Front Disc Brake Conversion - Part 2

The title of this post should be 'Hubs, Studs and Rotors'. As I always like to say, 'the devil is in the details'. What appears easy on the surface, rarely is - and this seems to apply to front disc conversions as well. 

So let's set the stage. We are converting a 68 Mustang with manual drum brakes to power disc brakes. We will be utilizing an adapter kit from Steve's Mustang and donor parts from a '94-04 Mustang Cobra. Sven already has written a superb in-depth article on how to do this correctly so I'm not going to replicate it here:

                               http://1970boss302.blogspot.com/search?q=disc+brake

The instructions that come with Steve's kit are clear and straightforward, but I want to expand on a few areas. Let's start with separating the brake drum from the hub. A really important detail to note here is that the brake drums are secured to the hubs by 'swedging' the wheel studs. Basically, after installing the drum over the shoulder of the wheel stud at the factory, a pneumatic tool expands the OD of the wheel stud, effectively locking the brake drum to the hub. You can see the marks left on the wheel stud by the swedging process below. 

So why is this important to know? Based on a number of posts I read in various forums, if you try and press these swedged studs out of the hub, in order to separate the drum from the hub, the expanded OD of the shoulder will over-expand the knurled hole in the hub as it passes through the hub flange. If you reinstall an OEM stud back into this enlarged hole, there's the potential it will spin in the hole when it comes time to torque the lugs nuts as there won't be enough material left for the new knurls to get a good 'bite'. I can't confirm this, but given the number of posts on Jeep and Model T forums on this issue, I chose to err on the safe side and remove the drum from the hub per Steve's instructions. And that is to simply place a plate across the top of the outer bearing retainer and press the hub from the drum, rather than the studs from the hub. 

But let's say you do want to replace the original studs with new OEM ones. You still need to get past the swedged stud problem. Well a company called Goodson makes the exact tool you are looking for, and here it is. It's a bit pricey, but after reading some of the backyard solutions to the problem that involved all manner of hacking, beating, grinding and overall general mayhem, this seems like the gentleman's solution to the problem.

OK then, let's get back to SusieQ. In my specific case, I actually wanted to save the original studs, so I had no need for the $92.99 tool above. And the reason I wanted to save the original studs was due to my wheel choice. As you recall, I'm going to run 2005 Mustang GT 17" rims. In order to do that, I need to run ( yep, you know it's coming) 1" wheel spacers. I feel as much shame about it as you do.  But I love the rims and they are exactly the look I want for the car. Yes, I know, I should just run a rim with the correct offset and do the job right. In my defense, all projects are ultimately a series of compromises - this is mine. 

And this is where 'the devil is in the details' raises its ugly head. Since Cobra rotors are used with a shoulderless wheel stud, they will not fit over an original OEM shouldered, brake drum stud. Worse, they really won't fit over a swedged, shouldered, brake drum stud. The stud holes in my OEM Cobra rotors were roughly .570" ID. An unswedged stud shoulder measures .605" OD, a swedged one almost .617". So it is a no-go by quite a bit. When I first discovered this problem, I thought I would be clever and just order a new set of OEM shouldered studs that hadn't been swedged - only to discover that even the un-swedged ones have too large an OD. As a heads-up here, Steve does sell a wheel stud just for this issue    (#610-368). They are non-shouldered, longer for the thicker flanges of modern rims and even have a larger OD knurled section for pressing into hub flanges that have had previously installed studs. Only thing is, I can't use them. The longer length causes them to protrude out past the outer surface of the wheel spacer. This would prevent the rim from sitting flush against the mating surface of the spacer. Fudge...

