Rear Brakes wont bleed, Where to start?

[JMarentette]

Hello, I am new to the new site used to be fairly regular visitor to the old yahoo site. I restored (cosmetic) my 1969 280sl Euro back in 2001 and have not done much with it since (raising kids). Well I am now getting back at it, I was annoyed by the condition of my brake reservoir (mice) and replace it today.  I bled the brakes for the first time and all went well in the front, however, the rear very little fluid drained and then upon filling reservoir and bumping brakes not bleed in the rears, fronts bled as expected.  Do I assume the lines are blocked?  Where do I begin.  I am not a gear head, but fairly self reliant, mainly because I wont trust anyone else with my baby.  Point me the way please.

Thanks
Jeff

[230slhouston]

Jeff,
Work you way backwards from the calipers. Crack the all fittings and then see if you get fluid out. I have had the case where the flexible pipes decayed on the inside and blocked the fluid passage. Looks great visually on the outside but they collapse.

Good Luck
Maistran

[JMarentette]

Maistran,

Thanks for the quick reply, does it stand to reason that the problem would be from the master cylinder to the point where the pipe devides because I am getting no fluid in either rear bleed screw?  Also what are flexible lines? All the ones I have seen appear to be riigid?

Thanks
Jeff

[glenn]

Hi, Each wheel has a flexible rubber hi pressure hose connecting the car body to moving(up and down, etc) wheel assembly.  The hoses plug up.  Loosen the hose ends.  Find the plugging. ..   ---?? Fix--- Problem solved

[230slhouston]

Jeff,

Glenn summed up where I would start. Look at the diagram from SLS item 5 an six are the flexible lines. I would crack the lines from the load sensing valve to see if you are getting fluid out. It will help isolate the problem.

Let us know how you progress, there are extremely know ledgable people on this who can provide further help.

Cheers
Maistran

[jameshoward]

Jeff,

If the car has sat pretty much unused for 8 years I would strongly recommend you replace the flexible hoses (the ones discussed below that run from the lines to the brakes). They need replacing periodically and I'd certainly do mine every 6-8 years with normal use. Brake fluid is pretty corrosive so I'd say yours would be unsafe after all this time. You could also look at replacing the brake lines if they're in a bad state, although trying disconnecting everything and blowing them through with air to see if there is a blockage. Replacing the hoses is not a hard job at all and it'll give you the confidence of  a safer vehicle.

Do some reading using the search function on brake bleeding. Note that you must NOT depress the brake pedal fully when bleeding or you'll probably end up needing to replace the master cylinder (some suggest a block of wood). I would recommend spending a bit of cash on a pressure bleeder. The Gunson one works off the tyre pressure (ensure pressure is below 15 PSI) and I've seen a Mightyvac work, which is much better. However, if the hoses are blocked or there's a blockage elsewhere, you need to sort that before attempting a bleed. You should also think hard about pulling apart the brakes if the car has sat for a long while and checking they all operate freely.

Lots of good info on the site, and ask questions if stuck.

JH

[glenn]

And, there is always--ream and clean with a piece of wire.  Eco-friendly

[graphic66]

Probably your proportioning valve is stuck. Mine stuck and I took it completely apart and cleaned it, it still wouldn't bleed until I pressed way hard on the brake pedal, really hard, and it must have pushed the little piston in the valve open because everything worked fine after that. It is located above the rear axle with 3 brake lines going to it. One from the master cyl., one from the right brake and one to the left rear brake. Loosen the one from the master cyl. and try pumping the brake, if fluid comes out loosen one of the rear brake lines at the valve, probably no fluid will come out. This means your proportioning valve is stuck. Again, mine was really dirty inside, but I would guess yours will just need some really hard pressure on the brake pedal to push the piston open. It is very simple to take apart and assemble. Just keep the adjusting bolt in the same place as it was. It is just a piston with a big heavy spring to take some pressure off the rear brakes.

