WTB M8/M20 wheel cylinder seals

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dlevy
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WTB M8/M20 wheel cylinder seals

Post by dlevy » Mon Oct 09, 2017 8:20 pm

Hi,

Does anyone have the wheel cylinder seals for the M8/M20? They look like a square profile o-ring.

Thanks,
Dave


Big D
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Re: WTB M8/M20 wheel cylinder seals

Post by Big D » Tue Oct 10, 2017 1:41 am

Hi Dave

Do you mean these:

viewtopic.php?f=82&t=270193&start=15

Thanks.
Darryl Lennane
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1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
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dlevy
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Re: WTB M8/M20 wheel cylinder seals

Post by dlevy » Tue Oct 10, 2017 3:46 am

Pm sent

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John Neuenburg
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Re: WTB M8/M20 wheel cylinder seals

Post by John Neuenburg » Sat Oct 14, 2017 1:40 pm

Big D wrote:
Tue Oct 10, 2017 1:41 am
Hi Dave

Do you mean these:

viewtopic.php?f=82&t=270193&start=15

Thanks.
Those don't look like the ones that were in my car but it's hard to tell. Here is a thread that includes a photo of the piston/seal that came out of my car, the different type with a traditional cup seal that I went to, the part numbers of those kits, and some opinions why it might be a good modification. Leak free 8 years and counting.
viewtopic.php?f=82&t=165723
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Re: WTB M8/M20 wheel cylinder seals

Post by Big D » Sat Oct 14, 2017 2:34 pm

Hi John,

These seals were the same type that I took out of my slave cylinders when I restored them. Some of the slave cylinders were heavily corroded and I figure had never been opened since they were manufactured. Interestingly, all cylinders had the same seal; US Lockheed, French and I seem to recall a couple of Italian ones.

A few M8 users I spoke to in Europe honed their slave cylinders and put these seals in them, and have been operating them with no problems. I'd describe them as fairly regular users of their vehicles though, which I won't be.

I have put stainless steel sleeves into the brake master cylinder and all 12 slaves, as well as the clutch master cylinder. I'm not sure yet about using silicone fluid and am inclined to just stick to standard brake fluid. I guess time will tell whether what I've done will be long lasting!
Darryl Lennane
NZ

1943 Willys MB
1941 LP2A MG Carrier
1943 White M3A1 AOP
1942 Willys MBT
1944 Ford M8 Armoured Car
1945 Ford M20 Armoured Car

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John Neuenburg
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Re: WTB M8/M20 wheel cylinder seals

Post by John Neuenburg » Sat Oct 14, 2017 11:03 pm

Here is a photo of the piston and seal that were in my cylinders. This is the fluid side of the seal. Piston pressurizes fluid which is supposed to get into the groove of the seal via those little cuts in the top of the piston. Fluid pressure pushes the rubber out, sealing the cylinder. The seal in that area is .12 inch thick with one corner touching the cylinder.
Image

Here is the bottom of the seal. Flat bottom.
[URL=http://s160.photobucket.com/user/Johnsc ... v.jpg.html]Image[/UR

Assuming this is the original type seal, and comparing it to the cup seal that I used years ago and wrote about on the G with a link a couple posts up, it is obvious the latter design puts more flexible rubber against the cylinder. Seems to me the original "donut seal" is a marginal design and will not work well if it gets old and stiff in the presence of any cylinder corrosion (pitting).

These cars have 12, 1.5 inch wheel cylinders, double-acting with two pistons per cylinder = 24 seals. Lots of possibilities for leaks. Here is the problem: DOT 3 and 4 brake fluid is designed to disperse water. Water gets into brake systems via condensation, past seals, and via the master cylinder cap. The idea is to not let a water droplet form, which migrates downhill to the hot brakes and then boils, making the pedal spongy. Water also causes corrosion. Brake fluid contains a corrosion inhibitor. Over a few or more years depending on your weather - the fluid moisture content gets above 3% and the inhibitor is used up and corrosion starts. A few tiny pits in several cylinders empties the master cylinder which is not large. So you get in the car to drive to a parade and you have no "pedal." Bleeding these vehicles is not fast and easy as with a truck. So you park it and maybe for months or a year. More cylinders get pitted. So it's important to come up with a solution. These things can indeed have leak-free brakes!

