Pad knock back

[260DET]

Strange that my experience with having preloaded wheel bearings is being ignored, oh well , leading horses to water and all that.

[RLY240]

Strange that my experience with having preloaded wheel bearings is being ignored, oh well , leading horses to water and all that.

Adding the bearing spacer/stub sleeve is more or less the same thing, the bearing inners are effectively tied together so the only way to put more preload on the bearings would be to irreversibly shorten the spacer or remove it. I'm sure I'll give that a try at some point.

Appreciate your feedback.

[dat2kman]

Roger, if bearings "feel" loose, just take 1 thou off at a time, reassemble ( dry) and check, it may take a few dissassemble/reassembles!

[HKSZ]

Are you running a pedal box?

[Cozza]

Struts are already braced (TTT), stub stiffeners fitted, calliper piston return springs installed, alloy dogbone calliper mounts used.

 

I think Jason was referring to wedges welded in between the strut tube and back face of the hub.

I think I could see webbing in this location on the fancy TTT struts you posted earlier.

[Cozza]

Struts are free more or less but there's also the costs associated with swapping again (brakes, wheels, dampers, etc) that is a little confronting.

Yeah, I can understand that.

[RLY240]

Are you running a pedal box?

Yes.

[CBR Jeff]

No brake noise (apart form squeals on some compounds).  It's fine after a straight (and on the road) it's only after corner loads.  Same for cold or hot.

Can drive on the road for kms and not an issue, head out onto the track and a couple of heavy weaves on the out lap is enough to make the pedal drop. Not dangerously low but enough to dent your confidence especially at Mallala which is all brakes.

By comparison the long run up Mountain Straight at Bathurst didn't need a tap before a big brake at 180kmh+

 

Roger same left and right?

Do you have access to a dial gauge with magnetic base?

Sorry for the slow and inconsistent responses but I have been flat out.

If you have a dial gauge try the following, it might give you some indication as to the extent of the problem.

1. take the car for a drive and park it on level rough hard stand after. Its needs to be rough and solid enough so you can jack one side of the car up without the tyres slipping 

2. set the dial gauge up to measure the deflection between the break disk outer edge on the friction surface and the bottom of the strut roughly around the centre line of the axel. set the zero point on the gauge.

3. jack the car up so the side with the dial gauge is on the ground and the other side if off the ground (both wheels) get it up as high as you can. support the car so it wont fall on you. This should (sort of) simulate cornering loads.

4. check the dial gauge and measure the deflection.

5 repeat this process for the other side. don't forget to drive the car in between.

 

The other question I have is and sorry if you have answered this previously, What master cylinder are you running? It might be that a small amount of movement at the calliper with a large volume is translating to a larger than desirable movement in the master cylinder the return the fluid to the callipers and push the pads back. If the volumetric ratio between the master cylinder and the callipers is incorrect it will manifest itself in a miss match in movement at either end. Less noticed under ideal conditions like when the system is at hydraulic positive pressure (breaking). You could also check the (not sure how? maybe the Go pro) difference in fluid level in the front master cylinder at max and min and when the problem happens.

 

Jeff

Edited June 22, 2017 by CBR Jeff

[PeterAllen]

Update on this one, finally got some track days in and I'm happy to say that the knock back issue is solved and even survived a 35 degree day at Mallala today with two drivers and still no dropping pedal....

 

I have done two changes at once (bearing spacers and springs inside the front pistons) do I can't give a definitive answer as to which solved the problem...

 

I'm dragging up this old thread as the pad knock back has gradually got worse again and although not as bad as before it's still annoying enough to require a confidence tap on the straights before a big brake....

 

Doesn't this suggest it's a wear/tolerance issue rather than a design problem.

 

Might it be worthwhile revisiting the changes you made prior to 31st Oct 2014?

Edited June 22, 2017 by PeterAllen

[RLY240]

Doesn't this suggest it's a wear/tolerance issue rather than a design problem.

 

Might it be worthwhile revisiting the changes you made prior to 31st Oct 2014?

 

Or that the inherent problem (stub stiffness) is getting worse over time.  I'm in the process of rechecking the tolerances to compare to the original work. This really was all triggered this time by the release of the new fabricated TTT struts suggesting the standard ones (with bracing) still had room for improvement.

[RLY240]

 

The other question I have is and sorry if you have answered this previously, What master cylinder are you running? 

 

Jeff

 

Tilton twin masters with bias bar and no booster. For sure the effect would be lessened with a larger master on the front but I'd need to spend more time at the gym to be able to press the pedal.

 

There's a couple of things I will try now including removing the spacers and loading the bearings, and sticking a camera under the guard to get a better look, stuff I can try between track days.

 

The pedal at the moment isn't terrible just that it could be and used to be better.

[CBR Jeff]

Tilton twin masters with bias bar and no booster. For sure the effect would be lessened with a larger master on the front but I'd need to spend more time at the gym to be able to press the pedal.

 

There's a couple of things I will try now including removing the spacers and loading the bearings, and sticking a camera under the guard to get a better look, stuff I can try between track days.

 

The pedal at the moment isn't terrible just that it could be and used to be better.

 

It might be that you could spend less time at the Gym?

