Brake Fluids

I have recently replaced my master cylinder and all four calipers (as well as pads/rotors). I am still having issues with stopping power being "not up to par". I believe that the harsh environment up here in northern Maine is very harsh on water attracting brake fluid (and being that the car is very well traveled all whilst being well loaded for very long distances and even having plenty of non-use time). What are some decent fluids to use? I am wondering if a complete purge and replace with a DOT5 (silicone) would be helpful or if just a purge and replace with 5.1 would be good. I am looking for a high boiling point fluid (I know I baked what good DOT4 fluid was left traveling the mass pike for the holidays and having to do a brake stand for a multi-vehicle pile up. Thanks! This is for my 2004 VW Golf PD TDI with 237K miles on it.

i dont think you want to use DOT5 at all. Use DOT5.1 that is compatible with DOT3&4 brake systems. As far as DOT4, most manufacturers offer good specs in DOT4, so if you are cooking it, then DOT5.1 is the way to go, just a little more money.

Do NOT use DOT5 silicone brake fluid! It is absolutely incompatible with the chemistry of the DOT3/4/5.1 group and will do a lot of damage if mixed. It is impossible to purge all of the old fluid out of the ABS controller, and some of it will remain trapped in the pockets where seals are mounted.

Stay with DOT4 (or 5.1 if you wish), just use any good quality stuff.

All of the DOT3/4/5.1 group are hygroscopic. Using DOT5 won't stop the water from getting in - but now it will sit in drips or pockets and if one of those spots happens to be inside a brake caliper, it will boil there at 100 degrees C, instead of at a considerably higher temperature.

What is the issue with the brakes? Soft brake pedal, or just not much happening when you press it?

Interesting issue, one that I have looked at myself. We have two Golfs and they both feel different when brakes are applied. All systems on both cars are in excellent shape, fluid changed at recommended interval.

Old Golf the brakes are scary close and sensitive. Slight pressure, you slow and stop.

Newer Golf you have to press and press like heck to get to the same degree of slowing down and stopping. I have to train myself to remember that.

Many discussions with others and even mechanics and no one can point at what might be different. High variation in systems is always mentioned but still a brain tease to this day.

What happens is that when you first apply the pedal (slight pressure) you feel the slight slow down as normal for just a second, then it goes away. Then there are times that the pedal just seems to go pretty far and you still don't stop like you should. I fixed my vacuum leak. Front pads are the best I could get from NAPA and the rotors are Bosch Quiet Stops. These worked great (these were replaced first) from the time they were installed this summer until about november. No unusual wear, bluing or sheen on the rotors/pads. All lines are good. Just not the car for city/highway traffic anymore ... for that matter I am not sure I trust it to stop in time for the moose that steps out in the road either.

Inconsistent brake pedal feel on application smells like master cylinder / vacuum booster issues.

Well, I paid someone to do the master cylinder and rear calipers, I have been wondering if they recycled the old fluid or actually replaced it all.

tdi50mpgnoob said:

Well, I paid someone to do the master cylinder and rear calipers, I have been wondering if they recycled the old fluid or actually replaced it all.

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your suspicions are probably correct....trust no one

dieselsipper said:

your suspicions are probably correct....trust no one

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Amen x2...My daughter unfortunately got scammed by a shop in Mass.
Claimed they replaced rear calipers, rotors and pads last summer and one of the calipers began leaking the other day and when I pulled it, I discovered a VW/Audi factory caliper that appeared original. When I was servicing the right rear earlier this fall we found the bleeder had been broken. She had been billed for "premium calipers" at $130/ side. If they had used factory parts the tab would have been twice that. So we documented the caliper by photographing it and will let the shop know that we will report them to the local BBB and notify all our local friend to boycott them .

TDI50mpgnoob,

Did you feel any improvement in the braking after they changed out the master cylinder?

Does the pedal feel spongy at all (while parked)? If you pump the brakes a couple of times will the pedal firm up?

Brake fluid should be flushed all the way through the system on a bi-annual basis. This doesn't mean that the shop can use a turkey baster and just replace what's in the reservoir,they need replace all the fluid all the way through the lines and calipers.

The hard plastic vacuum hose going to the brake booster is a common failure item. It develops hairline cracks in it and will give poor braking performance. They are cheap and easy to replace - might want to give it a shot.

A brake vacuum pump may also be on its way out. I replaced mine and I beli it have been bad for a while as the feel totally changed after the swap.

If you have ESP, it is recommended to use Low Viscosity DOT4 fluid.

If you use regular DOT4, the response is slightly slower... not necessarily a bad thing...

tdi50mpgnoob said:

Well, I paid someone to do the master cylinder and rear calipers, I have been wondering if they recycled the old fluid or actually replaced it all.

Click to expand...

Did this person use VCDS to run the ABS Hydro unit as part of the bleed process? If you change the slave cylinder, master cylinder or ABS unit you must follow this procedure.

Try bleeding using VCDS. you can hear it actuating the solenoids during the bleed process.

You may also want to replace any rubber hoses (when old they can expand) and check your rotors' thickness. I have had both issues on different cars. My personal best brakes were on a '91 Passat with ATE blue fluid, braided stainless lines, and Mintex pads. They sucked when cold but once warm they were great. The pedal was high and hard, like stepping on a golf ball, no mush.