ZT-T V6 - Brake drag after new front pads and discs

drjonts · 13th September 2016, 21:22

Hi foiks.

Bit of an odd one today...changed the front pads and discs (Pagid from ECP) on the ZT-T at the weekend and all went OK...sliders free and regreased after cleaning, caliper pistons retracted without too much hassle and then able to be retracted by thumb pressure on the pads. carriers wire brushed and Ceratec grease on the mounting lugs.

All went back together and seemed fine...swept area looked nice and even on the outside after a couple of miles.

Had to remove some brake fluid to retract the pistons as the reservoir was near full and ended up on the full mark after the job.

So...50 odd miles today and I thought at times I could smell brakes - by the time I got back boy were the fronts warm...even the alloys were very hot! Heat coming off the rears as well and I thought pads had been dragging on the fronts and I'd been braking with the rears only properly down the last big hill.

Had to get the hose and cool everything down with the mist spray as I was a bit concerned.

So, strip it all back down and check...all seemed OK once cool, everything moving and pistons retracted OK again. inner swept area of disc looked fine.

BUT...

The reservoir was much fuller now and somewhat nearer the top of the filler neck...and then I wondered if there was too much in there or heat had caused fluid expansion and expansion into the neck of the reservoid could have meant there was no room for fluid return after application of brakes - pistons stay out, everything heats up, expands and makes the whole system 'lock' hydraulically and thus keep the brakes slightly applied...perhaps the rears as well as the fronts?

So I drained some fluid off, put it all back together and went for a drive and coasted to a stop after some 50-60 mph roads without braking...brakes were cold. Some fierce braking from speed got things warm but not as hot as earlier. Perhaps a brake bleed and thus fluid change may be prudent in case everything got too hot. But at no time did the brakes feel like they were fading or there was any vapour in the hydraulics as the pedal was good...just dragging and hot, hot, hot.

So, can an overfull reservoir create hydraulic conditions that make brakes drag...I guess my answer appears to be yes (unless it was a combination of things but I don't think it was).

These guys seem to think an overfull reservoir does it:

http://www.mpbrakes.com/techtalk/how...ing-brake-drag

Any thoughts folks?

Jonty

Davey1991 · 13th September 2016, 21:29

Over filling is only normally a problem if the water content of the brake fluid is high, brake fluid is designed not to expand but I guess this is inevitable to some degree with it being a liquid. This is the reason manufacturers recommend brake fluid changes along with corrosion prevention.

If you have reasonably new brake fluid then ignore me haha.

trikey · 13th September 2016, 21:30

I have never seen an overfull reservoir cause an issue?!?

drjonts · 13th September 2016, 21:31

Ah...good question...no idea how old the fluid is to be honest!

Hmmm...to the brake bleeding kit Batman!

klarzy · 13th September 2016, 21:33

Quote:

Originally Posted by trikey

I have never seen an overfull reservoir cause an issue?!?

would there be a hydraulic lock issue if there was no head of air above the fluid...not allowing the pads to back off?

drjonts · 13th September 2016, 21:34

Quote:

Originally Posted by trikey

I have never seen an overfull reservoir cause an issue?!?

That's what I thought but I'm at a loss to explain it as nothing else seemed to be the cause. Also, having the rears hot made me think the whole brake circuit was slightly pressurised causing them to lightly drag.

By the time I checked the reservoir things had cooled down and perhaps if expansion was an issue the level had fallen?

Hmmm...is the reservoir cap definitely vented on the car?

drjonts · 13th September 2016, 21:36

Quote:

Originally Posted by klarzy

would there be a hydraulic lock issue if there was no head of air above the fluid...not allowing the pads to back off?

And that is my thinking Pete..no space to let the pistons pop back away from the discs.

klarzy · 13th September 2016, 21:40

Quote:

Originally Posted by drjonts

And that is my thinking Pete..no space to let the pistons pop back away from the discs.

i dont think they ever back away as such, more just reduced friction to next to zero...

my nee brakes and pads had a bedding in layer... They smoked a tad for the first day but are fine now...
be carefull spraying water as you will cool one side rapidly and may cause warping...

drjonts · 13th September 2016, 21:49

Quote:

Originally Posted by klarzy

i dont think they ever back away as such, more just reduced friction to next to zero...

my nee brakes and pads had a bedding in layer... They smoked a tad for the first day but are fine now...
be carefull spraying water as you will cool one side rapidly and may cause warping...