 

Jeff

Edited June 22, 2017 by CBR Jeff

[Mike260LW]

Sorry to drag this topic up again but we are running the same Willwood brake setup with Tilton pedal box and no vacuum boost assistance. I ran this set up for the first time at the HRCC Autumn Historic's meeting in May but with brand-new pads with plenty of meat on them and didn't really experience any issues. Ran again this weekend and experience exactly the same symptoms of pad knockoff. We are running the larger diameter 260 Z struts and coil over configuration but are obviously experiencing stub axle flexing. I was wondering how you are progressing with a solution to the problem?

[RLY240]

Hi Mike, the bearing spacer and piston return springs certainly helped but the effect is still there. I'm going to stick a camera up there for the next meeting and see if I can get some evidence of flex before making the next move. The TTT fabricated struts look very nice but are a bit of a budget breaker at the moment and tapping the pedal is free.....

[Mike260LW]

Thanks for the update. I think we will follow suit and go the bearing spacers and return springs. If that doesn't cure it we may pursue gusseting the foot of the strut. It's fine on a track where there are known straights to give it a confidence tap but I can't see it working on a Tarmac Rally stage. Heal and towing becomes a bit hit and miss with a long travel pedal. Mike.

[dat2kman]

Mike, as I said above, bearing spacer/support, as well as the wedges welded in between strut tube and rear of calioer mount/stub bracket. Ken Graham does this.

You'll still get some travel, i think it is just the nature of what you are working with

 

The big AP calioers on the 120Y and the Mazda Sports Sedan, all have thin coil type springs between piston and back of pad, they work well, pads are a higher temp range, on both cars.

[PeterAllen]

..., all have thin coil type springs between piston and back of pad, they work well, pads are a higher temp range, on both cars.

 

 You've lost me there? Wouldn't that induce free pedal travel whilst the spring is compressed, exactly the issue trying to be cured?

 

Sounds like the springs are there to maintain temp in the pads not eliminate free-play.

[dat2kman]

AP Racing use a thin wire coil spring sitting inside the caliper hole, with piston then inserted,

Ie the spring is imersed in brake fluid.

Spring, uncompressed is around 2" in length, once installed it gets compressed to approx 1/4"

4 per caliper

Due to pads being forced against rotor, via springs, the pads have higher heat ranges

Is a correct explanation. Last time I rebuilt them, was seven years ago.

[Mike260LW]

Wilwood's technical " trouble shooting" page talks about installing a 2 lb residual pressure valve in the line. Anyone tried this approach?

[RLY240]

Stuck a camera under the front guard at Mallala today, video is unfortunately inconclusive.  In some corners it looks like the strut-to-wheel gap changes but because the angle changes during steering it makes it very hard to judge.

What it does tell me is that as suspected there isn't enough travel in the shocks before the bump stops are reached, I don run long stops but clearly this could use an inch shorter strut. Another project.

Roger

 

 

[600Z]

Have you thought that it's the wheel it's self flexing and not so much the stub axle?

 

Could the wheel be flexing more then the stub as if it's the stub then bloody hell there a problem if it's flexing that much....... and I'm not saying that they don't flex as everything does to a degree.

 

Anyway just my 2 cents and why wheels aren't wheels and they make forged ones etc. There's alloy and then there's alloy.

 

I have done a lot of 4wding over the years and had extreme knock back but from a different source, shockies, road surface, tyre pressure all acting on the brake pads themselves causing them to bounce or vibrate due to the weight of them and in turn pushing the pistons back in.

 

Does it's seam worse the longer between braking...... if so them look at that because if it does then it's something else rather then flex which should be pretty much a constant deflection I would have thought as you can only corner so hard.

 

Could be worth trying some half worn pads as they are lighter and see if there is any difference.

 

Justin

Edited July 16, 2017 by 600Z

[RLY240]

Hi Justin, sure the wheels may flex but that wont make the calipers deflect compared to the rotors.

As discussed before there is no issue on the straight or even while cornering on the street, only when loaded up during cornering on the track and to a lesser extent during a rally.

The knock back actually gets worse when the pads wear as there is more travel in the pistons.

I resurected this thread recently because TTT now offer a fabricated chromolly stub strut which they wouldn't need to do if the 40 year old standard ones weren't causing some issues.

[CBR Jeff]

Roger.

Did you try jacking the car up and measuring the deflection so you can quantify (or attempt to) the problem?

 

Jeff

[600Z]

Hi Roger,

 

I totally agree I guess I should have made my comments a bit more separated as with the wheel flex I was more referring to it hitting the time rid end and yes no doubt a combination.

 

The TTT struts look very good and I'm sure they would stop the axle flex but it's a costly exercise if it doesn't fix the knock back issue with the brakes.

 

Have you asked TTT why they produced them apart from the obvious but was it to combat camber due the strut flexing or the axle flexing, no doubt both but the axle to where the caliper brackets are is very close so your talking about a lot of flex there I'd think to give much knock back. Harsh bumps put more stresses on the axle etc then cornering I'd think.

 

Maybe get a couple of dial indicators and set them up on your suspension e.g. from caliper mounting to disc and strut to disc then use a winch to pull your car sideways to try and simulate a corner, even chick the front wheel some how or in a shallow gutter so you can really load it up.

 

Might find something and be worth a try before spending that amount on those sexy struts though they are nice lol

 

Justin

[RLY240]

Roger.

Did you try jacking the car up and measuring the deflection so you can quantify (or attempt to) the problem?

 

Jeff

 

no visual deflection.