Differential Fluid change - C3-1968

[Richard D.]

When changing the dif fluid today (Mobil Syn. 75-90 + 2 anti chatter additive - GM), my friend who helped me said that one of the spring mounting bolts on his mid 70's Vette also served as as a "drain plug" for the dif.

Of course, I tried the the 2 forward bolts, but, no luck.

I ended up using a suction device to pull the fluid out. Not a real problem, but I did not get all the old fluid out the way I really wanted to (I think).

Did they ever go to putting a drain plug on the dif.?

Just curious about it.

Thanks, and Happy New Year to all the folks on the site!

I've really appreciated all the help over the past year from Joe, John, Jeff, and all the rest who've shared their expertise with me while I've undergone getting my '68 back together. I hope to get to a meeting some day to personally thank you.

Best regards,

Rich

[Jim T.]

Re: Differential Fluid change - C3-1968

Richard sounds like your friend had one of those special ordered Corvettes with this draining method. Even the C4's rear fluid has be removed like you did it.

[Joe L.]

Re: Differential Fluid change - C3-1968

Rich-----

No Corvette EVER had a differential "drain plug" at one of the four spring plate mount bolts. It's possible that someone could have so-modified a differential case, but GM NEVER did it that way.

[Chuck G.]

Re: Differential Fluid change - C3-1968

It's also more likely that at sometime in your friend's Corvette life, somebody use a spring bolt too long, and punched a hole in the diff case, and created his own "factory drain hole". I've seen several with holes punched up through the case from using bolts too long. Chuck

[frank mccracken]

Re: Differential Fluid change - C3-1968

A friend of mine who is a Corvette mechanic routinely drills out one of the strud rod bracket bolts into the housing to serv as a drain hole. You can tell which hole it is because the bolt sweats a bit. Sounds like my friend is not the only one who does that.

[Richard D.]

Re: Differential Fluid change - C3-1968

Thanks Guys, I kinda figured that.

I did not see anything in the Service Manual I have regarding a drain plug for the dif.

My friend's a pretty good mechanic and buff, I know he'll appreciate the info. (as I do also).

Oh, and by the way, I did the chassis on my car with the Magnet Paint "Chassis Saver" over the past 2 days. This is a really crappy job to do, thank God I had access to a lift to do it. It went on easy, and it seems to be real tough stuff. Time will tell!

Regards, and Happy New Year!

Rich