17. Braking news

on

Bob has said this multiple times and I’ve experienced it quite a few times – sometimes it seems you’ll spend 2 hours thinking about something that takes less than an hour to complete.  If you’ve made it this far you can tell I spend a good portion of the day just sitting on my butt thinking about what to do next, and how to do it as best as possible.  I’m constantly making design trades in my head and debating the merits of about 1000 different solutions before I get going on a solution I think is “right”.  Even then sometimes it’ll take a question or discussion with someone else to make me rethink that decision I spent so much time laboring over!  So it’s no surprise I had the same experience with the brakes.  I really struggled to come up with the optimum configuration for the braking system, in particular the e-brake calipers and hydraulic flex hoses.

I screwed up early on after having my uprights anodized as I should have machined the necessary mounting holes for the e-brake brackets either before or after anodizing.  Now that the suspension’s been assembled and dialed in, taking it all back apart just to tap 2 mounting holes made me feel like a furious beating with a wooden stick would have been more enjoyable.  So I’ve been pushing off on tapping these holes for as long as possible since I’d only get 1 shot to do it correctly.  Getting the hole spacing wrong or drilling the holes off at whacky angles would assuredly ruin the upright (or so I told myself).  I couldn’t put it off any longer so I tried to be as careful as I could with each step.  To ensure I drilled the pilot holes perfectly perpendicular to the mounting face I used a piece of scrap aluminum block and drilled holes of increasing size on the drill press.  I was sure the drill press would give me nice perpendicular holes which could be used as drill guides once I secured the aluminum block to the upright.  I selected a good number of drills to “walk the hole up” to the final size needed for tapping.  Minimizing the amount of material removed between each hole size helps to keep the hole clean and ensures the bit won’t grab or twist instead of cutting.

I decided I would use M10x1.5 bolts for the mounting hardware.  The upright is pocketed on both the inboard and outboard faces; based on my rough measurements the inboard side is pocketed to a depth of 17mm, the outboard to a depth of 6mm, with the upright having an overall thickness of 39mm (I probably got this measurement wrong and the actual thickness is 40mm).  This meant the centerline of my mounting bracket needed to be 8mm away from the outboard edge.  Putting the tapped holes at 19.5mm (or centered) would have resulted in the threaded hole getting exposed once it hit the pocketed portion of the upright.

For vertical alignment, I aligned the upper edge of the mounting bracket to the corner where the upright turns from angled to vertical.  This places the caliper square to the spindle centerline so the curve of the rotor hat and wheel match the curve in the e-brake caliper.  Get this position wrong and it’ll look like the caliper is twisted relative to the rotor – bleh.

I used a small c-clamp to secure my drilling fixture to the upright after marking my first hole – time to start drilling!

img_7341
Start small with the first drill and slowly step your way up to the final hole size needed for the tap.
img_7363
Drill guide clamped to upright, I used a spring loaded punch to give me a dimple which I then used to help use for alignment.  I had also tried to drill the guide holes such that when the edge of the drill guide was flush with the side of the upright, I was about where I wanted to be.
img_7364
I figured if I sunk my first drill bit in until it couldn’t go any deeper I’d have enough threads for the mounting bolts.  Here you can see how deep the hole will be, and where it is relative to the other features.  You want the hole to be high enough it won’t poke through the lower pocket, low enough it won’t crash into the bolt holding the hub in place, and shallow enough it doesn’t punch into the bore cut for the hub.
img_7365
Final drill diameter.
img_7362
Guide mounted and ready for the pilot hole!  Get this hole wrong and you’re basically hosed as every hole drilled thereafter will want to follow this initial drilling.
img_7358
6 drilling ops later and we’ve got a hole that didn’t pop through either side!
img_7372
You would be surprised how easy it is to screw up a tapping job, even one with a pilot hole as large as this.  Take your time and back the tap out if there’s any resistance.  Unfortunately I didn’t have a bottoming tap so I had to factor in that the bottommost part of the hole would not be threaded.
img_7361
We’ve got a tapped hole!
img_7375
To position the lower hole I positioned the mounting bracket and marked my lower hole using the pre-drilled hole in the bracket.  The bracket is likely precision machined and identical left to right, however not having precise enough measurement tools meant I had to do in-situ locating of these secondary holes.  The upper holes are less critical from a depth perspective as there is plenty of material; it’s the lower hole that has a tighter depth requirement.
img_7379
Alignment of mounting bracket to upright.  Edge of bracket should coincide with where upright face goes vertical.
img_7346
Mounting bracket orientation is such that the caliper retention bolts should be aligned vertically.
img_7384
Note the mounting bracket is almost centered relative to the upright; the holes need to be offset due to the “L” design of the bracket.  Washers used to position the caliper relative to the rotor, these will be replaced with machined spacers.  Minor shifting of the caliper can be made via adjustment of a set-screw.  However, initial positioning needs to be made with spacers.  Be sure to snug the rotors down so they are properly positioned before determining spacer height.

