I'm curious about this topic because I was looking at the brake pads on my race car and noticed that the left front pads are worn about 30% more than the right front. I've only done (I think) 4 TT and race weekends in this car. Also, at one place at VIR, the car was pulling right under braking. So here are a couple of things I noticed about the brake system:
- There was zero effort put into make the left and right lines the same length. I'd say the right is about two and half to three times the length of the left side. I have always assumed that they should be roughly equal length, though I suppose that if they are bled properly that shouldn't make any difference.
- There are several high spots in the lines where I was also under the assumption air could get trapped.
Does any of this matter or should I just shut up and bleed the brakes?
I'd bleed them and take a look at brake ducting as well as caliper health. It's unlikely to be trapped air because you'd be feeling that in the pedal, but it never hurts to bleed the brakes on a track car.
Was it both pads, or just an inboard, or just an outboard?
are these fixed calipers with opposed pistons? Because race car, I assume yes.
Lengths of hard lines are rarely the same, but lengths of soft lines are usually pretty close. Asymmetry doesn't effect output but in theory it could let one brake apply a little sooner than the other. In theory.
always try to avoid local high spots in the tube routing, as you noted they could make bleeding more difficult.
I'd have a look at all sliding surfaces and make sure you don't have anything hanging up.
The calipers are single piston. These beauties: https://howeracing.com/collections/brake-calipers/products/caliper-2-9-steel-howeno-bolts-not-for-highway-use
I'll see if I can get some pics this morning of the pads but the inner and outer seem to be worn about the same amount.
Here are the brake pads. I guess I didn't look close enough but the inner DS pad is a bit more worn than the outer. It is a little wedge shaped with this end being thinner. The PS side is not as worn but the inner pad is a little thinner.
Here's what I mean about the brake line routing. This is looking in from the PS wheel well. There is a braided flex line coming from the MC down to the hard line. The junction is well below the transmission hump but as you can see (barely), the line is routed back up and over the trans hump, down again to a frame member, then along the frame to the a spot in front of the UCA mount where it joins the braided flex line to the caliper. If I were routing these from scratch, I'd have mounted a T above the trans hump and run the flex line (or even a hard line) from the MC to that.
Here's the line running through the cockpit for the rear circuit. I get that it's kind of hard to avoid having high and low spots but it could be minimized. And this final hump in the line before it goes through the rear bulkhead...was that really necessary?
If the pedal isn't soft, it's probably not air. Does the pedal feel change the same amount when you're bleeding the left and right front calipers? Ducting?
In reply to Keith Tanner :
I haven't bled them yet. 
This will have to wait until I get the seat back in place so SWMBO can help.
If by ducting you mean air ducts, no. It doesn't have any. I'm still trying to get a feel for this car and the brakes are my nemisis at the moment. I've said elsewhere, that this car feels like I'm trying to slow down my trailering rig. Everything is new to me so I have no idea whether I'm applying enough leg pressure, if the pads are the wrong compound, if the MC is too big, the tires aren't grippy enough. And, no, I don't know what pad compound I currently have. Came with the car, the PO didn't provide that info and I didn't think to ask. The car is around 2850 lb w/ driver, same as my former e36, with nearly twice the contact patch as the e36 but the e36 stopped way better. However, I'm doing 140-ish at the brake zones with this car as opposed to 120, so there's that.
I'd spend the money for some known brake pads and take the time to bed them properly. Ducting is one the best bang-for-the-buck ways to improve track braking, and an adjustable proportioning valve will let you work the front and rear to their fullest potential.
Can you lock the wheels?
Those brake pads look cooked, agree with the assessment that cooling ducts would be a good idea.
That style of caliper rarely wears pads evenly even when everything is perfect. The pads locate on the caliper, which is a moving target. They work and are inexpensive to manufacture compared to calipers with a fixed pad carrier, but they have their idiosyncracies.
Keith Tanner said:
I'd spend the money for some known brake pads and take the time to bed them properly. Ducting is one the best bang-for-the-buck ways to improve track braking, and an adjustable proportioning valve will let you work the front and rear to their fullest potential.
Can you lock the wheels?
This car has dual masters and a cockpit adjustable balance bar. Yes. I can lock the wheels. I had an "Oh, $hit!!" moment at Summit Point deep in the brake zone of T1 where I was still carrying too much speed just prior to turn-in. Was about to hit a e46 in front of me so gave it all the beans and turned it sideways. The amount of leg pressure required makes it hard to get a feel. That's my excuse and I'm sticking to it. Video with horrendous contract problem:
https://rumble.com/v1a1zkx-nasa-summit-point-su-06262022.html
There are still pebbles from the gravel trap in my spring cups.
