Silicone Sealant And Torqueing Bolts

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Fitz98

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I have heard 2 different methods for torqueing bolts when using a silicone sealant for a differential cover install.
1) Apply a bead of sealant to the cover and install until sealant starts to squeeze out. Let dry for 1 hour and then torque bolts to spec. (This is for Permatex Ultra Black)
2) Apply a bead of sealant and tighten bolts in cris-cross pattern, then torque to spec.

I am using Motorcraft Ultra Silicone Sealant. Directions say to apply sealant and assemble while sealant is still wet. No mention of when to torque.

What do you guys do?
 
Originally Posted by Fitz98
I have heard 2 different methods for torqueing bolts when using a silicone sealant for a differential cover install.
1) Apply a bead of sealant to the cover and install until sealant starts to squeeze out. Let dry for 1 hour and then torque bolts to spec. (This is for Permatex Ultra Black)
2) Apply a bead of sealant and tighten bolts in cris-cross pattern, then torque to spec.

I am using Motorcraft Ultra Silicone Sealant. Directions say to apply sealant and assemble while sealant is still wet. No mention of when to torque.

What do you guys do?

Usually read the directions. Allow short time to begin set up as instructed, install the cover, torque to specs, done. I never retorque the bolts once the sealant dries. I do prefer gaskets for diff. covers and do RTV once in a while. If the surfaces are not perfectly clean, you are guaranteed to have a leak.
 
Last edited:
On all the applications where an RTV is originally specified for my vehicles there are "stop limits" molded or pressed into the flange on the pan or cover. This limits the squeeze out of the sealant in the joint. It's also why over torquing the bolts is bad as it deforms the cover in between the bolt holes and causes leaks.
 
Some sealants say to assemble them wet so both sides adhere, usually giving a max work time. Others recommend allowing a specific setup time before assembly. Then there is the tightening which varies too. Some suggest finger tight then allow an hour before torquing in a cross pattern, others say to tighten in a cross pattern when installing. Most say you need to wait 24 hrs before adding fluid and returning to service which I think most shops ignore because they do the service while you wait. If the instructions are not on the package you will probably have to go to their web site. Its all a cr*p shoot.
 
I like (1) though I go to maybe a couple in-lbs then come back for the re-torque.

Set RTV may not be "blowout proof" by itself so I don't want too much thickness.
 
I just tighten them the first time to snug. Don't need no torque spec unless the housing is aluminum.

[Linked Image from fototime.com]
 
Originally Posted by atikovi
Originally Posted by CT8
I prefer a gasket


I prefer no leaks.

I never had a leak with a differential gasket . I did 3 gear lube changes over 130,000 miles on the wifes f250 using the same gaskets and no leaks.
 
Originally Posted by CT8
Originally Posted by atikovi
Originally Posted by CT8
I prefer a gasket


I prefer no leaks.

I never had a leak with a differential gasket . I did 3 gear lube changes over 130,000 miles on the wifes f250 using the same gaskets and no leaks.


Dif not nearly as prone to leaking as say, transmissions, and most car makers have switched to liquid gaskets. Superior sealing for reduced warranty claims.
 
Originally Posted by atikovi
Originally Posted by CT8
I prefer a gasket


I prefer no leaks.


Many seals are designed for RTV and no gasket is available.
 
silicone is for sealing bathrooms, not cars!

the secret is to cut a gasket from flexoid gasket paper, and smear a thin skin of hylomar universal blue on both sides of the gasket. it will NEVER leak.

flexoid is very storngly water/oil/fuel/solvent resistant, and hylomar which was delveloped by rolls royce is a non-setting jointing compound so is impervious to vibration/movement. If its good enough for Rolls Royce aero engines and RAF fighters then its more than good enough for any car that belongs to anybody on this forum.

https://jointine.co.uk/flexoid-gasket-material/ this is the gasket paper youll find in just about every garage, delaership, repair shop, home hobby workshop etc in most of europe - even OEMs use flexoid in this part of the world!

https://www.newmantools.com/chemicals/hylomar.htm - like I said if it's good enough for Rolls Royce to seal their aero engines then its perfect for a paper gaskets on road cars.
 
