Hawk HP+ and EBC Slotted Brake Rotor wear - Opinions

[sgernon]

In March I swapped all my pads and rotors and now am seeing some issues with my rear rotors wearing excessively. Car is a 72 Camaro with C5 calipers all around, C5 front rotors and LS rear. I was running a 1 1/8 master with the front lines split with a T fitting and the rear has an adjustable prop valve that is wide open. I also have hydroboost and had a very touchy brake pedal. I'm now swapping to a 1" master and have reduced the power steering pressure by adding a washer to the valve to try to get some touchyness out of the brakes. The trans is out of the car right now so I can't say what this has changed in the overall feel.

I was running stock rotors and pads without issue for the last year or so. The rear pads were wearing faster than the front but overall it did not seem too different. Before heading to a track day at Thunder Hill in April I swapped to HP + pads all around and DBA slotted front and EBC slotted rear rotors. I was going to use DBA all around but was told there was a quality issue with the LS rear rotors so I chose EBC instead. I've now run a full 5 session day at Thunderhill, ~500 miles of street driving and a autocross day. I bought the pads and rotors on 3/29.

I pulled the wheels off last week and found the front rotors look almost new while the rears are very worn. The right rear rotor is almost worn through the slots and even most strange to me is the fact that it is not eveny worn (see pic). The pads in general look fine and are not worn at all.

I contacted EBC and they were very nice to talk to and responsive. EBC is even nice enough to send me a new set of rotors due to the issue. They say the pad compound is causing the wear which seems reasonable since the pad looks new but also seems odd to me since the fronts run the same pad and the rotors look almost new. I asked them which pad they recomend for the maximum stopping without excessively wearing the rotors. They responsed
"I would recommend our Yellowstuff brake pad for an aggressive friction material that is gentle on rotors. Our Yellowstuff brake pads are made of a ceramic base and feature Kevlar for friction. The reason they are gentle on rotors is because we use no semi metallic metals or fibers in the pads. They have a mild bite during normal street driving and a aggressive bite when the pads heat up, this makes them great for street, track, and aggressive driving.

Here is more information on our Yellowstuff pads-
http://www.ebcbrakes.com/automotive/yellowstuff_brake_pads/yellowstuff_brake_pads_4000_index.shtml"



Has anyone had similar issues with EBC rotors or using HP+ pads? Any idea why the rotor is wearing uneven?


60242

[Apogee]

FWIW, by reducing the bore size of the master cylinder from 1.125 to 1 inch, you are increasing the caliper pressures by about 25% and therefore increasing the effective brake torque by the same amount, essentially making them even touchier than they are now with even less modulation.

Are you sure that the rotor is wearing unevenly or could it be that the slots weren't machined into the rotor evenly to begin with? It's possible to get a chip under a part when setting it up in a machining center depending on their manufacturing processes which I would think could create the wear situation shown above. Is it just occurring on the one side of the rotor, or both sides? As for the amount of wear, that comes down to metallurgy and pad compound more than anything else. While the EBC pads are slightly more rotor friendly than the Hawk HP Plus, the fact that the DBA's are holding up so much better in the front application tells me something considering it's the far more demanding application. Which DBA rotors are you running? Street, 4000, or 5000-Series? Older directional vane or Kangaroo Paw pillar vane?

Tobin
KORE3

[sgernon]

Tobin - Thanks for the reply

I was thinking that by reducing the MC bore size I would increase the pedal travel because more travel would be needed to move the fluid and the caliper pistons the same amount. Am I right about that? I don't know why MC sizing is so difficult to me. I don't really understand how the pressure vs the volume works. I assume you explained that to someone else before and I'll look through some other posts. I had the 1" MC in the car with a vaccum booster long ago and liked it so I'm hoping the smaller MC and the reduced power steering pressure will work together for a better feel with the hydroboost. The other thought was that I had the 1" MC sitting around so there was not cost in swapping them out and trying. If this doesn't work I'll swap back the larger MC and maybe move the linkage father up the pedal to change the ratio.