I think you're right on the pads but I wanted to get another weekend or so out of these. Since the front and rear pads/calipers are the same, I'm considering switching them because there is still plenty of life left on the rears.
Hawk's DTC-70 or DTC-80 compounds are likely candidates but they're damn expensive. I got another recommendation for Willwood A's, which are comparable in price to the DTC-70, but the heat tolerance of the Hawk is better.
One of my other options is to switch to a slightly smaller MC. The current are 1" so I might change to a 7/8". I'm holding off because I want to see if I can develop a feel for these, thought you're think I'd have done that by now.
Pete. (l33t FS) said:
Those brake pads look cooked, agree with the assessment that cooling ducts would be a good idea.
That style of caliper rarely wears pads evenly even when everything is perfect. The pads locate on the caliper, which is a moving target. They work and are inexpensive to manufacture compared to calipers with a fixed pad carrier, but they have their idiosyncracies.
Thanks! One more thing to put on the punch list. Seems like every time I check off one item, another one gets added.
The dual masters apparently require a pressure bleeder instead of the old school two person method. The two person method apparently damages stuff due to the balance bar design. At least thats what i leared from gimps camaro thread.
Motive bleeder and correct master cap and be done.
Dusterbd13-michael said:
The dual masters apparently require a pressure bleeder instead of the old school two person method. The two person method apparently damages stuff due to the balance bar design. At least thats what i leared from gimps camaro thread.
Motive bleeder and correct master cap and be done.
Thanks for that heads-up. I had no idea. But it kind of makes sense given that you'd be maxing out one MC while the other isn't moving. I'm not sure what would be damaged though. Was it something with the balance bar itself getting damaged?
In reply to jimgood :
If i remember correctly, it was bending the pushrods on the masters. Take that with a shaker of salt though, as I've slept since then....
I doubt your front and rear calipers are the same - they likely have different piston sizes. But you could certainly swap the pads. Keep in mind that pads wear faster as they get thinner because their heat capacity goes down, so you won't get the same life out of the last quarter than the first.
You can lock the wheels, so playing with the hydraulics will only make that easier. Decreasing the amount of force needed on the pedal is a legit fine-tuning step, though.
Given that spin, I wonder if you've got too much rear bias?
So we're looking at two things - one, the car doesn't stop the way you want it to and two, you've got some asymmetry in how it brakes and wears pads. For the latter, definitely look at the slider pins as the first step.
For the former, I'd get some known good pads in there so you know you're not dealing with something that's outside its comfort zone or that's been cooked. If the pedal always feels super-hard and needs a lot of force, that could be hydralics. If the pedal has some travel but it just doesn't feel like you're getting the braking level you expect, that's more likely to be pads.
Do you have access to someone else who's used to this chassis who can comment on how they feel?
I have done many street car brake jobs, and am usually confused as to why the left side front pads wear faster than the right side. I've quit trying to figure it out.
When I build cars I always try to run the brake lines lower than the calipers to avoid air traps. Not always possible.
If one pad in a caliper wears faster than the other pad, it could signal a sticky piston.
In a lot of formula cars I've worked on, we see tapering of the pads. Its so easy that usually every couple of sessions we just flip the pads. Because we don't use a lot of brakes, and open wheel cars cool the brakes fast on the straights, some guys use spacers behind the pads as they wear. That keeps the pistons from coming out a long way and then tending to cock in the bore.
YMMV
In reply to Dusterbd13-michael :
Thanks. I'll go the vacuum bleeder route. I have one somewhere around here.
Keith Tanner said:
I doubt your front and rear calipers are the same - they likely have different piston sizes. But you could certainly swap the pads. Keep in mind that pads wear faster as they get thinner because their heat capacity goes down, so you won't get the same life out of the last quarter than the first.
You can lock the wheels, so playing with the hydraulics will only make that easier. Decreasing the amount of force needed on the pedal is a legit fine-tuning step, though.
Given that spin, I wonder if you've got too much rear bias?
So we're looking at two things - one, the car doesn't stop the way you want it to and two, you've got some asymmetry in how it brakes and wears pads. For the latter, definitely look at the slider pins as the first step.