Originally Posted by Olas
silicone is for sealing bathrooms, not cars!

the secret is to cut a gasket from flexoid gasket paper, and smear a thin skin of hylomar universal blue on both sides of the gasket. it will NEVER leak.

flexoid is very storngly water/oil/fuel/solvent resistant, and hylomar which was delveloped by rolls royce is a non-setting jointing compound so is impervious to vibration/movement. If its good enough for Rolls Royce aero engines and RAF fighters then its more than good enough for any car that belongs to anybody on this forum.

https://jointine.co.uk/flexoid-gasket-material/ this is the gasket paper youll find in just about every garage, delaership, repair shop, home hobby workshop etc in most of europe - even OEMs use flexoid in this part of the world!

https://www.newmantools.com/chemicals/hylomar.htm - like I said if it's good enough for Rolls Royce to seal their aero engines then its perfect for a paper gaskets on road cars.


Yes silicone is for sealing bathrooms, not cars! Cars use RTV compounds. Funny how you mention using a gasket but also link to hylomar, a liquid sealant.
 
Originally Posted by atikovi
Originally Posted by Olas
silicone is for sealing bathrooms, not cars!

the secret is to cut a gasket from flexoid gasket paper, and smear a thin skin of hylomar universal blue on both sides of the gasket. it will NEVER leak.

flexoid is very storngly water/oil/fuel/solvent resistant, and hylomar which was delveloped by rolls royce is a non-setting jointing compound so is impervious to vibration/movement. If its good enough for Rolls Royce aero engines and RAF fighters then its more than good enough for any car that belongs to anybody on this forum.

https://jointine.co.uk/flexoid-gasket-material/ this is the gasket paper youll find in just about every garage, delaership, repair shop, home hobby workshop etc in most of europe - even OEMs use flexoid in this part of the world!

https://www.newmantools.com/chemicals/hylomar.htm - like I said if it's good enough for Rolls Royce to seal their aero engines then its perfect for a paper gaskets on road cars.


Yes silicone is for sealing bathrooms, not cars! Cars use RTV compounds. Funny how you mention using a gasket but also link to hylomar, a liquid sealant.


its not funny, its an accepted practice. Hylomar is not a liquid sealant, it is a jointing compound - the idea has always been to use a thin skin of hylomar on both sides of a paper gasket for a garunteed dry joint. sealants donts always seal and gaskets dont always gasket but a gasket with jointing compound is 100% watertight, every time.
 
Originally Posted by Olas
silicone is for sealing bathrooms, not cars!



Pretty much every OEM auto manufacturer on the planet would disagree.

Originally Posted by Olas
the secret is to cut a gasket from flexoid gasket paper, and smear a thin skin of hylomar universal blue on both sides of the gasket. it will NEVER leak.



What about when the two joining surfaces have very precise tolerances in relation to each other which a non liquid gasket would interfere with?
 
Originally Posted by atikovi
Yes silicone is for sealing bathrooms, not cars! Cars use RTV compounds.


I'm pretty sure that the vast majority of automotive RTV compounds are silicone
 
I always use The Right Stuff because I'm impatient... Never had a leak. For diffs I use either just a gasket or gasket and sealant.
 
Originally Posted by Fitz98
I have heard 2 different methods for torqueing bolts when using a silicone sealant for a differential cover install.
1) Apply a bead of sealant to the cover and install until sealant starts to squeeze out. Let dry for 1 hour and then torque bolts to spec. (This is for Permatex Ultra Black)
2) Apply a bead of sealant and tighten bolts in cris-cross pattern, then torque to spec.

I am using Motorcraft Ultra Silicone Sealant. Directions say to apply sealant and assemble while sealant is still wet. No mention of when to torque.

What do you guys do?

I use a gasket on differential covers. And, I never torque the bolts. I have NEVER had one leak on me yet (in 35 plus years).
 
My differentials and transmission pans are the same on two vehicles. All metal reinforced nitrile gaskets.
I reused all 4 … Same as previous vehicle.
If the factory had used silicone … I would have as well.
Way back when I did … getting everything smooth and oil free was my focus … then let it cure overnight …

Always wanted to try a LubeLocker gasket
 
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