F700 grain truck question #2

[Howard H.]

After getting the old truck rolling (per fuel question), I found out it won’t stop!

There are no brakes at all. They were working fine when I parked it…. In checking, I guess I last used it about 5-6 years ago.

The pedal goes all the way to the floor with no resistance.

What should I be looking at first?

Thanks again for any advice,
Howard

 

[joeysmith]

Add fluid to the master cylinder
Just wiggle the peddle a little bit at the top of the stroke several times an keep adding fluid aa needed
May still have to bleed the brakes

 

[mtf]

Check reservoir for brake fluid, you will probably need to bleed system.

 

[rustred]

That’s a pretty normal situation when them old vehicles sit. The brake fluid will leak out on worn brake cylinder rubber. Look around at all the wheel backing plates and u might spot the leaking problem at the bottom. Make sure u add only brake fluid and not any other oily stuff or u will creating a bigger problem. Fill up the brake cylinder then u got to bleed the brakes. And if you know the leaky and then open that bleeder and fill the master cylinder. The fluid will eventually leak out. Other wise I need a helper. Or a bleeder tool which I am sure u don’t have as your asking what to look for.

 

[paul]

Check the brake fluid, bleed the brakes as others mention.

This becomes a common issue on older trucks, and can happen repeatedly. Be aware of it….

As well if you pump the pedal to the floor a lot now, you might upset the pistons in the brake cylinder as they pass into areas they haven’t been to. And make them leakier. Shallow pumping as suggested is better while you bleed them.

And getting all the air bleed out is important, air bubbles in the limes can give some unexpected results.

Paul

 

[JMOR]

If it has a hydra-vac, that is a whole new set of worms.

 

[johnnmr]

Very common on drum brake vehicles that sit, the cups in the wheel cylinders aren't being pushed against the bores and they every so slowly weep fluid. Assuming you can keep the master cylinder topped off with brake fluid (AND you have decent pedal) there's nothing really to be concerned about. New cylinders will do it too.

 

[Bruce from Can.]

Is it hydraulic/electic ? Lots of luck finding brake parts if you need any.

 

[RedMF40]

Besides the brake fluid suggestions, I’d pull all the wheels and tap the brake drums with a heavy hammer to wake them up. A truck sitting that long in my area would have a lot of rusted brake parts and could pull to one side if everything isn’t working properly.

 

[used red MN]

Besides the brake fluid suggestions, I’d pull all the wheels and tap the brake drums with a heavy hammer to wake them up. A truck sitting that long in my area would have a lot of rusted brake parts and could pull to one side if everything isn’t working properly.

With respect, that is an interesting suggestion, if the wheels will turn this seems like a lot of work that would have fairly questionable positive results. Maybe you could explain what “waking them up” means? I can see the possibility of knocking some rust loose but as I said a lot of work, this truck has a tag axle. I agree with what rustred has posted as a good approach.

Just wiggle the peddle a little bit at the top of the stroke several times an keep adding fluid aa needed

This is a good suggestion, by wiggle he means move the pedal short strokes. This allows the air in the master cylinder bore to bubble up and be displaced with fluid. The more fluid you get in the master cylinder bore the less air you are pushing into the entire system which then needs to be bled out at the wheel eventually. Also it is almost a given that it has a hydro-vac booster on it this will also have a bleeder on it maybe 2. Also having the brakes adjusted properly is also part of being able to successfully bleed one of these systems. Proper adjustment in my books is cranked out to where they lock and then backed off until it spins free for part of a turn of the wheel but has a drag on the other part of the turn. Many of these have automatic adjusters that need held away from the star wheel to back them off. Many times the adjusters become rustred and froze. Here may be where you end up pulling the drums to free up the adjusters. This takes you into bearing and seal land on those old trucks that didn’t have dismountable drums.

 

[Bruce from Can.]

On my F800 you would need to cage the brakes just to move the truck.

 

[RedMF40]

With respect, that is an interesting suggestion, if the wheels will turn this seems like a lot of work that would have fairly questionable positive results. Maybe you could explain what “waking them up” means? I can see the possibility of knocking some rust loose but as I said a lot of work, this truck has a tag axle. I agree with what rustred has posted as a good approach.

This is a good suggestion, by wiggle he means move the pedal short strokes. This allows the air in the master cylinder bore to bubble up and be displaced with fluid. The more fluid you get in the master cylinder bore the less air you are pushing into the entire system which then needs to be bled out at the wheel eventually. Also it is almost a given that it has a hydro-vac booster on it this will also have a bleeder on it maybe 2. Also having the brakes adjusted properly is also part of being able to successfully bleed one of these systems. Proper adjustment in my books is cranked out to where they lock and then backed off until it spins free for part of a turn of the wheel but has a drag on the other part of the turn. Many of these have automatic adjusters that need held away from the star wheel to back them off. Many times the adjusters become rustred and froze. Here may be where you end up pulling the drums to free up the adjusters. This takes you into bearing and seal land on those old trucks that didn’t have dismountable drums.

“Wake them up” get the springs and shoes used to the idea of moving again. Maybe some of these suggestions will get the shoes to expand. Whether they want to return again is anyone’s guess. I tend to think worst case scenario which would be all new wheel cylinders and possibly even steel brake lines. If the truck is in Arizona or New Mexico, someplace dry, the brakes should be fine. In my area, where it’s very wet, everything would likely need to be rebuilt.

