[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?

[JeepHammer]

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.

[Dborns]

Cool, thanks for the in-depth explanation!

[CJ7VFR]

Originally Posted by JeepHammer

You are looking at about 6 quarts to fill the AMC 20 back up, and about 2 quarts to fill the Dana 30 back up.

Whoa there horse!!

6 QUARTS to fill an AMC 20?

That's a GALLON AND A HALF gear lube!

The AMC 20 requires 4.8 PINTS of fluid, which equates to about 2.5 quarts.

Maybe your thinking of engine oil perhaps? The 258 takes 6 quarts of oil.

And the Dana 30 front diff takes 2.5 PINTS, which is just over one quart.

You wouldn't be able to put a gallon and a half in an AMC 20 anyway, as most of that
would just poor right out of the fill hole and onto your garage floor, or
driveway, making quite a mess for you to clean up!

I know Jeephammer just a made a mistake in his units of measure. If
it went uncorrected, there would be alot of people out there spending way
too much for gear lube, and then wondering why their differentials will not hold that
much, as it poored out onto the floor!

Make sure you fill your differentials up when the Jeep is parked on a FLAT
surface. You will know when they are filled when the gear lube starts to come
out of the fill holes. They actually act as a safety to stop people from over filling
the differentials with too much fluid, and possibly ruining your axles.

Once the lube starts to flow out of the fill hole, you STOP adding more fluid
and re-install the fill plug. Thats how you will know you have the proper amount
in there.

Jim

[80cj]

AMC 20 uses 5/16-18 x 1/2" bolts. I just did an oil change on mine a couple weeks ago. Used about 4.7 pints of Valvoline GL-5 80W90. Front axlle (D30) uses 2.5 pints.

[attworth]

Agree with the above. I in fact did break an old torx bolt. Was easy enough to drill it out. Once the hole in the bolt was slightly smaller than the threads, it was very easy to spin the old bolt out with a screwdriver and pressure.

Good luck!

[JeepHammer]

Originally Posted by attworth

Agree with the above. I in fact did break an old torx bolt. Was easy enough to drill it out. Once the hole in the bolt was slightly smaller than the threads, it was very easy to spin the old bolt out with a screwdriver and pressure.

Good luck!

Not hard to do, but it does require a reasonable set of drill bits and take your time to get the old broken bolt out.

Yup, I screwed up and put quarts instead of pints, and I put a 1" long bolt in than I needed... :Brickwall

That's what I get for trying to answer three posts at the same time.

1/2" to 3/4" bolts, usually 5/16" diameter, but some of the early Dana 20s will have 1/4" diameter bolts, but the same length.

[Dborns]

Thanks to everyone for the replies. Hopefully this goes a little smoother than the brakes did! Can someone explain to me how I know which transmission I have? Is it stamped on it somewhere?

[attworth]

Is it an auto or a manual? How many forward gears?

[80cj]

I've found that one of the problems leading to stripping of torx bolt heads is that mud, etc., tends to accumulate in the heads. Unless you take a piece of wire and a spray jet of brake cleaner, etc., and clean the heads out, your torx bit will not enter full depth which promotes stripping. It may also help to have proper fitting torx bits. Mine are Snap-On. I still have the factory torx bolts on the rearend cover and have not stripped any of them out in 29 years.

[Dborns]

Its a four speed manual. The Jeep is a cj7, '77 body on what I think is an '85 frame. The motor is an Amc 360.

[Dborns]

I'll grab a torx bit set at westlake in the morning. I can spray the bolts with pb blaster and let that set in for awhile before I get to work. Thanks for the heads up on cleaning out the bolts.

[attworth]

I'd guess a T-18, but I honestly have no real knowledge of the 4-speeds.

Grab a hammer too. Lightly tapping the torx socket into the bolt seems to help as well.

Edit: Check this site out for good info on Jeep stuff. The Novak Conversions Transmission Information Gateway Looks like if it's stock, it should be a T-18 with the lower 1st gear, which is pretty desireable.

[Dborns]

Will do. Also, my Haynes manual shows to use 80-90 gear oil in the f/b diffs., but I'm reading in some of the other forums to use a different fluid. I've already bought a big jug of 80-90, but can take it back if needed. And this is going to be a daily street driver; probably not much off roading. Whats your suggestion?

[80cj]

A T-176 or T-177 will have an ID tag as in the picture. A T-176 will have the number 5359390 on the tag. A T-177 will have 5359389.