For the former, I'd get some known good pads in there so you know you're not dealing with something that's outside its comfort zone or that's been cooked. If the pedal always feels super-hard and needs a lot of force, that could be hydralics. If the pedal has some travel but it just doesn't feel like you're getting the braking level you expect, that's more likely to be pads.
Do you have access to someone else who's used to this chassis who can comment on how they feel?
You're correct that the calipers are not the same. Both front and rear based off the same GM III design (that's where I got the "sameness") but the rears are Willwoods. The front Howes have a 2.93 piston diameter and, if the rears are these from Willwood, which I think they are, they are 2.75. I need to measure to be sure. Both call for D52 pads.
I'll look at the slider pins and make sure they aren't binding. And I guess I should just go ahead and spring for the pads.
Thanks for all the advice.
I've tried to contact the previous owner but he's not returning my calls so I think he just doesn't want to be bothered with this stuff.
So we know the front and rear calipers have different size pistons. Have you told us the size of the front/rear master cylinders? With that info a ratio can be calculated to get at a starting point t adjust the balance bar.
I'm with Keith, sound like you have too much rear bias.
You need to study the balance bar to see which way to turn it. Is there an adjuster on the dash? If so does it have an arrow telling you which way to turn it?
Purple Frog (Forum Supporter) said:
So we know the front and rear calipers have different size pistons. Have you told us the size of the front/rear master cylinders? With that info a ratio can be calculated to get at a starting point t adjust the balance bar.
I'm with Keith, sound like you have too much rear bias.
You need to study the balance bar to see which way to turn it. Is there an adjuster on the dash? If so does it have an arrow telling you which way to turn it?
Didn't take much study. 
The master cylinders are 1". I've already measured and calculated my pedal ratio at 5.25:1 and the pedal currently has about 2.5" of travel with room for at least 3.5" more. Not that I'd want 6" of travel. Just sayin' there's room for more if I use a smaller master. (EDIT: that's the motion ratio of the pedal itself)
While we're on the subject, it looks like the caliper is going to need rebuilding. Clearly it's getting too hot. The right front piston boot is fine. This one is literally toasted. And now that I have the pads off, there is no way there's even another weekend on them.
I have to wonder with the imbalance left to right if there's just air in the RF but not the left. I'm embarrassed to say I've not bled the system since I bought the car a year ago. I only ran it the first half of the year so it's been parked since last June.
Also, with the design of these calipers, it doesn't look to me like it's possible for the calipers to bind on the pins. The pins are a very loose fit where they pass through the caliper. The calipers and pads just sort of hang on them.
Doesn't matter where the air is, you'll feel it as sponginess that can be pumped up.
I'd throw some Syl-Glide (you can get it from NAPA) on those slider pins after you rebuild the calipers. Can't hurt to make sure they move smoothly. It can't be that loose a fit or you'd get a noise every time you put the brakes on.
OE Moraine calipers (I think that is the term for these?) used rubber O-rings as bushings between the calipers and the pins. These lightweight calipers may not have those as an expedience for manufacture. They're circle track parts, people won't care if they are clattery
Keith Tanner said:
Doesn't matter where the air is, you'll feel it as sponginess that can be pumped up.
I'd throw some Syl-Glide (you can get it from NAPA) on those slider pins after you rebuild the calipers. Can't hurt to make sure they move smoothly. It can't be that loose a fit or you'd get a noise every time you put the brakes on.
I'll try pumping the pedal to see if it makes any difference in the travel. As to the pins, I'll certainly put on the Syl-Glide. I have that.
Pete. (l33t FS) said:
OE Moraine calipers (I think that is the term for these?) used rubber O-rings as bushings between the calipers and the pins. These lightweight calipers may not have those as an expedience for manufacture. They're circle track parts, people won't care if they are clattery
I don't think these are Moraine calipers. When I search on that, the results are 4-piston calipers. When I search on "GM III calipers", I get these single piston things. The Howe version of these is just a little beefier than the standard GM caliper from what I can tell and the holes for the guide pins are oversize. Howe also makes them so they are ambidextrous; which really just amounts to having a bleeder hole at each end so you can plug one and orient the other at the top. Apparently, this caliper design is one of the most popular on GM older vehicles. Hell, a reman'd caliper for, say, a '70 El Camino is between $25 and $37, depending on brand and finish.
I ordered a set of new o-rings, piston boots and guide pins to rebuild these. Ordered from Howe to make sure I got the right stuff.
