Out of Proportion - 2001


Which valve do I need? There are so many to choose from and they are all different sizes and the fittings change as well. This is why it is difficult to pick out the right valve for you car. Some valves are used in conjunction with others and many are singular units which require no other valves. Most people call these items proportioning valves but very few are just that. Some are distribution blocks and others are hold off valves. Below we will go through all the different years and the applications.

Proportioning valves come in all shapes and sizes. These valves vary depending on the car you are working on. The problem is which valve should be used on which car. We asked the experts at Inline Tube and received the full scoop from installing a used valve to going with a new one.

There are plenty of disc brake sets on e-bay, at the swap meet, on junk yard cars, but most people don't know what will fit their car. It is important to know the exact year make and model of the car the brakes came off of. Most of the parts cross over to work on a number of cars but knowing what to look for is the hard part. When ever I see a disc brake set up at the swap meet and I ask what year it came off and the standard answer is 72 Chevelle. When I look closer I can determine the exact year. The 69 to 72 GM A-bodies and the 67-69 Camaro are not the same setup. Most people know aftermarket disc brake kits fit 64-72 GM a-body and 67-69 Camaro's but that does not mean a 67 Camaro can use a 72 cutlass set and consider the car to have factory disc brakes. Lets start at the beginning.

The first year for disc brakes on GM products is 1967. All cars before this point in time had four wheel drum brakes. Disc brakes were introduced as an option from 1967-1972. Starting in the 1973 model year front disc brakes were standard and front drums were no longer available. When disc brakes were developed so was the dual master cylinder, so all 1967 and newer cars had dual masters. Disc brakes required different pressures so the master was divided into two halves to provide pressure to the front and rear separately. This also meant that if a front line blew out the car would still have pressure to the rear brakes and vise versa.

The first thing that has to be cleared up is that all 67-68 Factory disc brake cars came with dual piston calipers, if the car is a 69-72 it had single piston calipers. All after market sets come with the later 69-72 single piston calipers but this is not technically factory correct for the 67-68 cars. The single piston setup will bolt on all the 64-72 GM A-body's and 67-69 F-body's. The first issue to converting a car to disc brakes is what kind of car is it. If the car is all factory correct and that is a concern, single piston calipers on a 67 or 68 car will certainly catch the judges eye and throw up a red flag. If the car is a driver or modified car no one will care if it has the single piston or dual piston calipers. The first question we ask at Inline Tube is are you looking for original appearance or are you looking for something that just bolts on and appearance may not be an issue.

The next issue is the proportioning valve since disc brakes were new in 1967 the valve was still being worked out for the next few years. The 1967-70 valves could comprise of as many as three pieces and with out all the pieces the valves would not work properly. In 1971 the valve was finally worked out and this design was used on most cars from 1971 into the 1980's. This is why it is important to know what are the correct pieces for your car. People generally refer to all blocks as proportioning valves. There are metering blocks, hold off valves, adjustable proportioning valves, residual valves, and what is the right combination? Once you get past the spindle and calipers the brake lines will drive the average guy insane. With the wrong caliper the hose may not fit. With the wrong valve combination the lines may not fit properly. The fittings sizes change with the year of the valve, and valves that look the same are not. Factory lines do not work with aftermarket valves and in some cases headers will hit blocks located on the frame. I have put together a set of photos to make anyone the expert. Next time you go to the swap meet you will know what to look for. Inline Tube makes lines to work with all the valves but you still have to know what valve your car has on it. Remember most of these cars are over 30 years old and parts have been changed, just because the car has disc brakes does not mean they are factory.

In 1967 all cars went to dual masters and disc brakes was an option. 1966 and older cars had a single master with drum brakes. On the right is the 1966 distribution block that can not be up graded to the dual master because there is no inlet for the second master cylinder line. The block on the left is also a distribution block but for the 1967 dual master cylinder. It does have the prevision for the second master line but can not be used on disc brakes alone because it does not proportion any fluid it is still just a distribution block but now has a low pressure warning light lead. This light comes on in the dash when low pressure is detected.

In 1967 when disc brakes were ordered it received the same brass block to the left as the drum car but had an additional hold off valve that is to the right. The function of this valve is to apply the rear brakes until the system built up pressure to activate the valve applying pressure to the front brakes. The rear brakes were to come on a split second before the front. This brake method soon caused braking problems that took years to solve. The largest problem was the car had uneven braking causing the car to want to slide out, just like doing donuts with the parking brake cables applied on front wheel drive cars. This is great fun in a parking lot with no other cars or obstacles around but not on the highway.

These hold off valves were used on 1967-70 disc cars and changed just about every year. Starting on the left is the 67-68 valve ,the middle valve is the 69 valve, and the right valve is off the 70 cars. Notice the fittings change on the valves so they will not work with the brake lines from different year cars. It is important to note these valve are not available new, the ones with the large nut can be rebuild but it often costs more than going to the later 71-72 valve that Inline Tube offers new.

In 1969-70 a third valve was added to correct problems from the previous years. This valve now went in the rear line to restrict pressure to the rear because rear drums were now locking up before the front brakes were even activated. By 1971 GM had all the problems worked out and combined all these valves into one valve that is now called a proportioning valve.

In 1971 the three 1970 valves to the left were combined and superseded by the valve to the right. This valve gives 70% of the stopping power to the front brakes and the remaining 30% goes to the rear drums. This valve is proportioning fluid and has corrected all previous braking problems.

This set up on the left is from a 1970 Camaro and the valve on the right is from a 71 Camaro. Again the mess on the left is replaced with a one piece proportioning valve. When looking to put disc brakes on any car the valve to the right which is available new at Inline Tube is the way to go.

In the 70's these valves were made in both the cast iron and brass. The cast part did not hold up very well to the elements, the brass valves clean up nice and are easily reused. This valve was used on most GM cars up until 1981 and is also available new from Inline Tube. (pictured to the left)

Inline Tube offers this set up for most cars that are converting to disc brakes. The valve is neatly tucked under the master and away from header heat on the GM A-bodies. The valve is available in the Disc/Drum version and the four wheel Disc version. The brass construction prevents rust and the bracket holds it securely in place. Inline Tube also offers disc brake conversion line sets for most of the more common applications.

The adjustable proportioning valve is usually used to tune in brakes. The valve goes in the back brake line affecting only the rear brakes. The valve reduces pressure to prevent the tires from locking up. If the car is running wider tires in the back and narrow tires in the front there is now more surface area in the back causing the rear drums to do all the stopping. This valve reduces pressure to even out the brakes. This valve is also ideal to be used with the distribution block shown earlier. The distribution block provides equal pressure to all four wheels and again this valve goes in the rear line to reduce the pressure to the rear brakes. Ideally the front brakes should be getting 70% and the rears 30%. On four wheel disc applications 50/50 is normal.

Inline Tube can help with all your disc brake and valve needs. Valves are available new for most applications and your unanswered questions are only a phone call away.

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