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Gtir Motorsport club » Tech room » Help and Advice » Problem with brakes

Problem with brakes

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1 Problem with brakes on 24th July 2014, 5:46 am

sunnygtir

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In search of a stronger braking power I have replaced standard front brakes with a 4 pot 286mm K-Sport kit and completely replaced the brake oil

But I still have the same problem I had before! The first 1/3 or even half of the pedal is not braking at all!
If I press it immediately after it's working properly and start to brake also in the first part of the pedal...

What could it be? I don't think air in the system because it was completely cleaned-up

2 Re: Problem with brakes on 24th July 2014, 7:43 pm

johnny gtir

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moderator
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weak master cylinder ? air leak as the vacume effects them. air can be awkward to bleed out you bled oppersits front to rear ?

3 Re: Problem with brakes on 24th July 2014, 8:24 pm

nomad

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Totally agree could be weak master cylinder .... or vac leak on servo .... or could just be air in the system ....


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4 Re: Problem with brakes on 11th August 2014, 8:35 am

sunnygtir

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Checked and there's no air in the system...

I have also noticed that this happen only after a few corners (usually strong corners) that the pedal has no braking power for the first 1/3 of the pedal

Next pressures of pedal are working fine till next few strong corners! If I'm driving straight no problem at all...

I have spoken with a mechanic and he told me that this happen because when you are turning the brake pots are slightly pushed back from the brake disc

This happen also with standard system but because it is 1 pot only the problem is less notable, with 4 pots the problem is more relevant!

This is something you already noticed too? Any solution?

5 Re: Problem with brakes on 11th August 2014, 6:38 pm

johnny gtir

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don't agree with that personally hows the pots further back as caliper moves with disc

6 Re: Problem with brakes on 11th August 2014, 7:06 pm

Guest


Guest
you sure that its not just a caliper sticking?

7 Re: Problem with brakes on 11th August 2014, 7:19 pm

nomad

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Yep i disagree with that too i understand there is a certain amount of flex between parts but if thats the case you would surely be constantly pushing air from the reseviour ....


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8 Re: Problem with brakes on 11th August 2014, 8:55 pm

nomad

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I do believe gaz had the same problem wich turned out to be internaly seized rear calipers ...


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9 Re: Problem with brakes on 12th August 2014, 12:29 am

Gaz GTiR

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nomad wrote:I do believe gaz had the same problem wich turned out to be internaly seized rear calipers ...

Yep 5 years ive had my problem... Thought it was standard front calipers at first so bought some wilwoods & still the same.. So i Tried 3 mastercylenders, 2 servos, Braided lines & 20,6734655867 times of bleeding  Rolling Eyes  Never sorted the issue...

Then I moved house & found a Evo speacialist just down the road & got talking to him... I explained the issue & he said he would take a look & at first he said mastercylender is fooked so I bought a new 1 instead of keep trying 2nd hand ones. Anyway still didn't solve the issue.
He scratched his head & rememberd that when he used to work for VW before he started his own Buisness in tuning Evo's that VW used to suffer from the same problem.

It turns out it was the back calipers & he got a lump hamer & twatted each rear caliper on the side about 10 times (good hard hits) He put the wheels back on & told me to go try it... Guess what I had a good pedal feel & my brakes worked & locked up  cheers 

Apparently on the VW's he worked on, if the handbrake cable was adjusted in the wrong way over the years the pistons in the calipers don't wind themselves back in & settle in the wrong place... So he said over the years & with our cars being over 20 years old then its probably the same issue.

So all I can say is try giving each REAR caliper a good smack with a lump hammer 10 times & see if it works Smile Did for me after 5 years of having no f**king brakes & I was ready for giving up & selling it at this point aswell... And that's all it was  Rolling Eyes  Glad he knew what my issue was or id still be sat hear scratching my head... Or without a GTiR  Shocked 

10 Re: Problem with brakes on 12th August 2014, 6:03 am

sunnygtir

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Thank you all for the answers!

