SBC Brake fluid change, DIY or not?

[dan1w]

I know this is something that has been talked about a lot on various forums, but I'd just like to pick your collective brains on whether you think doing this DIY is effective enough to make it worthwhile.

This is one of the jobs I need to do on my 'new' W211 and I usually do all work myself, but after doing a lot of reading I decided to get some quotes off of the dealer and a few indies that ranged from £45 to £135. When I asked the indy that quoted £45 whether the job would be done on star, as I suspected they said no but said they could do it on star for that price if I wanted, not sure I'd trust them on that one.

They also said that the idea that not all fluid is changed when doing the procedure by pressure bleeding isn't true accompanied by 'where did you read that, the internet?'

This is kind of backed up by the fact you can apparently find an official pressure bleeding procedure on WIS.

Also, I've read one report of a screwed up SBC being caused by the procedure being carried out on star.

So now I can't decide what to do, do it myself and perhaps not change all the fluid, or pay someone to do it and maybe they'll end up doing it exactly as I would have anyway, or worse using the wrong fluid.

Conversely, I could be paying the dealer to do it on star when it's unneccessary anyway?

 

[toolman1954]

Hi,
This may give you some insight as to what to do. I seem to recall reading another post where a Star was not used to bleed the system and all was ok. You may have to do a search on here for that.

How to Replace Brake Fluid on Mercedes AMG | MBStarTool.com Official Blog

Steve

 

[RAJ55]

Ive personally been pressure bleeding my SL55 brakes whenever its been due and never had any issues. Pressure bleeding is obviously very easy to do but as ive heard too it may not be a complete full flush. This has never bothered me as i guess the old fulid would mix with the new eventually and on the next flush it would be taken out.

 

[dan1w]

Hi,
This may give you some insight as to what to do. I seem to recall reading another post where a Star was not used to bleed the system and all was ok. You may have to do a search on here for that.

How to Replace Brake Fluid on Mercedes AMG | MBStarTool.com Official Blog

Steve

Thanks, I have the WIS document with the procedure on, I am also sure all would seem okay after pressure bleeding the brakes, but whether it actually changes the majority of fluid and is worth the saving I'm not sure about.

 

[dan1w]

Ive personally been pressure bleeding my SL55 brakes whenever its been due and never had any issues. Pressure bleeding is obviously very easy to do but as ive heard too it may not be a complete full flush. This has never bothered me as i guess the old fulid would mix with the new eventually and on the next flush it would be taken out.

Thanks, can you recall roughly how much fluid you used? I've read a report of someone using as little as 1 litre before seeing fresh fluid come through at all corners.

 

[RAJ55]

1 litre is enough but I've always flushed 2 litres through. At £10 per litre for the genuine MB dot 4 plus fluid I don't give it much thought. I flush 1.5L then drive it and use the remaining just to top up the reservoir bottle.

 

[190]

With respect to the possibility that not all the fluid is changed, the moisture in any remaining old fluid will migrate throughout the new fluid effectively reducing the percentage moisture content. It's a fundamental aspect of brake fluid design that this dispersion of water happens otherwise pockets of high moisture content would lead to brake failure. So you will still get a big improvement in boiling point provided the percentage of old fluid remaining is not too big.

 

[dan1w]

With respect to the possibility that not all the fluid is changed, the moisture in any remaining old fluid will migrate throughout the new fluid effectively reducing the percentage moisture content. It's a fundamental aspect of brake fluid design that this dispersion of water happens otherwise pockets of high moisture content would lead to brake failure. So you will still get a big improvement in boiling point provided the percentage of old fluid remaining is not too big.

I've read that when carrying out the procedure on star the pump ejects nearly 2.5 litres of fluid, whether the procedure is wasteful I don't know but you wouldn't have thought so. If that is correct then a considerable amount of the old fluid is left somewhere.

I found a good in depth analysis on another forum http://www.benzworld.org/forums/dis...ed-again-great.html#/topics/1349735?_k=qjgisg (hope I'm allowed to post that.)

Using the SBC schematic this guy figured out the areas that are inaccessible to the pressure bleeding process then calculated the volume of those areas and came to the conclusion that 1/3 to 1/4 of the old fluid is left in the system, so it seems a fair compromise to take his advise and do the procedure DIY so long as the fluid has been changed regularly in the past.

In my case I don't have any history of a bleed being done for quite some time so I'll probably try to get the first one done on star and hope the dealer/indy is honest about it and go diy from then on.

Dan

 

[dan1w]

It removed my link so guess I'm not allowed to post it!

 

[John]

I've posted links to other forums before so not sure if that is the reason - I would expect a mod to post stating they'd removed it for that reason:

http://www.mbclub.co.uk/forums/1242950-post6.html

 

[dan1w]

The link was gone immediately when I posted it, and definately there before I pressed submit.

I'll try again clickety click

 

[Druk]

I've posted links to other forums before so not sure if that is the reason - I would expect a mod to post stating they'd removed it for that reason:

http://www.mbclub.co.uk/forums/1242950-post6.html

If a mod or admin had removed it there would be a notice to that effect in an edit box.