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  #1  
Old 04-04-2003, 04:31 AM
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Question SAFE brake fluid level for pad/rotor change

'95 W124 E420...what is the "safe" brake fluid level to be pretty sure that none spills out/over when I do a front pad/rotor change? Also, after the pad/rotor change, should I simply pour back in the brake fluid I siphoned out, or get a brand new bottle of brake fluid from M-B parts shop and top it off? I just had my brake fluid changed less than 1000km ago during my maintenance...so the fluid is new...thanx for any info...
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  #2  
Old 04-04-2003, 08:12 AM
LarryBible
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Definitely do NOT pour in the old brake fluid!

Your best course of action is to siphon suck out as much fluid as you can from the reservoir before doing your pads. Replace pads one at a time, do not remove both pads from the same caliper and then push the piston in. The pressure will push the opposing caliper too far out and require caliper disassembly. Just one pad at a time.

Once the new pads are in place and everything buttoned up, suck out the remaining fluid from the reservoir and fill with fresh fluid, then flush the brakes at all four wheels and the clutch if it is a manual transmission car. The entire brake hydraulic system should be flushed annually. If you do this, the hydraulics will most likely never need any attention.

BTW, if the brakes have not been flushed in awhile, run about a quart of fluid through them. Then if you flush them annually after that, you can probably flush adequately with something less than a quart.

Good luck,
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  #3  
Old 04-04-2003, 11:44 AM
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What Larry said.

Reuse is a big no-no. One of the worst possible ways to attempt to save $3.

You can use a plastic dollar store turkey baster to remove excess fluid from the reservoir.
Great 'specialty tool'!
That, or Williams-Sonoma sells stainless-steel basters with an MB logo on them...
(Do not use it for cooking afterwards, just to be safe...)

Some folks insist that one should never compress the pistons without the bleeders open to prevent the most contaminated fluid that lives in the calipers from getting pushed up through the Master.

I only take this extra precaution if the fluid has not been flushed for far too long.

Best of luck.
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  #4  
Old 04-04-2003, 04:55 PM
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[QUOTE]Originally posted by LarryBible
[B]D

Replace pads one at a time, do not remove both pads from the same caliper and then push the piston in. The pressure will push the opposing caliper too far out and require caliper disassembly. Just one pad at a time.

Larry,

You are scaring the begeepers out of me.

I am about to install new front pads on my W 202.
I assume. because it is a single piston caliper, I can remove both pads at once & retract the piston?
Thanks
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  #5  
Old 04-04-2003, 05:18 PM
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Yes, you can take both pads out at the same time for the single piston caliper front caliper.

But if you change the rear brake pads, the rear caliper is a 2 piston fixed caliper, and then only do one pad at a time.
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  #6  
Old 04-04-2003, 05:33 PM
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I think Larry meant 'do one caliper at a time'.

If you were to pull both calipers off, then compress the pistons on one of them, the pistons on the caliper on the other side might pop out too far. Don't bother asking me how I know this...

For a multi-piston caliper, it is nice to have a 'pad-spreader' tool to retract the pistons.

I have a couple that resemble a small scissors-jack. I think this type works best.
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  #7  
Old 04-04-2003, 06:19 PM
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Thanks guys.
I feel much better now.
There are probably a lot of things for me to learn on my first M-B, but that's okay, because I intend to keep it for a looooooong time.
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  #8  
Old 04-04-2003, 07:11 PM
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Opening the bleeder before pushing the piston back not only makes piston retraction easy [as there is no residule pressure left], but clears the old caliper fluid out . [-and that is where all the crap accumulates]..
Using this method , the Master level never changes BC you are not pushing the fluid back up the line...
A hose on the bleeder to a can/bottle makes it a clean, easy job...
Just make sure to close bleeder when piston is fully retracted.
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  #9  
Old 04-04-2003, 09:32 PM
LarryBible
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No, I DID mean ONE PAD at a time. Remove ONE pad, leave the other pad in that caliper in place, push the piston back into the bore and put the new pad in that slot. Then, remove the other pad in the SAME caliper, push THAT piston back into its bore, then put in the SECOND new pad in that caliper.

