Power Brake Booster Rod Adjustment

[aluminum]

Hello Forum :-)

1967 Mercedes 250 S 108 type sedan Power Brake help needed Please thanks in advance .


Wow I got this great 250S 4 Door and am working on it . The Power brake Booster is bad .
I replaced it but am having Problems I think with the adjustment to the master cylinder .


(1) I see under the Dash where you hook the Brake Pedal to the Booster Linkage a

attaching Bolt that is a Special " Eccentric " Bolt . You can turn it to make the Linkage longer or shorter . I also Note a Mark on the bolt perhaps as a reference Mark , Now perhaps someone just marked that But I think it came Marked ?

(2) I see No Adjustment on the Brake Rod coming Out of the booster going into the Master cylinder unlike most I have worked with on other Cars to set the stroke .


after the install of the booster the Brakes now work with Power rather then having no Power and having to push very hard to stop the Car and get it home .


(3) However the Power Brakes do not work as they should . When you hit the brakes is about a 1.5 second delay then the pedal go's down a bit more and the power effect begins to work like power brakes . However at first they don't seem like power brakes .


(4) after driving the car some distance like about 15 Miles a rear Caliper began locking up the brake pads on the rotor and the Wheel became very hot.
Suspect was the Master Cylinder Rod was to tight ( I replaced the Master Cylinder with the Brake Booster with a good one )
(5) However being not sure I then replaced the
" Rear brake pressure regulator " from a 67 Parts car I was lucky to get from a friend .
This . At first I thought this solved the problem but after driving some miles again the other rear Wheel began to get hot and the brake pads began to lock up again .


I think I need to make the under the dash " Brake Pedal Eccentric Bolt adjustment " and make the rod shorter .
So My Question's As I think the problem is the system is building up pressure and applying the Brakes

( A ) just how do you adjust This Under the dash Pedal to Brake Booster rod ?
Do I make the Rod shorter so that the Brake system well not build up pressure by turning the brake Pedal Eccentric Bold adjustment ?



I Am thinking this is the Problem the Master cylinder gets its stroke from the Non adjustable rod coming out of the Brake Booster under the Hood where Master cylinder bolts to the Booster . So I Guess you must adjust this from under the dash where pedal
hooks to Under the dash rod going to Booster.


Thanks in advance do you think I am on the right Track ?

Unfortunately I see no mention of how to make this adjustment in the Repair manuals

I do see that the
" Rear brake pressure regulator " reduces the brake pressure to the rear brakes so the tires well not skid when Brake pressure is applied Mentioned in Manuals .. Humm

but nothing on how to adjust the Under the Dash Pedal Rod to Booster ?

[BWhitmore]

Based on your description I would recommend the following:

Ensure that your brake booster is getting adequate vacuum (15-20” of vacuum) to operate properly

The mark on the adjustable rod was probably placed there by the factory or a previous technician and would be a good starting point for adjustment

Replace all of the brake hoses in the car - older brake hoses can collapse internally which will then cause a caliber or wheel cylinder to lock up

Rebuild the brake calibers.

[aluminum]

Thanks for reply
everything in the brake department is in good shape. Calipers are new in front / Hoses / Vacuum are all good .

the old brake booster I replaced was bad would not hold Vacuum so was replaced with a good one .


What this post is about Again: is exactly how do you adjust the " under the dash " Pedal to Brake Booster Eccentric that control's the amount of Push upon the Brake Booster , simple as that But ? How ?.
Anybody out their who knows how to adjust the Pedal rod to Booster under the Dash ?


No Mention of how in Manuals I found ?


When you drive the Car some miles the pressure builds up and the rear brakes begin to Apply & Drag become Hot and lock up



Thanks everyone and enjoy your Mercedes 108's and More

[dobrodan]

When you say "everything in brake department good" do you mean that you replaced the hoses in the front and the back? You didn't list the parts that you replaced, thus I am asking. As far as the brake pedal eccentric adjustment goes, there is very little travel in the adjuster. The idle travel should be 0.2 mm at the rod and 1 mm at the pedal plate. It can't be measured and should be adjusted by feel. Here is a picture of the page out of the manual on adjusting the pedal. By the way, the FSM is available through your dealer for about $100. The part number is 6510 1404 13. If they tell you it is not available they are wrong.

[aluminum]

Thanks a Bunch for reply
This is what I was Hoping for .
(1) This confirms that the ( Brake Power ) system well not work unless the Rod only returns to the " end of it's travel "
(2) As well it mentions that the Graduation mark must be turned to the rear ( so is a factory mark ! )

I shall try that and at the same time confirm whether if this is the shortest amount of travel setting or not . ( this well be easy as I have a extra Brake Booster with the Eccentric adjusting Bolt and linkage )

Great manual
The Car involved BTW is a 1967 Mercedes 250S with Manual 4 speed transmission Column Shift . ( So Photo in your Manual page Photo is exactly right )
As well I have the small Clutch Master cylinder that supplies pressure to the Slave cylinder As in the page photo from manual

Now as far as the travel for the Clearance of the brake Pedal master cylinder Rod
Eccentric Bolt Adjustment brake:
" Related to your post " I would say your wrong on that .
I looked close at that but did not measure it however I can tell you its about 1/8 of a inch adjustment and that's a Lot of adjustment .
As well " again as mentioned in Post is no adjustment at the Rod ( under hood ) from Booster to master Cylinder at all .

Re what I have replaced . well I was a line Mechanic for many Dealers for many years
as well as many independents . Point being I have a Lot of experience however always learning of some specific model setting . The Brake Hoses , Calipers , Master Cylinder ,
brake lines and the rear Brake Pressure Compensator are all in order

The Information you have given me is "great thanks for the help / heads up " right from the manual . Most often I don't look much at manuals except for Specks but not always

[aluminum]

Well I have Photos to load showing the Power Brake Booster Adjustment Eccentric so people can see what it looks like
However I don't see how to load Photos here ? Photos / Thumbnails / whatever they are called here ? I see no way to load the Good Photos related to this post if anyone knows where I Click on to load Photos please Thanks ..

Photos show the Slash Mark on head of the Eccentric Bolt adjustment shorten the Pedal Rod all the way when the Slash Mark is to the Rear of Car .. as well it shows just what the Adjustment Eccentric looks like . As well it shows a Photo image of how much adjustment their is in fact. Looks like about 1/8 th of a inch .
I have not yet had time to Make the Adjustment and road test the car as the seats are out just now and such . However I expect and Hope this well solve the Problem ending the pressure Build up as the car is driven some miles and the Power Brake not feeling like a normal Power brake .. With the adjustment Wrong it I expect is the same as the Brake is already on or depressed applying the brake somewhat and using vacuum as well to a point.
I was thinking I had to shorten the Rod However as well I thought perhaps the Adjustment was just to make the pedal's Match up Evan to each other . Car is standard Shift so has Clutch and Brake pedals side to side . Perhaps is a separate Pedal adjustment as well ? not sure .

is strange I see no attachment to add photos here if someone can enplane how to do such thanks in advance