Bleeding silicone brake fluid

Dear All,

I'm recommissioning my Herald at the moment. After a certain amount of swithering, I decided to go for silicone fluid in the brake and clutch. The clutch, which I did first, was fine. However, the brakes have been a real pain. After a first session, with almost a litre of fluid through the system the pedal was still very springy. A second session a week later improved things a bit. A third session today shows no bubbles at all emerging, but there is still a fair bit of spring in the pedal.

However ... I also have new shows and pads, which always adds a bit of bounce on the Herald till things bed in

And ... I have read claims that silicone fluid is a bit more compressible than glycol

So ... should I be worried? Have folk here had problems bleeding silicone fluid? Experience of it giving more spring to the pedal? Shall I just take the car out for a drive - the MOT station is 20 miles away over twisting moorland roads - and hope that everything firms up a bit.

Incidentally, I know that I could switch to glycol, but my reasons for silicone are fairly good, and I'd like to stick with it unless it simply isn't going to be possible to get satisfactory performance.

Ian

PS New master cylinder, calipers, rear cylinders, hoses (Goodrich) and most pipes.

Reply to
Ian
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Ian formulated the question :

Does it have a servo and you are testing it with the engine running?

If so they can feel a little soft and springy with the servo working, try it again without. Its to do with you applying much more pressure on the pedal than you would when actually driving.

Reply to
Harry Bloomfield

Personally I don't like silicon fluid not worth the expense. If you correctly flush your fluid every two years you should have no problems, except wear and tear on the system components, which is normal what ever the fluid you use.

Ok having had my rant, make sure that the rear brake shoes are adjusted fully up, this can induce soft brakes, these should also be adjusted up after the linings bed in.

After the system has been bleed let the car sit and check the pedal next day. You may check the play in the rod on the pedal and adjust that up as well.

r
Reply to
Rob

Make sure the shoes are adjusted properly, have you tried bleeding with the shoes backed off, then adjusting the shoes to the correct postion?

Also make sure that all seals in the system are happy with silicone fluid, silicone fluid is not reccomended for my Morris Minor because it is said it can damage the seals.

Reply to
chongqing.marshall90

Like I said, it was a close call, and if all else fails I'll go back to glycol.

They're as well adjusted as any new shoes in new drums can be - I'll certainly expect to re-adjust them after everything has bedded in.

No adjustment at the pedal or in the cylinder. However, leaving the car to sit for a few days after the first bleed did seem to improve things a bit - mainly, I think, by allowing microbubbles to coalesce into bigger, bleedable lumps of air.

I've done some limited road testing and the brakes work OK, without pulling - it's just that the pedal feels bouncier than I'd like. And, I fear, than the MOT tester will like ...

Ian

Reply to
Ian

No servo - just a bog standard Herald system.

Ian

Reply to
Ian

I have got silicone fluid in my PI - it wasn't my choice, the previous owner put it in after a complete brake overhaul.

And at the time I bought the PI, I had a 2000 with ordinary brake fluid. And there was *always* a different feel to the PI brakes. The systems are pretty well identical except the PI has a vacuum storage thing and the 2000 didn't, and both stopped well enough to get MOTs, but the PI pedal never felt as solid as the 2000 one.

When I had to replace one of the brake parts for an MOT, I let the garage do it for the cheap retest, and provided a bottle of DOT5 to make sure he used the right stuff. It got the MOT, but when I collected the car afterwards the pedal felt even more spongy than before. I used it for a week or so, then decided I really didn't like it so took it back for him to bleed again. It was better second time, but still not as good as it had been when I bought it. A third bleed a month later finally fixed it.

Apparently, silicone fluid gets "micro-bubbles" which are too small to see in the bleed jar but affect the braking system. You have to leave the system unused for long enough for these micro-bubbles to coalesce into larger ones and then bleed them out.

