Best method to bleed the brakes

[IMMX5]

I've been struggling to return the feel back to my brakes after finding virtually nothing under the pedal going into turn 2 on my NC at Wakefield last time... In relative terms it does bite - but it feels mushy going down - & seems to go too far down before it takes. Pumping the pedal does help - but that shouldn't be the case after a proper bleed.

I've now rebled the brakes twice - method 1 is following the old method of 1/4 turn open on the bleed nipple, depressing the pedal slowly, closing the bleed nipple, relieving the pressure on the pedal - repeating until a) clean fluid & b) no air bubbles is achieved - with the tube immersed in a clear bottle with the end below a level of brake fluid.

This didn't restore the proper feel so back again to bleed using method 2: pump pedal 3 times, open bleed nipple 1/4 turn, pedal to floor, close nipple, release pedal etc. until no air bubbles achieved.

I've replaced my old bleed hose and gone to clear vinyl tubing - thus have a dual check on bubbles sourced from air trapped in the tube vs from the hydraulic system.

Bleeding starts at furthest from master cylinder - ie. LR, RR, LF and finally RF.

Pads are original. Brake fluid used is Nulon (OK - so not the best - and interestingly not all bottles come with a foil seal!!).

Even if the fluid is not of the best quality I would expect it to be OK at least for the first few km's.

I've done a visual on the hoses for signs of any weak points (but not under any significant pressure though). Also, no signs of any leaks on the whole system.

So - any further suggestions on bleeding the brakes? What brake fluid is recommended - and where is the best place to buy from?

[Fatty]

have you checked the pads, they could be glazed.

[Mokesta]

I've found on one of my cars (not MX-5) that the slow pedal press doesn't carry the bubbles out of certain fittings (pressure limiting valves, failure circuit close valves etc.). I have to press the pedal very quickly to drag the bubbles out. Another method that seems to work is to pressureise the system and then crack the nipple. It's a two-person job. The sudden rush of fluid seems to drag out those pesky bubbles that won't budge otherwise.

Pads worn at an angle (tapered) will give the same feel as a spongy pedal due to air in the lines.

Another thought, is the car fitted with ABS? I don't know much about ABS but I have seen one older style unit that had a bleeder on it. I suppose it had a high-point that couldn't be bled through the wheels.

M

[JBT]

It's for all the reasons above I don't even try to bleed brakes anymore.

I recommend going to a brake/clutch specialist workshop to have them flush/check the systems.

[Charlie Brown]

I was having a similar problem at and after Wakefield, now it’s just at Wakefield.

Wakefield is very hard on brakes compared to a lot of other tracks, T2 redline 4th to 80kph, T8 redline 3rd to 2nd, T10 4th to 2nd, all in relatively quick succession and this puts a lot of heat into the brakes and the fluid. At Eastern Creek although the speed is higher there really is only T2 and T9 that you really jump on the brakes, the rest are a dab here and a dab there.

My current problem is that they are fine for the road, nice and firm, progressive, no mushiness but get to T8 (the Fish hook) and the peddle starts to soften up and by the time another lap or two is put down, the peddle starts to disappear through the floor and I’m starting to brake 30 metres before I should be just to retard the speed enough to get through the corner. Still managed a lap record but if only it stopped better there would be another half a second in it.

Back to the problem. I’ve tried a number of different DOT 4 & 5.1 fluids, Castrol, Penrite and now Shell for the last two months. Penrite was the best as it worked well for 12 months but then died so quickly it made me think that the pads had passed their used by date.

On all occasions when changing the fluid it took sometime to ensure that all the bubbles were removed. I use a speed bleeder and then when the system is fully changed with new fluid, go back to the old two man method of locking off the nipple mid stream. I also have often done mini bleeds on a number of occasions, finding that there is still a little bit of air in the fluid.

I think that in conjunction with the brakes I’ll do a clutch bleed next time and see if that improves things as the clutch line still has the old fluid in it and maybe moisture in there is being absorbed into the brake line fluid and that is where the bubbles are coming from.

What is frustrating is that it works fine when tested on the road but under the extremes of track work these little problems show up.

If anyone has used a good fluid that doesn’t need draining after a track day and is compatible with the brake system for every day use, ie doesn’t eat the seals etc away, please let me know.

[bruce]

have you checked the pads, they could be glazed.

....mmmmm, with chocolate sprinkles.

[mx5racing]

Phil, we run the Valvoline VR1 racing brake fluid in our cars and have done for some time. Like all racing fluids this one does not have DOT approval as you wont get it to meet the requirements that brake fluids need to gain it. Racing fluids usually get changed every few races and sometimes more frequently. This fluid is great for all cars including the MX5 and has a boiling point of 300 degrees. As you know from your drive at Wakefield Park our brakes in the NC are not too bad . When I ran the RHT at the last event it was hopeless after 2 laps. We pretty much baked the pads so much so that we had to fit another set to it so it was good again on the road........