OEM Front Brakes worked well (not enough braking power but worked properly) since a put K-Sport 4 pots kit so I don't thing it's the master cylinder

robd wrote:you sure that its not just a caliper sticking?

What you mean robd? Pads are sticking a bit but I think this is normal because they are new, right?

Any other ideas?

11 Re: Problem with brakes on 12th August 2014, 6:24 am

Guest


Guest
I meant with it sticking more or less what gaz said
As said the cars are 20 years old how many people out there have ever got the calipers overhauled or changed the brake fluid

12 Re: Problem with brakes on 12th August 2014, 7:31 am

sunnygtir

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I have brand new Front brakes (K-Sport 4 pot), overhauled OEM Calibers on Back + new Pads, new Stainless Steel brakes line Front/Back and completely replaced the brake fluid

All this stuff was already done and I had no problem till I replaced the Front brakes with K-Sport kit

This is why I'm thinking the problem is related to them

13 Re: Problem with brakes on 12th August 2014, 8:07 am

ducie54

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Also check the condition of the wheel bearings. This is something that gets over looked.

14 Re: Problem with brakes on 12th August 2014, 6:19 pm

Gaz GTiR

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If the rear calipers arnt working as they should then they will effect your front brakes... Dousnt matter if there brand new on the front or not!

Like I say try what ive explained

15 Re: Problem with brakes on 12th August 2014, 9:29 pm

GTI-R US

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Management
Management
ducie54 wrote:Also check the condition of the wheel bearings. This is something that gets over looked.

^^^
What he said
Check anything that's allowing wheel to move including track rod end and lower ball joint as all will affect brakes whilst cornering and even more so with larger discs and 4 pots
You just wouldn't have noticed it so much on stock calipers as the rotational mass is smaller

http://www.gti-r-us.co.uk www.force500.com

16 Re: Problem with brakes on 6th December 2014, 7:34 pm

Mr B

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gtir technician
gtir technician
Knock Off
Some good points here but original comment by the mechanic is a valid area to be looked at given the specific symptoms by OP.
Wear in the wheel bearing could allow enough float to allow disc push against pad thus pushing pistons back a little.
This is known as Knock Off or Knock Back .
Just having a pad knocked back 2mm can cause exact pedal symptom as OP describing
On fixed caliper (2pot 4pot 6pot etc) the cailiper is fix solid to the hub knuckle, The disk is on the hub spindle & wear here in terms of bearing & spindle tolerances can cause excessive disc movement to create Knock Off.
See this a lot on rally cars, even with perfect hubs/bearings as loads they get subjected to in rough stages actually flex the spindle & bearing assembly.
problems with disc alone can cause mild Knock Off from run out caused by temporary warping causing runout & knocking pads back.
Original R style floating caliper & the evo style floating 2 pots don't suffer so much from knock off due to the floating design of caliper on slides as it can move too along with disc float/runout (part of reason they picked for evo 123 etc).
Expensive real race brakes have a lot of design in caliperpiston & discs are floating as helps prevent knock off & disc warpage damage.
Certainly think OP needs test hub float with dial guage especially as seems only be after heaving cornering.
Gaz point or rears calipers is worth looking at too where pedal fault almost constant as all cars that use the same self adjusting system screw piston for the handbrake mechanism can cause pads sit too far off disc giving you that wasted pedal travel & awful weak feeling brakes.
Most people fitting new upgrade front brakes should be including possible quality rebuilt rears as at 20 to 25 years old they well past best & holding your braking potential back.

