August 18, 2004
Hi Glenn,
Thanks for the reply. I have had to explain this many times and will do again for you as you may run across this again. The '69 model P1800 was a crossover year for Volvo in the US, and they were trying to conform to EPA and safety stuff. They went to calipers in front and drums in rear and they also went to a dual line system. Because the front calipers need more brake pressure than the rear, they installed a creature called in-line reducer valves for the rear. This prevented the rear brakes from locking up. They are located above the rear axle, drivers side. The reducers are small and have valves in them with little O-rings and a piston so that when pressure is applied to the system they reduce pressure. Cool thinking for the time, but in '70 they went to rear calipers too!
Because it is a dual line system, Volvo set it up so that one rear brake was fed from the front of the master cylinder and the other side was fed from the back of the master cylinder, thus avoiding complete rear brake failure if the front or the back of the master decided to poop out. You can find this in your Volvo maintenance procedure technical manual under poop.
Not only that, but they put six bleeders on the front calipers, three per side. Two each came from the front of the master cylinder and one each from the back, given the same reasoning as mentioned above. The system works well, unfortunately they only used it for a short time and the reducers seldom went bad, so there are few of these parts around.
Don T. in Mass. has them for @ $100 apiece and I hate to bite the bullet on this. Volvo no longer carries them nor the rebuild kits. I have the part #'s, but they do me little good. I have checked Sweden, UK, most Volvo websites and boards and am waiting for replies. Most folks want to know what I'm talkin' about and I am tired. On top of this I towed this car to a local "Volvo Specialist" because it wasn't running properly. He charged me $300 to replace a float in my Stromberg, got it running and then charged me another $300 to replace the master cylinder. The master was good as I had good pressure to both front (6 bleeders) calipers. He still has my car, and I will drive it home if I have to use the emergency brake. -Carl.
Carl - Oh, now I know what you mean. I have always heard this item called a "proportioning valve". I looked it up on the GCP site (you really need DSL or faster Internet access for this), and found several listings*. These valves were introduced on 1800s earlier than 1969, but they had a different part number from yours. The earliest 1800s did not have the valve, and you may be surprised to learn that later models with rear disk brakes did have it.
As I understand it, the function of the valve is to prevent too much fluid from flowing out of the rear wheel cylinders (or calipers) when they are at rest. With the fluid level thus maintained by the valve, the brake pedal does not need to travel as far to deploy the rear brakes. I have no proof that this is the function of the valve, except that my '63 has no valve and alarming pedal travel if you're not accustomed to it. I was discussing this with another enthusiast at a meet once, and he ventured the opinion that the proportioning valve was introduced to correct this.
If this is true, it seems the most economical fix would be to remove the valve and make up new brake lines to go directly to the rear brakes. Or it might be possible to remove components from inside the valve to accomplish the same end. Note that I have never tried this, and given the dire hazards of malfunctioning brakes, you should test the brakes very carefully in a deserted area after making any modifications. If you make this modification and survive, I'd love to hear the tale. -Glenn.
*The GCP web site (http://www.gcp.se) displays copies of pages from Volvo's parts books for the cars. Brake proportioning valves and repair kits are recorded in the books for the 1800 with B-18 engine and B-20 engine. Only two of the following parts** show to be available from GCP, and the price is 0.00, so you'd have to contact them to find out if they really are giving them away. According to the catalogs:
part number description notes
B-18 671894-4 brake valve chassis number 16500 onward
273104-0 repair kit supercedes part number 273028
B-20 673760-5 brake valve, left up to and including chassis number 37549
673761-3 brake valve, right up to and including chassis number 37549
**677588-6 brake valve, left chassis number 37550 onward, including 1800ES
**677589-4 brake valve, right chassis number 37550 onward, including 1800ES
273090-1 repair kit There is a note, but it is not reproduced on the GCP site.