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I'm currently working to restore my 1970 SS396's front end and engine
compartment. My immediate project is brakes related: master cylinder, booster,
hold-off valve, pressure differential valve/switch, and hard & soft lines.

There is precious little information concerning the hold-off valve - the item
that is attached to the outboard side of the master cylinder. There is also an
incredible amount of confusion as to what it is actually called as it sometimes
called a proportioning valve (as is the pressure differential valve/switch,
which mounts to the frame rail underneath the booster and by the Z-bar (if you
have manual trans.) My searches for information on how to refurbish it, both
here and on the net in general, revealed virtually NOTHING. That is until I ran
across this site completely by accident:

https://www.musclecarresearch.com/gm-1233464-rebuild

The GM part number they list is 1233464 and not 2226261, however the photos
shown clearly show the 2226261 stamping. I wrote to Scott Hollenbeck of Muscle
Car Research and asked him about compatibility between the two numbers, and
received the reply that they are similar enough for the rebuild kit to work for
both. Further investigation by Scott showed the GM part number and the stamping
in the cast iron are two entirely different things. Not sure what the stamping
refers to, but I personally have two units with the same stamping, and
musclecarresearch.com shows a valve with the stamping.

This is the rebuild kit:

https://www.musclecarresearch.com/gm-metering-seal-kit-2

Go here to view images from the break down of unit:

https://picasaweb.google.com/106242937059319515061/ChevelleBrakesRestoration#618
6630302374576882
 

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Step 1 - Carefully remove rubber dust cap. My rubber cap came off cleanly and
easily without tearing. Yours may, too. Wire-brush the exterior to clean it up
as much as possible.

Step 2 - Soak piston end in PB Blaster. There is a snap ring that is very hard
to see and probably pretty coated in surrounding rust.

Step 3 - Compress the piston into the case body using a C-clamp. Use a socket to
protect the piston and its central aluminum pin from marring and damage. I used
a pick to clean the snap ring and valve body of as much rust scale as I could. I
let it soak again overnight in PB Blaster with piston compressed and ring
exposed.

https://lh3.googleusercontent.com/-RxMIBgjfvus/VdtTdpK2DBI/AAAAAAAAToM/g53B
c3JDVGI/s912-Ic42/IMG_5552.JPG

Step 4 - With piston compressed, pry out snap ring. I found that rapping the end
of the snap ring with a very small blade common screwdriver and a very tiny
hammer (upholstery in my case) was enough to get it loosened. From there is was
easy to pry the ring out.

The piston on my unit stayed completely compressed. Using two broad common
screwdrivers I gently levered the piston up enough to get a grip on the top ring
with soft jawed pliers. I found that working from 180° opposite directions gave
the best and gentlest results. When you can get a grip on the top ring of the
piston with protected pliers, twist and pull at the same time to remove the
piston.

https://lh3.googleusercontent.com/-Lf5DWLOIqsE/VdtTes1VNDI/AAAAAAAATog/f61L
9XZw39g/s720-Ic42/IMG_5554.JPG
https://lh3.googleusercontent.com/-I6nNUmDDisI/VdtTkOQ_2aI/AAAAAAAATqM/OJOQ
2FXxDo4/s720-Ic42/IMG_5575.JPG
https://lh3.googleusercontent.com/-I3L4NKtsApM/VdtTkSTcHZI/AAAAAAAATqQ/w5hu
wbYOnTg/s720-Ic42/IMG_5576.JPG
https://lh3.googleusercontent.com/-9txRa27ccHQ/VdtTkhpT9II/AAAAAAAATqg/uuOu
zGer5Bk/s720-Ic42/IMG_5577.JPG

Step 5 - Dissemble the piston assembly. Remove o-rings and rubber seals in
preparation of soaking metal parts in cleaning solution.

https://lh3.googleusercontent.com/-BcSSJJjv-Yk/VdtTmFGIgGI/AAAAAAAATq4/xVR2
Ts5rYG0/s912-Ic42/IMG_5583.JPG
https://lh3.googleusercontent.com/-c0uSE7nU1yo/VdtTmWh_PaI/AAAAAAAATq8/ZHx2
4Gvo8W8/s912-Ic42/IMG_5584.JPG


WARNING - only perform Step 6 if you are absolutely certain you have or can
get replacement seat inserts. The rebuild kit cited above does NOT include
replacement seats, nor does musclecarresearch.com offer them at the time of this
writing. I had tremendous difficulty finding a source for them (from a retired
brake man) and do not suggest their removal as a matter of course. If anyone
knows of a reliable source for replacement tube seats, please share. These are
the seats' specs to help you find replacements:


https://lh3.googleusercontent.com/-L6GHaybCECE/VegslKOcSmI/AAAAAAAAT9k/FXhA
-iHcWB0/s225-Ic42/TubeSeat.png

