Pad knock back

[d3c0y]

Pretty sure they arent road legal in any state.

[44014]

Interesting that the ACT Govt RTA and local engineer have not accepted wilwoods on modified cars, because the lack of seal breaches the national guidelines for vehicle modifications, Ive read the sentence. 

We have the strictest RTA staff in the world down here !

Has nothing to do with the dust seals.

Notice how everyone complains about the lines and nipples leaking?

They use gas threads not banjo bolt or double flared brake lines like on our z.

And talk to anyone that is serious about brakes and they will tell you how much the wilwoods flex over a good pair

Of AP or Alcons.

[PeterAllen]

While the dust seals have nothing to do with pad knockback I'll just make this note.

 

The requirement for dust seals is stated in vsb14, however, vsb14 is a guideline in NSW and not the law. If you comply with vsb14 you are "deemed to comply" with the ADR. You can comply with the ADR without compiling with vsb14.

 

My engineer is a Canberrian and has approved my Wilwoods.

 

Now back to pad knockback.

[RLY240]

So I fitted my bearing spacers on the weekend, the setup of the spacers is a little time consuming as the assembly needs to be installed in the hub and the play measured then accurately mount the spacer in the lathe to zero the run-out then machine some off and trial fit.

Repeat.

About 6 or 7 times to creep up on the correct tolerance.

Probably took about three hours using a spare spindle on the bench plus the time spent removing hubs from the car cleaning etc and then repacking and assembly. The most time consuming part is clocking in the lathe to zero the run-out.

Unfortunately a quick run on the road suggests that the problem isn't fixed and there is still knock back but wont know the full extent until the next track day as you can't experience track loads on the street.

Next step is to install the piston return springs in the calipers and see if that helps.

[dat2kman]

An advice,

When machining in a lathe the spacer tubes, take off  a few thou at a time.

 

Did you find this the case?

I have done this using a hub and spindle with a set of dry bearings on a work bench, got it spot on, only to discover the hub/bearings/spindle on the car were ever so slightly different.

Can only put that down to machining tolerance variations at factory, or, different manufacturer bearings, where the shells are slightly different widths, add all the variations, compared to the test fit unit on the workbench, there were differences.

Talking a number of thou, approx6-10.

[RLY240]

An advice,

When machining in a lathe the spacer tubes, take off  a few thou at a time.

 

Did you find this the case?

I have done this using a hub and spindle with a set of dry bearings on a work bench, got it spot on, only to discover the hub/bearings/spindle on the car were ever so slightly different.

Can only put that down to machining tolerance variations at factory, or, different manufacturer bearings, where the shells are slightly different widths, add all the variations, compared to the test fit unit on the workbench, there were differences.

Talking a number of thou, approx6-10.

 

Yes, I used the hubs and bearings from the car (after cleaning the grease and lightly oiling the bearings) and a spare strut.  The spacers need to be matched to the hub/bearing combination and can't be switched around. Label everything.  New bearings in future may require a repeat of the process.

We ended up with more than a few thou difference left to right (more like 15 thou) and as we got close to the end we are taking .002 each pass.

The spacers were about 3mm (120 thou) longer than required so basically went 100, then 10, then 5 then 2 then 2 then 2 until we got to the tolerance/preload we were looking for. Have to take your time with this as you can't add that .002 back on if you go to far.

The instructions suggested to get the slightest drag and then remove another .001-.003 off for preload.

The preload of the oiled bearings on the bench was very close to the preload once greased and fitted to the car, aimed for about 1kg drag force when measured from a wheel stud.

 

I wasn't convinced this process would yield results as I feel the issue lies in the calipers somehow but it's all part of the process.

During this work we also determined that the LHS hub face was not true (looked like some impact damage from an FB hammer) that I hadn't noticed before as only just started using these hubs.  Not related to the current problem but nice to pick it up before it caused a loose wheel or worse. Getting this trued up along with clocking the rotors for run-out.

Roger

 

[PeterAllen]

Roger, are you using the 4 spot or 6 spot front callipers?

[RLY240]

Roger, are you using the 4 spot or 6 spot front callipers?

SL6 six piston front and 4 piston rear. AP J hook rotors and the AZC mounting hardware.

I'm actually very happy with the AZC package for the price, just need to resolve this issue to make me happier.  On the road this really isn't a problem that comes up and I know others with the same parts as me going quicker on the track and not experiencing the knock back.

Roger

 

[PeterAllen]

I wonder if it might be worth trying to stiffen the mounting arrangement by replicating the AZC red bracket so that another bracket attaches to the other side of the calliper lugs.

 

You would need to drill an extra hole in the new bracket to access the bolt securing the original bracket to the stub axle (or simply tighten that first) and a spacer (the thickness of the Wilwood lugs) for the upper mounting lug. If there is twist in the original AZC bracket a second bracket may assist rigidity.

 

Mine are 4 spot and there doesn't appear to be any meat left to use larger bolts to tie the two halves of the callipers together and any outside strengthening brace would run into wheel rim clearance issue.

 

Just some thoughts.

[RLY240]

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.

Unfortunately 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.

Either way I'm happy it's fixed and would recommend both to anyone experiencing this problem.

Thanks as always for your feedback and suggestions.

Roger

[RLY240]

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.

The bearing spacers are still in place and don't seem to have lost their tolerance and there are no other changes to the system to explain the faults.  Have even used temperature paint on the rotors and f.expensive brake fluid to confirm that it's definitely not an over temp fluid problem.

