I'm considering tapping my differential for a drain hole/plug while I have it out of the car... are there any recommendations against this? I'm mainly wondering if this will have a signifiant strength impact on the diff housing. Right now, I'm considering a 1/4" or 3/8" NPT hole drilled into the bottom of the housing where I'd be able to get to it with the diff installed in the car to drain. Are any certain locations better than others?

What have others done?

Thanks,
Eddie

 

I have a built rear end setting on the floor ready to put in. I have the drain plug installed. Can take pict in AM. Know of several who have done this. NO PROBLEM. Makes easy to drain when changing gear oil.

 

Yeah, my diff has been rebuilt for a couple of weeks now, I'm just working on finishing the rest of the suspension first so I can paint it all... the current problem is removing u-joints from a half shaft and a-arm bushings.

Thanks for your help - I'm looking forward to the photos!!!

 

E-mail sent

 

I put a drain plug in years ago. There is no problem with drilling a hole and taping it with a NPT tap.

 

I do that to all the differentials I rebuild unless the guy doesn't want it. I do with the case empty so I can wash it out to get rid of the chips.
Gary

 

I want to do this as well. I bought a Irwin Hanson 1/4" 18 NPT tap. It requires a 7/16 hole. I have not drilled anything yet because this seems a little big to me. Is this the right size? Also, where can I find a magnetic plug? I searched and I was only able to find brass plugs that state that they are 1/4" 18 NPT. How about the hole required in the strut bracket, 5/8"?

 

2nd 76,

You can use the 1/4" npt. I don't like drilling into an assembled differential and wouldn't take the job if asked. I also don't like the kit with the hole saw that you drill into the strut rod bracket-too much of a "Bubba" for me. I've heard where the chips will flow out with the oil but I put too much time and money into these to take a chance on a chip getting into a bearing. Over concerned,maybe. It's your car so you have to decide. Good luck,
Gary

 

I am going to have to take my rear diff out and redo the seals all around. Not looking forward to this one at all. I think at the same time I will go ahead and add the drain hole. Are you guys using a kit or just buying a tap at Lowes and a drain plug to match?

 

I'm wondering how often this drain would be used? I just drained mine and doubt its ever been drained before, maybe it has?
Just how often are we talking about draining and replacing oil and additive? I could see the benefit on a rebuild though.
I can easily install one but don't really see the benefit if I don't need to change it again.



second76, what happened to first?
A pipe is measured by the ID add the walls and you can see a 1/4" pipe is closer to 1/2" It gets more complicated but close enough to understand the huge diff. Also the T in NPT means taper. You don't thread right through like a regular tap. Enough to get 3-4 turns on the plug. A magnet prob. You can magnetize any steel by swiping it across a magnet. Same direction and lift on the return.
Easier to buy a neo boroaahghowl something magnet and glue it into a hole drilled.

gtr1999- what he said. Your playing the lottery here. If it does cause damage the drain plug could have been installed on the rebuild that wasn't needed. A maintanance fix that causes damage.

 

Thanks for the advice.

I wanted to put in the drain plug because my side yokes were so badly worn that one of them had a burr lip from rubbing the cross shaft. I had to file and dremel the 1/8 lip away before it would come out. Even though I have rinsed the insides, I am sure there is still a considerable amount of metal frags still in there. Therefore, I planned on changing the fluid a few times after driving the car in hopes of removing the rest.

I have thought about rebuilding the rear end but the risk/reward ratio does not look good because I don't have experienced eyes to give me a hand. I just committed to a Keisler auto to TKO-600 conversion so the grand to have someone else rebuild it is not in the budget.

Techno, the first was eaten by hurricane Andrew in '92. I lived by the ocean in S. Florida and it got a saltwater bath from the storm surge. I managed to start it after and the engine rocked so much that it looked like it would roll right out of the car. Everything was starting to rust after two weeks. I was 18 and did not have a job. I needed a reliable car for school so I used the insurance money to buy an '84 vette. Insurance adjuster was a corvette owner and he gave me top dollar.

 

Where have people located this drain hole? I'm thinking of drilling/tapping on the underside of the diff infront of the strut bracket mount, in the vein that runs below the pinion gear.

Thanks!

 

I too have one on the floor.(69 model)..now would be a good time to put in the plug...can someone post a picture of the location of the drain hole...or send me a pic by email.

on the same lines...are there sources for the bearings at local supply houses...I would be interested in the p/n if possible.
Thanks in advance. Tom

 

Here's a picture of the drain hole I put in the housing.

 

GTR - that's exactly where I was thinking of putting mine... you haven't had any cracks or strength issues due to the hole being on the parting line of the casting, have you?

 

No problems. Pepe Estrada owenr before Tom has been doing this for the past 30 years on the rear ends that build for drag racing. I've done it to all my vettes and the ones I've rebuilt.
Gary

 

I want to know too. Where do you get the plug, what size hole do you drill, and what size tap?

 

All you need is a 1/4 npt pipe plug, either socket head or hex. I use brass plugs. Tom's sells magnetic plug too. With a tapered pipe tap you don't want to go completely through or you'll end up with loose threads and a leak for sure. Tap then fit the plug, tap and fit until you have about 1/2 the taper in the hole. There's not a lot of material there so you have to be careful if this is your first time doing this.

Gary