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1981 280SL AT
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275 Posts
Discussion Starter #1
Renewing my brake fluid on my '81 280SL and have been doing some reading here. There seems to be some debate over using regular (Valvoline, Prestone e.g.) fluid vs. that from MB. Does the system require a specific formula that only MB produces? Are there parts that can deteriorate if one does not use the MB?

Also, I'm not sure if the system uses DOT3 or DOT4. Valvoline has a product that says DOT 3 and 4, is that going to be OK?

Thanks.

Anovak
 

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It Is What It Is, Dude
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22,841 Posts
.


You want DOT 4, any name brand is good, it need not be MB. DOT 4 is backwards compatible for Dot 3 systems, not the other way.
 

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1981 280SL AT
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275 Posts
Discussion Starter #3
Isthisdave, does that mean that the Valvoline stuff that says on the label "Synthetic DOT 3&4, Recommended for all ABS Disc and Drum Barke Systems Requiring DOT3 or DOT4 Fluids" will be OK? Just clarifying.

Thanks,

Anovak
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,326 Posts
Depends on where you are located. Hint. Hint.
 

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1981 280SL AT
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275 Posts
Discussion Starter #6
Thanks, guys.....I'm in New Mexico, about 195 miles from the nearest MB dealership, but I suppose I could have ordered some online. What do those little bronze-colored clips/springs under the front wheel hub do? I heard someone call it a radiospring, is that what it is called? One of mine broke off and I'm wondering how necessary it is to replace it?
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,326 Posts
I would need a picture to ID what you are referring to..

Hint=Complete your profile.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,498 Posts
Thanks, guys.....I'm in New Mexico, about 195 miles from the nearest MB dealership, but I suppose I could have ordered some online. What do those little bronze-colored clips/springs under the front wheel hub do? I heard someone call it a radiospring, is that what it is called? One of mine broke off and I'm wondering how necessary it is to replace it?
Rowdie is asking politely, if not mysteriously, to fill out your profile so we are not always guessing where you are and what you drive. Quick glace to the left...and we know.

Those clips you speak of have something to do with static and AM radio. I beleive an MB bearing kit comes with new ones. Important? I would not lose sleep over it.

Any name brand DOT 4 brake fluid is fine. Another member here likes to use 2 different fluids. One of which is blue. He alternates between the two so that every fluid flush he can tell if the flush is complete by the colour that flushes out.

How are you Anovak...long time no speak.
 

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1981 280SL AT
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275 Posts
Discussion Starter #9 (Edited)
Greetings and thank you very much for the useful information. I also apologize to the group for not filling out my "profile" earlier....I was actually ignorant about the thing to the left under the avatar and how it is used, but again appreciate the "education."

Nobby, yes, I think that is why I have seen them called "radio springs" before and I believe it was in an excellent post on this forum by slik560 (really admired your generosity for putting together such a helpful guide!). And, if so, I'll just wait until I renew the bearings to replace it.

Been fine, Nobby, thanks for asking and providing the link to benzypalooza, enjoyed the pictures and your 280 is too cool! I haven't seen one in that color combination since I left the "old country," very nostalgic!
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,326 Posts
Greetings and thank you very much for the useful information. I also apologize to the group for not filling out my "profile" earlier....I was actually ignorant about the thing to the left under the avatar and how it is used, but again appreciate the "education."

Nobby, yes, I think that is why I have seen them called "radio springs" before and I believe it was in an excellent post on this forum by slik560 (really admired your generosity for putting together such a helpful guide!). And, if so, I'll just wait until I renew the bearings to replace it.

Been fine, Nobby, thanks for asking and providing the link to benzypalooza, enjoyed the pictures and your 280 is too cool! I haven't seen one in that color combination since I left the "old country," very nostalgic!
Here is his twin
 

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Registered
1981 280SL AT
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275 Posts
Discussion Starter #11
To the naked eye, I am surmising those are 195 tires that came as original on the 280SL....how close am I?

