RTV Curing and Diffs

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JHZR2

JHZR2

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Hello,

Ive seen lots of applications where RTV is used for sealing a differential.

Ive also seen notice where a good long amount of time should be spent allowing the RTV to cure before applying new lube.

Can anone comment on the long-term effects of not letting it cure a "long time" before putting lube in? Im sure that a shop/dealer doesnt wait a long enough amount of time...

What happens? Does it cause the RTV to degrade, or does it put bad stuff in the lube? Id imagine that there could be some solubility of the stuff if not cured...
 
I used to just remove covers and put on RTV then tighten bolts and fill right after. I cleaned the covers and diffs so they were clean and dry. That was in shops, never had anybody come back with leaks. That being said, I try to let them cure for awhile now when doing them.

I would like to here from anybody with more insight as well.
 
My father who was a mechanic and engine builder for many years always told me to let the RTV cure for at least 25 minutes on a sunny day, and more when it is cold. He said after that time period to put the cap on (this is after cleaning both the cap and diff surfaces well.) put the bolts on finger tight in a cris-cross pattern wait another 30 minutes tighten each bolt till they were snug, then fill.

He also said that after applying the bead to the cap to use your finger and do a swirling motion to get the rtv even and kill any air bubbles in the silicone. Also to go around bolt holes too.

I have always used this method and never had a diffy leak.
 
Originally Posted By: defektes
My father who was a mechanic and engine builder for many years always told me to let the RTV cure for at least 25 minutes on a sunny day, and more when it is cold. He said after that time period to put the cap on (this is after cleaning both the cap and diff surfaces well.) put the bolts on finger tight in a cris-cross pattern wait another 30 minutes tighten each bolt till they were snug, then fill.

He also said that after applying the bead to the cap to use your finger and do a swirling motion to get the rtv even and kill any air bubbles in the silicone. Also to go around bolt holes too.

I have always used this method and never had a diffy leak.


I do pretty much most of what he does. I don't worry about air bubbles unless I can see it's going to cause a problem. I also don't wait to fully tighten the bolts as a second step. On occasion I will wait awhile then fully torque them up.
 
If you completely clean the old RTV or gasket off there isn't much of a problem just tightening the bolts and filling it. RTV skins pretty quickly and the lube is not going to wash it away and into the oil. It's the old bits of RTV that can get in the oil so it's essential that you remove it all.
 
I never really worried about it. I rebuilt a lot of 7.5/8.8 diffs, and never had a problem zipping the rear cover down, and filling the diff immediately. Never had a recheck on diff overhauls either (knock on wood).
 
There's a permatex RTV in a easy cheese aerosol tube that sets up in 60 seconds or so, says the can.

can also use anaeroibic sealant, sets up in 15 min
 
Originally Posted By: eljefino
There's a permatex RTV in a easy cheese aerosol tube that sets up in 60 seconds or so, says the can.

can also use anaeroibic sealant, sets up in 15 min


Wow I don't think I could even get all the bolts hand started in that time.
 
Call me overly paranoid, but last time I let RTV cure for 24 hours before filling. Was it necessary--probably not, but with ambient temperature of 50F and overnight of 35-40F, every little bit helped. September in Alaska for you.
 
humidity helps RTV cure like crazy. If you live in the muggy part of alaska you're all set.
 
It's a non-issue. I clean the parts up, put on a bead of RTV, bolt it together, and fill it up. No cure time required.
 
onion - You are extremely lucky!
I have seen all sorts of leaks on valve covers, differential, manifolds, etc, with too short cure times of RTV.
A clean substrate and enough cure time is essential to proper RTV use.
 
I guess we'll have to agree to disagree, because my experience says otherwise.

For a differential, automatic transmission pan, etc- cure time is irrelevant in my experience- assuming that the parts were cleaned and sealed up correctly. Granted, if a vent is plugged or something like that, then you're gonna have problems if you don't give the RTV time to set up. But unless the vehicle is caked with mud underneath- chances are the vent will do its job.

Valve covers are a different story- as engine will have some amount of pressure or vacuum in the crankcase (depending on whether we're talking gar or diesel; PCV or no PCV). And in those cases, I'd allow at least an hour of cure time- depending on the RTV in question.
 
I just did my rear differential yesterday afternoon. I used the new Permatex gear oil sealant. Napa was the only place here that had it, it's in a silver tube with green writing. Says it is specially made for use with "harsh gear oil".

I drained the differential and cleaned the old sealant off, put the new Permatex on and then bolted the cover back on yesterday afternoon about 4:00. I let it set overnight and filled with 2 quarts Valvoline 75W90 today about 11 am.

I always let it cure overnight then add the gear oil the next day. Permatex doesn't say anything about it, just says it hardens in 24 hours. I drain and refill my rear differential every 12,000 miles and have never had a leak.
 
I've ended up putting a drain plug in the rear diff of some of my RWD vehicles- got tired of removing/resealing the cover just to change the gear oil. I've done this two different ways depending on how the diff is made.

A few times I've drilled a hole straight up through the bottom of the casting- right below the ring gear... then tap it out and plug with a pipe plug. This isn't as difficult as it sounds. Probably not really worth the trouble though unless you enjoy this sort of thing- and I do.

I used a different approach with the front diff in two mid 80's Ford trucks, though. Both of these have a Dana 44 front diff. I had one apart one time and noted how the casting was shaped inside. All you have to do is remove the bottom bolt, take a 1/4" drill bit and drill the hole deeper- that will open up a drain hole right in the bottom of the diff housing. Then once it drains (which will take a few minutes), install a bolt in the hole with a copper washer. Works great- but not for the faint of heart.
 
Originally Posted By: onion

A few times I've drilled a hole straight up through the bottom of the casting- right below the ring gear... then tap it out and plug with a pipe plug. This isn't as difficult as it sounds. Probably not really worth the trouble though unless you enjoy this sort of thing- and I do.


The diffs with drain plugs I've seen offset them to one side. Yes you don't get every drop out, but you also don't bust them off on obstacles/stumps etc.
 
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