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Pad knock back


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#61 RLY240

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Posted 22 June 2017 - 05:51 PM

 

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.



#62 CBR Jeff

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Posted 22 June 2017 - 06:49 PM

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 by CBR Jeff, 22 June 2017 - 06:50 PM.


#63 Mike260LW

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Posted 03 July 2017 - 12:35 PM

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?



#64 RLY240

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Posted 03 July 2017 - 09:05 PM

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.....
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#65 Mike260LW

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Posted 05 July 2017 - 09:57 PM

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.

#66 dat2kman

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Posted 05 July 2017 - 10:04 PM

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.

#67 PeterAllen

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Posted 06 July 2017 - 05:22 AM

..., 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.



#68 dat2kman

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Posted 06 July 2017 - 09:57 AM

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.

#69 Mike260LW

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Posted 08 July 2017 - 03:21 PM

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

#70 RLY240

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Posted 16 July 2017 - 07:50 PM

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

 

 



#71 600Z

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Posted 16 July 2017 - 08:57 PM

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 by 600Z, 16 July 2017 - 09:41 PM.


#72 RLY240

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Posted 17 July 2017 - 11:20 AM

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.



#73 CBR Jeff

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Posted 17 July 2017 - 03:34 PM

Roger.

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

 

Jeff



#74 600Z

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Posted 17 July 2017 - 03:51 PM

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

#75 RLY240

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Posted 17 July 2017 - 04:40 PM

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.



#76 RLY240

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Posted 17 July 2017 - 04:42 PM


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.

Justin

 

I did, they tell me they have had no issues with the standard ones and the new sexy struts are just an upgrade.

Of course any flex could also be in the bearings but I've already got as much preload as I'm prepared to run.



#77 600Z

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Posted 17 July 2017 - 06:49 PM

Roger just another thought are you sure it's the front? And not rear axle defection causing it as it would be hard to know if it's the front or rear as I'd say your just sensing your pedal going further down?

Edited by 600Z, 17 July 2017 - 06:51 PM.


#78 600Z

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Posted 17 July 2017 - 07:56 PM

Interesting article also mentioning road surface and rear brakes causing it as well.

https://nasaspeed.ne...to-do-about-it/

#79 RLY240

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Posted 17 July 2017 - 08:20 PM

Sure, could be the rear, there doesn't appear to be any run out or end float in the rear and a quick pull on the hydraulic handbrake doesn't affect the pedal height which suggests the front. Effect is noticeable even warming the tyres on a warm up lap which isn't really worrying the rear tyres much.

#80 600Z

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Posted 17 July 2017 - 08:42 PM

Certainly sounding like it's in the front then




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