DIY Car Mechanics Explained - Changing Brake Pads & Discs

Simon · 15 Sep 2005 at 10:54

Tesla said:
What is the best way of bleeding the break system? (For a newbie with few tools)

Lopez, thanks for clearing up my question

Either a vaccum bleed off the engine, can make one yourself out of a glass jar, but maybe that's for another thread.

The way to do it is with a mate, one on the pedal, one on the brakes. Press the pedal to build up pressure then open the nippled and press half way down, before you lift the pedal get whoever is on the brakes to close the nipple. This stops air being drawn back through the thread on the nipples, repeat this process until the fluid is nice and clear and bubble free.

You press the pedal only half way as in normal operation you never use the full length of the pedal, this part of the master cylinder bore is therefore hardly used and can has slight corrosion which will wreck the master cylinder seal.

Dogbreath · 15 Sep 2005 at 11:26

Simon said:
Worth noting that some calipers need winding in rather than simply forcing back in. My rover and lots of honda's need the rear calipers winding in.

The MR2 has these as well, as do most cars that have the handbrake mechanism built into the rear calipers.

Simon said:
It's also a good idea on ABS equipped cars to open the bleed nipples when pushing the pistons back rather than forcing fluid through the ABS unit.

A very good point, have heard a few stories of damaged ABS units from forcing fluid through them backwards.

50/50 · 15 Sep 2005 at 11:39

Great thread. 5* from me.
Although I wouldn't attempt it, it seems like a waste of effort. I would prefer to pay the £50 labour and get the mechanic to do it!

Simon · 15 Sep 2005 at 12:17

50/50 said:
Great thread. 5* from me.
Although I wouldn't attempt it, it seems like a waste of effort. I would prefer to pay the £50 labour and get the mechanic to do it!

Its only an hour job, you must be on a lot of money to prefer to pay £50 per hour. And of course you know the jobs been done properly

volospian · 15 Sep 2005 at 13:57

Good thread, why is there not more of this sort of thing. I'll be doing my GT6 brakes sometime soon. New calipers, disks, pads and pipes, with a full fluid replacement to silicone stuff. No ABS to worry about though

Simon · 15 Sep 2005 at 14:11

volospian said:
Good thread, why is there not more of this sort of thing. I'll be doing my GT6 brakes sometime soon. New calipers, disks, pads and pipes, with a full fluid replacement to silicone stuff. No ABS to worry about though

Why do you want silicone brake fluid on a road car? Normal dot5.1 is fine. Silicon isn't hydroscopic and so any water collects at the bottom of the brake system (more dense than the fluid). As you can imagine water isn't the best thing inside a caliper.

Silicone fluid is for race cars.

Ovr · 15 Sep 2005 at 14:22

Pushing the piston back in is just fantastic, after much swearing my dad came and pushed it against his stomach in much pain until it went back in ;D

volospian · 15 Sep 2005 at 15:48

Simon said:
Why do you want silicone brake fluid on a road car? Normal dot5.1 is fine. Silicon isn't hydroscopic and so any water collects at the bottom of the brake system (more dense than the fluid). As you can imagine water isn't the best thing inside a caliper.

Silicone fluid is for race cars.

Really? Are you sure?

http://www.keystonemg.com/tech/conv-silicone-brake-fluid.html said:
D.O.T. 3 and D.O.T. 4 brake fluids are glycol-based, while silicone-based fluids are classified as D.O.T. 5.

Glycol-based brake fluids in particular, are hydroscopic (moisture absorbing), some more so than others. When water is absorbed, the boiling point is sharply lowered. This occurs because water boils at only 212° F. When brake fluid is mixed with water, the boiling point of the mixture is less than that of the "dry" brake fluid. See chart for D.O.T. minimum boiling point specifications.

