M151a2 master cylinder leak

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
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54 Dodge
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M151a2 master cylinder leak

Post by 54 Dodge » Sun Sep 11, 2022 8:10 am

I have a M151a2 that developed an MC leak a couple of years ago. I checked the block on the bottom of the MC and there was a slight drip. I checked the banjo bolt and brake fitting an both were tight. I replaced the banjo bolt seal washers and made sure the brake line and pipe plugs were tight and the leak stopped. About a month ago the leak started again, I again checked all fittings for being tight and found that the pipe plug could be snugged a little more and did so. Now the leak is even greater. I think maybe the brass block is distorted or has a crack in it to cause this. I am contemplating replacing the MC and the brass block but I know it is a bear to change. I would like to find a new block and banjo seals first to try. I can't find a part number for the block, can anyone steer me to the number or a vendor?
Thanks,
54 Dodge


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Re: M151a2 master cylinder leak

Post by Rickf » Sun Sep 11, 2022 8:27 am

I doubt the block is cracked, brass does not readily crack. I will bet that those copper sealing washers have work hardened from being tightened several times. You can take them out and anneal them with a propane torch and that will soften them up again. Most of the washers I have seen coming in kits are very hard and have to be annealed before they will ever seal. Heat them with a torch until they just barely start to show some color, no hotter and then let them cool and good to go. But you have to heat them evenly so be sure they are setting on something that holds them up a bit. I use steel mesh that came from heavy duty parts trays. But any mesh that will allow overall even heating will work.
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muttguru
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Re: M151a2 master cylinder leak

Post by muttguru » Sun Sep 11, 2022 11:13 am

54 Dodge wrote:
Sun Sep 11, 2022 8:10 am
................ I would like to find a new block and banjo seals first to try. I can't find a part number for the block, can anyone steer me to the number? Thanks,54 Dodge
Here are the specs you need:-

1. Brass block. There are two descriptions used for this in the TM ....Master Cylinder Outlet Fitting / Connector-Multiple. The P/N is 8754571. The NSN is 4730-00-678-1878.

2. Copper washers. There is a small one and a large one. The smaller one fits between the master cylinder and the outlet fitting. The larger one fits between the hollow bolt (fluid bolt) and the outlet fitting.
The smaller washer is P/N 5214539. NSN is 5310-00-275-6635.
The larger washer is P/N 5160323.. NSN is 5310-00-777-0223.

I hope this helps.......
Ken
Contact address - muttguru@aol.com
Always wanted - Details and pictures of M416 Trailer data plates & M151 data plates & body-tags for my research. Thanks!

54 Dodge
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Re: M151a2 master cylinder leak

Post by 54 Dodge » Mon Oct 24, 2022 6:59 pm

Thanks, I replaced the seals, banjo bolt and brass block a couple of years ago and the leak was fixed at that time. I found the brass block and the washers and bolt again, all NOS. I did the anneal trick and put everything back together and bled the brakes. The last time I did not have any issues with the brakes after replacing the block. This time I had a left front brake pulling hard and removed the drum to find that it had gotten brake fluid on the rear shoe at the bottom. I flushed that shoe with VM&P Naptha which cuts the silicone brake fluid and the pulling went away. I did all of that about 2 weeks ago and I check the fitting for leakage several times. Today I noticed that the floor looked like I had a leak again. I checked and there was a small amount of brake fluid on the banjo bolt head again. I wiped it clean and cleaned up the floor board. I checked again a couple of hours later and all was dry. I think the seal around the cap may have been holding some fluid from bleeding and that leaked down (I hope). I have a new master cylinder ordered just in case. I also have extra copper washers if I have to change the MC.
Thanks for the help everyone.


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