17 Re: Problem with brakes on 6th December 2014, 7:41 pm

toaster55

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i had same problem as gaz, brakes were total dogshit! had the rears completly overhauled by biggred and theyre completly better, you wouldnt believe, stops 10 times better than before

18 Re: Problem with brakes on 6th December 2014, 8:02 pm

Gaz GTiR

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toaster55 wrote:i had same problem as gaz, brakes were total dogshit! had the rears completly overhauled by biggred and theyre completly better, you wouldnt believe, stops 10 times better than before

Yeh amaizing how it worked... 5 years of ownership I had to be so carefull with stopping the thing

19 Re: Problem with brakes on 6th December 2014, 8:05 pm

Mr B

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gtir technician
gtir technician
I can believe it toaster.
the rear calipers with handbrake mechanism on the main piston are a cock when new, 20+ years down the road they even bigger cock.
Anyone spending big money on front upgrade should be looking at quality recon rear calipers at the least ... people with constant poor brakes should for sure inspecting rears for this known fault.
OPs fault due to details given sounds typical Knock-off symptom as my previous post implies so he needs check hub spindle & disc float under load.

20 Re: Problem with brakes on 8th December 2014, 6:53 am

gtirnick


its also possible the front pistons are just plain so big the 15/16 can't keep up.

i replaced my master to a 1inch master and the pedal travel shortened to what i liked.

21 Re: Problem with brakes on 8th December 2014, 8:53 am

Mr B

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gtir technician
gtir technician
With OP's symptoms it not sound like hydraulic ratio mismatch due to fact his issue not constant & many use that brake kit on standard cylinder ok.
Would agree though that the bigger 25.4mm cylinders such as ADN15127 is good upgrade route for big fluid displacing multi-pots .

22 Re: Problem with brakes on 8th December 2014, 5:41 pm

Supernova


Gaz GTiR wrote:
nomad wrote:I do believe gaz had the same problem wich turned out to be internaly seized rear calipers ...

Yep 5 years ive had my problem... Thought it was standard front calipers at first so bought some wilwoods & still the same.. So i Tried 3 mastercylenders, 2 servos, Braided lines & 20,6734655867 times of bleeding  Rolling Eyes  Never sorted the issue...

Then I moved house & found a Evo speacialist just down the road & got talking to him... I explained the issue & he said he would take a look & at first he said mastercylender is fooked so I bought a new 1 instead of keep trying 2nd hand ones. Anyway still didn't solve the issue.
He scratched his head & rememberd that when he used to work for VW before he started his own Buisness in tuning Evo's that VW used to suffer from the same problem.

It turns out it was the back calipers & he got a lump hamer & twatted each rear caliper on the side about 10 times (good hard hits) He put the wheels back on & told me to go try it... Guess what I had a good pedal feel & my brakes worked & locked up  cheers 

Apparently on the VW's he worked on, if the handbrake cable was adjusted in the wrong way over the years the pistons in the calipers don't wind themselves back in & settle in the wrong place... So he said over the years & with our cars being over 20 years old then its probably the same issue.

So all I can say is try giving each REAR caliper a good smack with a lump hammer 10 times & see if it works Smile Did for me after 5 years of having no f**king brakes & I was ready for giving up & selling it at this point aswell... And that's all it was  Rolling Eyes  Glad he knew what my issue was or id still be sat hear scratching my head... Or without a GTiR  Shocked 

Yep early golf calipers mainly mk2 golf calipers were prone to seizing due to what they were made from. It was popular to uprade them to mk 4 rear calipers due to them being made from aluminium.

23 Re: Problem with brakes on 13th December 2014, 6:17 am

splmum

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Mr B wrote:With OP's symptoms it not sound like hydraulic ratio mismatch due to fact his issue not constant & many use that brake kit on standard cylinder ok.
Would agree though that the bigger 25.4mm cylinders such as ADN15127 is good upgrade route for big fluid displacing multi-pots .

Does this upgrade brake master cylinder ADN15127 fit with ABS brakes?

24 Re: Problem with brakes on 13th December 2014, 4:56 pm

Bones

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the two star club
the two star club
How much was it to have your rears re built toaser ?

25 Re: Problem with brakes on 13th December 2014, 5:59 pm

Mr B

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gtir technician
gtir technician
^ @Bones . http://www.gtir-motorsport-club.com/t3078-brake-caliper-rebuilds?highlight=caliper
Has a nice pic too, something for you to dream about while on your sofa.

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