Which Bolts Need Thread Locking Compound?
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
Which Bolts Need Thread Locking Compound?
Just recently began the process of an engine/transmission swap in my '73. Also plan to swap the gas tank and pull the differential to have Gary R rebuild it for me.
Curious as to what the gurus think regarding which bolts should be installed with thread locker. Is there any consensus as to which type of bolts need thread locker and which do not on our C3s?
Bolts such as:
Transmission bellhousing to engine block.
Transmission torque converter to flexplate.
Transmission cross member.
Header bolts.
Rear spring bolts.
Differential mounting bolts.
Front drive accessories.
Others?
Also, how do torque specs change, if at all, when using thread locker?
Do any of the answers change when bolting into aluminum (i.e. cylinder heads, etc)?
Thanks,
DC
Curious as to what the gurus think regarding which bolts should be installed with thread locker. Is there any consensus as to which type of bolts need thread locker and which do not on our C3s?
Bolts such as:
Transmission bellhousing to engine block.
Transmission torque converter to flexplate.
Transmission cross member.
Header bolts.
Rear spring bolts.
Differential mounting bolts.
Front drive accessories.
Others?
Also, how do torque specs change, if at all, when using thread locker?
Do any of the answers change when bolting into aluminum (i.e. cylinder heads, etc)?
Thanks,
DC
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Even an over torqued fastener can back out. Thread-locker was not invented for people with weak arms but rather a safety margin of potential failure.
Any place where harmonics are involved should receive a drop:
Flexplates / Flywheels
Torque Converter bolts.
Differential Mounting bolts.
Spring bolts should be locknuts.
Header bolts, you could use anti-seize. Retorque after 3-4 heat cycles.
Any place where harmonics are involved should receive a drop:
Flexplates / Flywheels
Torque Converter bolts.
Differential Mounting bolts.
Spring bolts should be locknuts.
Header bolts, you could use anti-seize. Retorque after 3-4 heat cycles.
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
I used to believe that too until I started coming across loose fasteners that I knew were torqued properly. I also realized that every modern vehicle I've owned has come from the factory with at least some fasteners installed with thread locking compound. It would be interesting to find out what today's factory engineers would do if given the task to re-spec all fasteners on our C3s.
I certainly trust advice from guys like Lars who disassembled cars on a regular basis.
DC
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
DC
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Burning Brakes
Joined: Dec 2005
Posts: 1,164
Likes: 224
From: Pawleys Island, SC
I was always taught to replace any split washer that remained flat and also those that did not spring back to original configuration. If they spring back to normal, supposedly they are okay for reuse. Do you know of any technical articles that support tossing them after one use?
DC
DC
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
Something to think about. Back in 1976 GM did away with the hardened lockwashers and shoulder bolts used for the vette ring gear. They replaced them with flanged head bolts,no thread locker. A huge amount of them backed out in use, properly torqued.
When you are thinking about the use of Loctite be sure to understand the properties of the metal you want to retain. Brass, SS, plated metals I use the correct primer for bonding otherwise it won't work. I took a grade 8 cad plated 3/8-16 nut and used #271 Loctite on it then screwed it onto a steel socket head cap screw and waited 24+ hours in 68*F temps, then tried to break the bond. It broke free without much effort. At the same time I just finished up a polished and tuned posi that I installed a new Tom's 373 gear on. I had cleaned the holes in the gear and the ARP bolts with Acetone, installed the bolts with the same #271 Loctite that failed on the bolt test. This sat in the same room and temp for 24+ hours. I went to back off the bolts and they were solid, they broke the sears 7/16 box wrench in the process.
When you are thinking about the use of Loctite be sure to understand the properties of the metal you want to retain. Brass, SS, plated metals I use the correct primer for bonding otherwise it won't work. I took a grade 8 cad plated 3/8-16 nut and used #271 Loctite on it then screwed it onto a steel socket head cap screw and waited 24+ hours in 68*F temps, then tried to break the bond. It broke free without much effort. At the same time I just finished up a polished and tuned posi that I installed a new Tom's 373 gear on. I had cleaned the holes in the gear and the ARP bolts with Acetone, installed the bolts with the same #271 Loctite that failed on the bolt test. This sat in the same room and temp for 24+ hours. I went to back off the bolts and they were solid, they broke the sears 7/16 box wrench in the process.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
Just recently began the process of an engine/transmission swap in my '73. Also plan to swap the gas tank and pull the differential to have Gary R rebuild it for me.
Curious as to what the gurus think regarding which bolts should be installed with thread locker. Is there any consensus as to which type of bolts need thread locker and which do not on our C3s?
Bolts such as:
Transmission bellhousing to engine block.
Transmission torque converter to flexplate.
Transmission cross member.
Header bolts.
Rear spring bolts.
Differential mounting bolts.
Front drive accessories.
Others?
Also, how do torque specs change, if at all, when using thread locker?
Do any of the answers change when bolting into aluminum (i.e. cylinder heads, etc)?
Thanks,
DC
Curious as to what the gurus think regarding which bolts should be installed with thread locker. Is there any consensus as to which type of bolts need thread locker and which do not on our C3s?
Bolts such as:
Transmission bellhousing to engine block.
Transmission torque converter to flexplate.
Transmission cross member.
Header bolts.
Rear spring bolts.
Differential mounting bolts.
Front drive accessories.
Others?
Also, how do torque specs change, if at all, when using thread locker?
Do any of the answers change when bolting into aluminum (i.e. cylinder heads, etc)?
Thanks,
DC
Last edited by SH-60B; Feb 13, 2020 at 09:22 AM.
Melting Slicks
Joined: Oct 2003
Posts: 2,162
Likes: 814
From: Chapel Hill NC
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Loose bolts? Its usually impact wrenches, breaker bars, busted bolts, and gallons of Kroil/PB Blaster for me.