1967 Master Cylinder and Pressure Differential Switch Rebuilding

**Joe L.** · June 29, 2015, 10:07 PM

Re: 1967 Master Cylinder and Pressure Differential Switch Rebuilding

Originally posted by Richard Mozzetta (13499)

1967 Master Cylinder and PDS.

Here is a pictorial of the Master Cylinder when I took it apart. The photos will do most of the the talking, but as you can see, it was doomed to fail soon. I had to break the pistons free from their bind due to heavy sediment. It had water in the fluid also. Nasty.

[ATTACH=CONFIG]61753[/ATTACH][ATTACH=CONFIG]61754[/ATTACH][ATTACH=CONFIG]61755[/ATTACH][ATTACH=CONFIG]61756[/ATTACH][ATTACH=CONFIG]61757[/ATTACH][ATTACH=CONFIG]61758[/ATTACH][ATTACH=CONFIG]61759[/ATTACH][ATTACH=CONFIG]61760[/ATTACH][ATTACH=CONFIG]61761[/ATTACH][ATTACH=CONFIG]61762[/ATTACH][ATTACH=CONFIG]61763[/ATTACH][ATTACH=CONFIG]61764[/ATTACH][ATTACH=CONFIG]61765[/ATTACH][ATTACH=CONFIG]61766[/ATTACH][ATTACH=CONFIG]61767[/ATTACH][ATTACH=CONFIG]61768[/ATTACH][ATTACH=CONFIG]61769[/ATTACH][ATTACH=CONFIG]61770[/ATTACH][ATTACH=CONFIG]61771[/ATTACH][ATTACH=CONFIG]61772[/ATTACH][ATTACH=CONFIG]61773[/ATTACH][ATTACH=CONFIG]61774[/ATTACH][ATTACH=CONFIG]61775[/ATTACH][ATTACH=CONFIG]61776[/ATTACH][ATTACH=CONFIG]61777[/ATTACH][ATTACH=CONFIG]61778[/ATTACH]

Old brake systems like this can wreak havoc if you try to do a conventional "pedal" bleed after brake work at the wheels(replace hoses, lines, etc). When the pedal goes to the floor, it will inevitably tear the seals on the piston when they pass the sediment build-up areas in the bore. This would have happened to this one. Then the MC is defective.

After a general cleaning and removing all traces of the sediment, I honed the bore using my cylinder hone with a cutting lubricant. A constant all in then out motion was used to keep the stones moving horizontally at all times. It cleaned up well.
[ATTACH=CONFIG]61779[/ATTACH][ATTACH=CONFIG]61780[/ATTACH][ATTACH=CONFIG]61781[/ATTACH]

I then used a 0.018" wire to clear the 0.020" diameter ports clear. They were quite dirty.
[ATTACH=CONFIG]61782[/ATTACH][ATTACH=CONFIG]61783[/ATTACH][ATTACH=CONFIG]61784[/ATTACH][ATTACH=CONFIG]61785[/ATTACH][ATTACH=CONFIG]61786[/ATTACH]

I then blocked all ports and openings to prepare for media blasting.
[ATTACH=CONFIG]61787[/ATTACH][ATTACH=CONFIG]61788[/ATTACH][ATTACH=CONFIG]61789[/ATTACH][ATTACH=CONFIG]61790[/ATTACH][ATTACH=CONFIG]61791[/ATTACH][ATTACH=CONFIG]61792[/ATTACH][ATTACH=CONFIG]61793[/ATTACH][ATTACH=CONFIG]61794[/ATTACH][ATTACH=CONFIG]61795[/ATTACH]

The rebuild kit including complete Primary and Secondary pistons and seals. A new circlip is included also, not shown.
[ATTACH=CONFIG]61796[/ATTACH]

I will also be removing the brass outlet port seats. Standard rebuild kits don't include them. You can barely see them here. It's a good idea to replace them after this many years, especially if using DOT 5 Silicone brake fluid.... as I am.

[ATTACH=CONFIG]61753[/ATTACH]
I've located them here..... DB-518
It comes with a few screws and a washer. One taps the center hole, the other one pulls it out against the washer. You can also tap it for 1/4-20, use a old line flare end fitting and a 1/4-20 screw, hold the screw then unscrew the fitting to pull it out. This right out of the CSM.
[ATTACH=CONFIG]61797[/ATTACH]

When I get the needed remaining parts in I'll update this MC assembly process.

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The Pressure Differential Switch is seriously seized as I expected.
[ATTACH=CONFIG]61812[/ATTACH]

I closed the ports then media blasted, then removed all fittings and switch fitting.
[ATTACH=CONFIG]61798[/ATTACH][ATTACH=CONFIG]61799[/ATTACH][ATTACH=CONFIG]61800[/ATTACH][ATTACH=CONFIG]61801[/ATTACH][ATTACH=CONFIG]61802[/ATTACH][ATTACH=CONFIG]61803[/ATTACH]

The switch pin should not have fluid around it. The internal piston seals must be leaking. I'll have to size those when I get the port seats removed later.
[ATTACH=CONFIG]61804[/ATTACH][ATTACH=CONFIG]61805[/ATTACH][ATTACH=CONFIG]61806[/ATTACH][ATTACH=CONFIG]61807[/ATTACH]
The above switch is slightly different from what I've seen before. Here is another type below. Note it requires a o-ring at the threaded joint. Last 2 pics here is the piston shaft and threaded opening for the switch contactor.
[ATTACH=CONFIG]61813[/ATTACH][ATTACH=CONFIG]61814[/ATTACH][ATTACH=CONFIG]61815[/ATTACH][ATTACH=CONFIG]61816[/ATTACH][ATTACH=CONFIG]61817[/ATTACH]

