Hello everyone,

Recently the brakes on my 96 850 became really poor. I was headed for work one morning and noticed that the main brakes did not stop the car as well as the emergency brake (which is not very good).
I got the car home that evening using back roads and using the
emergency brake along with the main brakes. The pedal wasn't
spongy so I just ordered new front brake pads- I assumed I was down to the metal because I'd had another car do the same thing a few years ago.
When I replaced the pads yesterday I was surprised to find that
the old pads still had 1/2 to 2/3 of the pad material left. The pads
look smooth and shiny (glazed?). The inside and outside pads are
worn equally so I think the calipers are ok and the rotors are not
badly worn. So now I have some questions:

1. I don't know what type of pads were on the car. I replaced
them with Mintex . The car stops better with the new pads but it
still isn't great. Is there any way to tell if the old pads were Volvo pads? There is no marking on them.
2. I haven't driven the car hard, in fact I'm pretty gentle on the brakes. I didn't see any evidence of fluid leakage from the calipers
or oil, any thoughts on other causes of glazing?
3. The dust boots are partially off the caliper pistons, that is the
edges are not down in the space between the piston and the caliper
walls that it rides in. I could see portions of the pistons before I
removed the inner brake pads. I think they have been that way
since I got the car. Can I press these back down between the
caliper and piston or do I need to take the pistons out?
4. What is the procedure for "breaking in" the new pads? So
far I have driven the car at low speeds (25-30 mph) and very
gently applied the brakes a couple dozen times.

I know I need to also check the back brakes. Sorry for the long
post.

John

 

Hi John,

I hope you're well. It's been rainy in Japan, which is typical at this time of the year.

Anyway, as to poor braking, I'll list the possible causes, starting from the most likely culprit:

1. Glazed pads (loses friction).
2. Defective/glazed rotors that are not dissipating heat quick enough.
3. Brake fluid that has never been replaced and absorbed moisture at enough quantity to cause vapour lock (the brake pedal feels positive but the brakes are not actually functioning as they should) or lowered boiling point.
4. Piston-related problem (some gunks entered through the boot opening and preventing the piston from fully deploying?)
5. Master cylinder problem.
6. Caliper slider pins seized (but if you could replace the pads, this does not apply).

I am suspecting the pads you took off were not OEM, as OEM parts usually have mfg stamp (Volvo), if they were installed either at the factory or ifthe previous ownerbought them from dealer. So, my personal guess is that the pads were of very poor quality and got glazed, even you did the break-in procedure almost impeccably. Glazing is usually induced by overheating, but I bet you knew it without my telling. BTW, there seems to be a few OEM pads for the 850, and I used Textar (German) for fronts (Roulands Dan-Block for the rear). If the pads were glazed, the rotors may have been glazed too, in which case you may want to replace the rotors as well, since resurfacing the rotors on European cars doesn't seem to be a recommended practice. The OEM rotors are Brembo, ATE, and Zimmermann I believe, and I used Brembo (weren't made in Italy, though[8D]). Glazing could also happen with light-braking, when you're going steep downhill with your foot on the brakes (in this type of situation, I usually downshift into the 3rdor lower gear). But I doubt if you ever did this as you are a cautious driver.

As to brake fluid, I wonder if the previous owner had replaced it. Or if someone put DOT-3 fluid, rather than DOT-4. I replace my brake fluid at every 2-3 years or 30,000 miles.

As to the piston, it is difficult to determine the condition without actually looking at them. I wouldn't try taking it out, unless you haveservice manual & necessary tools. If not done right, the seal may be damaged. Or, the seal might have been faulty and did not release the pads completely from the rotors, which could have caused glazing.

As to master cylinder, I cannot determine unless I actually look at it.

As to rotors, I would replace them with OEM disks, since the pads seem to have been glazed.

It would be great if you could take some photos of the components. Also, it is a recommended practice to clean the new rotor surfaces with denatured alcohol, as sometimes they come with anti-corrosion material applied to them. Well, at this point, I would clean everything with brake cleaner and replace the rotors. But wait buying new rotors before you hear from Tech or other experts; they may know something I may be missing at the moment.

I hope this gets you started. If you must drive the car as is for now, keep the shifter in "3", drive slower than usual and yes, take advantage of the parking brake.

I wish you the best safety until the problem is solved.


Kanji

 

Hi Kanji,

I hope you're doing well also. We are in our summer rainy season
here with temperatures in the 90's and maximum humidity. I had
to rush to get the front wheels back on the car because a thunderstorm was approaching. Lightning hit a house not too far from here, but that happens on
a daily basis with the storms.

I was thinking the same thing...really cheap pads and a poor job
on the installation. I looked at the back brakes as well as I could,
I didn't take the pads out yet and I couldn't get the 13mm bolts
out that mount the calipers. I may have the same situation in the
back. The back rotors rub on the pads part way around but I'm
not having any problems with the brakes shuddering.
The back brakes may not be doing much to stop the car. I guess
I'll replace the back pads too and do the emergency brakes also.

But I still don't know what to do about the dust boots on the
front, should I try to push those back in somehow?

Good to see you back, you and tech are my automotive heroes.

John

 

Hi John,

Life in Japan for me is like a ultra-powered vacuum cleaner (it sucks[8D]), since I have spenta good portionof my formative years in the States.

As to the dust boots, I too am not sure what you can do unless I can see it. As long as it is not damaged, you could perhaps try pushing it in with something like plastic with round tip (Ensure that everything is clean). But waiting for Tech's reply is probably the safest thing to do.

If you decide to replace the rotors, make certain to replace the caliper bracket bolts on the fronts, and caliper bolts on the rears (but this is just a quote from Haynes, and I am not sure how Tech does it). JimKW once had a rear caliper bolt head breaking off on him, so you may want to soak the bolts with PB Blaster (wipe off any that gets on the pad/rotor surfaces) and let it soak overnight before removal. Brake cleaning spray is imperative, and I would get 2 cans from Walmart. Make certain not to inhale that stuff, though, as it contains toluene and is strong enough to melt a Styrofoam dish.

The caliper slider pins on the fronts have to be lubricated with brake grease, and I used a little pack of synthetic version from local AutoZone. As for anti-squeal, I use CV-joint grease rather than generic brake-quiet stuff. Molybdenum-based grease seems to be the best choice for high-pressure applications, and moly grease is also used for a certain part ofturbine-powered (jet) engines (shroud between fan blades, etc...).

Jim also noted that he had a low-tone noise from the rears and the half-size shims cured it. I myself had the ordinary high-pitch squeal, even with the half shims, so I used CV-joint grease and the noise never came back. I also replaced the pad retainer spring kits on the rears, as they were rusted.

>Good to see you back, you and tech are my automotive heroes.
Tech is for sure, but I don't know about myself[8D], but thanks. You & Axel are my electronics heroes.

Anyway, I'll wait for your updates.


Kanji/JPN