Originally Posted by Dborns
I'm going to change the fluids on my front and rear diffs. tomorrow. The front is a dana 30 and rear is an amc 20. I'd like to replace the bolts on the amc 20 when I do this but I didn't look at what size/ thread they are before I left for work this am. Can anyone tell me what bolt I need to pickup so I can save myself a trip to the house tomorrow?
Also, I've searched the forums and have seen people suggest using rtv sealant and some people saying not to. If I have the two gaskets, do I need rtv sealant, and if so whats the correct application of it?
Nothing fits/seals like Fel-Pro gaskets.
Depending on what year your AMC 20 differential is,
The rear bolts are either 1/4" or 5/16" standard 'Course' (USS) threads on the bolts, and you need them about 1/2" to 3/4" long to do the job correctly.
Don't forget lock washers!
Torque to 25 Ft.Lbs. and they won't leak if you use a Fel-Pro gasket.
Tighten the bolts in a 'Criss Cross' pattern to pull things down evenly...
You MUST get the cover and housing CLEAN,
The gasket for an AMC 20 rides in a 'Step' groove inside the bolt circle, so make sure you use something to clean the 'L' step in that housing out really well.
Do NOT over tighten the bolts!
Pulling the bolts too tight will 'Squish' the gasket out, or distort the cover, and that will cause leaks.
Pull one of your cover bolts (out of the top) before you go to the store to get bolts if you don't have a bolt bin.
You will need 12 bolts and lock washers.
Don't forget to 'Never-Seize' the bolt threads before you put them back in so this job won't be this tough the next time!
I suggest you take a pick and brake cleaner and clean out the Torx heads on the factory bolts before you try and loosen them.
They are usually REALLY stubborn (Rusted In) and you will need all the contact area you can get with the Torx bit to get them loose.
Crud in the bolt pocket will cut down on your engagement and cause 'Round Over' of the tool bit when trying to take them out.
The 'Impact' type of Torx bits usually stay together longer than the 'Common Socket' type do.
They are harder to break, and they just live longer in rough service.
If you twist off a bolt, DON'T PANIC!
It's common, and anyone that has done very many AMC 20 differential covers HAS twisted off a bolt before!
Just center punch the bolt shank with a SHARP center punch, and drill the CENTER of the bolt out.
Usually when you get the bolt thin enough (using progressively larger bits) the remaining part of the bolt will come loose.
Start with a SMALL pilot hole and slow drill speed so you can control the bit and keep it centered,
Progressively working up to larger and larger bits...
If you get in a hurry, and try to 'Hog' out the hole with a large bit, you WILL wind up off center!
Left hand twist drills will help with 'Unscrewing' the broken bolt if you have them...
If it doesn't screw on through or back out when drilling (Blind hole bolts won't screw through)
You can drill until you start to see threads, then use a common starting tap to clean out the rest of the threads and reuse the hole.
Worst case scenario is you drill off center, so stay CENTERED!
If you can't get the threads to clean out,
Then you can drill the hole OVERSIZE and use a HELI-Coil to restore the proper threads.
Heli-Coil kits come with the correct drill and tap to make new threads, and they come with thread inserts to make the new, larger hole/threads the correct size.
Bumper jacking the vehicle usually gives you more room to work on the differential, (frame lifts, axle 'Droops' on the suspension exposing more of the differential)
But if you do that, remember to use JACK STANDS under the FRAME to make things safe!
I know I'm beating a dead horse, but nothing fits the 'O' ring groove like a Fel-Pro gasket.
The 'Cheap' and 'Import' gaskets from the Jeep suppliers never seem to fit correctly.
You are looking at about 6 pints to fill the AMC 20 back up, and about 2 pints to fill the Dana 30 back up.