Rebuild of M8/M20 Armored Car Hydraulic Accelerator

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SteveM8
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Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by SteveM8 » Sat Apr 06, 2019 7:44 pm

After twenty years, my accelerator stopped working. I found the seals on accelerator slave cylinder fell apart. This was 1945 or 1950 dated rubber. I have several replacement pistons with original seals, but I did not want to use old rubber again. I redesigned the piston and was amble to modify it on my lathe. You can buy modern 6202 EPDM rubber seals for the primary seal, and you can modify 5/8 cups by putting a hole in the middle to make the secondary seal. Neither of the two original seals is in production. I created a test stand and the system works fine. This new system requires a brass spacer to be fabricated.

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Remy
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by Remy » Mon Apr 08, 2019 12:34 pm

Nice work. Thanks for the info!

Remy
Ford M8
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Don Shaffer
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by Don Shaffer » Mon Apr 08, 2019 3:04 pm

We had the same problem on our M20 and we worked for 3 straight days trying to get ours to work. We finally bought a Boat throttle cable and after welding up 2 brackets it works Great ! Not original but it works very smoothly . Don Shaffer N.E. Ohio

SteveM8
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by SteveM8 » Mon Apr 08, 2019 3:23 pm

I have noted all the mechanical throttles used by folks over the years, and it is something I would never do due to the issue of originality. I have at least three replacement slave pistons and rubber seals that I have picked up over the years. I never came up with a new system because I did not find it necessary. This failure got me off my hind end. Machining the piston is not hard. It just needs to be turned down to 0.250 inches - no less. Then it can use the 6226 EPDM seal. This is the good material for modern brake fluids. This one seal is good enough to do the job, but we have room for two seals, why not go for two? You can still buy 5/8 inch brake cup seals. A simple hole punch will cut them for the 0.150 inch shaft on the piston. Centering the hole is an issue, but if you have several, you will get one close enough. I will finalize the design and publish a photo of the spacer drawing. I might even do a Youtube video.

Big D
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by Big D » Mon Apr 08, 2019 3:36 pm

Hi Steve M8,

Looks good! So it is just the piston that is modified? Would you consider producing a few spares and making them available for sale?
Darryl Lennane
NZ

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


SteveM8
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by SteveM8 » Mon Apr 08, 2019 3:53 pm

I am doing one for a friend. And, I will modify the four spares that I have. We can work out a deal. Only the piston has been modified.

FUBAR
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by FUBAR » Tue Apr 16, 2019 5:00 pm

That's great thinking Steve. I rebuilt my M20's throttle hydraulics about 4 years ago and I spent quite a lot if time looking for a replacement seal. When I realized that they just weren't available I installed an NOS piston and crossed my fingers. It never occurred me to make the piston fit the seals I could get!

So far my master and slave are still working well and are not leaking. I went with silicone fluid.

BTW, I'm thinking of having some accelerator hydraulic reservoir decals made up. Do you think there would be enough interest from other G136/176 owners to share the cost?
Bill Kish
Millerton, NY

GPW 59058, USA 20137991, DOD 8-27-42
'52 M37 8008286
'45 M20 7009-C

SteveM8
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Re: Rebuild of M8/M20 Armored Car Hydraulic Accelerator

Post by SteveM8 » Wed Apr 24, 2019 2:24 pm

Here are the plans for the piston modification:

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