It could me that the rotors were not machined straight. The lip around the edge seemed pretty consistent and the uneveness in the slots was only on one face of the rotors. I'm running the DBA 4000 directional slotted rotors on the front. The fact that they are untouched and the rears are so worn is what really puzzles me. For a moment I even thought I might have plumbed the brakes backward given the wear. The fronts are plumbed to the front of the MC which has the larger hole. Can you confirm that is correct?

[Apogee]

A smaller bore master cylinder should increase your pedal travel, but I think you're going to find that it makes the brake pedal feel a bit more like a light switch...off/on...without any real modulation, but you've got the parts so give it a shot. The reduction in pressure may make a bigger difference, so post up what you find out. In my experience, the human body is better at regulating force than it is at regulating location with a brake pedal, but everyone has their own opinions when it comes to driving preferences. My only concern with the changes that you've made is that you're making one too many at a time since you won't know which change necessarily had what effect on the overall system, so you may want to consider only making one change, evaluating the difference, then proceeding on to the next change.

Fitting size on the master cylinder does not indicate anything necessarily, as volume and pressure are determined by the bore size of the master cylinder, nothing else. Volumetric requirements are dictated by the caliper piston area multiplied by the travel distance to actuate, the caliper piston area tends to be fairly large (C5 Frt = 4.0 in^2) while the piston travel on most modern calipers tends to be rather small and measured in thousandths of an inch. Assuming you don't run out of pedal travel or MC stroke, these will natural find a balance. As with any hydraulic system, you have a master (MC) and a slave (2X caliper per MC piston) and you gain force mulitiplication due to the difference in areas. For example, a 1.125" bore master cylinder has approximately a 1.0 in^2 piston area and a C5 caliper has a piston area equal to 4.0 in^2. Assuming a pedal force of 100 lb and a pedal ratio of 6:1 in a manual configuration just to keep things simpler, then you would expect an outlet pressure of (100lb)*(6)/(1.0in^2) = 600 lb/in^2 or 600 psi given that Pressure = (Force)/(Area). At the caliper, the clamping Force = P*A, or F = (600lb/in^2)*(4.0in^2) = 2400 lb. I've chosen the component sizes to make the math easy as I wouldn't run a 1.125" bore MC in a manual configuration, but hopefully you get the idea and while all of this may seem overly simplistic with a MC piston area of 1 square inch and no booster, the principles apply the same for any combination of components.

I can't tell you what the proper plumbing configuration is for your master cylinders since you haven't specified which ones you're running in either size, 1.125 or 1 inch, and they're not all the same. A C3 Corvette disc/disc master cylinder is front/front and rear/rear and available in those bore sizes, however an OE second-gen disc/drum unit is opposite whichh is evident due to the small and large reservoir volumes where the larger reservoir is always intended to supply the front calipers in a disc/drum application. The reason for the added volume is to account for fluid transfer into the calipers due to pad wear, something not encountered with drum brakes.

Tobin
KORE3

[sgernon]

I know I did make too many changes but I am waiting on my new trans to come in and got bored. They were both simple, free and easily reversible so I decided to go for it. After reading this and looking at the parts in more details I may have more problems than I thought.

Here are the details of the 2 MC's I am playing with. After looking them but I found I am actually moving from a 1.25 (PN 18012985) to a .94 (PN 18010023) so I definitely may be making too much of a jump. Once again I have the parts so I figure why not. Looking at the data from Bendix it does state that the primary is 1/2 and secondary 9/16. The front output is the larger connector and has a larger hole. I figured they front brakes always attached to the front and would also need the larger hole to flow more volume but based on the data here I think I may have my lines backwards. Am I correct that I was wrong ???