My advice is to leave your Herald undriven for at least a week, then bleed again. Provided after that you get brakes without the pedal going so far down that you feel inclined to pump it, then it is safe to drive, it should get an MOT, and you need to do some driving to bed in the new pads and shoes. Once you are happy that they are bedded in, adjust them then leave the car as long as is practical without using it, and then bleed again. The pedal will still feel a little bit springy - it is a characteristic of silicone - but that last bleed should make it as good as it will get. And it should then stay like that for years!

Jim

Reply to
Jim Warren

I was about to say that'll be the same as my Vitesse then - unless yours is drums all round. I never had a problem with silicon and don't remember any great difficulties bleeding the system. But perhaps I was less sensitive to any sponginess than you are. I'd certainly recommend you persevere rather than switching back to normal brake fluid.

Reply to
Willy Eckerslyke

Thanks Jim - much appreciated.

Ian

Reply to
Ian

If the problem is micro bubbles, then the answer we found (on motorcycles) is to pressurise the system and leave it pressurised over night, the reduction in pedal travel the next day is quite amazing.

I use a brake pedal jack (home made from a mastic gun) to hold the pedal down. Also useful for checking brake equality and brake lights !!

Mrcheerful

Reply to
Mrcheerful

Splendid idea. I shall investigate a bodge along those lines!

Ian

Reply to
Ian

When I mentioned the trouble I'd had bleeding the front brakes of my Landy (notoriously difficult) to the MOT tester, he said that he always gravity bled them - i.e. opened the bleed nipples and just let the fluid run through on its own for an hour or so. I've never tried this, but guess it would avoid the problem of micro bubbles.

A web search suggested reverse bleeding them by forcing fluid into the bleed nipples via a syringe, but I'd already sorted them by then. Dunno if that method would help the OP.

Nice idea, and less hassle than searching around for a length of wood then trying to jam it against the seat back!

Reply to
Willy Eckerslyke

For checking brake lights I use a KrookLock. Adjust to length then lock with the key and jam it between pedal and front seat frame.

Jim

Reply to
Jim Warren

I've got a mirror on the garage wall. Just back up and have a look.

Reply to
Pete M

Bigger pipes on the clutch. Silicone is a problem because of surface tension issues meaning that bubbles won't come off the pipe surface as easily, especially if there's more pipe area / volume. The trick is:

  • Don't put bubbles in there. Use fluid that has sat in the bottle and settled out, then pour it gently.
  • Pressure bleed it gently, rather than pogoing on the pedal. The Gunson pressure bleeder is cheap enough and works fairly well. Run it from a spare tyre at no more than about 15psi. It also doesn't work on Alfa Romeos or other cars where the fluid-loss warning switch fits through a notch cut in the reservoir next (remove the switch, slip a collar of bike inner tube over it).

I have four Gunsons, as it's the only way I could ever bleed my fscking Rangie.

Reply to
Andy Dingley

It also doesn't work on Toyotas which have a pop-on rubber reservoir cap :-(

Reply to
Chris Bolus

The same thought occurred to me; Minis are buggers for it. Wedge the pedal down overnight, the difference is amazing. Like another poster here, I've made use of a Krooklock for the purpose.

Reply to
Chris Bolus

Krooklok went in at 10pm! Rebleeding sometime this evening.

Ian

Reply to
Ian

I'm not convinced. Provided you change ordinary brake fluid regularly - perhaps every couple of years - the parts should have a long life. And changing the fluid and the subsequent bleeding forces you to examine the condition of the hoses and pipes.

Reply to
Dave Plowman (News)

But realistically, how many of us want to change the fluid that often? Now that he's bought the stuff, and the cost factor is gone, I can't see any reason not to stick with it. I'm certainly not convinced that the system will feel noticeably different once properly sorted, and am also dubious that the trouble he's been having so far is down to the type of fluid.

ISTR the OP said he'd fitted steel braided hoses, so inspecting _them_ won't tell him much anyway.

Reply to
Willy Eckerslyke

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