6.9 - Brake Master Cylinder

[Styria]

I have been the proud owner of my 'Gleaming Beauty' for some fifteen years now and in that time, I have just about carried out all of my maintenance tasks, including a valve grind and de-coke some eighteen months ago with the invaluable help of Mercules.

Maybe some eight years ago, in line with carrying out a general brake overhaul, such as calipers, replacement of front and rear disc rotors, I also replaced the Master Cylinder. Not that there was anything wrong with the old unit, but I considered it prudent to 'go all the way' in the interests of reliability and employing my motto of "replace as much as you can all at the same time". I clearly recall the amount of difficulty experienced in bleeding the system - it just did not want to respond to 'bleeding' even with clamping the hoses and trying to bleed one caliper at a time. Of course, eventually, we sort of managed to attain some sort of braking efficiency, but I have never been really all that happy with their stopping performance. But like with some things, you tend to ignore some shortcomings by changing your driving habits, and after a while you just forget matters until, of course sooner or later, you get to compare.

In this instance, it is with my 450SE Goldie. The pedal action is super positive, the pedal does not depress when you start the engine, I had absolutely no trouble bleeding the brakes (remember, I rebuilt the front calipers and replaced the front hoses, and new pads). In fact, it was so easy, I just couldn't believe it. This now makes me think, maybe realize, perhaps with justification, that the Master Cylinder on Gleaming Beauty has a fault issue. When I bought it, it was an after market unit, brand new of course, but also well priced in comparison with genuine. Thinking back now to the difficulty in bleeding, the marginal action of the brake pedal, it could well be that the Master Cylinder has been faulty right from the start. Regards Styria

 

[BenzBoy]

And yet again, the moral of the story is buy genuine?
I put non-genuine accumulators on the front of the Spirit and the braking began to feel soft. The accumulators tested within specs but we replaced them with genuine and the brake performance and feel is back to what it should be.
Sometimes alternatives are OK but often OK is just not good enough.
Regards,
Benz-Boy

 

[Michel]

I tend to agree with BenzBoy.

Unless the disparity in the price is overwhelming or if the genuine parts are no longer available.

 

[Styria]

Michel, the disparity in pricing IS overwhelming and, of course, there are any number of parts that are not safety or driving related, where the genuine part is just so hugely more expensive. A lot's been written on this subject matter, and it was also a topic of some controversy when owners have referred to dealers as stealerships - in my opinion, a totally inappropriate remark as we really do not know what profit margin they're working on, nor do we know to what extent Mercedes Benz Australia is instrumental in setting the retail prices. Regards Styria

 

[TJ 450]

I'm reading this thread with interest.

I have observed much the same with my 6.9's braking sustem versus the 450SEL. I even pulled apart the master cylinder to find it in good condition inside. I still do suspect that there is a fault with it, though.

Not to digress too much, though regarding the subject of Aftermarket/OEM vs. "Genuine", obviously this is an ongoing topic of discussion, however the latter option is going to be superior 99.999% of the time.

A classic example of this is my recent (and ongoing) windscreen seal saga. I just purchased a genuine seal from the local dealer at the discounted rate of $330AUD. Bearing in mind that the RRP is $440AUD, they did their best. As expected, the part is far superior to the Febi-Bilstein version in that it has contoured corners and is of the original profile.

We shall see how well it fits in practice, however.

With brake parts though, you should be pretty safe with OEMs such as ATE/Teves etc. I theory, these should match the MB branded product in terms of performance and aesthetics.

Tim

 

[WGB]

THe brake feel of my 450 is much more precise than my 6.9.

I thought this was because the two cars had different master cylinders.
The advantage with the 6.9 system is that the fronts do not lock up so easily but I find the 450 system prone to early lock up.

Maybe it's just a difference between the weights of teh two engines.

I am about to replace my entire 6.9 braking system for no reason other than that it is all old but otherwise functioning quite well.

A new master cylinder, a new left front caliper (titty for pad wear sensor broken off my caliper), new caliper kits, new pads, new hoses, new M-B dot4 fluid.

I also shouted myself one of these as a luxury and it will free my wife up for more important domestic duties.

Motive bleeder 0260

I hope my efforts produce a good pedal.

Bill

 

[Styria]

Hi TJ 450, I too read with interest your comments regarding the Brake Master Cylinder and also the front windscreen rubber. Firstly, regarding the Master Cylinder - my brake man maintains that he will not, or does not like to pull apart, nor wii he recondition the unit on account of 'limited' access to certain areas of the Master Cylinder and also perhaps for lack of availability of reconditioning parts. Personally, I have never attempted to dismantle a unit, primarily on his advice. Nowadays, he says he will not touch them and I respect his judgement. Thus I am wondering if, in fact, you were able to recondition/rebuild your unit and were you able to procure all parts necessary to do this ?

Regarding the screen - very good, and appropriate advice. Many times I have read regarding the difficulty in fitting an after market rubber to the screen, especially when it comes to the fitment of the chrome (stainless ?) trim strips. I remember once spending some two to three absolutely frustrating hours with a windscreen guy, and there was just no way it was going to work as the rubber was 'continuous' and did not have the corners and I finished up returning it to the after-market supplier. The question I have is this : Do you have knowledge of any after market screen rubbers, whether front or rear, that one could use in our 116s ? A number of USA outlets are advertising various body rubbers, including those for front and rear screens, as well a door rubbers, claiming that they are as good as the genuine OEM items. I'd value your opinions or actual findings.