If you remove them both and push one piston into its bore, you risk pushing the other piston too far out of its bore. If this happens, the piston is beyond the seal and it will not go back in without disassembling the caliper.

I would NOT open the bleed screw when doing this UNLESS you have a pressure bleeder or a helper to properly BLEED the brakes afterwards. If you leave it closed, do one PAD at a time, then you can thoroughly flush afterwards. Flushing is much easier and more trouble free than BLEEDING air out of the system.

There are TWO lessons here; one PAD at a time and FLUSH YOUR BRAKES ANNUALLY. If you are flushing annually, there will be no ill effect from pushing fluid back through the lines. Thoroughly flushing annually will almost certainly prevent the need for ANY brake hydraulic repair during the life of the car.

Best of luck,
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  #10  
Old 04-04-2003, 09:52 PM
Bud
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The very first rule of brake work is to remove the cap on the brake fluid resevoir and cover the opening with a folded cloth/shop rag.

The purpose is obviously to prevent inadvertant damage done by fluid overflow.
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  #11  
Old 04-04-2003, 10:32 PM
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I always bleed the excess fluid out the bleeder screw when changing pads. It's very easy and there is zero risk of introducing air to the system -- since you're not pumping the brakes, there's no "draw back" pressure. When you stop squeezing, the fluid stops dead in the line, it is not drawing fluid and air back into the caliper.

Jeff Pierce
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  #12  
Old 04-04-2003, 10:35 PM
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Brake pad spreader?

I have always used a common old C-clamp to push the piston back into the caliper assembly. It seems to work quite well.

I have never done a brake job on a Mercedes, though. Will a c-clamp work, or should I be on the lookout for the thing that looks like a scissors-jack?

What do you call it, by the way?
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  #13  
Old 04-07-2003, 11:42 AM
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Richard,

It depends.
For single piston calipers, a c-clamp is usually fine.
For multi-piston calipers, it is not always possible to get a c-clamp in there. Sometime you can use 2 or more c-clamps to good effect on the ends instead.

That is why the expanding 'scissors-jack' type pad spreader is such a nice tool. It simply goes in between the old pads (where the rotor was), and retracts all pistons at once.
Otherwise, you would certainly need to observe the precautions Larry mentions.

There are a million other ways to skin this cat without special tools, however. Prying, pushing, prodding, twisting, vise-grips, channel-locks etc...
I have certainly had to make do over the years, but now I have the perfect tool that works %100 for all (well, almost all;not the spin-in type) configurations.

There are a number of popular brake pad spreaders marketed that resemble c-clamps in principle. Those seem rather silly if one has the right c-clamp already.

Best of luck.
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Last edited by csnow; 04-07-2003 at 12:05 PM.
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  #14  
Old 04-07-2003, 03:11 PM
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Also, don't use a screwdriver or some other prying device and leverage against the disk. You can easily put a wave/dent on the disk and then have to replace it as well.

I use large channel locks and grab the edge of the backing plate for the pad.

Larry is absolutely right: Do one pad per caliper at a time. I know from first hand experience: A stupid and costly lesson. My neighbors still remind me of the expletives they heard from my house that afternoon!
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  #15  
Old 04-07-2003, 04:49 PM
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Thanks for the wise words

I am beginning to see why both my 300D and my 300TD both stop when I want them to, and not 15 feet later, as did my 82 Buick egal: the MB's have two calipers, which surely should grab better and stop faster than one. The 1990 300D has ABS brakes which are definitely superior.

So whereas I was smugly satisfied with my collection of C-Clamps, I am beginning to covet that jack-like device previously mentioned and am considering buying one, as it could almost certainly pay for itself in a brakejob or two.

Who makes this? How much does it cost? Where can I buy one?
I imagine that it is too rare to get it from my usual source of tools: yard and garage sales.

I once bought a Snap-on 3/8 inch rachet for a measley $2.00, but such bargains are exceedingly rare. I got it from the former deceased mechanic's sister-in law.

It was her suggestion for a price, not mine.
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