 

To recap, under racing conditions the brake pedal drops after cornering (not after braking) such than even weaving on the warm up lap is enough to make the pedal drop.

 

I'm now convinced that the issue is in flex or movement of the spindle compared to the strut making the rotor push the pads and pistons back into the calliper.  If I'm right then the only recourse is to stop this flex somehow.  I've recently noticed that TTT now offer a fully fabricated front strut in CrMo which would presumably be stiffer than the 50 year old cast iron ones.

 

https://technotoytuning.com/nissan/240z/evolved-front-coilover-conversion-datsun-240z-260z-and-280z

 

Anyone got any insight into this issue?

Roger

[260DET]

Are you sure that the wheel bearings have no loosened off a bit? With my S30 I used to give the wheel bearings a touch of preload, at the time using Slick 50 grease which is not available now so I'm looking for a substitute for the project car, the factory adjustment is too loose for a race cars and tapered roller bearings are commonly preloaded in diffs, etc. Never had any knock off or bearing problems.

[Cozza]

Just out of interest have you tried rebuilding the calipers, replacing seals?

Those TTT struts are sexy. Considering they are made to order, any idea if you could have alternative caliper ear mounts instead of the standard locations?

Edited June 20, 2017 by Cozza

[dat2kman]

I'd like to see someone prove this works before I'd go down this path.I have wielded in a gusset, triangular pice of steel in between the strut tube and stub axel to stop flexing.

Before fitting, the tie rod end was 5mm from rim lip on inside.

A few hard laps, and rim lip had gouges, and tie rod end had alloy build up.

After fitting stub bearing spacers, and the plateing between caliper mout bracket and strut tube.

No more 5mm foexing of the rim lip onto stub.

Yes it works.

Also have fitted same to the Sports 2000 stubs, as old original stubs, one had snapped, other had hairline crack forming.

They flex

[RLY240]

Before fitting, the tie rod end was 5mm from rim lip on inside.

A few hard laps, and rim lip had gouges, and tie rod end had alloy build up.

After fitting stub bearing spacers, and the plateing between caliper mout bracket and strut tube.

No more 5mm foexing of the rim lip onto stub.

Yes it works.

Also have fitted same to the Sports 2000 stubs, as old original stubs, one had snapped, other had hairline crack forming.

They flex

Any difference between the 240 and 260 hub in this department? Looking at them it's hard to imagine and flexing within the hub but Nissan must have changed them for a reason. Edited June 20, 2017 by RLY240

[RLY240]

Just out of interest have you tried rebuilding the calipers, replacing seals?

Those TTT struts are sexy. Considering they are made to order, any idea if you could have alternative caliper ear mounts instead of the standard locations?

Not yet but it's on the list. TTT do some custom stuff so you could certainly ask them.

[CBR Jeff]

Do you have anti-knockback springs fitted to the callipers?

 

Jeff

[Cozza]

It might be worth rebuilding to see what's inside, check the seals and the anti knock back spring you installed.

Maybe this is getting a little off topic and not the direction you're interested in but...

Are you restricted to the z strut? I ask because if you were to go to a later model strut like Skyline. You would be able to use the skyline brakes with no dog bone brackets etc. and OEM brakes instead of Willwoods, which don't seem to get a great review by reading this thread.

[RLY240]

Do you have anti-knockback springs fitted to the callipers?

 

Jeff

 

yes.

[RLY240]

It might be worth rebuilding to see what's inside, check the seals and the anti knock back spring you installed.

Maybe this is getting a little off topic and not the direction you're interested in but...

Are you restricted to the z strut? I ask because if you were to go to a later model strut like Skyline. You would be able to use the skyline brakes with no dog bone brackets etc. and OEM brakes instead of Willwoods, which don't seem to get a great review by reading this thread.

 

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.

[dat2kman]

Due to the geometry of the later R31/32/33/34 Skyline, and Z31/32/33

The angles of stub to strut are somewhat different, along with wheel offsets ( these later cars used greater positive offset wheelrims)

They can be used but require alteration to LCA's, tie rod lengths, and compression strut.

Which end up giving you further headaches trying to then get bump steer, alignment etc, and grwater pissibility of turn/toe in-out, on bump and droop.

 

The closest one could be the strut/knuckle assy from the S13 Sylvia.

The S14 Sylvia gets "worse" for use on a S30 chassis.

 

Dogbones, wedged and braced struts, and bearing/stub support tubes, will be easier!

[RLY240]

Dogbones, wedged and braced struts, and bearing/stub support tubes, will be easier!

 

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

 

Going to add a camera or tell tale device to actually see what's happening at the next event.

Or just put up with the confidence tap.

[CBR Jeff]

Roger are the brakes noisy? And is it the same every time you apply the breaks or is it worse at the end of the longer strait? ie does it get worse the bigger gap between stops?

 

Jeff.

[RLY240]

Roger are the brakes noisy? And is it the same every time you apply the breaks or is it worse at the end of the longer strait? ie does it get worse the bigger gap between stops?

 

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+

[dat2kman]

In the Gp S car, always had to give pedal a double tap, if not, pedal travel was always further.

Discs had no runout, heat buildup was an issue.

This was after the stiffening was done.it had a crap pedal beforehand though.

The stiffening greatly helped cornering.

The flexing, i put it down to, the strut tube to lowercast steel bottom assy joint.