PS - Nobby, I have been trying to adjust my engine hood to be more perfectly aligned with the fenders on each side.....there doesn't seem to be any adjustment to get it to go up and down. I have been able to loosen the bolts up next to the firewall and get a side-to-side adjustment, and the rubber bumpers up front allow some upward adjustment, but the "movement you need" seems to be a downward one slightly to make the hood match the fender line. Thanks.

Andreas Novak
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Good eye. They are 195/65 15. The car is now sporting 14" bundts with 205/70 14.
Those wheel that were on it are 15x7 ET 44 which is just not right.

That hood position may be normal. They all look a little off at the very front.
 

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1981 280SL AT
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275 Posts
Discussion Starter #13
Totally agree.....I put 15's on mine too, and in the 205 width which creates a much "healthier" looking footprint.

Hey Rowdie, I just finished draining the brake fluid reservoir atop the mastercylinder but found it has a front and rear compartment....only the rear emptied, any idea of how to get at the fluid in the front reservoir? It appears that the whole plastic reservoir being divided into two would probably mean the front part feeds the front brakes while the rear feeds the rear, but can't find a way to drain the front....any help appreciated.

Thanks,

Andreas Novak
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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I don't think it is possible to empty the front from the filler opening.
 

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1981 280SL AT
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Discussion Starter #15
Thanks. So, do I just empty the rear and then add new fluid? Will that then replace the old fluid in the front as I'm bleeding the front and adding the new fluid?
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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You must keep the reservoir full to make sure the front chamber does not run dry. Many posts on this where someone didn't realize this. I use a pressure bleeder.
 

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Premium Member
1975 450SL
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2,440 Posts
Welcome to the asylum, Anovak! Brake systems are a good place to start a DIY (Do It Yourself) habit: they're fairly easy to do, and you get to learn about how things work.

You don't really want to just drain the master cylinder reservoir and replace the fluid to change it out. The cylinder reservoir is a supply tank for the entire braking system, and it's a critical safety system. You want to do the full procedure to make sure everything is working properly when you're done.

Basically, when you push on the brake pedal, the rod from the back of the pedal linkage pushes on a piston in the 'master' cylinder. This forces brake fluid through the brake lines to each 'slave' cylinder, causing small pistons to move. On the end of each piston is a pad of metal and fiber that contacts the surface of brake rotor, creating friction and making the car slow down.

This is the most basic and bare description of how the system works. There are other things involved as cars got newer to increase the pressure on the pads with less pressure on the pedal, make the system safer and more reliable, inform the driver if something is wrong, and try to prevent the wheels from locking up during braking to lessen the possibility of skids.

Brake fluid has to have some very special properties to do its' job reliably. It can't be compressible. It has to withstand the heat generated by the brake pad + brake rotor contact (can get VERY hot; in racing, glowing hot rotors are common) It has to be non-corrosive to the parts of the brake system. And it has to be stable over a fairly long span of time.

Engineering for all these requirements have resulteed in a fluid that works very well, but has a few special problems that makes brake system maintenance just a little more complex than making a bowl of microwave ramen soup.

The fluid is hygroscopic: It absorbs water out of the atmosphere. When it absorbs water over time, the heat from braking will cause said water to boil to steam in the brake lines, and steam is very compressible. This can cause brake fading (the pressure in the system decreases) and steam is also somewhat corrosive. As the fluid absorbs water, it very politely changes to a brownish color, informng you of its' compromised status.

Brake fluid is also rather corrosive to auto paint, so you don't want to leave any drips or splashes alone, you want to clean them up promptly. It's also very toxic, so don't go drinking it. :)

Now that you have a bit of an idea of how the system works, let's get to your situation where you are changing out the brake fluid.

You need to change out all the fluid in the whole system. Mercedes reccommends doing this every two years, since the cars are fairly heavy, and to keep with their reputation for safety. The system can be looked over for signs of possible problems. (also, it's a revenue generator for the dealerships;) )

The correct way to change out the fluid it so flush it with new brake fluid. There are small valves at each slave cylinder called Bleeder Valves. If new brake fluid is put into the reservoir, and the bleeder valve is opened, the old fluid will be flushed out by the new fluid., basically. The trick is that it can be slow and it may not work all that well to do just that, so there have been tools and procedures created to speed things up, make sure all the old fluid is replced, and make sure no air bubbles get into the system. (Air is compressible, we went over why compressible is bad earlier.)

