M151 brake adjustment

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
67N20
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M151 brake adjustment

Post by 67N20 » Wed Mar 03, 2021 1:24 pm

I forgot what is the proper way of adjusting brakes. I had it at one now I can't find it.
THANKS
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markrdje
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Re: M151 brake adjustment

Post by markrdje » Wed Mar 03, 2021 2:29 pm

I thought you adjust it til the wheel don't move, then back it 12 notches?Or with a slight drag on drums when moving wheel?
change user name to mark

67N20
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Re: M151 brake adjustment

Post by 67N20 » Tue Mar 09, 2021 2:58 pm

Your right Mark only its eleven back, Found the problem though The left rear kept gripping to much. These brake shoes are really thick I had to back that one all the way off,

Rickf
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Re: M151 brake adjustment

Post by Rickf » Tue Mar 09, 2021 4:17 pm

Are you sure you have the right wheel cylinders on it? A2 has 1" on the front and 3/4" on the rear and A1 has 3/4" all around. I put 1" on the front of my A1 and it worked out perfect but what has happened in the past is the cylinders are not marked and they get mixed up and people end up with a 1" on one side and a 3'4" on the other side. If this happens in the back it will result in a mild pull and usually the 1" side wheel locking up. If it happens in the front it can be a very dangerous situation.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

67N20
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Re: M151 brake adjustment

Post by 67N20 » Fri Mar 12, 2021 7:04 am

Thank you Rick

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Re: M151 brake adjustment

Post by 67N20 » Sat Apr 24, 2021 10:58 am

Well I'm still having brake issues, Drivers side rear likes to lock up. Like if if its either full on or full off. it is adjusted backed off all the way. the passenger rear is adjusted with a slight drag, I used compressed air to blow out the passenger side rear line from T to wheel cylinder, i do not see any leaks in the system. The wheel cylinders appear to be the same size 3/4 inch. Tire pressure is the same.

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Re: M151 brake adjustment

Post by muttguru » Sat Apr 24, 2021 12:17 pm

Here's some options for you to think about:

1. Brake shoe(s) contaminated.
This can sometimes be hard to spot, because the heat generated by braking can burn off the surface contamination, so the shoes look clean, but the contamination goes deep into the shoe. Compare the shoes on the seizing drum with the shoes on the side that are "free" for differences in texture and shade caused by brake fluid contamination.

2. Air remaining in system.
Air pockets can be really hard to get rid of. The only way to get rid of air bubbles is to bleed systematically and never, NEVER, reintroduce the fluid you bleed out, back into the system, no matter how new it is.

3. Seized piston(s) on the non-lockup side.
The fact that one drum is braking hard doesn't automatically make it faulty. It could be working correctly but the other cylinder(s) could be defective, binding or seized. Just because the system is using silicone fluid (BFS), it doesn't guarantee against seized pistons in the brake cylinders. Check 'em all for free movement.

4. Brake shoes replaced on one side but not on the other.
Not reading the manual is a regular cause of brake problems. The TM states that brake shoes should be replaced on THAT AXLE...ie both front drums, or both rear drums. Lots of people replace the shoes on just one drum, then wonder why the vehicle stops unevenly.

5. Improperly adjusted brakes.
The 11-click method of adjustment is usually adequate, but here again, it has to be done correctly. Both fronts and /or BOTH rears need to be done at the same time. When for example you adjust the rear drums, both rear wheels should be off the ground so that you can judge when both wheels are equally "locked". This is important when you release the adjuster by 11-clicks. It has to be 11-clicks from the same "baseline" for both wheels. Trying to adjust one wheel while the other wheel remains on the ground is just pointless, you will never get them equally adjusted.

6. Wrong-sized wheel cylinder(s) used.
Highly unlikely but possible. There are two different-sized wheel cylinders used on mutts. The M151 and A1 models use 3/4" pistons ALL ROUND. The M151A2 uses 1" cylinders on the front wheels, with 3/4" on the rears. There are NO EXCEPTIONS to this rule. I've noticed several wheel-cylinders for sale on E-Bay which have poor, or worse still, inaccurate descriptions about the usage of 1" and 3/4" cylinders. Make certain you have installed the correct sizes.