We only \"change\" the fluid every time we put new pads in - about 3000 -3200 km depending on the tracks we have dríven at. The rest of the time we just do a minor bleed to flush the super heated fluid from the calipers. This we do about every 500 - 600 km (again depending on the track)

I know of numerous people who run it in their road cars which they also use on the track and some guys only change it every year or so.

The NC is a bit of a bugger to bleed (especially the clutch) and if you do the \"gentle bleed\", as Mokesta says, you will struggle to get it air free as it does accumulate around the ABS unit (NB2 & SE's were prone to this as well) Power flush is the way to go if you can organise it.

[wun911]

Does slotted rotor prevent glazed pads?

[Fatty]

Does slotted rotor prevent glazed pads?

mine didn't.

[IMMX5]

Latest update ...

Did a further bleed last w/e (Castrol Response Super Dot 4) - this time being a bit more \"brutal\" (rapid push down of the brake pedal etc.) - still no improvement.

Monday night I had the pads out - still ~4.5 mm left on the front (~7mm on rears). I noted that the pad material was very soft - a light scrape with a blunt scribe easily removes some material. On both the front outer pads there was a slight depression (5c piece size) in the already soft pad material on the lower half of the pad. No glazing was noted front or rear - some parts of the pads had a few scores but nothing worth worrying about. Refitted all the pads after a slight rub across some flat Wet & Dry. After bedding in the pads - still no improvement!

Took it in to the dealer workshop this am - (after nearly 3 hours!) they claim there was some air trapped in the RF caliper, they then flushed & (vacuum) bled the brakes (Valvoline).

Net result is an improvement - but nothing like a colleagues NC that nearly shot me out the front window when I tipped the brakes in the car park on Monday...

So - seems like a finicky bleed process.

We will see how it performs from here...

[mx5racing]

Net result is an improvement - but nothing like a colleagues NC that nearly shot me out the front window when I tipped the brakes in the car park on Monday...

Does the pedal feel firm or squashy when depressed once? If you pump it does it improve?

If the pedal is firm but the brakes are not pulling you up you may have very well cooked the pads on your last outing at Wakefield and this is the reason they dont work as well - especially when cold.

If you want to try some other std pads let me know.... we have numerous sets from when we fit the race ones.

I'll be at Wakefield on Monday so if you want me to bring down a set let me know.

Chris.

[IMMX5]

Chris
Pedal feel is still a bit squashy - and pumping still seems to make an improvement - that said I haven't pushed it at all so it's all been on cold brakes...

Two things concern me on the front pads - first that they seem really soft (but stock pads don't dust much in normal driving!) and the 2nd this depressed spot on the lower half of the outer pads. This is a shot of the RF one - LF has a similar spot.



I'll take you up on the offer to try another set if you bring down a some pads on Monday - if nothing else it takes it back to a baseline.

Ian

[mx5racing]

Looking at the pad there is no mistaking the signs of them being \"baked\". The mark you can see is where the pad material is bonded to the backing plate (turn the pad over and you will see what I mean). They mark like this as there is a different temperature through this section of the pad and it is unsupported by the backing plate. You can also see in the top section how it has become very brittle?

Do you know if they are the original brake pad from Mazda? I ask as they are missing the large chamfer of the leading/trailing edge, which is std? If they have been changed this may also explain why they have suffered so badly as the OEM Mazda ones usually hold up better.

pumping still seems to make an improvement

they must still have air in the system - do you know if they were bled at the ABS unit as well as the callipers? If not I would try this 1st. You will need someone to assist you. You can also try drip bleeding them at the callipers. Do one at a time and start with the NSR, then OSR, then NSF, then OSF. If changing the fluid to another brand/type you really need to flush the clutch as well as they share the canister. The clutches on these are a bit of an art to bleed but you cannot drip bled them as they just end up with a heap of air. It is really a 2 person/vacuum bleed.

Will bring the others with me on Monday. Are your rears ok?

Chris.

[Mr Starlet]

Chris, Ian, I have the exact problem, have been annoying me for months, came about after I replace Bendix Ultimate back to OEM, less dust for everyday stuff. I've try bleeding it alot of time, textbook method, no improvement. There must be a leak or something that's compromising the entire system.

In my case, I have a suspicion that it's to do with my rear left caliper. When removing the rear 14mm nut to get to adjusting hex key, I get a bit of black and rather thick liquid coming out from that hole. The otherside is still nice and clean and no liquid pouring out. I'm thinking the caliper needs rebuilding. Yours could be suffering similar fate Ian. I'll start looking into replacing the caliper with known good working unit and see how it goes, failing that I could be up for a rebuild...that could be more exy though.

I'll keep you posted.

Cheers
Minh

[Charlie Brown]

Here you go Ian,

Old OEM front pads:




New OEM pads



At least yours don’t look as bad as mine did after Wakefield.
I ended up driving from Wakefield to Blackheath and then Blackheath back down to Blakehurst on those trying not to use them at all.