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Car Forum / Chevrolet / Chevrolet Corvette / July 2004C3 Rear spring, center support bolts
I'm in the process of re-installing my rebuilt diff on my '76. Had a ring bolt come out, fly around inside and eventually come out through the cover. Diff rebuilt (professionally), new ring and pinion, etc. I bought a used cover on Ebay. It came and looks good, but my bolts that support the spring in the center don't fit. Looks like mine have a shank diameter of 5/8", while the new cover fits bolts with 7/16" (5/8" head size) diameter. After a little research, it seems like my bolts and old cover are the odd ones. Corvette Central's bolt kit comes with 7/16" bolts. I'm planning on just ordering a new bolt kit and running with it, but am wondering why my old ones are so big. Also, can I use the original support plate - the holes seem too big (11/16"?) for 7/16" bolts. I've also considered trying to have my new cover drilled and tapped for the bigger bolts. Any thoughts? Dave My 75 Vette has the smaller plate holes and bolts and match the "newer" cover. From the reports I have gotten regarding the difference in bolt size is that the larger bolts didn't leave enough meat on the mount ears on the cover and many have broken off. Actually what is happening is the installer is torking the spring plate down before letting the car down off the rack. The correct way to install the spring is to locate it first and then snug it just enough to place it in the locator hole...(you may well need to let the car down to mount the outboard ends)...this will allow the spring to spread when the full weigh of the car is placed upon it. Once the full weigh of the car is on the spring then tork it down....inboard and outboard. Otherwise the ears will stress and potentially break. This thought you had of redrilling the holes out.......don't do it......you'll be back to the old problematic design of the larger holes. Also......new smaller bolts means new plate with smaller bolt holes......minimal slop here. I suggest you go with the newer smaller 7/16 bolts and the newer smaller hole plate........someone has already been at that rear case cover on that new diff you got.......and the changeout these days is the smaller bolt design......apparently. Problem though....finding the doggone smaller hole, smaller bolt plate! My supplier couldn't get a new one for me so I used the old one. I wanted to go new with all the rest of the new stuff I am changing out. > I'm in the process of re-installing my rebuilt diff on my '76. Had a > ring bolt come out, fly around inside and eventually come out through [quoted text clipped - 11 lines] > > Dave > My 75 Vette has the smaller plate holes and bolts and match the "newer" > cover. From the reports I have gotten regarding the difference in bolt size [quoted text clipped - 34 lines] > > > > Dave Thanks, good advice to go with the smaller bolts. I'll call around and ask about bolt kits and matching plates. If I tried to use my old plate I'd have to put a flat washer over the hole and could feasibly have the problem you are referring to. Also good to know about torqueing the center bolts down with car off the jack stands - assuming I can get underneath there enough to do it. I just finished doing this very same procedure.....and it is a tight squeeze.....but......if I could do it then so can you.....maybe place ample support under the wheels enough to cause the entire car to rest with full weigh but high enough above the ground because of the support and high enough to get under and finish the tork. I used "cribs" of 4x6s and 3/4 plywood and was able to get the support I needed and the height. > > My 75 Vette has the smaller plate holes and bolts and match the "newer" > > cover. From the reports I have gotten regarding the difference in bolt size [quoted text clipped - 41 lines] > torqueing the center bolts down with car off the jack stands - > assuming I can get underneath there enough to do it. Just back it up a set of car ramps. > I just finished doing this very same procedure.....and it is a tight > squeeze.....but......if I could do it then so can you.....maybe place ample [quoted text clipped - 63 lines] > > torqueing the center bolts down with car off the jack stands - > > assuming I can get underneath there enough to do it. No doubt Tom...car ramps would always be the choice over these wooden cribs I build...Thanks!! > Just back it up a set of car ramps. > [quoted text clipped - 81 lines] > > > torqueing the center bolts down with car off the jack stands - > > > assuming I can get underneath there enough to do it. > I just finished doing this very same