 

[used red MN]

On my F800 you would need to cage the brakes just to move the truck.

I suspect you are talking about air brakes. Could be true on some of the 1980 or later hydraulic park brake systems, never dealt with many of
those.

 

[Bruce from Can.]

I suspect you are talking about air brakes. Could be true on some of the 1980 or later hydraulic park brake systems, never dealt with many of
those.

89 , hydraulic over electric. Front disc, rear shoe/drum On the F800 I had brakes were in the late 80’s the same as they used in school buses.

 

[joeysmith]

89 , hydraulic over electric. Front disc, rear shoe/drum On the F800 I had brakes were in the late 80’s the same as they used in school buses.

Those canisters have gotten pricey to work on

 

[used red MN]

89 , hydraulic over electric. Front disc, rear shoe/drum On the F800 I had brakes were in the late 80’s the same as they used in school buses.

Not sure how familiar you are with old truck brakes like this, but it has nothing like that. Just old school hydraulic shoe brakes expanded out to the drums with brake cylinder. And a hydro-vac vacuum booster.

 

[Howard H.]

Thanks for the replies and advice!!

I should have mentioned that this booster is down on the frame and has a “Velvac” label on it. That (and wanting to knock off for supper ha ha) is what had me in the mindset it was more than brake fluid. It WAS low on fluid - but I sure can’t seem to get the air out of the lines or it to pump up like it should.

 

[used red MN]

Thanks for the replies and advice!!

I should have mentioned that this booster is down on the frame and has a “Velvac” label on it. That (and wanting to knock off for supper ha ha) is what had me in the mindset it was more than brake fluid. It WAS low on fluid - but I sure can’t seem to get the air out of the lines or it to pump up like it should.

Can you devote some time to this? Or at least be nearby doing something else? Get a piece of automotive vacuum hose and a pint/jelly jar. Connect it to the left front wheel cylinder bleeder and open it and stick the other end in the jar. Fill the master cylinder and set a timer for 5 minutes. When the timer goes off see if gravity has flowed any fluid into the jar. If it has see if any air bubbles are coming out of the hose as it flows. After it has put somewhere around a 1/4 cup in the jar (an inch plus in a 2” diameter jar) and there are no bubbles move to the right front wheel, then to the rear bleeders. Make sure the master cylinder is kept full during this process. Another thing I am not certain of but it may be that you need to bleed the hydrovac first before the front wheels I can’t remember exactly how the those old system are plumbed. If the line coming out of the master cylinder goes to the hydrovac, bleed that first. This method requires clean open bleeders they can’t be partially blocked or plugged. After you have done all this then see if the pedal pumps up better or is any solider. As I said earlier in reply 10 about the adjustment being a very important part to having a good outcome of this process bares repeating.
If there is a lot of breaks of air in the fluid in the line, there is a possibility that this can block the flow of fluid during a gravity flow bleed. Not sure if you have seen a siphon through a clear tube that has ran empty and pulled in air. This is the same principle as that.
Absolutely no guarantee on this, but it would be something I would try if working alone.

 

[caterpillar guy]

I'm not sure how well a siphon system would work on that with the fluid so close to the samew height as the wheel cylinders. Seems like it would need to be worked through like the pedal pumping will do. We had an old chevy one time I could not get the bleeders loose on so I just kept the fluid full and would go out and pump the pedal occasionally as I thought of it. The air finally came out of it. took about a year doing it that way but did finally work the air out. or at least was a solid pedal with good working brakes on it.

 

[used red MN]

Can you devote some time to this? Or at least be nearby doing something else? Get a piece of automotive vacuum hose and a pint/jelly jar. Connect it to the left front wheel cylinder bleeder and open it and stick the other end in the jar. Fill the master cylinder and set a timer for 5 minutes. When the timer goes off see if gravity has flowed any fluid into the jar. If it has see if any air bubbles are coming out of the hose as it flows. After it has put somewhere around a 1/4 cup in the jar (an inch plus in a 2” diameter jar) and there are no bubbles move to the right front wheel, then to the rear bleeders. Make sure the master cylinder is kept full during this process. Another thing I am not certain of but it may be that you need to bleed the hydrovac first before the front wheels I can’t remember exactly how the those old system are plumbed. If the line coming out of the master cylinder goes to the hydrovac, bleed that first. This method requires clean open bleeders they can’t be partially blocked or plugged. After you have done all this then see if the pedal pumps up better or is any solider. As I said earlier in reply 10 about the adjustment being a very important part to having a good outcome of this process bares repeating.
If there is a lot of breaks of air in the fluid in the line, there is a possibility that this can block the flow of fluid during a gravity flow bleed. Not sure if you have seen a siphon through a clear tube that has ran empty and pulled in air. This is the same principle as that.
Absolutely no guarantee on this, but it would be something I would try if working alone.

Another thing I just thought of would be bleeding the master cylinder by itself first. Not sure if you ever bench bled a master cylinder with a screwdriver prior to install they usually come with a bleeder hose set. Basically screws in the outlet port and the short hoses loop around back into the fluid. It is important that the end stays immersed in the fluid. Once the hose is on you pump the cylinder until the fluid is air free. This way you are not pushing all that air out of the master cylinder all the way through the system.
Example MC bleeder set
Auto parts stores would have these.