Brakes, of coures

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J

jblueridge

SILVER Star
10 Year
Joined
Aug 12, 2014
Threads
275
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3,357
Location
Near Charlottesville, VA
Briefly, I have bled the brakes several times, two different methods, and still the pedal travels almost to the floor; almost no brake action.
The brake pedal has been spongy since I got the BJ74 in January. I decided to take a look at the rears and replaced the shoes. I adjusted the shoes with a screwdriver once things were all back together. The pedal action has deteriorated to the point where I can't drive it now.

I bought this bleeder gizmo at Harbor Freight (I know) and it allowed me to run 3 pints of fluid through the system.
image_25274.jpg

http://www.harborfreight.com/pneumatic-brake-fluid-bleeder-61912.html
I thought I had a firm brake pedal but when I went out for a drive after just a few brake uses it went to the floor again. Tonight I had a neighbor kid pump the pedal while I open and closed the bleed nipples. No bubbles of any kind and another pint of brake fluid pumped through.

If there are no leaks and there is no air in the system, what's going on?
 
Could be the master cylinder, the piston can leak on the inside giving you firm pedal at first that quickly goes soft.
I had the same problem in my 60n could not fix it till I rebuilt the master.
 
Yep, I'd be looking at the master cylinder - strip it down before getting a rebuild kit if you can, if the bore is corroded you might need a whole new master - they're not usually too expensive.

I tried to bleed my brakes with a sucky thing like in your pic once & all it did was pull air in past the seals in the master cylinder.

Cheers
Clint
 
Never tried one of those bleeder systems but I've always had good results with a duster gun hooked up to the compressor to introduce positive pressure into the master cylinder reservoir and push fluid through the system, you need to hold the reservoir cap down really tight with your hand and put the duster nozzle over the cap vent and only apply a tiny (yeah I said tiny) bit of pressure, you'll know if you have applied any more than a tiny bit of pressure because you'll be looking for a rag to wipe all the brake fluid off your face and arms :) , and don't forget you'll need a bleed nipple open to bleed the fluid through.

The other common cause of a low spongy pedal is the rear brake shoes not being adjusted properly, easy way to check is to clamp off the rear brake hose with a pair of vice grips and see if the pedal improves, only takes 2 minutes to verify if that's the problem or not


DS-3.webp
 
Thanks for the responses guys! Before "fixing" anything I was feeling like there was a slight snag as I applied brake pressure. Maybe one piston seal was going bad and now the fluid just transfers from one area to another inside the MC?

No 70 series MC to buy around here.
There is a shop that will sleeve it for me.
Thanks for sanity check.

Sadam, I'm pretty sure the rears are adjusted correctly but I will check again using your method.
 
Brake pedal creeps – Vehicles with diesel engines.


Diesel engine vehicles usually use a pump to generate the vacuum for servo assistance. Unlike the inlet manifold of a petrol engine, there is no vacuum relief with a pump. If excessive pedal pressure is applied when the vehicle is stationary (and the engine is running) the hydraulic pressures required to stop the vehicle will be grossly exceeded and fluid will be forced past seals that are between circuits. Larger vehicles such as vans and 4x4s are more prone to this problem as they use servos with a higher boost ratio. The phenomenon is known as diesel creep; and it is often incorrectly diagnosed as being caused by a faulty master cylinder. The solution is to stop applying the excessive pressure.

http://www.brakesint.co.uk/technical.html
 
Oz,
I get the problem now without running the engine and also while driving.
Very interesting stuff though and more data for my very limited diesel knowledge bank.
 
If the engine is not running and you get brake peddle fad master cylinder or brake system needs looking at this only happens when engine is running and brake system is good.
 
ozcrusier said:
Brake pedal creeps – Vehicles with diesel engines.


Diesel engine vehicles usually use a pump to generate the vacuum for servo assistance. Unlike the inlet manifold of a petrol engine, there is no vacuum relief with a pump. If excessive pedal pressure is applied when the vehicle is stationary (and the engine is running) the hydraulic pressures required to stop the vehicle will be grossly exceeded and fluid will be forced past seals that are between circuits. Larger vehicles such as vans and 4x4s are more prone to this problem as they use servos with a higher boost ratio. The phenomenon is known as diesel creep; and it is often incorrectly diagnosed as being caused by a faulty master cylinder. The solution is to stop applying the excessive pressure.

http://www.brakesint.co.uk/technical.html
Click to expand...

Just so I'm clear on this, the upshot is don't apply the brakes vigorously while the engine is running and you're at a stop - correct?
 
Well, I had time to go out and get dirty on the ground.
I did as Sadam suggested and isolated the front circuit by clamping off the rear brake hose. The pedal feels very good! Or as good as it will get.
I also closely inspected the brake hose before and after clamping and it looks very good, i.e. not old.

I re-adjusted the drum brakes and one was off by a good bit.
I am 96% sure I did not mix up the adjusters Left, Right, but maybe someone before me did?

Which one goes on which side?
 
Went for a drive and the brake pedal is much like it was a few weeks ago. It is very stiff without any vacuum from the engine. With the engine running it is soft. There is a lot of travel before the brakes engage and then they are fairly lame.

I think I will invest in new drums and I will probably upgrade the master and the booster and the calipers too.
Not sure where this money will come from.
 
Yes. To contract or loosen, I insert my adjustment tool and move it's handle up. The engaged part of the star wheel moves down. Is that the correct motion?
 
You'll soon know if you tighten until you can no longer rotate your wheel and tyre, then back it off a couple of clicks until the wheel rotates freely again.
The above motion is correct, at least for my old cruiser it was. If the adjusters are installed opposite, Well you know.
 
Yes, that's how I adjusted them. If the adjusters were on the wrong sides, would they auto-loosen as time went on? That's why I asked about the motion direction.
 
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