Got Brakes?? No!!!

[fjpotenzano]

This is a great forum! After being in the background for a while I need some help. My 92 D350 has a brake problem. When I step on the brakes I have about 5 to 10 seconds of power assist, then the pedal effort gets hard, like no power assist. When this happens, the Brake and Antilock lights come on. The lights go out when I release the brake peddle. Cruise control works fine and the HVAC works OK. Have I got a power brake booster going south on me? She's stock except for the straight exhaust dumping in front of the rear wheel and a NV4500. Thanks in advance. . Frank

 

[Philip]

You could have a booster going bad or a vac pump going out.

Check the hoses for leaks.



This thread tells a little more on the pump spec's.

 

[fjpotenzano]

Thanks Philip, When you mentioned the vacuum pump, it reminded me that the engine does sound "different" and from the drivers side. If the pump is bad could the cruise still work OK?... . Frank

 

[Philip]

No the cruise will not work. There is a vac switch mounted behind the left hood hinge that will kill the cruise if the vac goes below a certain setting.



DUH I fogot the link in the other post. LOL



https://www.turbodieselregister.com/forums/showthread.php?threadid=60346

 

[fjpotenzano]

I had checked the vacuum by pulling the hose off of the booster and had 14-15 inches. Didn't have a manual to reference, so I don't know if this Ok. I'm getting the feeling it's the booster. Any idea what the output of the vacuum pump should read?

 

[Philip]

The manual says up to 25 inches. You will not get this much at idle. Bring the engine rpm up and see what the max you get that way.

 

[fjpotenzano]

Thanks for the info. I'll check it this weekend and if the vacuum comes up to the 25 reading then I'll get a new booster. Thanks Philip... Regards, Frank

 

[Paul Herioux]

Check hoses

Frank,

Check the molded 3/8" vacuum hose running up from the vacuum pump to the brake booster. I have seen quite a few of these that have deteriorated and collapsed on the inside of the molded curves. This restricts flow from the booster to the pump and gives the same effect as a leak in the booster. The cruise generally works on a low enough volume of vacuum that its operation isn't effected until the condition gets very severe. The booster in our truck is a hungry little monster on the other hand.

Hope this helps,

Paul

 

[keimmmo]

It is good that you have checked the vacuum pump. Your vacuum is reasonable at idle. Check the vacuum line too. However, I have had 2 boosters go bad over the years on my '92 W-250. There is a GOOD chance the diaphragm has ruptured! If so, it will cause the symptoms you describe.



Steve

 

[Scot]

The boosters I have had go bad made a great sucking sound inside the cab when you applied the brakes.

 

[fjpotenzano]

Got Brakes? Now I Do!!

Just a quick note to put this thread to rest. I changed the vacuum booster and master cylinder ( it came as one unit) for $172. Bled the brakes and had power brakes again. Sure is nice to be able to stop the beast! Thanks to ALL who took time to help me out. This forum is cool!!