Step 6 (optional) - Remove flared hose seal inserts. Drill out the centers and
tap the bras insert for an 8-32 screw. Using an 8-32 screw with nut and large
washer, thread the screw into the brass flare insert. Tighten down the nut so
that pushes the washer against the valve body. Keep tightening the nut until the
brass insert is pulled out of the valve body. Do both ports.

https://lh3.googleusercontent.com/-hDp4QMraUIg/VdtThMsMrpI/AAAAAAAATpY/qsdR
OAhoecA/s720-Ic42/IMG_5564.JPG
https://lh3.googleusercontent.com/-kO3TYyxWm7Q/VdtThus6IcI/AAAAAAAATpU/PLB-
s-_2M2s/s720-Ic42/IMG_5565.JPG
https://lh3.googleusercontent.com/-9qIB12ukrEY/VdtThgPsZZI/AAAAAAAATpc/-sgz
mP-9Jr8/s720-Ic42/IMG_5567.JPG
https://lh3.googleusercontent.com/-zCzqBmt2RE0/VdtTiN6uOhI/AAAAAAAATpg/0_Ti
08_VhLs/s720-Ic42/IMG_5568.JPG

Step 7 - Clean all parts. With all rubber pieces/seals removed, let internal
pieces and valve body soak in a cleaning solution.

https://lh3.googleusercontent.com/-FgZWdDAl6Ns/VdtTlVjDqWI/AAAAAAAATqo/cTuC
eFJvuvQ/s720-Ic42/IMG_5580.JPG
https://lh3.googleusercontent.com/-FAV5jAi2ILA/VdtTmVwuuEI/AAAAAAAATrA/AYOb
WqwGlM8/s720-Ic42/IMG_5585.JPG


Step 8 - Hone the bore. After a good soaking in cleaner, I used emory paper to
clean and give a fresh surface to the interior bore of the valve body.
musclecarresearch.com suggests a small ball hone (about 1" diameter). My valve
body did not show any pitting, so a light surfacing with emory paper is all that
it needed. Clean and wipe down thoroughly to remove all dirt/grit/residue prior
to reassembly.

Step 9 - Paint/powder coat/seal exterior of valve body. Before reassembly,
follow what ever steps you wish to take to seal the valve body's exterior to
prevent future surface corrosion.

Step 10 - Reassemble. Use musclecarresearch.com's instructions for reassembly:

https://www.musclecarresearch.com/gm-1233464-rebuild
 

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Discussion Starter #4
Major corrections!!!!!!!!!!

Firstly, I've mistakingly labeled this thread as Proportioning Valve… it's actually a Hold Off Valve. As I stated originally, there is a lot of confusion about this piece. Further research reveals that it "holds-off" allowing the front brakes (discs in this case) to engage until it sees a certain line pressure. I've read that that number is around 30psi, but I'm not absolutely certain of that info. In practical terms this valve's function is too delay front disc brake engagement while allowing the rear drums. This is, in effect, a way to improve ride quality for light braking and prevents the forward neck snaps of grabbing fronts.


DISCLAIMER
--------------
I've just discovered that the MuscleCarResearch does NOT have the brass tube seats, which are pressed into the cast iron valve body, for this application as I had previously thought. They have the tube seat inserts for the pressure differential valve (which mounts to the frame and has the "Brake Warning Switch".)

Do not REPEAT DO NOT drill, tap, and remove your tube seats!!!!

I am trying to find a source for replacements. I'm posting a picture of the bugger along with its specifics so that if anybody else knows of a potential source they can help me track it down. Please please please. Your help is appreciated.

The most important measurement to match for a replacement is D1.
 

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Re: 1970 Brake Proportioning Valve #2226261

That's not a proportioning valve... It's a brake delay on the front disc brakes to make sure the rear drums brake first, thus keeping the car straight during a hard stop.... (Much like an electric trailer brake controller when pulling a trailer with trailer brakes...)
 

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Discussion Starter #6
Re: 1970 Brake Proportioning Valve #2226261

Frank. If you would have read the entire thread, you'd have noticed that I self-corrected myself already.
 

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Re: 1970 Brake Proportioning Valve #2226261

Can you fix the photo links?
 

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Discussion Starter #8
Re: 1970 Brake Proportioning Valve #2226261

Philip, I apologize! I had checked my photo links, but they work on my end because I'm signed into my Picasaweb account. A quick check also showed the album set to private.

I'll talk to Rich about editing this post and correcting quite a few issues I have now with the content of this post, i.e. somethings I learned AFTER I did them. Better to have all of the info correct because you can't ensure that people will read all the way through the thread.

In the meantime, please visit my Picasaweb gallery here:

https://picasaweb.google.com/106242937059319515061/ChevelleBrakesRestoration
 

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Re: 1970 Brake Proportioning Valve #2226261

Nice write up, I have had one of those valves in my shop since the late 80's. Nice to know they can be rebuilt.
 
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