C3 Rear spring/differential question (69)

[Rob M.]

Hi all,

I just removed my rear srping to get it re-arched but when I removed the four bolt and loosened the holding plate a lot of oil from the differential was released. Is one of the bolts also a rear diff. oil-refreshing plug or something else going on here?

greetings,
Rob.

[Terry F.]

Re: C3 Rear spring/differential question (69)

Not to set off any alarms but it is possible to crack the differential plate in the process of removing the spring. I would look closely at everything and possibly plan on removing it. Did you loosen the 4 bolts before you released the end bolts that support the trailing arms?

No, none of the 4 bolts should go into the cavity of the differential. Good luck, Terry

[Wayne M.]

Check correct bolt length

As Terry says, you might have punctured the forward bolt boss on the rear cover. This picture is of the correct ('63-67 anyway) bolt (WB headmark, and 3.0 inches from under the thick lock washer to the threaded tip. The overall length and threaded portion is unique to this bolt useage.

[Harold# 43147]

Re: C3 Rear spring/differential question (69)

Does the oil come out of the driver side fowars hole? The carrier casting has a bump cast in the inside for the thread of this bolt I have repaired about 6 of these same spot. Remove the carrier and clean and inspect this area. The only solid repair for this is grinding the crack into a V and Tig weld with Nickel casting must be preheated before welding and allowed to cool slowly. Brazing this will not hold up. Hope this helps.

[Chas Henderson #28127]

Re: C3 Rear spring/differential question (69)

Three choices here. Replace cover. Weld hole in cover. Clean out hole and when installing the bolt, use a lot of sealer. Either way, you have to take the differencial out. I like the replace the cover as the best way to go if your car isn't being judged. It is possible to find a correct dated cover but takes time and luck. You know how I know. The other two fixes did not work for me. If you try to pack the hole with sealer, after you clean it out real well with acetone, mix up so JB weld, put tape on inside of cover, and pour some in. After it hardens, remove tape, measure depth of hole, cut bolt according, when you reinstall springs, use lots of sealant. Good luck.

Chasman

[Rob M.]

Re: C3 Rear spring/differential question (69)

Thanks for all your response.

I did removed both the side bolts to remove the tension from the spring. Then I removed the four bolts holding the spring in its place. Still no leaks. Then I tilted the spring slightly (and carefully) and then the flood of oil came down right on the garage floor (totally unexpected ofcourse). I guess the spring was blocking a hole or crack of some sort...

I'll clean thing up tomorrow and have a good look with a light torch... Maybe I'll take some pictures to investigate it a bit further!

greetings,
Rob.

[Rob M.]

Re: C3 Rear spring/differential question (69)

Removed spring (picture taken from my weblog on the C3Registry.org)...




C3 weblog !!!

[David N.]

Re: C3 Rear spring/differential question (69)

Rob,

Oh the joys of working on '69 Corvettes!! At least you have yours at home. My '69 BB convert has been in a restoration shop since May 16, 2005. But, it is close to finished and will have a completely new NOS front end, left rear fender, and rear panel as well as complete new "show quality" paint job maybe by the end of march.

David Nims #19639

[Chuck G.]

Re: C3 Rear spring/differential question (69)

Hi Rob. The 2 front-most spring holes are tapped into blind holes in the base of the case, whereas the 2 rear spring bolt holes are "open".

Somewhere along the line, somebody used a bolt TOO long in the front position, tightened it and "popped through" the case. Thus, the gear oil can leak out of the bolt hole. The bolt sealed it, UNTIL you took it out. Might have been that way for DECADES. LOTS of old Corvettes have this "problem".

If you're not tearing the rear out, I'd put it back together with LOTS of thread sealer. Probably will last another 20 years, as long as you seal the leak. Chuck

[Dick W.]

Re: C3 Rear spring/differential question (69)

If the housing is not cracket, a good sealer to use would be a product by Loctite called PST, pipe sealant with teflon.

[Rob M.]

Re: C3 Rear spring/differential question (69)

Ok, sounds reasonable but why did it not start leaking right when I took out the bolt but only after I started removing the spring. It was like the spring was blocking a hole in the cover. I'll have a look tomorrow using a torch and some cloth (for cleaning) to see I I can figure out why and where it was leaking.

Can the cover be removed easily without dismanteling many more parts of the rear suspension setup?

thanks for your replies,
Rob.

[George D.]

Re: C3 Rear spring/differential question (69)

Rob,

I had a similiar problem with my 69. The problem was not with the bolts. They were the correct lenght but the spring had been replaced and it was thinner that an original spring. After having the rear end rebuilt and during the reinstallation of the bolts I heard a crack which was the boss bump breaking which is located insige of the rear cover. It didn't take much to pop the boss. I took the rear end apart and removed the broken pieces. When I reinstalled the bolt with the broke boss I used teflon tape on hte bolt. It has not leaked in 8 years. I only realized what caused the problem when I installed a correct spring whiich was thicker.

Perhaps the reason the oil didn't flow out immediately upon removal of the bolt is there may have been an air lock inside the differential.

I think you should pull the rear cover to make sure there are no loose pieces inside the differential or that the cover is not cracked. If the cover is ok that I would just use a sealant on the bolt(s) when your reinstall them. Just check it periodically to make sure there are no leaks.

Regards,

George

[Dick W.]

Re: C3 Rear spring/differential question (69)

Rob, unfortunately the cover cannot be removed easily. You will have to drop the suspension crossmember (information on doing this can found in the archives) You are unable to get to the top bolts attaching the cover without either cutting holes in the floor of the car or dropping the crossmember

[Jim T.]

Re: C3 Rear spring/differential question (69)

Saw a car type tv show where they dropped the rear end out of a C3 Corvette with it attached to the crossmember, half shafts attached to the rear end and the trailing arms, trailing arms were unbolted from the frame. The rear cross member that gives some trouble seemed to come right out with all the weight still attached to it.