Thanks Pete. The Pagid discs have the silver anti-rust coating that comes off after a very short distance and a few applications of the brakes.

There was quite a sizzle and some steam when the water got on there. Seems OK on the anchors now, no pulsing or weirdness. Worried that the hot disc sat next to the pad once I'd parked up might create the 'sticky patch' on the disc that feels like it's warped. So thought just cool it down!

Jakg · 14th September 2016, 07:45

Quote:

Originally Posted by klarzy

would there be a hydraulic lock issue if there was no head of air above the fluid...not allowing the pads to back off?

It's not a sealed system - otherwise if you opened a bleed nipple with the cap on nothing would happen.

13th September 2016, 21:22	#1
drjonts Loves to post MG ZT-T 160 Join Date: Dec 2015 Location: Devon Posts: 288 Thanks: 179 Thanked 70 Times in 53 Posts	ZT-T V6 - Brake drag after new front pads and discs Hi foiks. Bit of an odd one today...changed the front pads and discs (Pagid from ECP) on the ZT-T at the weekend and all went OK...sliders free and regreased after cleaning, caliper pistons retracted without too much hassle and then able to be retracted by thumb pressure on the pads. carriers wire brushed and Ceratec grease on the mounting lugs. All went back together and seemed fine...swept area looked nice and even on the outside after a couple of miles. Had to remove some brake fluid to retract the pistons as the reservoir was near full and ended up on the full mark after the job. So...50 odd miles today and I thought at times I could smell brakes - by the time I got back boy were the fronts warm...even the alloys were very hot! Heat coming off the rears as well and I thought pads had been dragging on the fronts and I'd been braking with the rears only properly down the last big hill. Had to get the hose and cool everything down with the mist spray as I was a bit concerned. So, strip it all back down and check...all seemed OK once cool, everything moving and pistons retracted OK again. inner swept area of disc looked fine. BUT... The reservoir was much fuller now and somewhat nearer the top of the filler neck...and then I wondered if there was too much in there or heat had caused fluid expansion and expansion into the neck of the reservoid could have meant there was no room for fluid return after application of brakes - pistons stay out, everything heats up, expands and makes the whole system 'lock' hydraulically and thus keep the brakes slightly applied...perhaps the rears as well as the fronts? So I drained some fluid off, put it all back together and went for a drive and coasted to a stop after some 50-60 mph roads without braking...brakes were cold. Some fierce braking from speed got things warm but not as hot as earlier. Perhaps a brake bleed and thus fluid change may be prudent in case everything got too hot. But at no time did the brakes feel like they were fading or there was any vapour in the hydraulics as the pedal was good...just dragging and hot, hot, hot. So, can an overfull reservoir create hydraulic conditions that make brakes drag...I guess my answer appears to be yes (unless it was a combination of things but I don't think it was). These guys seem to think an overfull reservoir does it: http://www.mpbrakes.com/techtalk/how...ing-brake-drag Any thoughts folks? Jonty

13th September 2016, 21:30	#3
trikey Premium Trader Rover 75 Join Date: Nov 2010 Location: Devon Posts: 33,808 Thanks: 8,837 Thanked 14,831 Times in 8,030 Posts	I have never seen an overfull reservoir cause an issue?!? __________________ Lest we forget..

13th September 2016, 21:29	#2
Davey1991 Avid contributor MG ZT Join Date: Sep 2016 Location: Bingham, Nottingham. Posts: 240 Thanks: 66 Thanked 39 Times in 28 Posts	Over filling is only normally a problem if the water content of the brake fluid is high, brake fluid is designed not to expand but I guess this is inevitable to some degree with it being a liquid. This is the reason manufacturers recommend brake fluid changes along with corrosion prevention. If you have reasonably new brake fluid then ignore me haha.

13th September 2016, 21:31	#4
drjonts Loves to post MG ZT-T 160 Join Date: Dec 2015 Location: Devon Posts: 288 Thanks: 179 Thanked 70 Times in 53 Posts	Ah...good question...no idea how old the fluid is to be honest! Hmmm...to the brake bleeding kit Batman!