The historical, basic and cheapest method is the 'two man' method. One person sits in the car, one goes to each wheel cylinder with a catch bottle and opens the valve while the one in the car gently presses on the brake pedal and holds it down. At the bottom of the stroke, the valve is closed, the pedal is released, and the reservoir is checked. This is repeated until the new fluid comes out of the valve cean and clear of bubbles at each wheel. The traditional sequence is to start at the wheel farthest from the master cylinder and work to the closest wheel.

There are a couple of hitches to this procedure, the first being that it needs two people, second that it involves frequent checking and refilling of the reservoir, and third that the piston in the master cylinder can be run out of its' normal range. This can result in damage to the seals of the piston from deposits and wear in the cylinder. It also has been known to have a lot of trouble doing it correctly in a vehicle with ABS (Antilock Brake System).

The second method is to obtain a special vacuum pump designed for the purpose, and draw the fluid from the reservoir through the system and out the bleeder valves. Usually, you can get a Vacuum Bleeder Kit from most auto parts stores fairly inexpensively. You still need to check the reservoir often, but the job is only supposed to need one person.

I haven't had that much luck with vacuum bleeding, in my various tries. The vacuum hose doesn't get a good seal on the fitting of the bleeder valve, the pump doesn't draw enough vacuum, and the catch bottle in the kit always seems to leak, but some people have better luck than me, maybe they got the kit with a good pump or a non-leaking bottle:(

The third and most effective method is a Pressure Bleeder. This is a device that has a fitting in a cap that replaes the normal reservoir cap, and has a hose to a reservoir of fresh brake fluid that can be pressurized to force the new fluid through the system to the bleeder valve. They can be purchased for $70.00 or so on up, or there is even a set of instructions on the internet for making one yourself for $25.00 out of parts you can get at a hardware store and a reservoir cap for your vehicle. The DIY $20 brake bleeder

I went with the DIY brake bleeder, and it makes the job very easy. In fact, it takes longer to put the car up on jackstands and remove the wheels than it does to bleed the brakes. It is also supposed to be the best for working with an ABS equipped vehicle, as the valve and control body for the ABS can have problems with the other methods, reputedly.

Hopefully, I've answered your question and given you an idea of why and how, so you can do the job with confidence. But; according to Murphy's Law, there is something I left out or wasn't clear on, so please feel free to ask any questions. The guys here will usually be more than happy to help if I'm not around.

Good luck,
Scott

p.s.
As my dad used to say: "Why let some idiot screw the job up for parts and labor when you can screw it up for just parts?" :D
 

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It Is What It Is, Dude
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p.s.
As my dad used to say: "Why let some idiot screw the job up for parts and labor when you can screw it up for just parts?" :D


My dad used to say, "Doin' the labor is the easy part. And don't let me ever hear you tellin' your mother I said that".
 

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1981 280SL AT
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275 Posts
Discussion Starter #19
Radiotek, Rowdie, isthisdave, thanks for all the help. I completed the job and test-drove for about 30 minutes through the neighborhood, stopping every hundred yards or so from about 30mph and the pedal feels firm and stopping is very good.

My question (that was mostly answered) had to do with the fluid reservoir above the mastercylinder. It has two compartments, and I wasn't sure if I needed to try to empty out the front (towards front of vehicle) as well as the rear.....

Rowdie was right, can't do that until you have filled the rear, bled the rear brakes until the clear fluid appears and without any air bubbles, filling the rear reservoir after about every 2-3 pumps, and then moving to the fronts.

When you open the front right, you begin to see the front compartment of the reservoir lose fluid and then you fill the rear back up to the top, maybe a bit beyond the "MAX FILL" line and repeat the process, checking the reservoir and filling when it drops below the "MAX FILL" line. The old fluid in the front reservoir is slowly replaced with the clear new fluid. Repeat for the front left following the same process and that's about it.

So, successful and many thanks to you all for your help.

Andreas Novak
(PS - isthisdave, venture a guess as to where you got your username.....Cheech and Chong, right?);)
 
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