OEM brake drum wheel stud - C3AZ-1107-A (1 11/16"L)

Steve's Mustang - shoulderless wheel stud (2 3/16"L)

I pondered this problem for a few days. Thought about turning down the OD of the new brake drum studs I had already purchased and installing them. That would work. A pain, but at least a solution. Would need to buy the $95 de-swedging tool from Goodson though. I could live with that. But then while driving home from work one night the simple answer came to me. I currently have a .617" OD swedged stud - all I need to do is open the rotor holes up to .625" and problem solved. Next morning I threw the rotor up in the mill, indexed it in, and passed a brand new 5/8" ream through all 5 holes. As a nice by-product, the shoulder clearance is nearly spot on and the rotors go on with a comforting clunk. A heads-up here is that you need to remove the small burrs left from the swedging process. All it takes it a small fine hand file and a little patience. Downside? Yes, I now have a non-standard rotor. This could potentially cause me a head ache down the road, and anyone else who ends up with the car after I'm finished with it. Upside? I can still install the turned-down OEM studs down the road, but for now, it's forward and onward.

13" Cobra rotor in the mill w/ 5/8" ream

One last issue to note - and it's an important one. As Steve spells out in the instructions, the OD of the early Mustang hub is larger than the ID of the rear face of the Cobra rotor. It's not by much, but enough that the rotor won't sit flush on the hub face. So you need to remove some material from the OD of the hub so the rotor sits flush. Apparently they used different vendors for these hubs so there's no single, standard OD. In my case, I seemed to have an extra large one and needed to take .075" off the diameter to get a nice flush fit. I added a 45 deg chamfer for extra insurance. 

rotor chucked in lathe - plugged to keep shavings out

close-up of turned diameter and 45 deg, 1/16"wide chamfer

 




In Part 3 we'll finish up with some polishing and powder coating. Stay tuned!

Front Disc Brake Conversion - Part 1

Like Sven, I was busy in 2017 with things other than our Mustangs. And like Sven, I can't say much about what I was working on either. Let's just say it involved (2) Ford Raptors and a whole lot of fun. I'm always amazed they actually pay me to do what I do!

But back to SusieQ. As I mentioned in the previous post, while in Australia, I decided that upgrading to power disc brakes was a must. Unfortunately not as many options out there as there used to be. Settled on Mustang Steve's 1994-2004, 13" Cobra Front Disc Conversion. It's a straight forward design, the majority of it being simple, laser-cut steel plates. Three issues I think if addressed though would make for a better design:

 Issue 1: The 2 rectangular plates in the photo below could be combined into 1. I'm guessing the reason was to reduce cost by laser cutting the pieces from standard stock thicknesses, rather than CNC machining a more complicated part. The large plate is .375" thick, the smaller one .100". In order to get this same stack height from a CNC part, they would need to start with a lasercut part from .500" plate, mill it down to .475", then step it to .375" in the outer mounting areas. This lasercut method works, but I dislike the extraneous parts. I was VERY tempted to correct this - and I'm not saying I still won't.    

Issue 1: (2) Lasercut parts could be (1) machined one

 Issue 2: This one is getting nit picky, but I would like to see them expand the adapter plate perimeter a bit and match the contours of the spindle. This would be so much cleaner looking. I know, it's hid behind the rotor once it's mounted. But whether it's hidden or not, I still know it looks like this. Quite possible there's a potential interference issue with another part if you grow the perimeter so I'm not going to throw too many rocks.

Issue 2: Adapter plate doesn't follow spindle contour

  



Issue 3: Again, I think they are cutting costs by using a lasercut part here when a machined part would have been more appropriate. You can see the large gap between the bottom of the spindle and the ID of the adapter plate hole. Remember there are no backing plates on this set-up, so any high speed sprays of water are going to pass right through that hole - and right against the backside of the inner wheel bearing seal. They couldn't make the hole in the adapter plate any smaller or the back side of the hub wouldn't clear. I would suggest that a machined part here, with a stepped counter bore to eliminate that gap (but still allow for hub clearance, might be a better alternative. You would need to add a small drilled vertical hole in the stepped counterbore to allow water that could enter from the front side of the assembly to drain. But water coming from the front side is going to be mostly deflected by the rotor. What water that does end up inside that opening will just be "slow speed ricochets".  In their defense, I saw this same issue with both Vintage Venom and Street or Track's kits as well. So there may be a reason for this gap that I'm simply unaware of. 

