Brake Fluid Change Ouestion - BMW Luxury Touring Community
 
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post #1 of 7 Old Oct 8th, 2006, 3:59 pm Thread Starter
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Question Brake Fluid Change Ouestion

I am about to change the brake fluid in my 1999 LT which is for sale. It had a major service about 8 months ago, but I want everything to be fresh, so I can garner the best resale value.

My question: is it necessary to force the pistons back , as per the instructions, or does intermixing dilute the minute amount of contaminated fluid in the caliper ?

I've changed the brake fluid (following the BMW service manual) several times in the LT and recently found out that many mechanics subscribe to the intermixing theory, however I'm skeptical . What are your thoughts?
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post #2 of 7 Old Oct 8th, 2006, 4:03 pm
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my 2 cents

If you use speed bleeders and a Mighty-Vac pulling through from the bottom , it shouldn't be an issue.

ed early
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post #3 of 7 Old Oct 8th, 2006, 4:10 pm Thread Starter
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Quote:
Originally Posted by early1
If you use speed bleeders and a Mighty-Vac pulling through from the bottom , it shouldn't be an issue.
Yes, I use the Mighty Vac and pull it through.
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post #4 of 7 Old Oct 8th, 2006, 4:11 pm
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If you push the pistons back you will not overflow the brake reservoir. If you bleed the brakes with the calipers partially out, and you fill the reservoir to the top, the next person that pushes the calipers all the way in better be prepared for the excess brake fluid coming out of the reservoir.

Mike Trevelino
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post #5 of 7 Old Oct 8th, 2006, 5:00 pm Thread Starter
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Quote:
Originally Posted by mtrevelino
If you push the pistons back you will not overflow the brake reservoir. If you bleed the brakes with the calipers partially out, and you fill the reservoir to the top, the next person that pushes the calipers all the way in better be prepared for the excess brake fluid coming out of the reservoir.
I always suck the resevoir dry (turkey baster) before pushing the pistons back and then fill with fresh fluid before I hook up the mighty vac.

My question is whether it is important , or not, to go to the trouble to force the pistons back?
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post #6 of 7 Old Oct 8th, 2006, 6:25 pm
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I think that no matter what position the piston is in, you will still replace all of the fluid. There may be a ounce left in there that will be diluted with the new fluid. I say flushing it without pushing the pistons is better than not doing the flush at all.

Mike Trevelino
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post #7 of 7 Old Oct 8th, 2006, 6:32 pm
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Quote:
Originally Posted by patrick2000
My question is whether it is important , or not, to go to the trouble to force the pistons back?
I vote for a big YES.

There is a small amount of fluid behind the pistons and the circulation of the flush action is not sufficient to clear this out nor dilute it. If you retract the pistons there is NO old fluid left in the calipers. When the piston come back out to contact the pads there will be fresh fluid behind them.

John
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