Brake Booster Check Valve

[bpossel]

I will be replacing the brake booster check valve for a friend's '69 280SL this weekend.  It looks like the check valve is "heat shrunk" on the clear, plastic hose that sits between the booster and the intake man.

Is it possible to re-use this hose and simply replace the valve, or is a new hose needed also?

Has anyone ever done this one before?

Also, what direction should the check valve arrow be pointing?  Towards the brake booster or towards the manifold?

Thanks,
Bob

bpossel
Memphis, TN.
1971 280SL
1997 E320

[rwmastel]

My 230SL has the older vaccum hose that looks wrapped in black cloth.  The valve is just a snug fit and I don't recall if it had clamps or not.

I don't know about the clear plastic hoses, but I find it hard to believe that it's heat shrunk.  If the plastic hose was shrunk by engine heat, maybe you can cut the old valve out and still have enough hose left over?

Also, how do you know this valve needs replaced?  I replaced mine as a trouble shooting step when learning about my leaky brake booster.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[bpossel]

Hi Rodd,

Unfortunately the hose is not long enough to cut the valve out and connect the ends with the new valve.

I dont know for sure that this new valve will work, but from what I've read, its the next step in trouble-shooting.  The problem is that when the car is at idle and you apply the brake, the rpms jump by several hundred.  I disconnectd the hose with check valve, plugged the hole on the manifold and then stepped on the brakes again.  When I did this, no jump in rmps ...  so I suspect the valve?

Open to any other ideas...

Thanks,
Bob

quote:Originally posted by rwmastel

My 230SL has the older vaccum hose that looks wrapped in black cloth.  The valve is just a snug fit and I don't recall if it had clamps or not.

I don't know about the clear plastic hoses, but I find it hard to believe that it's heat shrunk.  If the plastic hose was shrunk by engine heat, maybe you can cut the old valve out and still have enough hose left over?

Also, how do you know this valve needs replaced?  I replaced mine as a trouble shooting step when learning about my leaky brake booster.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

bpossel
Memphis, TN.
1971 280SL
1997 E320

[rwmastel]

quote:Originally posted by bpossel

I disconnectd the hose with check valve, plugged the hole on the manifold and then stepped on the brakes again.  When I did this, no jump in rmps ...  so I suspect the valve?

If you disconnect the line, then you're not testing anything by pressing the brake pedal.  I suggest using a seperate line with no valve and see what happens.  Clamp on any kind of hose for the test.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[paults1]

My early 230SL does not have the brake booster check valve in the hose that connects to the intake manifold. Did the early 230SL's not have this valve? There is no noticable RPM increase when the brakes are applied. Also,I have a small leak of brake fluid that comes out between the master cylinder & the booster. Can anyone give me advice on these matters.

Regards, Paul

[waqas]

Bob,

I suspect the booster seals may be done. Rodd is correct, try a simple hose before you replace the check valve. These check valves have a little spring and a plastic cap, and I don't think they go bad very often (unless they experience some kind of trauma).

Waqas in Austin, Texas

[waqas]

Paul,

You should have that leak fixed as soon as possible. The brake fluid can also leak into the booster and eventually cause premature booster leaks. The two major reasons for booster diaphragm failure are brake fluid leaks and age of the rubber.

As far as the missing brake check valve is concerned, I'm not aware of any differences between brake systems of the earlier 230sl vs. later ones. My '65 230sl has the braided black vacuum hose and check valve mid-way from the intake to the little plastic bottle trap by the booster.

The 280sl is supposed to have a white plastic pipe instead of the braided black hose (not sure about the 250sl, but my '66 250se coupe has the black braided hose).

Waqas in Austin, Texas

[Anfinn]

The check valve is there to protect against blow-back pressure from the inlet manifold reaching the brake booster. So it should allow flow from the booster towards the manifold, to create vacuum in the booster.
Normally there is "no" flow through this pipe, so if you experience the surge in RPM when applying the brake, this would indicate that false air is sucked in through the booster. It is bust :evil:
The type of pipe you use in this line is not important. To check which way to mount the valve, blow thro' it.
Hope this helps.

'andy280

[mdsalemi]

Bob,

2 years ago, my replacement/new check valve assembly (all new) from MB was $23.  It was not worth fooling around with.  Of course it might be higher now, but as a consummate buyer of check valves and fittings (car wash you know!) it's a bargain at 3x the price.

Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America

[glennard]

quote:Originally posted by Anfinn

The check valve is there to protect against blow-back pressure from the inlet manifold reaching the brake booster. So it should allow flow from the booster towards the manifold, to create vacuum in the booster.
Normally there is "no" flow through this pipe, so if you experience the surge in RPM when applying the brake, this would indicate that false air is sucked in through the booster. It is bust :evil:
The type of pipe you use in this line is not important. To check which way to mount the valve, blow thro' it.
Hope this helps.

'andy280

If you get a surge in rpm, you must be running quite rich.  If your foot is on the brake pedal(right foot off the throttle), the engine should be idling.  Additional air from a leak should at first increase the rpm by 50.  A big leak's additional air should raise the air/fuel ratio and reduce rpm to eventually stall.

[paults1]

The M/B Service Manual for "Passenger cars starting after 1959" shows illustration of a check valve attached to the brake booster where the hose connects and goes to the mainfold. Its Fig. 42-16/4,item #21, for the 230SL, & shows it to be a black one. The one that I have is white & is illustrated, Fig.42-16/8,which is for other car models other than the 230SL. Now, because my ATE T51 200 booster has a white fitting on the Booster, do I need the inline check valve on the hose? Also I checked the inside of the Booster to see if any brake fluid has leaked into the cavity & luckly it apears to be dry. I guess I will replace the master cylinder instead of a messing with a repair kit.

Regards, Paul '63 230SL