Hi Bill, I was not aware that the Master Cylinder units differed between those for a 450, and those for a 6.9. Do we know for sure? Seeing that you are undertaking quite a bit of work, are you going to fit metal braided hoses and/or/or as well, slotted disc rotors ? You may well finish up with the ultimate brake system. Regards Styria

 

[WGB]

Hi Bill, I was not aware that the Master Cylinder units differed between those for a 450, and those for a 6.9. Do we know for sure? Seeing that you are undertaking quite a bit of work, are you going to fit metal braided hoses and/or/or as well, slotted disc rotors ? You may well finish up with the ultimate brake system. Regards Styria

I checked on my EPC last night and the two master cylinders are the same part number so the difference in feel must be down to the relative weight of the engines.

I'll see when the brakes have been replaced.- and no there will not be metal braided hoses and slotted rotors.

Bill

 

[TJ 450]

Hi Styria,

Regarding the master cylinder. I simply reassembled it as I found it after cleaning with metho, as there was nothing wrong with the original seals or the bore(s) for that matter. Aside from the relatively soft pedal feel, the brakes do function well. The pedal is just really firm on the 450.

I'll start up a separate post about the windscreen seal findings etc.

Tim

 

[motec 6.9]

Hi guys its nice to know its not just me that has had a soft pedal i have in the past taken it to various workshops about the soft pedal including mbspares in Canberra and f wann in Adeliade when my car was on the road both telling me mine was one off the better ones even asked my uncle in Wollongong to have a drive as he bought a 6.9 new in 79 hence why i have allways wanted one he confirmed that his brakes were allways soft on his when new but never seemed to affect brake performace so maybe its just a side effect off the hydro suspension and pedal just seems to be soft without really being that way

 

[John S]

I have been told that you can firm the pedal up by going to slightly smaller ID brake hoses, such as PTFE lined SS braded hoses.

 

[Styria]

My theory is, maybe incorrect, that braking control, feel as well as braking efficiency, could well be influenced by the vacuum operated Servo Unit.

I seem to remember that ChrisP.'s Wilhelm 6.9 had far better brakes, and I had replaced the Servo Unit with a reconditioned item, yet the Master Cylinder was never touched. Those Servo Units can be reconditioned, but expect to pay close to $300.00. excluding cost of labour for removal and replacement. That usually adds at least another $100.00 to the price - mate's rates. Regards Styria

 

[WGB]

I am considering removing my brake booster just to paint it when I do my brakes but those couple of nuts on the bulkhead look a long way away.

Bill

 

[Styria]

Hi WGB, a few weeks back I thought I'd make an attempt to move the servo unit but, in the end, I gave it away as a fruitless job - it's just downright awkward and time consuming. In days gone by, I had always passed it on to people that'd charge me $100.00 - as I said, I considered the cost to be 'mates rates' - quite frankly, I would not like to do it for that price.

BTW, if you get yours re-built, as a rule they don't charge you for the paint ! So, on that basis, you're getting a bargain. Mind you, not sure what paint the Sydney mob uses, but it's flat or satin, it's very thin and marks easily. Regards Styria

 

[WGB]

Hi WGB, a few weeks back I thought I'd make an attempt to move the servo unit but, in the end, I gave it away as a fruitless job - it's just downright awkward and time consuming. In days gone by, I had always passed it on to people that'd charge me $100.00 - as I said, I considered the cost to be 'mates rates' - quite frankly, I would not like to do it for that price.

BTW, if you get yours re-built, as a rule they don't charge you for the paint ! So, on that basis, you're getting a bargain. Mind you, not sure what paint the Sydney mob uses, but it's flat or satin, it's very thin and marks easily. Regards Styria

I started my brake rebuild today and removed the servo unit in about 35 minutes. Three nuts are visible after removing the knee roll and easily removed with a 13 mm socket but the left upper one is not visible from underneath - but is when the instruments are removed and a couple of long extensions allow the socket to slip betwen the cruise control module and the pedal bracket.

Getting the booster out of the tight area it lives in is another thing and a bit of "Obstetric" theory sure helps.

When I removed the master cylinder an observation was the amount of surface corrosion present at the area of the seal between booster and master cylinder which would probably have affected the integrity of the vacuum and lead to poor or variable booster response.



Anyway the booster has gone off for an overhaul and there is a new seal included with the new master cylinder to be fitted on it's return.

Bill

 

[Styria]

Hi Bill, it'll be interesting as to what the cost will be. Here in Sydney I have been paying $278.50 (to be precise). Regarding the seal between Master Cylinder and the body of the Servo Unit, isn't that just a square rubber 'O' ring ? It'll be interesting to see if there is going to be an improvement in brake feel once you install the new unit. Regards Styria

 

[WGB]

I'm hoping for a major improvement in feel after the near failure I had a few weeks ago when the front brakes went awol while descending a multistorey carpark.

I am replacing the master cylinder, one front caliper with new (Caliper had a broken off titty for the missing pad sensor wiring on that side) and rebuilding the other three calipers and replacing all the flexible hoses.

All has been going well until I managed to round off the right rear brake line fitting this afternoon even though I used a flare spanner.

Replacement/repair will be tomorrow's worry.

Anyway the new caliper and resurrected harness from my parts wreck look nice.



Bill