7. Crush damage / Swollen hoses
Even more unlikely, but worth checking if all else fails. Check out the metal brake tubing for signs of crush damage which would restrict the flow of fluid to the wheel cylinder(s). Also check the flexible hoses. They can look perfect on the outside, but can "swell" inside and restrict the flow, too.

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!

67N20
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Re: M151 brake adjustment

Post by 67N20 » Sun Apr 25, 2021 6:21 am

Thank you mutt guru......All those suggestions sound possible, after working on this forever and doing some of the things suggested I'm thinking the rubber hose on the passenger side(the side not locking up) is swollen inside.And since I've had enough of this truck I'm going to replace everything from wheel cylinders to the T fitting on both sides:(
Thank you for the help :)

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Rickf
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Re: M151 brake adjustment

Post by Rickf » Sun Apr 25, 2021 6:57 am

And regardless of what the naysayers and the 50 year old safety manual say I put the 1" wheel cylinders on the front of my A1 and it was the best thing I ever did because not too long after that I had someone cut me off and slam their brakes on in front of me which means I had to do the same and the A1 stopped arrow straight instead of the usual A1 trait of locking the rear wheels and going sideways which in turn causes a roll. With the bigger cylinders on the front it provides more stopping power to the front wheels where the engine weight is and offsets the braking towards the front just like any other modern vehicle. That is exactly why they went to that setup on the A2. Other than dire warnings of doom the brakes on an M-151 are exactly the same on both ends of both the A1 and the A2 so changing the front cylinders does nothing more than give an A1 the better braking of an A2. The problem is when the 1" wheel cylinders would get mixed up from front to back and side to side.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

67N20
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Re: M151 brake adjustment

Post by 67N20 » Sun Apr 25, 2021 2:54 pm

You rebel Rickf !!! :D

Rickf
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Re: M151 brake adjustment

Post by Rickf » Sun Apr 25, 2021 6:07 pm

I drove race vehicles all my life, does that tell you anything? Besides the fact I like good brakes?
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Fil Bonica
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Re: M151 brake adjustment

Post by Fil Bonica » Sun Apr 25, 2021 6:39 pm

If you do what Rick says and install 1 inch cylinders in front .make sure to install them there.
If you mix them up and put one in there rear Bad things can happen!
Dont ask me how I know!

Fil Bonica

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Re: M151 brake adjustment

Post by Crux444 » Tue Apr 27, 2021 10:55 am

Rickf wrote:
Tue Mar 09, 2021 4:17 pm
Are you sure you have the right wheel cylinders on it? A2 has 1" on the front and 3/4" on the rear and A1 has 3/4" all around. I put 1" on the front of my A1 and it worked out perfect but what has happened in the past is the cylinders are not marked and they get mixed up and people end up with a 1" on one side and a 3'4" on the other side. If this happens in the back it will result in a mild pull and usually the 1" side wheel locking up. If it happens in the front it can be a very dangerous situation.
What's an easy way to tell the difference?
Canadian Army (1988-2011)
Kandahar, Afghanistan 2006-2007

M151A2 CDN (1974)

Rickf
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Re: M151 brake adjustment

Post by Rickf » Tue Apr 27, 2021 1:16 pm

Some of the 1" cylinders were marked with a yellow stripe but the best way is to pull one of the rubbers off the end and measure the bore with a caliper. It will be either 1" or 3/4". If you are not changing to new ones it would not hurt to check them all just for piece of mind. Plus you get to see if they are frozen or leaking at the same time.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

67N20
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Re: M151 brake adjustment

Post by 67N20 » Sun May 02, 2021 5:15 am

Well i'm still having issues, I'm thinking I need help with bleeding the brakes, by myself to many things to hinder a reliable outcome.


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