I'm thinking of installing the rear differential drain plug kit from Corvette Central. Pricey,,like $70 with shipping, but I think it will make the yearly job so much easier. Anyone install this? Opinions? Is installation idiot proof? (I need that)

 

I'd like to do this as well.

 

Simple thing to do. The costs would be a 1/4" NPT tap, a 1/4" plug and a little time. Maybe 5 bucks and 10 minutes to drill and tap the hole.

I drilled a hole in the mounting flange part that bolts to the batwing on the bottom of the case. Gets a little oil on the left exhaust pipe, but you can change the lube in less than 1/2 hour.

johnny

 

i bought the kit from ecklers (i think). easy to install, no leaks.

worthwhile mod

 

Does the kit come with a depth stop drill bit? Thus to keep us hammer-drillin' fools from boring right into the gears?

 

Yes the kit comes with stops welded on the drill bit and tap but as others have mentioned it is way overpriced. The stops are at 1", make your own, it is a nice conversion.

 

$70 for that is funny! Does the drain help you to add fluid? When I change the gear oil there on mine, I still have to use a hand pump to pump the new fluid in. So a drain wouldn't really help me, I'd just be using the pump for a min. less not pumping the fluid out.

 

I like the drain mod because you can use forced air through the refill hole to blow all the old oil out faster.

 

Johnny

Could you shoot a picture of the spot you drill the case?

Jim

 

I'm with Johnnyevans. There was a Corvette Fever article years ago about doing this mod. It's pretty easy. I think it cost me about $15 bucks, The new tap was the most expesive part.

 

You put 30-60k miles on your vette a year?

 

I've been changing mine once a year, because of track use.

 

$70!
I did mine for nothing. Picked up an old magnetic drain plug from one of my buddies trashed outboard lower units. Drilled the hole until fluid started running out and ran the tap in the hole before it all ran out. It cleaned the hole by the time it was all out.
Jacking the vette up and eyeballing where to drill the hole took more time than doing it!

JS

 

Where is it safe to drain the hole. I have never seen the inside of a Dana 44.

Any one have photos or a diagram? The one I have from the 101 Projects book appears to show it just offset from the bottom center.

 

I've often considered doing this, but something has held me back.

That something is the fact that the factory elected to NOT put a drain hole in the diff case.
Why? They put one in the ZF's case. And the ZF is supposed to be filled-for-life.

Could it be that a hole would not let the case meet minimum strength requirements?? I don't know.

I do know that a hole will weaken any structural member, especially if you tighten a pipe plug into it. (pipe plugs are tapered-thread, so they will exert a wedging/expanding force in the hole.

All I know is that I'd rather be safe than sorry, and I purchased the pump for the first lube change performed a year or so ago. Guess I'll keep doing it the old way.
(PS: Plus, no drain hole = NO LEAKS....ever! )

Larry
code5coupe

 

Simple thing to do. The costs would be a 1/4" NPT tap, a 1/4" plug and a little time. Maybe 5 bucks and 10 minutes to drill and tap the hole.

I drilled a hole in the mounting flange part that bolts to the batwing on the bottom of the case. Gets a little oil on the left exhaust pipe, but you can change the lube in less than 1/2 hour.

The best place is not the most convenient place to do it.

The lowest inside point in the 36 and the 44 is below the ring gear, just about midways between the center and left lower bolts on the case looking it it from the back of the differential.

Where the case bolts to the carrier support (batwing), go about 9/16s to 5/8s" from the parting line and make a point. That should be about the center point of the flange thick part. It's about 5/8s to 3/4" thick, depending on the year case, early cases being thickest.

Don't remember the bit size for a 1/4" MPT, but drill slow, if the case is full of oil, until the oil starts to drip thru. Run the tap about 3/4" in and remove. You'll be covered with oil by this time. The best way to do it is to go ahead and drill the hole all the way and let the oil drain out. You're gonna wash it out anyways.

When it gets real tight tapping, you're probably touching the ring gear. Take the fill plug out and wash some carb or brake cleaner in it and let it wash any loose particles out thru the new drain plug hole.

Don't run the pipe tap too far in or you'll set the plug to deep.

Run the plug in until it's tight and then about 1/4 turn more will do it.

Fill with oil and you're through.

To do this the 1st time means you drop the exhaust to clear the drill.
Subsequent times involves loosening the rear hangars and the center exhaust support, takes 5 minutes and an allen wrench to get the plug out and in.

johnnyevans

 

The hole definitely needs to be drilled in the correct place, both to get maximum drainage and to not be in a high stress area. I did mine before installing my D44 so it was easy to look it over and evaluate the situation. Also, minimize the hole size for 1/8" pipe thread. I drilled mine precisely 1/2" forward of the case's mounting flange, that is the sealing area where it mates to the batwing. Measure a 1/2" forward from there and then go 1/4" to the left (driver's side) using the center of the bottom center bolt hole as a reference. Start with a small bit such as an 1/8" and then drill to the size to tap it to 1/8" pipe. You may want to go 1/64" smaller than the recommended hole size for the tap since you're dealing with a soft metal. Use a good, sharp bit, a dull or poorly sharpened one can easily hog out the hole too large. Also, don't run the pipe tap in too far at a time because it is tapered. Tap it a bit and then check your plug fit to insure the plug doesn't screw in too far. Remember, it will tend to go in a bit further each time it is removed and replaced. I used a brass pipe plug as it is soft like the aluminum case. I use no sealer but if you want to use a bit of pipe dope, it won't hurt anything. Also, don't get carried away tightening it, taper fits tend to seal very well and if overtightened, could cause problems later.

 

I did my 1st case out of the car. But have done several since then. It's very easy.

You're not going to weaken the case any appreciable amount. You only torque the bolts 30 and 35 lbs ft. I've never seen a case break in this location I suppose the ring gear could break. I've only seen them break around the pinion bearings and in front of the ring gear on the bottom, and that's been from parts in the carrier breaking or the pinion impacting the inside of the case trying to get out. Or from vertical movement in the front of the case which is usually caused by a loose C-beam or flex, aka parts moving from torque.

Technically, the case supports the carrier and pinion

Granted, this case is load supporting because the case, c-beam and tranny are connected.
And the lower control arms, or leaf springs, or pinion snubber, can't stop torque wrap-up, (pinion trying to climb up the ring gear), in this case the c-beam is the rear trans support and the case torque arm.
All for the want of a trans crossmember, which I am building, and a good torque arm.

But I digress, ask jburnett.

 

Waste time...just buy a cheap gear oil pump and run the tube into the diff...suck it out and fill back up.

No permanent mods and like what was stated...no leaks ever!

Yes I do mine regularly...

 

color me ignorant, but i think its a dumb mod. and $70 cracks me up.

just buy a cheap pump, $9.95, and be done with it. what, you'll maybe drain it twice in 150,000 mi. thats about all you should. you do it more, you're pretty much just masturbating. and i don't like masturbating unless i can blow a nut, and this doesn't make me blow a nut.