I am not saying original or original-type seals and pistons will not provide good service for years, but my guess is with them it is important to have perfect cylinders and change the DOT 3 or DOT 4 fluid every few years. Good to drive the car a few times a year too. Sleeving the cylinders with corrosion-resistant stainless steel or brass should prevent problems, but it's expensive. Going to DOT 5 silicone fluid which doesn't absorb water might be good but if water enters as described above and forms a droplet, it's not good. This is one reason why DOT 5 is not standard equipment in vehicles, except military ones that need it's ability to function in ultra cold temperatures. The other reason is that DOT 5 is not compatible with modern ABS braking systems. That's another story.

This may be more than the OP wanted to know, but it's what drove me to do the seal/piston upgrade described in the other thread.
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Re: WTB M8/M20 wheel cylinder seals

Post by John Neuenburg » Sun Oct 15, 2017 12:05 pm

A friend asked me to clarify what's important about brake fluid absorbing water. Sorry to the OP - not trying to hijack your thread but it relates somewhat to seals and definitely what fluid you choose.

Designers assume their brake system will pick up water in the ways described, including through microscopic pores in rubber. If hydraulic oil is used, water won't mix. It then migrates downhill, forming a droplet. When this is in or near a brake slave cylinder, heat from braking can boil it, making the pedal spongy and losing braking force. So the U.S. Department of Transportation created a DOT 3 spec with various minimum performance specs such as minimum boiling temperatures. Manufacturers chose a glycol-based fluid for this. It also happens to be hygroscopic, meaning it absorbs water and spreads it out amongst it's volume where it does less harm. The water won't collect in one spot. But the fluid will get more and more corrosive to iron (what steel is made from) as the water % by volume goes up, so a corrosion inhibitor is added to brake fluid. At about 3% water the inhibitor is nearly used up and corrosion commences. This pits the cylinder wall and will cause leaks.

The other thing that is bad about water in brake fluid is it lowers the temperature at which the brake fluid boils. Brake fluid has a Dry Boiling Point spec and a Wet Boiling Point spec. The former is when testing new fluid from an unopened container. For DOT 3 it's 401 F minimum boiling point. Shell is a major maker of brake fluid and they say change it when it gets to 3.7% water content. That's about two years in an average climate! This is the Wet Boiling Point and it's 284 F. There are DOT 4 glycol fluids and their minimums are 446 / 311 F. DOT 5 fluid is silicon based and the specs are 500 / 356 F. Back to glycol, there are enhanced DOT 4 fluids for higher temps, and there is a spec called DOT 5.1 which is a minimum of 518 / 374 F. Yes DOT 5.1 is not silicone like DOT 5! You can mix DOT 3, 4, and 5.1. You cannot mix DOT 5 silicone with any of the others.

Silicone fluid is often used by collector car people because when it spills and isn't removed it doesn't destroy expensive paint jobs like the glycol fluids will. In the MV world this isn't as big a deal except when you have a vehicle with a hull which has more places for spilled fluid to sit. Water flushing works but make sure your hull drain is open! I have not used silicone fluid and don't know how to get rid of it when spilled. I have heard it is hard to paint over areas that have had silicone on them. The military uses silicone to combat extra cold temperatures. Silicone fluid should never be used for racing because of the water drop thing mentioned above. Also never use it in an ABS-equipped vehicle. The rapid cycling during an ABS event beats air into the fluid, resulting in a spongy pedal.

Tip - M20s and M8s don't have much room above brake and clutch cylinders for adding fluid from bottles, so using a jug with a hand pump is nice, and have a wooden dowel to use as a dip stick. For doing fluid replacement or even simple bleeding, a pressure bleeder with caps that fit the cylinders is almost indispensable. One that holds a gallon and can be pressurized with shop air at 10-12 pounds or so makes bleeding a fairly easy, one person job.

Reminder to keep the caps screwed tightly on brake fluid bottles and don't let an open bottle sit too long. It loves water and will suck it out of the air, diluting itself. Take the remainder out of your pressure bleeder jug and put it back into a bottle that seals.
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