The e-brake calipers supplied in the kit are really nice units.  They’re finished in a really nice black anodize and the mounting brackets are billet.  I found it odd, but only one of my calipers came with the letters “SL-C” on the exterior face – the other side was blank.  I’m toying with the idea of powdercoating these eventually but my experience with the calipers leads me to believe I won’t be able to create a close enough match of the orange – so I’d have 2 different shades of orange fairly close to each other which might push my OCD issues into overdrive.  Best to just leave it as-is methinks.

img_7382
Completed assembly!  The arc along the right edge of the e-brake caliper should follow the arc of the rotor.
img_7381
Where did my “SL-C” go?

Surprisingly, the procedure went smoothly and I mounted the e-brake calipers without any drama.  Before vs after pic; I always get jazzed seeing how well the calipers turned out and in combination with the CF10 wheels.

Next up was install of the E-stopp emergency brake system.  I think “emergency brake” is a bit of a misnomer since the system has a disable switch that prevents it from working while the ignition is on.  It’s really just an electronic parking brake – which is what I wanted, no plans for handbrake turns for me!  Installation was pretty straightforward.  About the only thing I’d recommend is powering up the system and actuating it before performing final installation to ensure it’s in the fully extended position while tightening down on the e-brake pull cables.  If the actuator is in a mid-position then there may not be sufficient cable actuation during operation.  I had read in an online review of the system that this occurred to one user and they had to tear into their system to readjust the cable setpoints.  Since I opted to bury this behind the spider, accessing this after the car is complete would be major work.

img_7432
Nicely packaged and the hardware looks top notch.  However, the control box is flimsy plastic and not well sealed.
img_7514
Connecting to the e-brake cables.
img_7512
I added an extra plate to serve as a positive stop for the actuator body.  The actuator will pull until it reaches 600 lbs of pull force (or the actuator hits its internal stop).  Without a positive stopping feature it’s possible the housing may shift during actuation and lead to decreased or insufficient e-brake clamping.

Brake lines:

As with the e-brake calipers, I was putting off on completing the flex line install for the brembos.  The hoses and banjo fittings supplied in the kit just didn’t work well – I think these are likely hoses and fittings designed back when the hard lines used to be run inside the footbox.  Now that they’re run on the outside of the footbox they didn’t seem to work very well.  Some of the issues/concerns I was encountering:

  • The front brake calipers do not have an integrally cast anti-rotation ear.
  • The flex lines are too short to run in a way that a strain relief can be added.
  • The flex lines need to make a quick turn before hitting the 45-deg angled portion of the foot box.

To rectify the first two issues I procured a longer off-the-shelf hose from a local hose vendor.  24″ was the closest size they had which would work for me.  YMMV so measure if you decide to replace your hoses.  The longer flex line gave me enough slack to install anti-rotation strain relief tabs using a caliper mounting bolt to hold it in place.  There was also enough length so I could zip-tie the hose to the rearward arm of the lower a-arm.  The new assembly has slack for the suspension to fully articulate in the vertical direction with the wheel turning full lock to lock.  Low tech – yes, but the zip-ties are effective at keeping the flex line away from the wheel and coil spring.

To address the third point I used a 90-deg male/female -3AN adapter to turn the hose downward at the hard line joint.  It would have been better to have a 90-deg end fitted to the hose but I didn’t want to pay extra or spend the time for a custom line.  I also purchased a 90-deg banjo fitting to orient the hose downward off the caliper attachment point.

img_3426
My apologies – I don’t know whose car this is but it’s a photo I pulled from some time ago.  This shows an installation configuration I’ve seen on several builds.  There is no anti-rotation or strain relief feature and the flex line is in danger of getting sucked into the coil spring if the wheel is turned to the left.
img_7542
Driver side flex line.  This is the most extended scenario the line will need to accommodate; suspension fully drooped with wheel turned to the right.  Zip ties ensure flex line cannot contact wheel or shock during articulation.
img_7539
90-deg turndown immediately after hard line junction.  Without a turn, the hose tended to not want to turn quickly enough before riding the angled portion of the foot box.  The span between the clamp and zip tie needs to have enough slack/compliance for a-arm rotation.
img_7540
90-deg banjo fitting directs line down alongside caliper body.  Strain relief tab ensures any twisting forces going into the line are insufficient to cause preload loss at the banjo bolt.  Area between strain relief tab and next zip tie must have enough slack/compliance to accommodate suspension travel AND wheel rotation.
img_7541
Oversize strain relief clamp to allow for added slack/compliance.

In the rear, I used the kit-supplied flex line that has the integral 90-deg hose end along with a straight banjo fitting.  I still need to make some anti-rotation brackets similar to what I did for the fronts.  The rear flex lines were less of an issue because they don’t need to accommodate for a wheel which is steered.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s