340mm caliper problems

[H13XJT]

Hi all, I have a 2016 T32 that only came with the 308mm discs. I have upgraded to the 340mm calipers, all new disks, pads, lines, pins etc. but having issues.

At first then calipers caught on my Modular Steels so I took them off and fitted Devonports to clear.

Now the issue lies with pedal feel and bleeding. Had them in yesterday to be rebled by a different garage, I still don't get any pedal feel on the first press. Foot goes almost flat to the floor and bites HARD right at the end. But as soon as I release the pedal and press again I get a lovely solid bite and hardly any pedal travel.

The mechanic at ATS who have rebled said he's flushed them through and got air bubbles out but the pedals still the same. It's a bit of a concern as I can't really perform a heavy braking straight away so even pulling up to traffic lights can be a bit sketchy.

Any advice? The mechanic said it could potentially have had the seals flipped in the master cylinder but I'm unsure what symptoms that could cause

 

[Nutexa Frictions]

As your based in Nottinghamshire, I'd recommended a trip to @Dav-Tec and get him to look over them.

 

[Pauly]

Whats with the uneven marks on the disc
Looks like only part of the pad is contacting the disc ?

 

[H13XJT]

Whats with the uneven marks on the disc
Looks like only part of the pad is contacting the disc ?

That was after just a short drive home. I've only driven the vehicle half a mile and used the handbrake at that

 

[Pauly]

Still cleaning off the coating then

 

[H13XJT]

Still cleaning off the coating then

Yes buddy

 

[Pauly]

I did a similar job to you and upgraded my van when it was still quite new and had a similar experience, the pedal stayed a bit spongey initially and i ended up bleeding a couple times in between driving it and it sorted it out, i used brembo calipers though so not sure if that makes a difference ?

 

[phazer]

That picture looks like uneven piston pushing but perhaps just limited usage. How tight is the caliper to the carrier, will it wiggle much if you try? I had issues with the clips on mine being the wrong shape and had to bend them using a picture of OEM as a reference, they then held everything properly.

Sorry for asking this but I've seen it soooo many times over the years.....are your calipers on the right way around? Bleed valve at the top?

Once you get it bled correctly it's worth making the coding change on the ABS unit as that does affect pedal feel (not the cause of your issue) and ensures the braking is correct for the size etc. I posted the programming in another thread recently.

 

[H13XJT]

That picture looks like uneven piston pushing but perhaps just limited usage. How tight is the caliper to the carrier, will it wiggle much if you try? I had issues with the clips on mine being the wrong shape and had to bend them using a picture of OEM as a reference, they then held everything properly.

Sorry for asking this but I've seen it soooo many times over the years.....are your calipers on the right way around? Bleed valve at the top?

Once you get it bled correctly it's worth making the coding change on the ABS unit as that does affect pedal feel (not the cause of your issue) and ensures the braking is correct for the size etc. I posted the programming in another thread recently.

Hi buddy, thanks for the comment. This was literally from the garage test driving and then me driving it the 0.6mile back from the garage using the handbrake.

I will get it jacked up tomorrow and check the calipers are on the correct sides and check all the mountings are secure.

And by the clips do you mean the spring retainers?

I'll definitely have a look at the coding change. Is this with VCDS or do I need something else?

 

[H13XJT]

That picture looks like uneven piston pushing but perhaps just limited usage. How tight is the caliper to the carrier, will it wiggle much if you try? I had issues with the clips on mine being the wrong shape and had to bend them using a picture of OEM as a reference, they then held everything properly.

Sorry for asking this but I've seen it soooo many times over the years.....are your calipers on the right way around? Bleed valve at the top?

Once you get it bled correctly it's worth making the coding change on the ABS unit as that does affect pedal feel (not the cause of your issue) and ensures the braking is correct for the size etc. I posted the programming in another thread recently.

If you could post the link to that thread I'd appreciate it though fella

 

[Anakin]

As you get a good pedal on the second push, you still have air in the system. As you build pressure the air bubbles get temporarily smaller and allow fluid to move properly. Once the pressure is released, the air bubbles grow again and you get a poor pedal response.