Water contamination also leads to corrosion of brake pipes, wheel cylinders, calipers, and master cylinders, resulting in pipe leaks, "frozen" cylinder pistons, accelerated seal wear, and the formation of sludge. Silicone fluids avoid these problems by being non-hydroscopic (not moisture-absorbing), while glycol fluids can absorb as much as 6% water just by being in a "sealed" automotive hydraulic system for a few years. This moisture is generally absorbed from the air. Some moisture even works its way into brake hoses. Most comes from master cylinder cap vents and resultant condensation in the air space above the fluid, and from allowing cans of brake fluid and master cylinders to remain open to the atmosphere for too long. Silicone fluids absorb a tiny amount of moisture (on the order of 280 parts per million, or .0028%) and then absorb no more.

Silicone fluids, in addition to having high boiling points and being non-hydroscopic, do not damage paint as do glycol fluids. This is of particular importance in regard to show cars where a spill or leak of glycol fluid can have seriously ugly results. There are, however, some disadvantages to silicone fluids. They are slightly compressible, particularly near the higher end of their temperature range. While this is of absolutely no consequence for normal street use, this is why silicone fluids are not used in race cars. (Conversely, racing hydraulic fluids should not be used in street cars. This is because, although racing brake fluids have high dry boiling points, most are highly hydroscopic, and have relatively very low wet boiling points. They would probably work extremely well if you were to change the fluid every week or so.)

Sounds to me like DOT5 Silicone is a damn site better than Glycol based fluids in a classic car. Maybe we have a different interpretation of the term "silcone"?

Simon · 15 Sep 2005 at 16:45

volospian said:
Really? Are you sure?

Sounds to me like DOT5 Silicone is a damn site better than Glycol based fluids in a classic car. Maybe we have a different interpretation of the term "silcone"?

I was thinking of Racing silicone fluids, sorry.

However still Dot 5 silicone is not hydroscopic so you still get water collecting in the calipers requiring frequent changes, it might absorb water but any that isnt 'absorbed' tends to make it to the bottom of the brake system.

Gaijin · 15 Sep 2005 at 17:22

Excellent guide Mr Lopez

- now will you please make another step by step of either how to supercharge/turbocharge my B18C4 engine or a step by step of how to swap it with a B18C6 teg type R engine.

I'm not fussed which

Firestar_3x · 15 Sep 2005 at 19:04

Good guide that, looks very similar system to the Primera, taking the caliper bolts out to change the pads.

Wish i did a guide when i had the sax cause i change the pads and disks on that, total pain it was, had a bar and pin setup to hold the top of the pads in, you actually had to file the new bar down so you could bang it in with a hammer, nasty job, but hey once you have mastered it you can change disks and pads mega quick.

Dogbreath · 15 Sep 2005 at 22:50

Simon said:
I was thinking of Racing silicone fluids, sorry.

However still Dot 5 silicone is not hydroscopic so you still get water collecting in the calipers requiring frequent changes, it might absorb water but any that isnt 'absorbed' tends to make it to the bottom of the brake system.

Spot on. Also silicon fluids tend to be more compressible than mineral based ones so you get a "springier" pedal which is not good for feel. For road use, decent quality mineral fluids are still hard to beat.

volospian · 16 Sep 2005 at 10:03

Simon said:
I was thinking of Racing silicone fluids, sorry.

However still Dot 5 silicone is not hydroscopic so you still get water collecting in the calipers requiring frequent changes, it might absorb water but any that isnt 'absorbed' tends to make it to the bottom of the brake system.

You should only get water collecting if there's water in the system in the first place. Hygroscopic fluids absorb water, thus drawing water into the brake system from the atmosphere, silicone doesn't do that (well, it does, but only 0.0028% then it stops).

If you don't flush the system correctly you will still get glycol fluid in the seals and so on, then the water that is absorbed by that fluid will sink to the calipers, if there is no moisture in the system in the first place, silicone will not draw any more in (unless you pour water into the reservoir or something).

