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Trans axle-to-engine mounting bolts


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I have lost the trans to engine mounting bolts for 98 Deville 4.6L Northstar. There are 4 bolts I believe to be somewhere near to 12-13mmx2mmx70mm bolts but would like to know for sure so I get the right ones can anyone help wioth this

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The 1997 FSM, page 7-202, says that the transmission-to-engine bolts are torqued to 75 n*m (55 lb-ft). The 1997 FSM pae 6-17 has the thread specs in the engine as M12 X 1.75. The torque spec should get you the strength spec on the bolt. I'll leave the length to you, but the threads go through flanges on the engine so a millimeter or two of extra length won't hurt. And, yes, there are four of them. They may not all be the same length.

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2 upper bolts have smaller hex head. Not sure if all 4 bolts are M12 though. Why GM needed smaller upper bolts? Clearance around coolant crossover? Why not make clearance bump in casting such that all 4 bolts fit fine? I bet the junior engineer assigned to that task said "why the bleep" does the casting hit the bolt?

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I have lost the trans to engine mounting bolts for 98 Deville 4.6L Northstar. There are 4 bolts I believe to be somewhere near to 12-13mmx2mmx70mm bolts but would like to know for sure so I get the right ones can anyone help wioth this

Any GM dealer can order them for you if they are not discontinued. If they are discontinued, there is always the junkyard.

2 upper bolts have smaller hex head. Not sure if all 4 bolts are M12 though. Why GM needed smaller upper bolts? Clearance around coolant crossover? Why not make clearance bump in casting such that all 4 bolts fit fine? I bet the junior engineer assigned to that task said "why the bleep" does the casting hit the bolt?

I'm sure there is a solid engineering reason why it is designed as it is. They do not assign "Junior Engineers" to a major task like a water crossover or a transmission to engine interface.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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KHE *is* an expert. We have scads of experts on Caddyinfo.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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2 upper bolts have smaller hex head. Not sure if all 4 bolts are M12 though. Why GM needed smaller upper bolts? Clearance around coolant crossover? Why not make clearance bump in casting such that all 4 bolts fit fine? I bet the junior engineer assigned to that task said "why the bleep" does the casting hit the bolt?

lol. The engineers are there to design things to make money. The days of sitting in our fenders to work on things are gone. now we only have 2 fingers if we are lucky.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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For the thread specs, I'm looking at the "Thread Repair Specifications" on page 6-17 of the 1997 FSM. There are a total of 10 holes. They fall in three groups.

There are four transmission mount bolts. The thread size is M12 X 1.75, insert length "thru."

There are four crossover mount bolts. The thread size is M8 X 1.25, insert length 24 mm.

There are two starter mount bolts. The thread size is M8 X 1.25, insert length "thru."

The two lower transmission mount bolts are on the outer edge of the block, apparently on a transmission mount flange, the one on the left (looking from the rear of the engine) an inch or two lower than the one on the right. The ones on the top are right at the plane of the intake manifold mounting plane and may need smaller bolt heads to clear the intake manifold.

I read somewhere that the Northstar bell housing pattern is identical to that of the SBC and many other GM bell housing patterns except that one bolt hole is moved about an inch to clear the starter.

You would probably be OK to get the smallest bolt heads available for bolts rated for use with 55 lb-ft torque. Still, I don't have information on the lengths.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 2 weeks later...

another strange thing. i see the casting thickness at the top of the bellhousing is a different depth so 2 different length bolts may be needed. found a dealer with trans. nice and clean. i am not sure if it is reman or new.

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It looks new. But the only thing that really matters is the warranty.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Those are the ones above the starter. Good show. Thank you.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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