Two things to try: both old school and unlikely to have been done by ATS as they probably used a pressure bleeder. Firstly, wedge a length of wood between the seat and the brake pedal, to keep the brake pedal pushed fully down, and leave it like this overnight. Sometimes this makes the air bubbles so small that they move freely when you try the brakes in the morning.

Secondly, bleed the brakes by the two person method: One person pumps the brake pedal until it feels really firm, then you open the caliper bleed nipple and let fluid come out until the brake pedal hits the floor. Don’t release the brake pedal until you have tightened the bleed nipple. Repeat until the pedal pressure remains firm.

I did a complete brake system change on my Boxster, including master cylinder, hard lines and braided hoses, pressure bled for hours and no pedal pressure until I did the two person method.

 

[H13XJT]

As you get a good pedal on the second push, you still have air in the system. As you build pressure the air bubbles get temporarily smaller and allow fluid to move properly. Once the pressure is released, the air bubbles grow again and you get a poor pedal response.

Two things to try: both old school and unlikely to have been done by ATS as they probably used a pressure bleeder. Firstly, wedge a length of wood between the seat and the brake pedal, to keep the brake pedal pushed fully down, and leave it like this overnight. Sometimes this makes the air bubbles so small that they move freely when you try the brakes in the morning.

Secondly, bleed the brakes by the two person method: One person pumps the brake pedal until it feels really firm, then you open the caliper bleed nipple and let fluid come out until the brake pedal hits the floor. Don’t release the brake pedal until you have tightened the bleed nipple. Repeat until the pedal pressure remains firm.

I did a complete brake system change on my Boxster, including master cylinder, hard lines and braided hoses, pressure bled for hours and no pedal pressure until I did the two person method.

I'll have to try and get my dad in on this then I'll try the brake pedal and block of wood method.

I don't know if you can cycle the ABS pump using VCDS?

 

[Anakin]

Unless you had the system empty before the ABS pump, it’s unlikely to have air in, but once you get decent pedal pressure then you can simply activate the ABS by braking aggressively on a gravel car park/quiet road.

 

[H13XJT]

Unless you had the system empty before the ABS pump, it’s unlikely to have air in, but once you get decent pedal pressure then you can simply activate the ABS by braking aggressively on a gravel car park/quiet road.

Because this has all been done by garages... I'd hope not but I really don't know.

 

[phazer]

Hi buddy, thanks for the comment. This was literally from the garage test driving and then me driving it the 0.6mile back from the garage using the handbrake.

I will get it jacked up tomorrow and check the calipers are on the correct sides and check all the mountings are secure.

And by the clips do you mean the spring retainers?

I'll definitely have a look at the coding change. Is this with VCDS or do I need something else?

Yes, the retainers.

My post with the coding changes: Big brakes upgrade and yes VCDS to make those changes

 

[The Bear78]

It does sound like air in the system but I wonder if the pads are being held too far from the disk. Two quick pumps may not allow the pad to fully retract if it is being held away by a dodgy clip, possibly masking this fault.
When you get chance, look from the front at the pads. They should parallel to the disc (leading and trailing edge should look the same) and virtually touching the surface.

Are they EBC Yellowstuff pads? While not necessarily related to your problem, they may require a few good brake applications to bed in as the special compound is worn off the surface.

 

[H13XJT]

It does sound like air in the system but I wonder if the pads are being held too far from the disk. Two quick pumps may not allow the pad to fully retract if it is being held away by a dodgy clip, possibly masking this fault.
When you get chance, look from the front at the pads. They should parallel to the disc (leading and trailing edge should look the same) and virtually touching the surface.

Are they EBC Yellowstuff pads? While not necessarily related to your problem, they may require a few good brake applications to bed in as the special compound is worn off the surface.

Thankyou, and yeah I know the lads and discs are both coated. Equally I know something's not quite right

 

[H13XJT]

So got the wheel off today jacked up and the pad didn't appear to be sat right. Looks better now and the coating is fully worn off now too.

Bleed nipples at the top for certain too.

Will try and get this bled again. Maybe even using VCDS bleed it using the abs pump

 

[H13XJT]

So quick test drive with some heavy braking. The pads have reset to having a gap. Not sure if someone else can grab a picture of how their pads are sitting?