procedure.....and it is a tight > squeeze.....but......if I could do it then so can you.....maybe place ample [quoted text clipped - 63 lines] > > torqueing the center bolts down with car off the jack stands - > > assuming I can get underneath there enough to do it. Yep, I'm pretty small, should be able to squeeze under there. The lumber cribs are a good idea, though. I've done a little more research about my original post - I'm coming up with 63-77 using the plate with bigger (9/16") bolts and 2 1/4" spring, while 78 and 79 used the smaller (7/16) bolts and a 2 1/2" spring. I'm trying to negotiate with the dude who sold me the rear end cover on Ebay since he said it would fit a 76 (63 - 78) and a 2 1/4" spring, but it really only fits a '78 or '79 with a 2 1/2" spring. I would just use what I have and get new bolts and plate, but the brand new spring I have is 2 1/4 and I don't think it would be good to install the smaller spring on the cover I have - it looks like it would be too sloppy. I'll get a cover designed for the 2 1/4" spring and just be careful to not torque the bolts too much with no load on the spring. If anyone sees any errors in my reasoning here, could you let me know? Thanks Anyone need a cover for 78 or 79????? I think we really need to brain storm this one before going thru hell figguring this one out....sounds like you have the same thing happening to your Vette that I have on mine. This is what I have: apparently the 78-79 cover with the smaller bolts....the smaller plate and the smaller, width wise, spring. I just replaced what was there except for the bolt and plate because the supplier didn't have a new one for me. I would go back to square with a cover to match your new spring. Sounds like the newer cover ya got is basically a problem child here. So what ya got is a distance between the bolts on the old cover and the distance on the new cover? I am guessing that the distance between the bolts on the old cover were expected to match a 2-1/4 spring? So when you ordered the newer cover, per the dude's claim, you assumed he told you the truth and that it would fit your 2-1/4 spring? So first of all: what is the difference between the two fits? and is this within the design tolerances?.......from what I understand the diagonal twist action that could take place (if ya really got on it) would be merely 1/8 inch one way or the other. And then the outboard bushings would carry that, the struts (and of course the shims) keep the trailing arm in spot....so.......perhaps the slop you're thinking may be too much, may well be within design tolerance...... The spring isn't part of the alignment and if you have a sway bar to boot then you're really home square and the worry is for naught......maybe some of the other people here have more to add to this concern. This is a really good concern....we're all going to learn something on this one.....I'm looking forward to the discussion from others...... > > I just finished doing this very same procedure.....and it is a tight > > squeeze.....but......if I could do it then so can you.....maybe place ample [quoted text clipped - 82 lines] > > Anyone need a cover for 78 or 79????? I'm pretty sure I've got it figured out - 63-77 used the 2 1/4 spring and big (9/16) bolts. 79 used a 2 1/2 spring and small (7/16) bolts. 78 could be either. Both Ecklers and Corvette Central catalogs support this theory. I'll know for sure when I get my new cover (from CC) and see if it fits the big bolts and smaller spring. You are correct about only an 1/8" of "twist". It still worries me, though. With my old cover, the 2 1/4 spring fits snug against the groove, no twist. Customer service at CC also advised against using the smaller spring with the new cover. The dude on Ebay still disagrees with me about the above theory, but they said they'd give me a refund. If you buy a used cover ask specific questions like what size are the bolts that hold the spring on and what is the width of the spring that was on the car when they took the cover off. This has been a big hassle! > I think we really need to brain storm this one before going thru hell > figguring this one out....sounds like you have the same thing happening to [quoted text clipped - 138 lines] > > > > Anyone need a cover for 78 or 79????? Well...sounds like you got to the bottom of this.....ya did alot of research and thank you for your input. > I'm pretty sure I've got it figured out - 63-77 used the 2 1/4 spring > and big (9/16) bolts. 79 used a 2 1/2 spring and small (7/16) bolts. [quoted text clipped - 154 lines] > > > > > > Anyone need a cover for 78 or 79????? |
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