Is it normal when the truck engine is not running for the brakes to be EXTREMELY difficult to push and stop the vehicle? Brakes will stop on a dime with engine running, but I have to stand on them if the engine stalls to slow down the truck. 351W 1982 c/c dually, power brakes, manual tranny.

 

That is normal.
The brake booster is operated by engine vacuum, so when the engine stalls you lose most of your braking (& steering).

 

You should not lose your vacuum as soon as the engine quits. The booster has that big chamber and there is supposed to be a check valve in the line to prevent vacuum loss.

It shouldn't stall when you slow down either.

A little fix it is in order on both brakes and engine IMO.

 

Yeah, fix the engine stalling first.

 

+1 on that. When the engine is not running, whether it has stalled or has been turned off normally, the brake booster system should retain enough vacuum to allow 2 or 3 boosted applications.

There's a check valve in the vacuum supply line to the booster. On our trucks, it's a right angle fitting where the line plugs into the booster. If it has failed, vacuum will bleed off immediately when the engine stops running, and thus no boost. You could also have a leak within the booster itself. There's a massive supply of vacuum available from the engine, with the volume capable of masking any leaks to some extent.

Here's a good guide for troubleshooting:

https://m.roadkillcustoms.com/test-power-brake-booster/

This video is kinda long, but has some good info:


The subject vehicle is a Toyoter, but the general principles are the same. The check valve is different (metal vs. plastic) but is in the same location.

One possibility is the booster is leaking enough to cause the engine to stall during deceleration. One defect (leaking booster) could theoretically cause both the stalling and loss of brake boost. I'm not saying just throw a booster at the problem, but follow the guides above to figure out exactly what is going on. With any luck, you could kill two birds with one stone.

Can you duplicate the stalling while parked, i.e. rev the engine and then foot off the gas pedal? If so, disconnect and plug the big vacuum line to the booster and try again. See if the engine no longer stalls. That would indicate a big vacuum leak from the booster.

 

I guess I wasn’t clear on the OP. I don’t have a stalling issue, I just noticed that when I come to start my truck at the end of work and I’m on.a hill, the brakes will not hold the vehicle without really strong pressure. As soon as I turn it on, the brakes are easy to press and work fine.

Thanks for the video. I will check the booster and check valve. Does a new check valve come with a new booster? Or is that a separate item?

 

The valve is a separate piece. Easy to replace. You may want to check the hose attached to it, as it's 35+ y/o
https://www.google.com/search?q=brak...client=gws-wiz

 

When I got a new booster it did come with a new check valve but as said you can get the check valve at any parts store, help area.
If they dont have it in stock they can order it for you.
Dave ----