My brakes just started acting up, the pedal gets hard and can barely stop. I have vacuum brakes and not hydroboost. I pulled the large vacuum line out of the booster to inspect it and when I did you could hear it suck air. This was after the truck had been sitting for 15 minutes or so which means I don't have a vacuum leak.

 

I have no fluid leaks anywhere and the master cylinder is still full. Only thing I can think of is the booster just took a dump.

Does your truck have any ABS?  

Would a malfunctioning check valve cause this?

1 minute ago, Me78569 said:

Does your truck have any ABS?  

 

It has ABS but no lights are on.

any difference when you unplug the ABS computer?  

7 minutes ago, Me78569 said:

any difference when you unplug the ABS computer?  

 

No.

 

Checked the check valve and it's working correctly. 

If its a ABS issue it could be bad tone rings in the bearings which typically will not trip the light all the time. Like my ABS it will back pump the pedal and prevent you from stopping.

 

If vacuum booster it could be a bad diaphragm or seal internally.

Here's where I'm at. There was a vacuum leak around the vacuum pump check valve that screws in to the vacuum pump, it's not leaking anymore as at broke right the EFF off. So, where the hell does a person find one of these check valves?  

 

Not my picture but this is what happened to mine, except I still have to get the rest of the fitting out of the pump.

 

Edited June 29, 20168 yr by The_Hammer

use the part number lookup tool to find the part number and go to the dealer.

 

10 minutes ago, Me78569 said:

use the part number lookup tool to find the part number and go to the dealer.

 

 

Was reading on Cummins forum that it's a discounted item.

 

Once I get the threads out I'll see what size it is and order a fitting. 

Got the rest of the threads out. I'll head to the co-op in the morning and see if I can match up a new barbed fitting. 

 

I'm also going to replace the master cylinder since my pedal would go to the floor if you held it even before the vacuum issue. Does anyone know the difference between the 7500 gvw and 8800 gvw master cylinders? Will the 8800 gvw cylinder work on a 7700 gvw truck and if so does it offer any performance benefits? 

 

Found yet another vacuum leak, the line going to the vacuum pressure sensor was split. Tried to remove the line and the plastic nipple snapped off on the pressure sensor. WTF is up with everything breaking today? Damn already. 

Edited June 30, 20168 yr by The_Hammer

When it rains it pours. Sounds like it's time to start over and just replace all the vacuum lines. 

17 minutes ago, Buzzinhalfdozen said:

When it rains it pours. Sounds like it's time to start over and just replace all the vacuum lines. 

 

You say that as I'm still repairing my house from a literal flood we had a while back 

 

I'm for sure replacing all the lines, they're cheap and easy enough to replace. Hopefully everything will still work on without the pressure sensor.

1 hour ago, The_Hammer said:

 

You say that as I'm still repairing my house from a literal flood we had a while back 

 

I'm for sure replacing all the lines, they're cheap and easy enough to replace. Hopefully everything will still work on without the pressure sensor.

Cold hearted humor I know but it was too easy to pass up. Best of luck with the house and vehicle repairs.  

1 hour ago, Buzzinhalfdozen said:

Cold hearted humor I know but it was too easy to pass up. Best of luck with the house and vehicle repairs.  

 

It made me laugh, it's all good man. 

Well the pump threads are 12mm 1.25 pitch, something no one around here has. I'm going to try brazing the old one up and ordering something. If worse comes to worse I'll get a seal kit, pull the pump, then drill and tap it to a common size. 

That sounds like a OK plan to do. Don't have much choice unless you want to just replace the entire vacuum pump which may be rather expensive.

39 minutes ago, Mopar1973Man said:

That sounds like a OK plan to do. Don't have much choice unless you want to just replace the entire vacuum pump which may be rather expensive.

 

Well, it seems the fitting I need doesn't exist. Why the *&$#% they decided to use such an uncommon thread size is beyond me.

I managed to get the broken piece brazed back together and installed on the truck. My brakes are working pretty good again, just need to pick up a new master cylinder and it'll be 100% again. At least I can drive it now. 

Replaced the master cylinder with a brand new (not reman) unit and the brakes feel great. If you pump up the brakes and hold down on the pedal it will still slowly sink down but not bottom out. I'm guessing there might still be some air in the lines?

I would assume so.