BJ70: Brake problems-On and Off stiff pedal brake

[DieselDen]

Hi

I have started having brake problems lately and I am not sure of the exact cause of it. Here’s the problem:

When I give a medium to a hard push to the brake pedal, the pedal get very stiff and the truck don’t brake much. However, after a second or two, the brake pedal pressure get’s to normal and the truck brake normally. On the other end, if I apply a very gentle pressure on the pedal when braking, I don’t have the above symptom.

I’ve read a few posts but couldn’t find this exact problem. So far, I’ve check the brake lines and they don’t leak. Moreover, the vacuum from the alternator to the brake powerbooster is also OK.

I suspect that the problem is more related to the brake booster diaphragm. Am I on the right track?

Do you see something else as the cause of the problem ?

Thanks!
Denis

 

[gotoy]

I have had something similiar 2 times.

On the 1st occasion found a dodgy cylinder on the rear brake drum setup.

On the 2nd occasion, after I had installed rear discs, one of them was found to be slightly warped.

Not saying the above are the source of your problem, but worth a check to cross off the list.

 

[DieselDen]

Thanks!

Thank you for the hint, It's appreciated !
I'll have a look at it this week.
Take care,
Denis

 

[DieselDen]

Doesn't seem to be a cylinder problem.. I've check the cylinder and cleaned the brakes and the problem didn't go away.

Moreover, I notice that when I pump the brake several time in a row the pedal get stiffer and stiffer. I suspect more & more that it is either the vaccum pump or brake booster problem.

As I mentioned in my first post, when I brake the pedal get stiff and after that (after 2 second) it goes back to normal . If it would be a brake booster or un vaccum pump problem, I should observe be the opposite behaviour ( the pedal get stiffer and stiffer). But as I mentioned it does get stiffer when I pump the brake several time in a row.
Thanks!

 

[jake2far]

Doesn't seem to be a cylinder problem.. I've check the cylinder and cleaned the brakes and the problem didn't go away.

Moreover, I notice that when I pump the brake several time in a row the pedal get stiffer and stiffer. I suspect more & more that it is either the vaccum pump or brake booster problem.

As I mentioned in my first post, when I brake the pedal get stiff and after that (after 2 second) it goes back to normal . If it would be a brake booster or un vaccum pump problem, I should observe be the opposite behaviour ( the pedal get stiffer and stiffer). But as I mentioned it does get stiffer when I pump the brake several time in a row.
Thanks!

The booster can be leaking when your foot is off the pedal, as soon as you depress the pedal and hold it for 2 seconds the leak can quit or leak less and allow the vacuum to build up making the pedal feel normal, if you pump the pedal several times you can use up the built up vacuum making your pedal get stiff again, it sounds like you have a booster problem.


Jim

 

[DieselDen]

Very good suggestion!
Thanks!

 

[DieselDen]

Very strange...Oil in Brake booster

I’ve removed the brake booster and find out that it was full of oil. I had a few potential explications but it turned out that I had to reject them all:

1. I tough the oil could be coming out from the master cylinder that could leak into the brake booster. However, the oil wasn’t brake oil

2. The oil wasn’t engine oil. Moreover, the vacuum pump is located in the alternator so there should be oil coming from there.

3. The previous owner of the vehicle had installed a K&N air filter. Last year, I notice that my air filter bowl had a lot of oil in it. For those who don’t know, this kind of air filter required oil to work properly. I’ve cleaned everything and installed and standard filter. I though maybe oil could have come from there in some kind of fume and the vaccum pump aspired it in some manner (I know this is very unlikely). I check one of my vaccum hose with a Q-tip and there are no oil residues.

So where this oil could have come from ? Any Ideas…?

I would like to fix this issue before installing a new brake booster. Toyata is asking 500$ for a Brake Booster for my 1985 BJ. I would like to swap my brake for another brand that is less expensive. Does anyone knows a compatible model ?

Thanks!

 

[jake2far]

I’ve removed the brake booster and find out that it was full of oil. I had a few potential explications but it turned out that I had to reject them all:

1. I tough the oil could be coming out from the master cylinder that could leak into the brake booster. However, the oil wasn’t brake oil

2. The oil wasn’t engine oil. Moreover, the vacuum pump is located in the alternator so there should be oil coming from there.

3. The previous owner of the vehicle had installed a K&N air filter. Last year, I notice that my air filter bowl had a lot of oil in it. For those who don’t know, this kind of air filter required oil to work properly. I’ve cleaned everything and installed and standard filter. I though maybe oil could have come from there in some kind of fume and the vaccum pump aspired it in some manner (I know this is very unlikely). I check one of my vaccum hose with a Q-tip and there are no oil residues.

So where this oil could have come from ? Any Ideas…?

I would like to fix this issue before installing a new brake booster. Toyata is asking 500$ for a Brake Booster for my 1985 BJ. I would like to swap my brake for another brand that is less expensive. Does anyone knows a compatible model ?

Thanks!

If you know the oil is not engine oil than what kind of oil is it? The rig has only 4 or 5 possible types of oil in it, 1. engine oil, 2. power steering oil, 3. gear oil, 4. intake oil in the k&n filter, 5. automatic transmission fluid (if it has an auto).
Brake fluid is not an oil.
The vacuum pump on the alternator is directly hooked to the engine oil, it is feed pressurized engine oil so if the vacuum pump was leaking yes engine oil could go to the brake booster.
What color is the "oil"? How thick is the "oil"?
What type of transfer shift do you have? If it is a vacuum system then gear oil could be getting into the vacuum system.
If you have an automatic transmission you could get transmission fluid into the vacuum system.
In order to help a little more info on the weight (viscosity), color, smell, and feel would really help.

Jim

 

[DieselDen]

I let the stuff that was in the brakebooster rest for the night and it turned out that to be less homogenous than when I first got it out (see picture). It look more like very dirty brake fluide.

I think my master cylinder is leaking into the brakebooster for the following reasons:

• The hose that connects the brakebooster to the vaccum pump doesn't have any oily residues
• The only other way oil could come into the brakebooster is via the master cylinder and the stuff that was in it look very much like brake fuide now

Does this conclusion make sense to you ?

If so, thank you so much for your help...It has been really appreciated

 

[jake2far]

I let the stuff that was in the brakebooster rest for the night and it turned out that to be less homogenous than when I first got it out (see picture). It look more like very dirty brake fluide.

I think my master cylinder is leaking into the brakebooster for the following reasons:

• The hose that connects the brakebooster to the vaccum pump doesn't have any oily residues
• The only other way oil could come into the brakebooster is via the master cylinder and the stuff that was in it look very much like brake fuide now

Does this conclusion make sense to you ?

If so, thank you so much for your help...It has been really appreciated

Yes that looks like old brake fluid with rust and water, I think you have it right, the master is leaking into the booster.

Jim