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850 rear calipers "not' locked up 850

posted by gzulli on Fri Jul 13 08:02 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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I have had the locked brake caliper in the past on my 850's but today I found a new one (for me anyway.) My son's 94 850 rear brakes are not connecting with the calipers. Both calipers are showing surface rust. Last Sept I had new Volvo pads put on the car but no changes since then and no issues at time of the pad change.

I did some web surfing and see it could be an issue with the slide pins. I also see people hit the caliper with penetrating oil to loosen them up. But my question is since the calipers can lock up on the rotor and ruining them if driven can a caliper be frozen open still be safe. RIght now I cannot tell there is a problem based on the brakes only working up front. I am trying to avoid the cost of two rebuilt calipers if possible but will not do anything considered risky on my son's car. Is it possible for the issue to be some sort non-caliper part. Like I said, both rear brakes are doing this which seems odd to me.

Thanks for any suggestions.
--
1996 855 TL Platinum Ed., 1995 854 GLT 5 sp, 1995 854 (RIP), 2005 V70R (badly missed)

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850 rear calipers "not' locked up 850

posted by KlausC on Fri Jul 13 10:25 CST 2012
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last visit: Fri Oct 24 10:15 CST 2014

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Most of the braking action is on the front wheels, so it is not totally unsafe.

First try bleeding the brakes at the rear and see if that helps. There might be air in the lines from old fluid that boiled. If the DOT4 comes out almost black, that could be the problem.

It is easy to just remove the slide pins and clean them off. Get a tube of silicone brake grease at your autoparts store for about $1.20, its enough to do all 4 wheels.

I had a stuck rotor in the front, and that really was a safety issue!
--
My name is Klaus and I am a V♂lv♂holic

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850 rear calipers "not' locked up 850

posted by gzulli on Fri Jul 13 15:25 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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Sounds like the brake fluid is the first area to check. Thanks for the suggestions guys. Can I do the check by looking up at the reservoir or must I get the lines bled? Not sure if the brake fluid will show the dark color up front.
--
1996 855 TL Platinum Ed., 1995 854 GLT 5 sp, 1995 854 (RIP), 2005 V70R (badly missed)

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850 rear calipers "not' locked up 850

posted by KlausC on Fri Jul 13 15:49 CST 2012
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last visit: Fri Oct 24 10:15 CST 2014

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It sounds like the fluid hasn't been flushed in a while. You should drain the reservoir using a turkey baster or some other suction device, and then fill it with new fluid.

I use a pump, there are no 'helpers' around.

If no pump, then the procedure is just slightly different.

Open a caliper bleeder valve on one of the rear wheels and attach a clear 1/4inch tubing that will go to a clear bottle or catch can. Have helper push down slowly on the brake pedal while you watch the fluid. After the brake pedal comes back to the top, replenish the reservior with new fluid. Repeat until the fluid is clear. Move to the other brake and repeat the process.

You will need about a pint to do both rear brake lines.

When done, pump the brakes a few times, reinspect the fluid level. Then drive the car, braking hard a few times. Inspect the rotors and see if the rust is gone on both.

--
My name is Klaus and I am a V♂lv♂holic

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850 rear calipers "not' locked up 850

posted by gzulli on Fri Jul 13 16:52 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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Any special brake fluids needed for the 850's? I assume the idea is to push all the fluid out and replace. Correct?

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850 rear calipers "not' locked up 850

posted by gzulli on Fri Jul 13 17:26 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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Just necked IPD and see I need DOT 4. I'll go with the blue so I can see the new fluid passing the rear calipers.

Thanks for the suggestions.

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850 rear calipers "not' locked up 850

posted by Most Unusual on Sat Jul 28 12:04 CST 2012
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last visit: Tue Jan 7 20:53 CST 2014

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Since your fluid is already dark, just use clear DOT 4...you will see the color change when it comes out the bleeder valve. FYI: I bled my system last week.. The old fluid was dark green and full of "crud" that settled out in the jar.

Good luck!

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850 rear calipers "not' locked up 850

posted by gzulli on Wed Aug 1 11:35 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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My independent guy was not interested in this job for some reason. So I took it to my dealer (who is very good but expensive). The allowed me to bring my own part ($40 from an e bay seller as the local pick & pull gets $80 for an abs pump???) They did the work yesterday along with a bad control arm (plus alignment) for inspection. Now $600 later the car lives to fight another day (or hopefully a year longer). FYI the dealer charge for labor on this ABS pump repair alone was $225.

The dealer tech said he only ever saw one of these pumps bad back when the 850's were new and the pump was leaking. Other than that he never replaced one before. So it is a rare repair even 18 years after the car was built. The good news is used parts seem to be a good way to save on the cost. FYI, the 850's have two types of ABS pumps. These with TRACS and those W/O. I also believe later 1995 the pumps change to a square shaped unit whereas the older pumps look more like a black cylinder. You have to match the units correctly. I'm no expert in this repair so double check your part number for compatibility at the dealer.

I hope this helps someone if they get no fluid when trying to bleed their 850 brakes.
--
1996 855 TL Platinum Ed., 1995 854 GLT 5 sp, 1995 854 (RIP), 2005 V70R (badly missed)

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850 rear calipers "not' locked up 850

posted by jwalker on Fri Jul 13 08:08 CST 2012
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last visit: Fri Jun 6 08:39 CST 2014

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If the brake fluid is old the calipers can seize. Happened twice to the rears on my 240. Now I know better!

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850 rear calipers "not' locked up 850

posted by gzulli on Fri Jul 20 10:22 CST 2012
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last visit: Wed May 29 19:55 CST 2013

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The story keeps getting better. When trying to bleed at the rear brakes no fluid comes at all even with pumping the brake pedal. So I give up and take it to the dealer. (My dealer has two guys who do the tech competition and one of them goes to Sweden almost ever year, so they are good.) Anyway they get the same thing and say they started pulling the lines to see where a part went bad by seeing when fluid starts to flow. Apparently the ABS hydraulic modulator (the unit with all the lines coming out of it0 failed to the rear circuit. The internal valves must have frozen up and no fluid to the rear. The tech says he never saw one of these go bad, only a leaking unit some time ago when the 850's were newer cars.

So I am looking at a $400 rebuilt/used part and labor plus since the rear rotors are showing rust (from non-contact) the service manager says they should be replaced as well. I'm not sure if that is really necessary since they would show rust by sitting in my driveway if sitting for a long period of time.

FYI, in case anyone has the same issue in the future, there are different hydraulic modulators based on the vintage pre 95's different than 96 and newer as well as cars with TRACS and those without. So the pick and pull may be not have what I need.

So I am thinking a trip to the pick & pull is next up. How bad of a job is it to replace this unit for a shade tree mechanic? It's my son's car and I don't want him in something unsafe. I saw the parts digram and do have the service manual showing how this comes apart. It seems straight forward but I don't want to assume anything.
--
1996 855 TL Platinum Ed., 1995 854 GLT 5 sp, 1995 854 (RIP), 2005 V70R (badly missed)

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