolt uses a 3/8ths as do the two shorties that thread into the water pump. The pump itself is held down by 4 of those 3/8ths bolts as is the power steering pump brackets so the chance of there being an odd duck bolt are possible but not probable. The picture, however does raise the possibility that not only is the bolt missing but that there might have been a spacer between that bracket and the mounting hole which is also MIA.



Nick
Thanks for all the important information.
I will take. All this and learn as I am a newbie at the g body.
 

CopperNick

Royal Smart Person
Supporting Member
Feb 20, 2018
2,084
113
Canada
Thanks for all the important information.
I will take. All this and learn as I am a newbie at the g body.
And just so you don't feel neglected, yes, there is a BUT to all the joy that has just come your way. Starting with the long bolts that hold the motor mount clams to their frame mounts, almost everything else is METRIC. The bolts that hold the upper half of the clamshell mount to the motor are 3/8ths NC SAE Norte Americano Normal. They and the bolts that hold the T-mission bell housing to the bolt are the last bastions of normality. Even the bolts that hold the t-mission mount to the crossmember are furrin born. Where you might find some exception is in the rear end. The bolts for the cross bearing retainer plates are metric. The bolts for the upper and lower control arms could be metric; mine aren't but then again, neither are the arms, (Hee, Hee). The shock bolts and nuts are fractional, and a few other things along that line got upgraded back to Grade 5 or 8 according to my own tastes and preferences.

What you can find along the way is that if a part, like those shocks, has been replaced or upgraded, the hardware that comes with, is usually, but not always, fractional. I just finished both installing a UMI rear frame brace and replacing a pair of Napa Shocks at the same time. The brace came with 3/8ths fasteners, but the shocks were designed to accept 5/16ths, so in went a set of Grade 8 capscrews and some specialized heavy washers as a compromise. What settled the matter was that the holes in the frame bracket were 5/16 +/- by default and this was not a frame off exercise so expediency ruled the day. I personlally seriously doubt that that new cross brace will be going anywhere as it took a 5 lb dead blow hammer to beat it into position as it was. UMI said it fit but might need "persuasion" or "encouragement" to get it to be a good little part and go where it was meant to. They were right.

Major qualifier here. While learning Metrics can be a M-PITA, once you have some experience with them and learn to think in two systems at once, the process of conversion becomes slightly easier. Be grateful. AT least we don't have the old school version of British Metric/Whitworth to contend with.



Nick
 
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Dezimade

Apprentice
Thread starter
Sep 22, 2021
58
8
Boston Ma.
And just so you don't feel neglected, yes, there is a BUT to all the joy that has just come your way. Starting with the long bolts that hold the motor mount clams to their frame mounts, almost everything else is METRIC. The bolts that hold the upper half of the clamshell mount to the motor are 3/8ths NC SAE Norte Americano Normal. They and the bolts that hold the T-mission bell housing to the bolt are the last bastions of normality. Even the bolts that hold the t-mission mount to the crossmember are furrin born. Where you might find some exception is in the rear end. The bolts for the cross bearing retainer plates are metric. The bolts for the upper and lower control arms could be metric; mine aren't but then again, neither are the arms, (Hee, Hee). The shock bolts and nuts are fractional, and a few other things along that line got upgraded back to Grade 5 or 8 according to my own tastes and preferences.

What you can find along the way is that if a part, like those shocks, has been replaced or upgraded, the hardware that comes with, is usually, but not always, fractional. I just finished both installing a UMI rear frame brace and replacing a pair of Napa Shocks at the same time. The brace came with 3/8ths fasteners, but the shocks were designed to accept 5/16ths, so in went a set of Grade 8 capscrews and some specialized heavy washers as a compromise. What settled the matter was that the holes in the frame bracket were 5/16 +/- by default and this was not a frame off exercise so expediency ruled the day. I personlally seriously doubt that that new cross brace will be going anywhere as it took a 5 lb dead blow hammer to beat it into position as it was. UMI said it fit but might need "persuasion" or "encouragement" to get it to be a good little part and go where it was meant to. They were right.

Major qualifier here. While learning Metrics can be a M-PITA, once you have some experience with them and learn to think in two systems at once, the process of conversion becomes slightly easier. Be grateful. AT least we don't have the old school version of British Metric/Whitworth to contend with.



Nick
How great full am I for believing in a forum . Nick your great! Like no other to date. Thanks for taking time to tell your experience. Dez
 

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