Hi,

When you replace the fuild on a rear differential and put the cover and gasket back on do you use an oil resistant RTV or a rubber gasket?

Thanks

 

I used RTV gasket maker and applied a uniform amount of it around the cover and especially the bolt holes. Keep in mind that the type that I used needs 24 hours to dry before adding new fluid.

 

All the diffs i've done have been sealed with black RTV. Make sure the surfaces are clean and let the RTV set up alittle before bolting the cover on. Read the directions on the RTV tube.

 

Any parts store that sells FelPro gaskets will have a differential gasket. Using a gasket will allow you to add the fluid after bolting the cover on,no leaks,and better piece of mind.
8.8 diffential - FelPro part # RDS-55431
9.75 differential -FelPro part # RDS-55394

 

I've never had any luck with the gaskets. Blue or Black RTV have both worked every time.

-Joe

 

Gaskets have been around longer then RTV has.When combined together you have the best of both worlds. If you fail with a differential gasket that has no pressure on it,how are you with an oil pan gasket,valve cover gasket,or even a water pump gasket? These all require gaskets; you cant fail here,or else......

 

I'm not disagreeing with anyone, just relating my experience. On my Ranger, it went 160k on the original cover seal. I pulled it and wanted to use a gasket with RTV. It leaked. Scraped the gasket off and used RTV alone and never had a problem.

It comes without a gasket from the factory and they generally don't leak until they get taken apart. I'm thinking that it must work pretty well without.

-Joe

 

Joe,you would surely be correct as saying you had a leak on your "Ranger" differential cover when using a gasket.Reason being,the cover is made from a carbon fiber material and cannot withstand the torque required to tighten the gasket. Thats where the RTV comes in.Its soft and pliable and does not require as much torque.And,on the bigger differentials,which have steel covers,the factory decided to use RTV to save money on gaskets. I hope I did not offend you.

 

use the gasket with some blue silicone on both surfaces and say bye bye....make sure everythings clean...its not rocket science ...zap!

 

Zap,thats how I do it,except I use red RTV.
ZIPPPPPPPP

 

what is rtv?

 

i agree with zapster gasket with some rtv around bolt bolt holes you are good to go. every tranny ive done that way,never a leak.

 

RTV is a generic term that everyone uses for sealant. RTV is actually an acronym that stands for "Room Temperature Vulcanizing".

Vulcanizing is a term that simply means that when it dries, it has those elastic properties.

Essentially, when "RTV" cures, it has similar properties of rubber compounds. Very pliable and elastic in nature. Most RTV's contain some type of silicone which has excellent heat properties so it does not break down. It stays in the form in which it dries.

Hope this helps

 

Clean surfaces, new gasket, high-temp RTV. If you follow the RTV instructions, and let it set and get tacky before assembly, there is no need to wait to re-fill.

DO NOT forget to add friction modifier if you have a limited slip diff. It's cheap and every Ford dealer has it. Also, there is fluid available that supposedly has modifier already in it. Do not use this. Use the proper fluid and ADD modifier from Ford. Use a quality synthetic gear oil (I use Amsoil in the diff.) it absolutley lasts much, much longer and won't "go black" anywhere near as fast. This is very important if you race, tow, or go off-roading, any time your diff is under high stress. I also lube the slip yoke on the tranny/drive shaft at the same time (a COMMON source of clunk when starting from a stop or 1-2 shift). Use Ford silicon grease with PTFE additive for this. I have also used Mobile 1 synthetic grease (red) without any notable difference. Mark the drive-shaft where it meets the rear so you can re-install it in the same orientation. It doesn't make a lot of sense, but I am pretty sure all the newer rear ends have the bolt holes drilled in such a fashion that you can't install it in the wrong position (all the bolts wont go in), but I always mark mine so I couldn't tell you. Be aware that you will loose some tranny fluid when you pull the drive-shaft, so have some on hand and a catch pan in place. Use Locktite, or some thread locker, on the drive shaft bolts (IMPORTANT).

 

"Vulcanizing" originally referred to the process of heat-treating rubber to make it tougher, and so it wouldn't melt when it gets hot. It was first used in the production of tires.

"RTV" isn't actually vulcanized, but since silicone rubber doesn't melt when it gets hot, they applied the term to it.

Personally, I prefer NAPA's "Right Stuff", which is a neoprene foam rubber.