So at the brake fluid junction there is this pressure switch of some sort. Mine is leaking.

What is it's function?
And

Can I buy just the switch? all I see on IPD's website is the whole junction for sale.
Thanks

 

what year/model car is this? on a late 240, the contact kit is Volvo 272702... I'm not finding it on a 940's parts catalog.

the switch senses any pressure differential between the two brake circuits and lights the warning indicator on the dash that you have a braking problem, as any differential likely means a leaking brake cylinder.

 

Volvo used to offer a repair kit for it but is no longer available. Unless you want to source the o-rings for it yourself, your only choice is to buy a replacement.

I would buy the OEM part for this. Mine was leaking and I bought the aftermarket version (MTC) and it arrived defective. It leaked right out of the box.

 

272702 appears to still be available here, (this is a volvo dealer), Switch kit made by Volvo. #272702

but before you go out and buy this, what year/model Volvo is this?

 

Thanks pierce, That makes sense as to its purpose.
It's for an 86 240.
I used to have my year/model in my sig, not sure why it doesn't show it sometimes.

 

One more question is this switch threaded into the junction box?

Seems like mine would just turn freely but the leak had slowed too....?

 

dunno, I've never replaced one, but it can be seen here, in the bottom box...

 

You have a 240 - correct? The pictures that Pierce is showing are for the 740 master cylinder - not your junction box.

If your junction box is leaking where the switch is, the problem is not the seal around the switch. Instead the problem is the o-rings inside the junction box. They keep the brake fluid from getting to the center part where the switch resides. The rebuild kit from Volvo is no longer available but if you want to source the o-rings yourself you can repair your old one.

 

that is the 740 picture, but VADIS says the 240's used the same 'contact kit warning valve', PN 272702

 

Everything I found says the 240 & 740 share the same box....?

I will end up just getting the o-ring (probably viton?).

It's at least a little ironic that the switch that is supposed to tell you the system is losing pressure seems to be the most consistent leak on these cars....
To top it off the warning light never came on.

Thanks guys

 

Is this the part you are referring to:

https://www.ipdusa.com/products/5135...junction-block

The function of this part is to distribute the two circuits coming out of the master cylinder to the six lines running to the wheels. As far as I know neither the 740s or 940s had this feature (nor did the 240s equipped with anti-lock brakes). Inside this block is a little piston that should stay centered if the pressure between the two circuits is equivalent. If one of the circuits springs a leak, the pressure will not be balanced and the piston will shift to one side causing contact with the switch turning on the brake light. The piston has two o-rings - one on each side of the center switch. It is these that are leaking. Take it apart and you can easily see how the whole thing works

 

Ok Act, you've got me confused (happens often). I don't believe I've got a leak between the two circuits. I know that I have a leak at the switch though.
You were referring to some sort of internal o-rings, yes?

Btw now after bleeding my system and cinching down the safety switch on the junction box I still have a fluid leak and the warning light is coming on about 1/3 of the time. Yet my brakes have never worked better.....

 

I don't know what "Safety switch" you are referring to? Was the junction box I posted in my previous post the item that is leaking?

If so, you can take it apart by removing the end caps and the switch. You'll find that there is a piston inside that has o-rings on either end. This piston separates the two braking circuits. If pressure in the two circuits is balanced, the piston stays centered keeping the switch turned off. If the pressure between the two brake circuits becomes unbalanced, the piston shifts to one side turning the switch on which lights the brake lamp on the dash.

I didn't say you have a leaking circuit. The o-rings on each side of the piston are intended to keep fluid from getting to the center of the piston where the switch resides. The o-rings leak and you get fluid leaking out of the switch. Cinching down the switch won't help - you need to remove the piston in there and replace the o-rings.

Take it apart using care to document how to put it back together. If you look at it you can figure out how it works.

 

Ok, I am pretty sure I follow you. Like you said I probably just need to take the thing apart and see how she works.
Thanks for the awesome info.

 

Not an easy job. About 6h probably only 4 next time. The block isn't cheap either at around $140....

 

Yes it's not a fun one. Imagine how I felt after installing the aftermarket replacement to find that it leaked as well and I had to do it all over again.

Finding o-rings isn't that easy either. I did find this site yesterday:

The O-Ring Store LLC, We make getting O-Rings easy!

I was looking to replace the o-rings in my hydraulic jack. You should be able to find what you need there. However there is a minimum quantity of 13 so you'll have extras. They do only run around 4 cents apiece though. Shipping will cost you more than the o-rings but cheaper than the OEM replacement junction box.

 

The only reason I went with OEM was so I only had to hopefully waste one Saturday.

I thought about hunting some o-rings but again I could see myself wasting a couple saturdays if I messed up.

 

Yeah - I hear you. I just spent 2 hours educating myself on o-ring construction, chemical resistance, hardness, sizing, etc. All to repair my jack.

 

6 hours?

I replaced this on my 85 244 this summer and it took me about 2 hours with changing the master cylinder at the same time. I read that many recommended doing both at the same time. Clean all the brake lanes going to the junction box and spraying them with aerokroil the night before. Have a set of flare wrenches ready for removal and install.

Biggest pain is bleeding all the brakes when done.

 

Yeah - Portland isn't really in the rust belt. Try it on a 26 year old car that spent it's winters bathed in salt.