I am doing a drum to disc conversion using parts from a 90’ Corvette and referencing David’s Pozzi web page on converting 1st gen drums parts to 12” C4 discs. The conversion involves milling the upper drum boss flush with two mounting holes by the spindle, machining the OD of the drum hub to accept the 12” rotor, and adding an adapter bracket to mount the c4 caliper and caliper bracket.

http://www.chevelles.com/showroom/Enganeer/tempspindle-hub-androtor.jpg

Is there a difference between Camaro and Chevelle drum spindles as far as offset from the hub to the mounting flats on the base of spindle? The reason I am asking is I have a spacing / fit problem. When I reassembled the modified drum spindle, hub and rotor, I placed the caliper bracket loosely on the rotor to see how much space would be needed to center the caliper bracket over the rotor.

I would not be able to mount the ¼” thick adaptor plate without pushing the caliper bracket against the rotor.

http://www.chevelles.com/showroom/Enganeer/tempbracketdistance.jpg

I need about 3/16” more clearance to center the caliper bracket over the rotor. Here are some of the options I could do:

1) I could mill the bosses on the spindle down 3/16.
2) I could make an adaptor bracket with an offset where the caliper bracket would mount.
3) I could mill the back of the caliper bracket boss flats,
4) I could use spacers and move the rotor further out on the hub.

#1 would require a lot more tooling setup than I have and could weaken the spindle.
#2 would work and would not be too terrible difficult.
#3 easy to do but don’t know if I could mill off that much without getting into the base of bracket
#4 Rather not do, but could.

Thanks -John

John,
You are on the right track for your ideas on how to gain clearance. Its been awhile since I've read David's site on how to do this, but if I remember correctly you have to mill down the abutment mounting bosses to gain the necessary clearance to mount the caliper properly.

I remember a member named "novaderick" that took pics and showed where he milled/cut the C4 abutment and how much. I'll have to search and find his page.

graemlins/beers.gif

Joe

Joe,

I went back through David's site again line per line. He talks about adding shims between the bracket and adaptor plate to center the bracket over the rotor. That's were I got hung up. I needed the opposite of shimming, offsetting, to center the bracket. I was looking hard at his pics and found the last pic was a top down view and the bracket bosses look like they were milled down flush. Mine have still have the raised bolt bosses. I will mill that down and go from there. Getting closer. smile.gif Thanks. -John

John,
Good to hear you're getting closer!

Something you might want to keep in mind is this (http://www.chevelles.com/showroom/tempbracketdistanceII.jpg).

That is the minimum clearance you want or else the abutment may hit the rotor as its spinning.

Good luck with the rest of the swap and please post progress pictures! I'm sure there are lurkers here that are wanting to learn more about this swap!

graemlins/beers.gif

Joe

Thanks Joe,

I would love to see a c4 pic of how centered the abutment is from the factory over the rotor. I will try dead centered over the rotor for now. So I will go ahead and make the adaptor plate and measure from there.

I plan on making a web page on how I did the conversion, so there will be plenty of pics.

And for those looking to find those hard to find 14mm x 2.0 pitch bolts for the abutment...I found mine at my local ACE hardware store.

-John

Originally posted by Enganeer:
And for those looking to find those hard to find 14mm x 2.0 pitch bolts for the abutment...I found mine at my local ACE hardware store.

-John Sorry for butting in John, but I think there are a few things people should realize with bolts/washers and fasteners in general.

For your 14mm abutment bolts be sure you have a 10.9 metric class strength rating. They are easy to identify as a 10.9 (http://www.chevelles.com/showroom/tempBolt.jpg) is on the bolt head. It is equivalent to a SAE grade 8 bolt strength.

Also, use washers of the same strength class as the bolt you are using. These two components compliment each other. A lot of people don't realize either that there is a proper way to use the washer too. The surface that has a chamfer or a round goes towards the head of the bolt. If the other side is used, then a stress concentration factor can easily form from gouging the bolt thus shearing it (eventually).

I also found Novaderrick's site full of pictures (but not the pictures that shows the abutment mod as I thought :( ).

His site (http://community.webshots.com/user/novaderrik)

These pics should give you an idea of what your setup will look like soon :D

Joe

Joe,

The ace hardware had two strengths; 8.8 ($1.20 each) and 10.9 ($2.30 each) rating for bolt strength. I will be using the 10.9 as these are holding the brakes to the spindle and rather spend a few more bucks now rather than be sorry.

Good point about the washers and complimenting the whole fastening setup. graemlins/thumbsup.gif I think most people don't realize the proper orientation and matching the grades of washers. -John

John,
How's the progress coming along?

Joe

Joe,

The progress seems to go in short bursts. Though I had to set it aside this half of the week to go to a funeral for the wife's side of the family. :(

I was already to fab the bracket but only could find hot rolled steel. So I piggy backed an order through work for some cold rolled 1018 and proper size endmills. They did not arrive before I had to leave town midweek.

So while waiting for tools and steel, I took some time using a caliper to get all the mounting hole locations and spindle drawn up on cad.

Hopefully Friday I will have some pics of the setup loosely fitted together.

I have heard that if you can find a set of DISC hubs, these will solve your clearance issues as they will increase your track width (tire closer to the outside the wheel well) and then you can center your caliper on your rotor without having to further modify your spindle. I have not done this, but I have seen the side by side comparison between the disc/drum hubs and the disc hub would definitley solve your problem.

Getting closer...the trial fit. After dragging the cut off front frame of my parts car into the garage and setting up on jack stands. I loosely put together the passenger side control arms with machined drum spindle.

Using my measurements taken off the spindle, I machined some brackets. After assembly everything and using a worn rotor wear pattern as a guide, I found that I will need to adjust one hole location slightly to have the brake pads exactly centered on the rotor as it came from the factory (maybe I am picky but I want it exactly centered. If I would have had new rotors, I probaly would not have noticed it.)

Also, the caliper abutments raised bolt bosses have not been milled down yet, I shimmed the rotor out from the hub for the trial fit. -John

Once I get this conversion done and know it works to my satisfaction, I will make a web page with drawings and steps that I did for this. Of course some difference will found. I know of one right away. The hole size for the lower spindle hole. The 65' spindle has a 7/16 hole, and the later spindle (I think it was from a 69') I got from DerekSS69 was 1/2. But the hole locations should be the same, just different diameters.

I'll also look more into the hub difference between drum and disc. From the sister site (camaros.net) I did a search and it looks like about 9/16" difference.


http://www.chevelles.com/showroom/Enganeer/tempc412inchbrakes.jpg

Looks good John!

graemlins/beers.gif


Joe

I whipped up some pages with what I have done so far. The details are lacking for now but it does have some pics.

http://home.earthlink.net/~ajenga/Corvette_C4_12__Disc_Conversio/corvette_c4_12__disc_conversio.html

John,
Nice site. Looks like someone else hangs out at the machine shop too. ;)

One thing that you might think about (and you could probably say NO to it) is to resize the pictures and make them smaller and clickable so us dial up geeks can load your page faster.

Your new Elky subframe is turning into a handy tool to have!

Joe