Braking Effectiveness

[EddySpaghetti]

Hi All,

Just trying to think through some reasons why my brakes don't seem to have as much bite in them as before I changed pads and reconditioned my calipers. Some observations and thoughts I'd be interested to get your feedback on:

The old pads were worn pretty thin, and I had pretty chronic plate lift. After replacing with new (Pagid) pads and getting rid of the plate lift I expected the braking to be as good or better, but I think they are weaker.

I replaced suspension at the same time, and the front is now 20mm lower than before, I haven't adjusted the back ride height yet, could this mean I'm over-reliant on the front brakes only, due to weight transfer, and hence lower overall braking effectiveness?

I climbed the Stelvio and back in the summer after the change and pedal went very soft right at the bottom on the way back (was scary). I stopped the car and the brake master reservoir was 'bubbling' ever so slightly through the push button on the cap. Could this mean I haven't bled them out properly? - I used an Eezibleed and thought I'd been thorough - but nagging thought that I may need to bleed the master cylinder separately? - If I need to do that would I need to rebleed the whole system again afterwards? Not quite sure on the procedure if anyone has any advice on this if likely to be at fault.

The car has been laid up over the winter, after a spirited outing a week ago I noticed the surface rust on the front discs indicated only about 1/3rd of the discs were 'shiny' again. What could I do to get a more even pressure across the disc?

I only replaced the front pads - could this be an issue?

I fitted goodrich braided hoses at same time as new pads and suspension and expected the performance to be even sharper, but I think I have a slightly softer pedal feel if anything.

Any thoughts or advice welcome!

Cheers,

Eddy

 

[Mike_Pollock]

I'd guess air in the system, so a thorough bleed is in order.

Don't think the suspension set up will have any effect

It will take a bit to get the new pads to match the old discs.

 

[sticker guy]

do the discs need replacing? with your comment regards to only part being shiny, is it possible they have warped also?

as stated though, it will take a little time to bed the pads in, and if the discs are scored that time will be longer.

 

[robwright]

What you explained about the fluid sounds like brake fade to me because of over use on your spirited hill run. I think you boiled your fluid. There is only about 200ml in the system so not much to cook up!!! You don't need to bleed the MC. Get some better fluid I think if you intend doing it again then bleed EVERY nipple on EVERY caliper at lkeast twice and try again. Make sure that you don't have any leaking unions or pistons after refurbing the calipeers.

 

[EddySpaghetti]

Hi,

How could i check for a leaky cylinder? - Visual inspection of the caliper off the mounting only?

I hadn't thought of that...

I think I must have boiled the fluid too, but it was brand new ATE Blue - so does that mean I MUST have a leak, or can that stuff boil from hard use anyway?

I might replace the discs anyway - they are pretty rusted and I understand that doesn't help at all with heat transfer away

Thanks!

Ed

 

[robwright]

My front discs aren't the best in the world but are still a long way off needing replacing but it hasn't seemed to affect the breaking efficiency. Make sure all of the unions you disturbed are clean and dry and fully tightened. Then have a glamourous assistant press the pedal hard whilst you inspect them. Do this with the engine running so that you get full servo assistance. That makes a big difference. Other than that monitor closely for any fluid loss. If all is good then I would bleed, bleed and bleed again!! I had to do mine twice before I could get any decent brake effort. When I first did mine I was a little underwhelmed but I hadn't drove the car for a month and had to get used to the long pedal travel of the 944. This is because of the right hand drive conversion. The servo and cylinder are set up for LHD and you have a long bar under the dash joining the pedal to it. This can introduce a lot of travel depending on wear. Then although the pedal was firm I thought that the should be better. A hundred or so miles down the road after the pads have bedded in they are now STONKING!!! I think you have done more miles than this but it is worth bearing in mind. I really do think your problem is down to bleeding or a small leak. This may not even bleed fluid but may draw air back in to the system. I have heard of this happening. Hapy hunting mate []

 

[zcacogp]

Wot Rob Sed ^^^^.

If you boiled the brakes on the Stelvio pass then you were working them very hard and would explain the fade then. However they should come back OK when they cooled again.

It does sound like there is some air in the system somewhere. You talk about plate lift so I presume you have a turbo or S2 with the brembo calipers, in which case did you bleed both nipples on each caliper? If you did, and still think that there is air in there, give the calipers a good hefty thump when you bleed them (rubber hammer is a good thing to use) and try and dislodge any air from inside them.

When you say that it appears that only a third of the disc area is being used, what do you mean? Is the rust still showing in even circles around the disk, or that there are patches which the pads appear to be skipping over? Also I presume it was DOT5.1 fluid you used?

From what you described you have a recipe for excellent brakes. I am sure your problem lies in a small detail - like air in the system, for instance.


Oli.

 

[EddySpaghetti]

I did bleed both nipples, but I do also like the idea of giving them a thump to dislodge air bubbles. One thought though, do you have both nipples open at the same time? Since they are at the top i wouldn't have thought it necessary, but perhaps...?

Good news that I don't have to bleed the master cylinder, that sounds like a real PITA. I will go round checking each union as you recommend, and I guess if that doesn't help then I should check the pistons too. The professional that helped me drill out the bolts to get the calipers off the hubs said they looked OK, and I trust him, but worth a check.

The wearing away of the rust on the discs is concentric circles. I am getting about the 'middle' third worn and the inner and outer bands still have the surface rust on them. Mind you I only drove about 30 miles since it was laid up for a few months.

Because of the boiling and the fade I reckon its air too, and that the pads will bed in again with a bit of use, I'll go around again with the Eezibleed and this time give them a whack too! I am using ATE Blue and its a '90 Turbo SE.

Cheers guys!

 

[zcacogp]

No. One nipple at a time. Thump while it is open.

Jammed pistons could be an explanation for what you are seeing. Although clearly there is some movement as there is braking taking place. When you levered the pads back to get them out, did the pistons appear to move freely or not?


Oli.

 

[Fat Albert]

Mine was like this when I changed my first set of pads, my disks were a bit warped and when I had bedded the pads in I did a couple of 'enthusiastic drives' one with a mate in his Chimera following, I got lots of fade and he said that he has never seen a set of brakes smoke like that, not even on track!

I changed the disks and normal service was resumed....

 

[Hilux]

If you are boiling ATE blue you have a problem probably with the pad type transferring too much heat

Try better pads

A hundred or so miles down the road after the pads have bedded in they are now STONKING!!!

Then you are not bedding them in properly as it only takes the first half mile. To do it gently does not bed them in and glazes them.

To bed in new pads do 5 or 6 50mph-0mph panic stops one after the other and then drive around for 15 mins without trying to use the brakes or using them as little as possible to let the discs cool

It will smell and steam awfully but dont worry.

Once the discs are cooled (and blued) your brakes are bedded in and the discs tempered - job done. If they arent then check for other issues and if ok repeat BUT dont stop with the brakes in contact with the pad until cooled down as you will deposit pad material onto the discs.

 

[zcacogp]

ORIGINAL: Hilux
To bed in new pads do 5 or 6 50mph-0mph panic stops one after the other and then drive around for 15 mins without trying to use the brakes or using them as little as possible to let the discs cool

It will smell and steam awfully but dont worry.

Once the discs are cooled (and blued) your brakes are bedded in and the discs tempered - job done. If they arent then check for other issues and if ok repeat BUT dont stop with the brakes in contact with the pad until cooled down as you will deposit pad material onto the discs.

That is very helpful - thanks. I have been told that there is a good way to bed in new brakes but never been completely certain what it is ...

Now I know.


Oli.