Issue 3: Gap between spindle & adapter plate

Once I got everything unboxed and sorted, I took the Dewalt with the abrasive pad to the edges and got rid of all the laser cut kerfs. Cleaned everything up, sprayed on a nice heavy coat of PMB 6525 (otherwise known as BMW silver) and popped into the powder coat oven at 400 deg for 20 min. Hard to see in the photo, but a very subtle hint of metallic in this silver. I like it. Sophisticated without being snobby :)

Stay tuned for our exciting Part 2 follow-on!!!

Yes Virginia, there is a Mustang in the shed!

Well, after 3 years of hibernation, I finally cracked the shed today and spent some quality time with SusieQ. It was a glorious Spring day and since I've finally fixed most of the broken stuff around the house after 3 years of zero maintenance, it was time to do some wrenching again.

And though I've not worked on the car during my absence, that hasn't stopped me from thinking about it. One of the things I've decided to change is upgrading to front disc brakes. The car came with drums all way round and I had thought it 'quaint' to leave it that way. But after thinking my wife is probably going to drive this car more than me, I just couldn't send her out with 4-wheel drums. So that's the first thing on my list.

After much research in Australia, the Cobra upgrade seems the most bang for the buck. But unfortunately Vintage Venom is no longer producing their kit (my preference) and neither is Street or Track - so my choice seems limited to Steve's Mustang. I liked the Venom kit as it was a single-piece billet aluminum part while Steve's kit is two-piece steel. Probably could recreate Venom's bracket for myself. Let's face it, it's 6 bolt holes and an odd-ball shaped perimeter. But...all these kits have been road tested, and again, if my wife is driving this car, do I really want to experiment with her life? As an engineer, I fully realize that the devil is in
the details and what seems elementary on the surface, most times is anything but.

Vintage Venom Front Brake Cobra Adapter Bracket

Steve's Mustang Front Brake Cobra Adapter Bracket

So while I percolate this bracket dilemma, I'll start cruising Ebay looking for Cobra/Mach1 calipers. I see they come in both 38 and 40mm piston diameters but unless she plans on racing this thing at Watkins Glen, I don't think she is going to notice +/- 2mm of piston diameter. I plan on powder coating them to match the car so I'm just going to track down some used ones and pull them apart for powder coat then rebuild. So not much progress but at least some - one bite at a time right?

Checking In

Hi guys,

Thought you might be interested in what I've been doing with myself with no Mustang to work on for the past year. This sort of fills the gaps while I'm gone. Scratch built by 3 guys in about 6 months. Just getting ready for first field trials in a few weeks. So far so good. Haven't run down over the hill and caught on fire yet - always a good things with robots as they tend to do that a lot. Enjoy!

https://www.youtube.com/watch?v=Z5whrF4SDes

I've been popping in once in awhile to check all your progress. Seems like we have all been a bit distracted these days. That's the nice thing about not having a deadline. You can work when the time allows it. Take care!

ray

Some Sad News

Well gentlemen, I've been putting this off but since time is rapidly running out, I need to come clean. If you remember, last year I spent some time working in Australia on a robot project. Just before this past Christmas, I was contacted by the university we worked with to see if I was interested in continuing on with the project down there with them. Talked it over with wife, daughter, parents, siblings, friends, etc as at our age, one's life is not to do with as one pleases. There are duties and responsibilities to others that must be considered before you can consider your own. But the general consensus was 'Are you crazy - GO!!!!. It's actually a good time - Daughter Julie is out of grad school and working at her first 'real' job. Both sets of parents are in good health and gave us their blessing for taking off. Off we go then - for at least 2 years.

So we've been scrambling to reorganize my own business here since January - and to try and wrap up SusieQ so she was in some movable form. In a Herculean effort last week, we got the front/rear valances installed, the taillights in, the rear bumper on, the front fenders on and the stone guard bolted up. Bought a one-stall garage from a local Amish building company and planted it in the backyard. Last Saturday, we loaded up the car and transported her about 5 miles from the shop to my house.