[JMarentette]

Update:

 Well the good news is I finally got brave enough to get the car elevated and me underneath it to work on the brake lines.  The bad news is fluid goes into the proportioning valve , but does not exit either outlet.  I presume it is "stuck" as suggested.  It is currently out of the car.  First question, prolly a stupid one is what do I clean dirty , grimy greasy car parts with.  And secondly what process should I take to "unstuck" my proportioning valve?  Assuming I get this fixed I plan on replacing all lines /hoses from valve to calipers.

Thanks
Jeff

[JMarentette]

Well no guts no glory, I took the proportioning valve apart, the piston was "stuck" I was able to get loose and now does slide back and forth but feels "gummy" should I flush the valve with something or soak , I presume I don't want to lubricate it?

Help! I'm a danger to myself if left without guidance  

Jeff

[ja17]

Hello Jeff,

Go to you local auto parts store and pick up a couple of aerosol cans of "brake cleaner".   It the most widely used solvent for all brake parts.

[graphic66]

Clean it up with some steel wool and brakkleen as mentioned above. Get it to move easily and smoothly in the bore. Make sure the passages are clear with some compressed air. I used a brass brush from my gun cleaning kit mounted in my drill  to polish the bore. I lubed mine up with brake fluid before assembly. I used Loctite on all the bolts to ensure they stayed put. On mine, even after a full cleaning and reassembly it took a huge amount of brake pedal pressure to get it to start flowing. At first I thought I had put it together wrong or it was not going to work. I finally pushed really hard on the brake pedal and it must just push the piston in place and it has worked perfect ever since. These things are just a very simple piston spring combo and are way easy to take apart and service. My favorite cleaner for things caked with oily deposits besides brakleen is a marine product called decarbonizing fluid, an aerosol sold by outboard motor manufactures to melt away carbon deposits in cylinders and on pistons. It just melts oil and carbon deposits off. So don't be alarmed when you reassemble and it doesn't work with normal pedal pressure, give it all you got and it will spring to life and work great after that.
  Does anyone know how these things are calibrated? They are very adjustable and are factory set. They must have used a pressure gauge of some sort to calibrate them. It is very simple to change the proportioning with an allen wrench and a regular wrench. I left mine just like it was and it works great. But there must be a reason they aren't just built as a fixed unit and have an adjustment.

[JMarentette]

Hey thanks guys, with persistence I may have saved my self $300.  I did soak the unit overnight in vinegar, then coke.  It did  start to free up.  I applied pressure from a home made brake bleeder. I did then do a bench bleed and got a small amount of fluid out of both holes.  I then saw your picture you posted and decided to take the piston fully out. It is currently apart and I can see some corrosion in the regulator that was holding the piston from moving freely.  I will  clean as instructed and reassemble then do another bench bleed.  Thanks a bunch for your advice guys.  I will be buying a full membership tonight.

Jeff

[glenn]

Graphic66,  What is the name of the 'decarbonizing fluid' from the marine engine co.?

[graphic66]

 Here is a link to the product http://www.usboatsupplies.com/mm5/merchant.mvc?Screen=PROD&Product_Code=777185&Category_Code=BEJE&Store_Code=USBS
  The aerosol decarbonizing stuff is a must have for any shop. It really makes quick work of carbon and varnish buildup anywhere. We used it on the granite fireplace at my girlfriends Summer home, it really made quick work of the black stains and nothing we used before cleaned it.
  I copied this from here, and if you want to read a pretty good thread on this stuff   go to-  http://continuouswave.com/ubb/Forum3/HTML/007656.html  .
                  Mercury Marine has three products of this type for engine care:

• QuicKleen Engine Treatment--"Unique fuel tank additive for 2- and 4-cycle marine engines that combats buildup of combustion deposits, corrosion and performance-inhibiting effects caused by using poor quality fuels." This product comes in a bottle and is usually poured into the fuel tank is a recommended ratio to the gasoline.

• Fuel System Cleaner--"Maximizes fuel economy and horsepower and extends spark plug life. It does this by cleaning the carburetor, fuel system, intake valves and injectors." This product comes in a bottle and is usually poured into the fuel tank in a recommended ratio to the gasoline.

• Power Tune--"Keeps your engine running smoothly and quietly by helping remove internal carbon, varnish and gum deposits. Not for use during storage." This product comes in an aerosol spray.