Most people I have spoken to using silicone have experienced none of this supposed water build up in the calipers, mainly because the switch to silicone has been done correctly, or they have rebuilt the brake system (as I'm doing) using clean new parts.

I'm sorry, but I don't believe you about silicone being worse than glycol, I've spoken to a few people on the cc scene who have used silicone in their systems for years without changing fluid and have suffered no corrosion, fade or other signs of water build up. If you do it properly and ensure there is no water in the system in the first place, silicone will not draw any more in, unlike glycol.

Dogbreath · 16 Sep 2005 at 10:15

Have a read of this thread for good reasons why not to use DOT5 fluid:

http://locostbuilders.co.uk/viewthread.php?tid=17577

volospian · 16 Sep 2005 at 11:25

*shrugs* doesn't tell me anything I don't already know. As I've said this is going into a clean system, providing there is nowhere water can gain ingress the system should be stable. Silicone will not suck moisture in via the atmosphere like glycol based fluid. It may be "spongier" but this is only relative, the current brake system is spongy, it's a 33 year old car with rubber hoses and so on, the brake feel is not fantastic at its best, the new braided hoses will probably make up for any increase in sponginess.

As I've said, a lot of people in the classic car world use silicone fluid, some have reported a slightly spongier feel over a good glycol system, but apart from that feeling, most have reported only benefits.

Simon · 16 Sep 2005 at 11:44

Is the brake system open or closed on a classic car? All modern ones are open with a draw through valve allowing air into the master cylinder. With condensation etc and natural water vapour in the air you will get a build up of water in the system, this is why glycol systems need replacing after 2 years. The water content builds up and reduces the boiling point of the fluid.

Anyway it's up to you at the end of the day, I certainly am not very knowledgeable with classic cars. Then of course i doubt they are driven very hard to notice any effects.

Mickey_D · 16 Sep 2005 at 11:50

I will be doing a thread this weekend on oil changes.

Top marks from me, Lopez. Very well written guide!!

Dogbreath · 16 Sep 2005 at 13:30

Simon said:
Is the brake system open or closed on a classic car? All modern ones are open with a draw through valve allowing air into the master cylinder. With condensation etc and natural water vapour in the air you will get a build up of water in the system, this is why glycol systems need replacing after 2 years. The water content builds up and reduces the boiling point of the fluid.

A lot of the older cars had a vent that was open to air, and this is exactly where the moisture comes from as you say. Many modern cars have a flexible diaphragm built into the cap to seperate the air in the reservoir from the air outside, whilst still allowing the level to rise and fall.

volospian · 16 Sep 2005 at 15:48

Simon said:
Is the brake system open or closed on a classic car? All modern ones are open with a draw through valve allowing air into the master cylinder. With condensation etc and natural water vapour in the air you will get a build up of water in the system, this is why glycol systems need replacing after 2 years. The water content builds up and reduces the boiling point of the fluid.

True, but that's where silicone is better than glycol. It's the glycol itself that absorbs the water from the atmosphere, that's what hygroscopic means (http://ptcl.chem.ox.ac.uk/MSDS/glossary/hygroscopic.html).

Simply put hygroscopic chemicals attract moisture from the atmosphere, that is, they will draw moisture from the air into itself.

Silicone fluids are not hygroscopic, that means that they do not absorb water from the atmosphere, so you will only get moisture ingress due to condensation. You will not get water ingress from the atmosphere.

The amount of water you will attract via condensation as opposed to hygroscopic absorbtion is very low. You will always need to change brake fluid, I'm not disputing that, but you will not suffer as much water ingress with a silicone system as you will with glycol.

volospian · 16 Sep 2005 at 15:49

Dogbreath said:
A lot of the older cars had a vent that was open to air, and this is exactly where the moisture comes from as you say. Many modern cars have a flexible diaphragm built into the cap to seperate the air in the reservoir from the air outside, whilst still allowing the level to rise and fall.

Yep, and most of that moisture is absorbed hygroscopically, which silicone doesn't do, hence the change to it.