M1009 Braking Issue

[hrbergeron]

I've read through several posts on here trying to find a solution to my problem but I haven't found it yet. It's on a 1984 M1009 CUCV

Here is my problem:

When braking, the vehicle will pull hard to the left or to the right. It appears that only one of the front brakes will get the majority of brake pressure and engage. When slamming on the brakes on the road, I leave a nice skid mark on only one side of the vehicle. There appears to be no reason behind which side it pulls to, sometimes it is to the left, sometimes it is to the right, with the same result. It also will do it regardless of which side the wheels are pointing towards when braking.

Ever since I restored this CUCV, it had pulled to the right when braking, not too bad, but noticeable. I wanted to get this vehicle braking correctly before next weekend when I have a couple people riding with me.

When I restored it last year, I put these new components in:
New front brake calipers
New brake pads front and rear
New rubber hoses that go from the front calipers to the steel brake line
New front rotors
New rear brake cylinders
Used, but functional at the time of install (from a parts CUCV I had), master cylinder and hydrobooster

All brakes were bled with a bleeder pump and I used DOT 5 fluid.

Because I was bored and the original looked crusty, this weekend I put in a new proportioning valve. This weekend I bled the brakes three times with DOT 5 fluid and still had the same result.

I read in some other post that someone was having an issue similar to mine and they diagnosed it as the hydrobooster because the steering wheel would be ripped out of their hands, I don't really have that issue, it jerks to whatever side the brakes decide to lock on, but I can turn the wheel and still have control of the steering, even though the brakes are fighting me.

 

[NDT]

Is the skidding tire on the front or rear axle. What are the caliper pistons made of. Heat could cause them to seize in the bores. Are the calipers free to slide easily.

 

[Garagefull]

In my experience,make sure the rears are working. Does it have the ride height proportiong valve in the rear?When my lift was installed on me m1031,it changed my ft/rr proportioning which made it woller all over at lights ect. A simple adj fixed both the steering pull and far better brakes.

 

[hrbergeron]

In my experience,make sure the rears are working. Does it have the ride height proportiong valve in the rear?

Don't know about the ride height proportioning valve. The one on top of the rear differential? Yes. Rear brakes work.

Is the skidding tire on the front or rear axle. What are the caliper pistons made of. Heat could cause them to seize in the bores. Are the calipers free to slide easily.

The skidding is the front axle. Don't know what the pistons are made of. It's whatever O'Reilly's sells. Don't know if it is heat related because it will do this as soon as I apply brakes after starting.

 

[NDT]

My best guess after thinking about this for quite a while is the smoking gun is the calipers. Either the piston is binding randomly or the caliper is binding such that it can't slide and only one pad is allowed to apply.

 

[hrbergeron]

My best guess after thinking about this for quite a while is the smoking gun is the calipers. Either the piston is binding randomly or the caliper is binding such that it can't slide and only one pad is allowed to apply.

So you are recommending replacing both front calipers? because it happens to both sides.

 

[NDT]

So you are recommending replacing both front calipers? because it happens to both sides.

I would verify the calipers are free to slide on the mounts and I would disassemble the piston and verify nothing is binding. But I would also wait to see if anyone else chimes in on your thread.

 

[Garagefull]

Don't know about the ride height proportioning valve. The one on top of the rear differential? Yes. Rear brakes work.


On the rotating part of the ride height proportioning valve you will see a little dot. Making note of where it is currently positioned. Unhook the linkage and rotate that dot counter clockwise approximately 90° and take it for a drive. You don’t even need that linkage hook back up until you find a sweet spot in that proportioning valve adjustment. I think you will find that if the rear brakes are tightened up and proportioned correctly you will stop that pulling.

 

[cucvmule]

The one thing I did not see is the condition of your tie rods or ball joints. Are you toe in or toe out. May not be the brakes at all.

 

[cucvmule]

Get the front end up off the ground and inspect the joints. Get Soldier B to help inside the truck and turn the steering from lock to lock. Inspect the tie rods, how easy do they rotate by hand. Under hard braking the issue is amplified even more.

Jack up each side off the ground and watch for any movement of the spring packs, broken leaf, and bushings. Not only up and down but front to back.

Any excess movement that is not normal is even worse when driving a shorter wheelbase vehicle. Also look at all rivited hangers shackle, shocks, frame, look at the front axle rear frame shackle bushing rivited to the frame, is the bushing wore thru.

 

[cucvrus]

I am thinking it could be the slides on the knuckle and the caliper. They need to be cleaned and polished and greased well so they can move in and out freely. they should be able to return to the neutral position as soon as the pressure is released. Remove them and replace the attaching hardware and polish the upper and lower slides surfaces o both sides. Lube and give it a try. Rust is abrasive and things get stuck on abrasive surfaces. Good Luck.

Meet Mr Rusty

The brakes were tight and the wheel was hard to turn. I se why now. Easy fix. The tightening wedge is broken. I have extras. I pried the brake caliper away from the rotor to get some free play in the caliper. The slide surface tells the whole story. I have DOT 5 in mine from bleeding the brakes...

www.steelsoldiers.com

I chimed in when I read height sensor. I looked and you are working on an M1009. Same deal make sure everything is free and check your rubber brake hoses. Good Luck.

 

[scooter421]

It's worth a shot here....

I have an 85 M1009. Your problems sound similar to what I experienced with mine. It would nose dive and lock up pretty easy, pull to one side or the other, leave a skid mark occassionally under light braking. It was odd behavior to say the least. My front hubs would get rather warm also which you've not mentioned. I did the standard replacements and bleeding as you've done. I replaced the master cylinder and that's when I learned about preload. I won't bore you with the details as it may not apply to your situation. However, what got me thinking was when I unbolted the MC for upteenth time I noticed the push rod was holding the MC face from touching the mating surface on the HB slightly. After reading up and doing some measurements, I calculated the gap needed between HB push rod and the MC. I shimmed it accordingly and it now brakes properly. I searched high and low for the symptoms you described and found very little that made sense until I read an article on a preloaded Master Cylinder. You mentioned the proportioning valve...did you have the little tool for the proportioning valve to help bleed the brakes properly? It's a pain and really takes two people.

Hope this helps.....Scooter

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[hrbergeron]

Fixed the issue today. I thought I had replaced the front rotors in the past, but I was incorrect. Upon inspection of the pads, they were destroyed despite only having around 6000 miles on them. Brake pads were covered under warranty, and I got new rotors and a master cylinder. Replaced it all, bled the system, and now it works properly and I do not have any more brake issues.

 

[scooter421]

Wonderful news, it always feels good to get a problem solved! Well done....

Scooter...

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