240 brake fluid leak

myspv · Post by **myspv** » 29 Oct 2006, 10:48

hey folks --
i have a 1987 245 and am trying to figure out a mysterious brake fluid leak. i have checked all lines, around the calipers, at the distribution box, below the master cylinder and the resevoir. all seems okay. i also just bled the brakes and flushed the system with fresh fluid. in doing so i used my power bleeder and didn't find any loss in pressure through the system there.
i think i may have found some fluid, but i'm not sure if it's even brake fluid though it's light and slightly oily. i found it just under the car where the firewall meets the floor pan under the driver's seat. thing is i can't figure out where it might be coming from if it is brake fluid. nothing drips down the engine compartment side of the firewall and i pulled up the carpeting inside the car to see if i could get a better look from in there, but nothing.
my hunch is that it could be coming from the brake booster, but that's really just a guess. i'm hoping someone here has experienced similar problems and can help point me in the right direction. are there any known problems with a seal in the brake booster?
thanks in advance.

Post by **billofdurham** » 29 Oct 2006, 11:45

Is the fluid in the reservoir going down at all?

When you pressure bled the system did you spill any fluid in the area of the master cylinder?

Also check where the fluid reservoir sits on the top of the master cylinder for leaks. It is just a push fit into the cylinder with two seals to stop the fluid coming out.

There should be no brake fluid in the brake booster, it is there to assist the driver to apply pressure to the master cylinder by vacuum. If fluid is getting in there it will be leaking from the rear seal of the master cylinder.

Bill.

myspv · Post by **myspv** » 29 Oct 2006, 14:36

Bill, thanks for your response. You saw I cross listed this question elsewhere.

"Is the fluid in the reservoir going down at all?"

Yes, that why I believe there's a leak

"When you pressure bled the system did you spill any fluid in the area of the master cylinder?"

No.

"Also check where the fluid reservoir sits on the top of the master cylinder for leaks. It is just a push fit into the cylinder with two seals to stop the fluid coming out."

I see no leaks here either. Before I started bleeding the system with the pressure bleeder I pressurized the system at the resevoir to 10 psi and didn't see any pressure loss after 10 minutes or so.

"There should be no brake fluid in the brake booster, it is there to assist the driver to apply pressure to the master cylinder by vacuum. If fluid is getting in there it will be leaking from the rear seal of the master cylinder."

My thought exactly. So you suggest I look into replacing the rear seal of the master cylinder? Not that I can see into the booster to tell if there is any fluid in there, but maybe it's around that seal where the leak is?

Post by **billofdurham** » 29 Oct 2006, 15:52

If the leak appears to be coming from the booster area it is a fair bet that it is coming past the main seal.

When you use a pressure system to bleed or flush the brakes you actually put pressure on the master cylinder seals in the reverse direction. In view of the age of the car and assuming that the seals are the originals this reverse push could have been enough to upset one or more of them.

Bill.

myspv · Post by **myspv** » 29 Oct 2006, 19:05

that all makes sense.
i don't believe that my using the power bleeder when i flushed the system upset the seals in the first place, however i suppose it could have worsened the situation. i say this because the leak manifested itself before i ever started bleeding the brakes. i noticed the soft pedal feel, saw that the level in the resevoir had dropped off, i topped it up as a temporary measure, and then bled/flushed the entire system with new fluid because i figured there to be some trapped air in the system and that it was due to be changed out anyway. days later the fluid level dropped again confirming for me that there's a leak somewhere. the only spot of wetness that i've found is by the left floor pan under the driver's feet. it's hard to confirm that it's even brake fluid as it was just kinda wet and oily, but it's a strong lead to follow.
thanks for your help. i'll post back with my findings.

Post by **billofdurham** » 30 Oct 2006, 12:18

Loosen the master cylinder from the booster and if it is leaking you will find fluid there. If you do it carefully enough, without bending pipes, you will be able to replace it if it is not the culprit.

Bill.

wojeepster · Post by **wojeepster** » 01 Nov 2006, 18:12

240 frequently leak brake fluid from the junction box where the brake warning light is connected. I think you can read about it on the www.ipdusa.com site Mine did this but I was able to fix it withoult resorting to buying it.

myspv · Post by **myspv** » 08 Dec 2006, 21:29

thanks for all your help. i unbolted the BMC and found that fluid had leaked past the main seal.
i have now just finished doing a bunch of work on the car (pads all around, new brake hoses, new rebuilt RF caliper, new ball joints, new BMC) and now all is good. after disconnecting everything and reinstalling i had to bleed the brakes twice (!) to get all the air out. but it all is well.
thanks again.
i know all this started a while ago, but i had to wait to get money situated ...

Post by **billofdurham** » 09 Dec 2006, 12:13

Thanks for the update.

Good to know you are all fixed up.

As a matter of interest I have known professionals who have had to bleed the system more than twice to get rid of all the air. The main thing is, it is all gone.

Bill.

stjames · Post by **stjames** » 23 Nov 2012, 13:10

billofdurham wrote:Is the fluid in the reservoir going down at all?

When you pressure bled the system did you spill any fluid in the area of the master cylinder?

Also check where the fluid reservoir sits on the top of the master cylinder for leaks. It is just a push fit into the cylinder with two seals to stop the fluid coming out.

There should be no brake fluid in the brake booster, it is there to assist the driver to apply pressure to the master cylinder by vacuum. If fluid is getting in there it will be leaking from the rear seal of the master cylinder.

Bill.

Hi, I have a related question/situation: I do appear to have a leak directly beneath the brake fluid reservoir. When you say it is "just a push fit" I assume that means I can just pull it off, replace the grommets, and push it back into place - is this correct? Can you tell me any more specifics on performing this task? It sounds like I'll need to be careful not to get air into the system etc.? Sorry, not much of a mechanic and can't find any specific How To info on this task. Thanks.