Inline Tube - In Proportion
Tips for choosing the correct valve for your F/X-body disc brake conversion or
restoration
You bought that dream Camaro but the brakes is like stomping on a
brick. They fade, pull and don't stop the car any better than the parking brake. 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 69 Camaro. When I look closer I can determine the exact year from the valves that are with the set. Although that 69 Camaro will fit the 68 Camaro but this does not mean the car now has factory disc brakes. Lets start at the beginning.
The first year for disc brakes on GM F-body products is 1967 although most had four wheel drum brakes. Disc brakes were introduced as an option from 1967-1969. Starting in the 1970 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 brake masters are different from the drum brake masters in the size of the division and the size of the bore. Disc brakes required different pressures so the master was divided into two unequal 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-newer it had single piston calipers. Most after market sets come with the later 69 single piston calipers but this is not technically factory correct for the 67-68 cars. The single piston setup will bolt on all the 67-69 GM F-body's and the 68-74 X-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.
Lets start in 1967, engine performance was rising and braking
needs had to start to change. All 67 Camaro's came with standard drum brakes
with the option of power drum or power disc. All cars weather they were power or
manual, disc or drum had the same distribution block that hung below the master
cylinder. This distribution block was to provide equal pressure to all four
drums but also had a second brake warning function. When there was a loss of
pressure in either the front or rear system the piston in the valve made contact
with ground and the brake warning light would light up in the dash. The dual
master cylinder separated the system and the distribution block let you know if
there was a problem. This distribution block was used on all 67-69 F/X-body,
70-74 Drum only X-body.
1967 was also the first year for the dual master cylinder and disc brakes. The dual master was developed because disc brakes operate at a different pressure than the rear drums so now the systems had to be separated. Disc and drum master cylinders are very different. The drum is equal 50/50 and the disc master has a larger front bowl than the smaller rear drum bowl. Another change was all disc brake cars had an additional hold off valve up at the master cylinder used in junction with the distribution block. The function of this valve was to hold off the front brakes for a split second and once enough pressure was built up to activate the valve spring the valve applied 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 a couple of years to solve. The largest problem was the car had uneven braking causing the car to want to slide out.
1967 was a big year for brakes there were lots of changes
and components to work out. When disc brakes were introduced the dual piston
caliper was used on all 67-68 cars. This caliper proved to have many problems
with sticking and freezing up. A new design was soon on the way for 1969 which
was the single piston caliper that proved to be a problem free caliper and was
used from 69 until the late 80's. So all 67-68's had dual piston calipers and
all 69 and newer had the single piston caliper.
In 1968 the braking system remained mostly
unchanged. 1968 also carried over the dual piston caliper for the
last year. Engineers were trying to work out a weight problem.
Big block engines caused cars to be front end heavy and
current hold off valves cause the front brakes to dig in and the rear of the car
to lift causing the rear brakes to skid. So a rear hold off valve was added to
all big block cars and it is located right below the driver door. This is
another hold off valve so once there is enough pressure built up in the line it
bypasses the valve and continues to the rear wheels. Now there is a hold off
valve in both the front and rear brakes and the car is stopping nice and even
just the way it should. The new disc brake option is now beginning to be noticed and orders
are increasing and 1969 is going to bring big changes.
In 1969 the problem free single piston caliper is
introduced and the refining process of valves is in the beginning stages. A new
larger hold off valve is introduced and is working much better with the caliper
and the rear hold off valve is still on all big block cars.
Now disc brakes and performance go hand in hand and while disc brakes is still
an option so is horse power and people are beginning to realize to go fast you
have to stop fast and they are now willing to pay for the brake option. Now the
famous JL-8 option is available and this means four wheel disc brakes. On JL-8
cars since the pressure is 50/50 the same as drum brake cars it used the same
distribution block with out any other hold off valves.
In 1970 drum brakes are no longer available on the F-body
but live on a few more years in the X-body. With disc brakes now standard the single piston caliper is proved to be a winner
and is used up until the late 80's. The valves in the system is a different
story. Another change to refine the front hold off valve changes the shape of
this valve and the rear hold off valve that unused to be under the door is moved
up by the master cylinder and the distribution block in now made of brass and it
is all connected with a rats nest of lines (left picture).
In 1971 the mess gets cleaned up. Now that the system is worked out the engineers combine all three valves into a one part valve that is call a proportioning valve and is mounted below the master cylinder on a bracket (right picture). This new 71 valve works great and is used until 1981. This is also the valve that is first choice of the disc brake conversion companies and that is why it looks so familiar to us.
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. The ones with the large nut can be rebuild but it often costs more than
buying it new.
In the 70's these valves were made in both the cast iron and brass depending on
the year and the vendor. The cast
part did not hold up very well to the elements, the brass valves clean up nice
and are easily reused. The pin style wire lead was used until 1977 and the
plastic lead housing is 78 and newer. This valve was used on most GM cars up until 1981
and is a great valve for disc brake conversions. It is available from inline
tube in brass with both wire lead options although most cars use the metal pin
style.
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 on four wheel disc
cars. 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 offers valves, brackets and master
cylinders for any kind of conversion you choose to do. If your car is going for
that factory concourse correct look (pictured left) or is modified (picture
right) they can help. Inline Tube offers
kits for cars that are converting to dual master drum brakes, Disc / Drum
conversions or four wheel disc applications. In the modified version the valve is neatly tucked under the master. 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 brake line sets
for all valve applications.
Inline Tube can help with all your disc brake and valve needs. Valves are
available new for all applications and your unanswered questions are only a
phone call away.