Right now then, she is sitting about 50 ft from me, snug in her new home and wrapped up for a 2 year hibernation. A shame as it looked like we would have probably gotten her on the road this summer. But she'll be here when we get back and I'll probably get a few weeks worth of work on her when we come back for vacation. Here then is your last look at SusieQ for an extended duration. Of course, I expect you all to continue your own work, and look forward to your postings as I live vicariously through your work while I'm gone. Take of yourselves then and keep those wrenches warm!

SusieQ heading towards hibernation - March 29, 2014

Tail Light Recovery

Finally got back around to those tail lights buckets that I managed to mangle last month in a fit of impatience. I'm blaming it on cabin-fever and the need to see sunshine again :/ Anyway, during the cooling off period, I went ahead and purchased a set of the satin-finished tail light bezels from Scott Drake.I would have rather de-chromed the originals and powder coated a matte-silver - but de-chroming stuff is such an environmental disaster if you do it at home - and expensive if you send it out. The Drake option seemed the best choice as I was looking for a little less chrome to start with. 

Once the bezels arrived, I used them as the color template for picking a powder that would match them. The intent being to strip the chrome trim that attaches to the rear 1/4 caps and deck lid and powder coat in a color to match the bezels. I've read that these pieces are stainless but I'm pretty sure they are just anodized aluminum. Being such, I decided to try the oven-cleaner trick to remove the anodizing prior to powder coating. Surprisingly, it worked fairly efficiently. I placed them in a shallow tray and just kept them 'wet' with the cleaner for approximately an evening of shop time. You could literally see the anodizing sloughing off the pieces. Once I got the anodizing off, I took them to the weld table and VERY carefully tapped  a few nicks/bumps out of them using a small hammer and various small round pieces of scrap metal. A quick trip to the blast cabinet and they were ready for powder coating. I ended up sending to Prismatic Powders for 5 different color samples, and the one that seemed the closest was Silver Satin. So I ordered a pound of that and a pound of Casper Clear (Sven recommended) to topcoat with.

While waiting for the powder to arrive, I sucked it up and went after the buckets. First step was chemically stripping as much of the damaged powder coat off as I could. Took three applications to finally get to a point where I could finish them in the blast cabinet. Even then, it was a long hour for each one. That powder coat is TOUGH stuff!!! I took my time this go-around - did the proper surface prep - set the oven for 400 deg and let 'er rip. Happily there were no surprises when I popped the oven door this time. Beautiful, mirrored surface like I was looking for the first time. Lesson learned...

Tail Light Bucket - Satin Silver Powder Coat

Tail Light Assembly

Front Fenders and a Quiz

Got a rare window of above 40 deg temps on Saturday in this 'Winter That Will Never Quit'. Took advantage of the 'warm' sunshine and dragged the front fenders outside for final prep of the inner surfaces. Another glamourless job that no one will ever appreciate save for the few of us crazy enough to do it. Used my standard protocol for jobs like this:

1. Scrape old undercoating off with putty knife

2. Remove residue with solvent

3. Scour with SOS pads. (I like using them for this as you get the combination of soap and steel wool. Leaves a nice clean, smooth surface.)

4. Treat with TSP, rinse with water, let air dry in warm sunshine

5. Coat with Rustoleum's trusty, rusty metal primer

6. Top coat with Rustoleum's Truck Bed Liner

Got the second fender top coated just as the sun ducked behind the hilltops and the temps dropped 10 deg. Nice to get that job done outside as the bed liner contains Xylene which is some really nasty stuff for working with indoors. 

Once I get the inner splash shields in place, I should be ready to mount the fenders. At that point she should start looking like a car again rather than a 20 year long high school science project.

 So for the quiz. Anyone wants to guess why there isn't an antenna hole in the top of the passenger fender? You'll be surprised by the answer. And no, I didn't weld it shut.

Mystery Fender