Low Vacuum warning light

[Bikersmurf]

When I connected a vacuum gauge, it confirmed that after 3-4 pumps there is no vacuum left in the booster. It is also very noticible in that there is no longer any assist.

The ebrake switch is currently disconnected, and not the source of the problem. It is definitely a Drop in vacuum. I just need to figure out why.

 

[NevadaLover]

Do you have and how big is the vacuum reservoir, most of our diesels have small reservoirs and you may just need to find a bigger one or an extra one, they can be hooked up anywhere in the system and may be the key fix to this trouble.

 

[Bikersmurf]

I've been considering a vacuum reservoir. There is a minuscule one on the heater duct, but it is quite useless for brakes.

The more research I've done, the more I think I need to tighten up the brake adjustment, and also rebleed the brakes. I believe there is too much travel before the brakes engage. In the process too much of the available vacuum is used because there is no reserve outside of what is in the booster itself. At low RPMs the small vacuum pump takes a moment to replenish the vacuum in the booster.

 

[cjken]

I was getting frustrated with my brakes that were just not working as well as in the past.
Occasionally I would get the brake light coming on.
Started thinking of going to a hydro boost setup.

In the end replacing the vacuum pump and booster solved the problem.

The brakes are good enough that I am no longer looking at the hydro boost option.

 

[Bikersmurf]

I was getting frustrated with my brakes that were just not working as well as in the past.
Occasionally I would get the brake light coming on.
Started thinking of going to a hydro boost setup.

In the end replacing the vacuum pump and booster solved the problem.

The brakes are good enough that I am no longer looking at the hydro boost option.

Did you replace both at the same time? Or one or the other first?

Adjusting the rear brakes has improved things. I’m hesitant to replace the vacuum pump again because they want $250 for one. I’m thinking bleeding the brakes will be next on the list... over the years I’ve changed out all the brakes a few parts at a time, and it’s possible there could be a bubble somewhere... unlikely, but worth checking.

Hydro booster is $245ish... but then I also need lines etc. I’m considering it though.

 

[NevadaLover]

One thing I have found is the sterling rear ends don't self adjust very well, they like to be adjusted pretty often but when adjusted correctly offer great braking, try checking the rear brakes and make sure the adjuster is working, if you can hook a vacuum gauge to the system try that and watch the level while you pump the brakes, if it degrades significantly you may just need a bigger reservoir, if the pump recovers quickly then you know it is still working and doesn't need to be replaced, you can also find a junkyard 6.0 PSD and scavenge the electric vacuum pump to augment the belt driven pump and that should help!

 

[Bikersmurf]

Vacuum recovery is slow at less than 2300 rpm. Max Vacuum is 15”. Been doing a bunch of reading... came across these numbers a few times.

“17-21 in-Hg is what my book shows = 57-70 kPa
At idle below 10in for more than 7 seconds will illuminate the brake lamp.”
The absolute most the engine driven pump could draw was 14”/40 kPa which is about 65% of what the minimum should be. Consensus seems to be that 17” is about the minimum... since it barely recovers at idle, I’m confident the pump is on its last legs.

When I use the Mighty-Vac hand pump I can quickly and easily increase the Vacuum to way higher and there is zero loss over 5 minutes. I could wait longer, but even at 25” it was holding strong with no losses.

 

[Bikersmurf]

One thing I have found is the sterling rear ends don't self adjust very well, they like to be adjusted pretty often but when adjusted correctly offer great braking, try checking the rear brakes and make sure the adjuster is working, if you can hook a vacuum gauge to the system try that and watch the level while you pump the brakes, if it degrades significantly you may just need a bigger reservoir, if the pump recovers quickly then you know it is still working and doesn't need to be replaced, you can also find a junkyard 6.0 PSD and scavenge the electric vacuum pump to augment the belt driven pump and that should help!

I’ve found the same with the D70 rear end. The brakes work well, however, after a couple quick & short applications the assist Peters out... unless the RPMs are high enough for the Vacuum to recover.

 

[Bikersmurf]

A new vacuum pump arrived today. It should improve the vacuum recovery rate. The current pump recovers slowly so it's likely near end of life.

 

[The Punisher]

I am on my 3rd vacuum pump (Dorman from advance auto) and this new one is going out..... thinking about using a electric vacuum pump of a different vehicle. Some GM trucks have electric pumps on their brake booster.

 

[Bikersmurf]

My last was Dorman... this one Cardone. I’d go hydro booster before electric.

 

[Bikersmurf]

We got the pump installed

The new pump moves so much more air. The old pump had no suction when spun by hand.

Now the Low Pressure light goes off in about 2 seconds at idle rather than having to rev it up and having it take 20 seconds to go off. I'm confident the boost will work much better when driving.

 

[NevadaLover]

It sucks that the after-market pumps don't last, glad to hear it's back to normal!

 

[Bikersmurf]

So far I cannot say if any others last better. Bearings are still great
I’ve got a special kind of luck for finding duds

 

[NevadaLover]

The last couple I replaced were motorcraft, so far no problems.