JPSC Forum

Hi,

My front brakes have been dragging a bit for some time now, so after a blast out on Saturday when I was able to stop on a hill without the handbrake, I though it best to get them off...

The pads have worn very unevenly top to bottom, with the piston travel massively different between pistons. There was about 5mm difference between the upper and lower piston, hence the uneven wear on the pads. I had hoped a clean up would allow me to put them back together, but the pads are unusable, despite having over 50% left on them. I suppose the uneven travel puts the pad at an angle, hence it dragging.

I know that Hi Spec brakes have some fans and some detractors, but when I took the caliper apart and saw how the whole thing works I was a bit surprised. The holes that allow the fluid from one half of the caliper to the other, and from one piston to the other, are tiny, say 2-3mm. I understand that the pressures in there will be high, and so the fluid will travel around easily, but it still looked a bit restrictive.

The pistons, bores and seals all were in good condition, so I cleaned everything up and reassembled. However, before I go and spend £60 on some new Mintex 1144 pads, I was interested to hear of other's experience, either with Hi Spec or Wilwood front brakes. The uneven piston travel seems wrong, and I'm not sure how I could prevent it in future. I don't fancy destroying another set of otherwise usable (and expensive) pads if it's likely to happen again.

Any thoughts or advice appreciated.

Thanks, Ian

Hi Ian

I had similar issue with my Hi-Specs when I first fitted them, & I know of at least another set that gave problems too.
Mine are the 4 pot, escort lug replacements, not sure if that makes them "Ultralites".

I fitted it all up & when driven the car pulled violently to one side under braking & reacted to road surface camber.

Basically, on closer inspection the problem I had was that the supplied union on the end of the brake flexi (from the brake lines) was too long.
When screwed in & done up, with new pads, the end of the thread acted onto the back of the lower piston, pushing it onto the disc.

Seems similar to what you have ?

Anyway.... changing to a 90' banjo fitting & using copper washers I was able to cure the problem.
Still wasn't perfect, but as friction material was taken away, the additional space gave the piston more room & the pedal feel is much better.

I'm halfway through the second set of pads, & they're fine, even on the odd trackday.
Overall, Quite happy with them now, but have not actually driven a car with Wilwoods.

Matt

Ian Kelly wrote:The pads have worn very unevenly top to bottom, with the piston travel massively different between pistons. There was about 5mm difference between the upper and lower piston, hence the uneven wear on the pads. I had hoped a clean up would allow me to put them back together, but the pads are unusable, despite having over 50% left on them. I suppose the uneven travel puts the pad at an angle, hence it dragging.

In my experience of HiSpec Ultralites that's a design feature, it happens all the time.

Ian Kelly wrote:I know that Hi Spec brakes have some fans and some detractors, but when I took the caliper apart and saw how the whole thing works I was a bit surprised. The holes that allow the fluid from one half of the caliper to the other, and from one piston to the other, are tiny, say 2-3mm. I understand that the pressures in there will be high, and so the fluid will travel around easily, but it still looked a bit restrictive.

That isn't an issue. When a disc brake is working properly there's essentially no fluid travelling anywhere. When you're not braking the pads are still essentially in contact with the disc; all that happens when you hit the pedal is that you increase the pressure on the disc, nothing moves (much). Hence, you don't need any significant size bore to things like the fluid linking holes between the two parts of the caliper. If you've got disc run out so that you get pad knock off (the pads being pushed away from the disc) then it's truly horrible as all of a sudden you do have to move the pads. Trust me, if you are moving the pads more than a gnat's scrotum thickness, you'd know about it.

So, why do the Hispecs do this? My personal hypothesis is that the calipers are just not sufficiently sturdy and they flex in use. That would certainly explain the uneven wear which is common to all the Ultralites that I've looked at. It would also explain why the brake feel, in my experience, is so completely lacking with these brakes. I found that when I was racing with these the only way I could tell that the brakes had locked was because the world stopped slowing down, I couldn't tell through the pedal at all. I ended up in quite a few gravel traps as a consequence. All of this might also explain why I was going through pads so quickly, I was using up a set of 1155s every three races or so, although due to the uneven wear there was still lots of pad material on the pads I threw away.

Since I converted to Wilwoods and filed the HiSpecs in the bin things are much better. I can feel what the brakes are doing, a set of pads lasts most of a season, the bleed nipples don't seize in the calipers all the time and when I phone the suppliers they talk to me and actually do what they say they're going to do, quite a novel situation...

(As you can tell, I wasn't a happy customer. Your experience might, of course, be better.)

Tim

Thanks so far chaps,

Matt - I have the 90 degree fitting, so no issues with it hitting the piston.

Tim - I have to agree about the pedal feel, it's pretty wooden which has always been a bit dissapointing from the car.

I was wary about changing over to Wilwoods, as the powerlite calipers look fairly cheap at c£90. Or, if they do the job well, then they are something of a bargain!

Just popped out and got some new pads for the hi spec's, now they're all cleaned up I'll give them a try and I'll just have to keep an eye on them. It wasn't a big job to strip them down and clean them up anyway.

Any more experience of hi specs, wilwoods, or others would be interesting.

Thanks,

Ian

Ian Kelly wrote:Tim - I have to agree about the pedal feel, it's pretty wooden which has always been a bit dissapointing from the car.

I was wary about changing over to Wilwoods, as the powerlite calipers look fairly cheap at c£90. Or, if they do the job well, then they are something of a bargain!

My experience of the Wilwoods has been hugely positive and they are indeed a bargain. So much so that for the Spectre build I've already bought some Powerlites for all four corners, just as my Fury has. They are, in my opinion, a vastly higher quality product than the HiSpec. For example, the bleed nipples (which sieze on the HiSpecs because the steel nipples seizes in the aluminium body, I ruined two calipers that way) run in a steel bush on the Wilwoods so that you don't get this problem. The pads wear, certainly in my race car, exactly square and I can actually feel what's going on. As I said, I suspect this is because the Wilwoods (which use a forged body) are dimensionally stable.

T

Not had any compaints about my Wilwoods...well once I got rid of the Wilwood SmartPads and put in 1144's.

Is your thinking that the binding was the pads jamming (cocked over) in the caliper? Or was the wear/binding because one piston was sticking out?

Ant more thoughts on the suspention... better/worse?

adrian

Hi Adrian,

Suspension wise, I've not driven the car since Saturday, it's currently got no pads in it so am hoping to sort it tomorrow and get out tomorrow night.

Brakes - I think the pistons being forced out at different levels must make it more difficult for the pads to fully retract. I'm toyng with the idea of getting rid of the whole lot, but it will have to wait till funds allow.

Ian

hi Ian. were all the pistons free in the caliper when you started to take them apart or were the pistons which were against the unworn part of the pad tight? .m.