I tried to move the piston at either end with a 0.100" drill bit through the brass seat hole but no luck. End seats must be drilled, tapped and removed, much like the MC seats will be.
[ATTACH=CONFIG]61808[/ATTACH][ATTACH=CONFIG]61809[/ATTACH][ATTACH=CONFIG]61810[/ATTACH]

Here you can see the shaft of the double ended piston. When the piston moves to either side, it touches the bottom of the switch contact, completing a ground path to the lamp which is always powered when in Ignition RUN.
[ATTACH=CONFIG]61811[/ATTACH]

This item is not a Pressure Regulator. It's merely a balance indicator which lights the Dash "BRAKE" light if the brake system looses pressure on one side. The port seats are 2 different sizes. I did some measurements and it appears that the main input seats behind the switch piston(at each end) are identical to the Master Cylinder Seats. I have some coming for these also. I also found what I believe are the output seats, which are a smaller diameter. Also ordered.

More to come when parts arrive...

Rich

Rich-------

I hate to tell you this now but I do not recommend honing of these master cylinder bores. I have never had one perform satisfactorily after honing. By the way, GM did not recommend honing, either. Their instructions were that if a master cylinder bore could not be cleaned up with crocus cloth, a new master cylinder was required. Fortunately, sleeving has replaced the need to replace the master cylinder.

**Richard M.** · June 30, 2015, 06:24 AM

Re: 1967 Master Cylinder and Pressure Differential Switch Rebuilding

Originally posted by Joe Lucia (12484)

Rich-------

I hate to tell you this now but I do not recommend honing of these master cylinder bores. I have never had one perform satisfactorily after honing. By the way, GM did not recommend honing, either. Their instructions were that if a master cylinder bore could not be cleaned up with crocus cloth, a new master cylinder was required. Fortunately, sleeving has replaced the need to replace the master cylinder.

Joe, It's better to know now than later. I'm glad you commented.....

I will take your advice and get it sleeved. I just dislike sending it out for fear of loss. I've had some bad experiences in the past with other items....lost parts, cheaters, fixing their mistakes, etc, etc. I've heard some not so great stories lately about Whitepost.

However, I have had good experiences with Ken at Lonestar Caliper in Texas. That's who does all of my calipers and PS pumps for me. I'll start there and give him a call later. I'm pretty sure he does these MC's along with calipers.

What's the best sleeve material? Stainless or brass?

Thanks,
Rich

**Joe L.** · June 30, 2015, 10:35 AM

Re: 1967 Master Cylinder and Pressure Differential Switch Rebuilding

Originally posted by Richard Mozzetta (13499)

Joe, It's better to know now than later. I'm glad you commented.....

I will take your advice and get it sleeved. I just dislike sending it out for fear of loss. I've had some bad experiences in the past with other items....lost parts, cheaters, fixing their mistakes, etc, etc. I've heard some not so great stories lately about Whitepost.

However, I have had good experiences with Ken at Lonestar Caliper in Texas. That's who does all of my calipers and PS pumps for me. I'll start there and give him a call later. I'm pretty sure he does these MC's along with calipers.

What's the best sleeve material? Stainless or brass?

Thanks,
Rich

Rich-------

I believe that either stainless or brass is going to last longer than anyone is going to need it to last. I used to recommend brass, though. However, now I lean a little more to stainless PROVIDING it's 304 or 316 stainless that's used. I'll add one caution, though: sleeving with stainless slightly increases the chances that "something can go wrong" in the sleeving process and render the master cylinder scrap.

**Richard M.** · June 30, 2015, 06:50 PM

Re: 1967 Master Cylinder and Pressure Differential Switch Rebuilding

Thanks Joe, I'm very glad you checked in with your information and suggestions.

I called 2 places today, Lonestar and Apple Hydraulics. Lonestar uses stainless, and will not just sleeve it. They require a complete rebuild to be purchased.... $282.

I then called Apple Hydraulics and had a nice conversation with Lazar. He uses brass, and can do just a sleeve($115) or a complete rebuild($245). I decided to go with him for just the sleeve. I want to complete the rebuild when it returns. I have the MC all boxed up with a Fedex label going to him in NY tomorrow.

Rich
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Also today between other tasks, I disassembled the PDS. It was dirty inside as expected, and seized. I cleaned it thoroughly and readied it for rebuild. Unfortunately I had no correctly sized o-rings in my kits, so I'll have to do some hunting for those. I've included some measurements below for future interest.

Here is how I removed the brass port seat. The ID of the seat is apx 0.105, just right for a 6-32 tap to thread into it. I tapped it far into the seat. I then used a 6-32 screw, some washers, and a clean flare fitting to remove it. I threaded the fitting down against the seat, then inserted the screw with washers, Then held the screw then unscrewed the fitting against the washers/screw. It came out easily.
P6300001.jpg P6300002.jpg P6300003.jpg
P6300004.jpg P6300005.jpg P6300006.jpg
P6300007.jpg

Here is the internal piston and 2 springs, one each side. To remove the piston I used a small drift from the opposite side and pushed it out, then the other spring drops out.
P6300009.jpg P6300010.jpg P6300011.jpg P6300012.jpg

I thoroughly cleaned all pieces and the bore. All I need now is my replacement brass seats and new o-rings.
P6300013.jpg P6300014.jpg

Here is the dimension chart for the o-rings for reference.
P6300017.jpg

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1967 Master Cylinder and Pressure Differential Switch Rebuilding

1967 Master Cylinder and Pressure Differential Switch Rebuilding

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