The brake force calculations make since but is there any reference available for the clamping force necessary to stop a specific weight with a pad area without lockup? I know that's a very complicated question depending on the friction of the pad and the traction of the tire but I'm curious if you know of someone who has already built a we based tool that calculates it. Also, do you have any idea of the additional boost the hydroboost can give at a specific line pressure? I know you are they brake expert so I figured I'd ask. Right now I really wished I finished my ME degree.....

18012985
60288

18010023
60289

[Apogee]

The two master cylinders you noted are opposite with the rearward ports being the circuit for the front brakes and the forward ports being for the rears. The dead giveaway on the Astro unit is that the larger volume reservoir is closer to the firewall, indicating that it is for the front brakes to account for pad wear in a disc/drum application.

FWIW, the S10 MC should be a stepped bore, quick take-up unit with either a 31.75mm [1.125"] or 36mm [1.417"] primary bore and 24mm [.941"] secondary bore. The smaller primary bore unit was used on manual brake applications, the larger with vacuum assist. These essentially behave like two master cylinders in one, working from the larger bore at low pressures and then switching over to the smaller bore when a certain (and fairly low) pressure has been reached, resulting in a relatively high/firm pedal while reducing pedal effort required to achieve maximum braking/lockup.

Tobin
KORE3

[sgernon]

Oops, looks like I screwed up when I was plumbing the car. Yet another lesson I'll never forget. I'm actually surprised how well the brakes worked considering. I'll replumb the lines, will evaluate both MC's once the trans is put back in. Once done I'll post back up the differences.

I'll also post up how the new EBC rotors are performing after approximately the same amount of driving just as an FYI to those reading this thread.

Tobin - Thanks again for your help

[sgernon]

I finally have my new trans in and was able to drive the car today. I decided to put the 1/4 bore MC from the Astro van back in but this time plumb it correctly. I also decided to leave the washer in the PS check valve to reduce the pressure. The brakes now feel good. I have not done any crazy hard braking but did stomp on them a few times pretty hard. They seem much easier to control and the car feels more stable while braking. I also like the steering a bit more with the reduced pressure, it has a bit more feel to it. It's amazing what happens when you put things in correctly.....

After I hit the track a few times I'll update on the condition of the EBC rotors.

Steve

[Skip Fix]

Another thing to look at is pedal ratio, where is your pedal hooked? Was it originally a manual brake car and now you have boost? Even a dual diaphragm power booster over a single booster makes a world of difference. On second gens when Pontiac added a dual diaphragm booster for their 79-81 4WD system the decreased the pedal ratio even less than the normal single power booster used, which was less than the manual to start with. Trying the regular power booster pedal with taht dual booster gave good stopping just no feel at all.

Where did you get the spec sheets based on the original MC casting #?

[sgernon]

I got the spec sheet directly off the Bendix website. They have some good data out there.

I am going to change the pedal ratio next. I have the linkage hooked to the lower stud now and it's still more sensitive than I like. I hooked it to the hole ~1" higher and the feel was much better but the pedal was too high for me. I'm going to cut the linkage this weekend and add an adjustable rod end to it so I can dial in the height I want better.

[Skip Fix]

The 4WD pedals have it even a little lower on the pedal. I think I have a picture somewhere the exact spot.

[sgernon]

Attended a track day at T-Hill yesterday and did my best to put the car through it's paces with the corrected brakes. The setup was the 1 1/4 MC from the astro van with the brake lines hooked up correctly, the PS pressure valve has 1 washer installed to reduce pressure slighty and the hydrobooster is connect to the upper hole on the pedal. Front rotors are DBA's and rear are EBC. All 4 wheels have Hawk HP+ pads.

Overall the feel was MUCH better. The car was predictable under braking, was not twitchy and had more than enough stopping power. I noticed much less brake dust on the rear wheels and there appeared to be no visible wear to the rear rotors after 5 20 min sessions. It definately appears I am the reason for the first rotors wearing out and have to say EBC's confidence in their product and customer support is terrific.

[Skip Fix]

I think some of the 60-70s Chevy trucks even had a manual 1 1/4 MC.