Bombardier has similar products for engine care:

• Engine Tuner--"To prevent harmful carbon, gum and varnish build-up, use once every 50 hours of operation. Just spray through the carburetor intake of any 2- or 4-cycle engine." This product comes in an aerosol can.

• 2+4® Fuel Conditioner--Routinely added to the fuel tank in a recommended ratio to the gasoline.

Yamaha also has:

• Ring Free--"Special formula removes deposits that cause ring stick and wear. Cleans carbon and varnish from rings, pistons, combustion chamber, intake and exhaust manifolds, and carburetor. Aids in improving power and efficiency while extending engine life." This product comes in a bottle and is added to the fuel tank in a recommended ratio to the gasoline.

• Octane Improver--"Adds between 1 and 2 octane for more horsepower. It also cleans the carburetor and fuel intake system in the process." This product comes in a bottle and is added to the fuel tank in a recommended ratio to the gasoline.
  There are also some generic versions of the aerosol I have used, they all seem to work the same.
   Here is a thread on Seafoam fuel additive if your bored    http://continuouswave.com/ubb/Forum4/HTML/004251.html  I think I am going to try the Seafoam in my V-8 2 stroke outboard this year after the OMC decarbonizing treatment to see if it gets more gunk out. I always run the OMC carbon guard fuel additive in my fuel on all my 2 strokes. Now all the OMC stuff is Bombardier I think.
   Another link for the perpetually bored on fuel additives  http://www.fuel-testers.com/is_gas_additive_safe_with_e10_list.html
   Keep us posted on the results of your brakes. That little piston thing is way simple and there are no threads so far really covering this. I searched like crazy here previously and just decided to take it apart and try and fix it. It was just to simple. If anybody ever finds a rebuild kit with the rubber stuff that would be a good thing. I am not sure why, in the end it took so much initial pedal pressure to get it to bleed, but it has worked fine so far.
 

[114015]

Hello Jeff,

Good to see you and your silver colored 280 SL-Euro back in the Pagoda World !

We both had lots of discussions around your restoration process back in 2001 when I was still in Madison, WI before I returned to Germany in 2002.
I have missed your appearance in the internet pagoda world since then ; so, it is really nice to see you eventually back (here). Yes, the old Yahoo group has tremendously evolved since then. 

As to your brakes,
I recommend replacing the rear brake hoses (as supposed by Glenn & others) as well. Those really gum up with the years (perhaps decades ) and you never know how old they really are. The hoses are not expensive, so it is a meaningful replacement and maintenance issue to replace them by time.
Also, as you are already in into the brakes; I'd check the rear calipers as well. Perhaps you should clean out the pistons and replace the gasket kit.

Good luck and let us know about your progress.

Achim

[JMarentette]

Achim,

Fantastic, I am very happy to see you around and hopefully doing well.  I have a dirty little secret, I did buy a 107 and did a cosmetic restore on it since our last conversations.  I then sold it on eBay to a gentleman in Sweden.  I made a nice profit and invested it in some new parts for my 113. One of my up coming projects is replacing the softtop. I will tap the resources of the board without question. As you know most of my restoration before was making it look pretty, Now I am focusing on the mechanicals in hopes that I am not all show and no go.

Thanks for your input on the brakes, I have ordered all four flex hoses and will replace upon receipt.  I also am going to replace the rear brake pads while I'm at it. Again, very happy to see you here now and in the future.

Jeff
 

[graphic66]

Make sure to "fit" the brake pads. They need to slide easily into the caliper and sometimes need to have the edges filed and smoothed or you may get some brake squeal. I also put a little bit of never seize on the edges of the brake pads. I also put never seize on all of the brake line and brake hose threads.

[114015]

I also put a little bit of never seize on the edges of the brake pads.

...
Please forgive me my ignorance for not knowing what "never seize" is...

Maybe it's the same as copper paste ("Kupferpaste") which is commonly used on brake parts assembly.
At least copper paste can seize somehow on (very hot) exhaust manifold nuts with the years ...


Achim