Adding Vacuum Pump for brakes

[vintovka]

Adding a vacuum pump to try to make Power Brakes work better. I would like to add it inline with the existing manifold vacuum line to the booster. Plan to just add a "T" to do this. Anyone else running a pump? comments tips etc appreciated. (Searched site and net and there is very little on how to do this)

[mikebte]

I am assuming your running a supercharger or something that’s killing your vacuum.
What truck, engine, brakes are you running?
Have You considered hydraulic brake booster that runs off the power steering (if equipped)

[vintovka]

Originally Posted by mikebte

I am assuming your running a supercharger or something that’s killing your vacuum.
What truck, engine, brakes are you running?
Have You considered hydraulic brake booster that runs off the power steering (if equipped)

Just a GM crate engine. 18" at idle and downhill from there. Brakes are about 85% ok but can't really lock them up in an emergency. Would love a HB but finances and good mechanics are in very short supply here.

[GreasyLikeaBurger]

What brake master cylinder do you have? Are you running discs front and rear? Do you have a proportioning valve set up?

[vintovka]

Originally Posted by GreasyLikeaBurger

What brake master cylinder do you have? Are you running discs front and rear? Do you have a proportioning valve set up?

ALL brand spanking new stock parts for 84 GMC k10. New discs . calipers, drums, cylinder, booster, Master cylinder the works. Stock Disc front, Drum rear correct proportioning valve. Like I said brakes are almost right but can't lock them up when needed. Been to several shops and No matter what we tried it comes down to a low vac issue.

Specifically Need to know if ok to put T in line from vacuum pump to brake booster. T is for manifold vacuum so pump doesn't keep running.

[mr48chev]

OK, what is wrong with the system that it doesn't pull enough vacuum at all times to properly operate the brakes?

Cammed up? Vacuum leak? No check valve between the intake and the booster? Issue with the vacuum line running to the booster? Too small a passage way somewhere in it due to a fitting with a small orifice?

Or you just going by redneck measurements where it has to slide the wheels to have good brakes rather than actually stopping quick and straight without sliding a tire?

How does it actually stop? Straight, reasonably quick? Poorly? Or???

[vintovka]

Thanks but actually, we went thru all that you have pointed out (several times) and everything is correct. Think engine cam may be root cause but it rums great. Pedal is very hard, truck does stop straight but power assist is weak.

At this point the vacuum pump is installed and routing the lines tomorrow. The question remains. How best plumb it to make most efficient use of pump and manifold vacuum? May still just "t" manifold vacuum into the line from pump to booster and see what happens. If this fails will move on to a HB.

[1project2many]

First, to answer your question, the vacuum pump should be Teed into the line from the manifold. You need a check valve between the manifold and the Tee to prevent the pump from continually drawing air and vapor from the manifold. Use a vacuum switch to operate the pump. The vacuum switch should sense vacuum in the booster, not in the supply line. The booster will most likely already have a check valve in the inlet fitting. This is OK to leave in place as a safety measure.

Second, 18" of vacuum should be enough to provide plenty of assist for at least one stop. If the engine idles at 18" the booster should also be at 18." Additionally the check valve on the booster should keep the vacuum level at 18" even when manifold vacuum drops. As a further test if you drive the vehicle in low gear with the engine at 3000-3500 RPM, then close the throttle to decelerate, you will generate maximum vacuum in the booster. Vacuum should easily climb above 23" at this point and again the check valve should hold the vacuum level in the booster at maximum. If you do this, and you cannot get the brake pedal feel and brake system response you are looking for during the very next stop, then a vacuum pump will not help.

I realize you may have checked all of this but I am putting it out for consideration anyway. I fear you may be heading for an HB unnecessarily and you may also be dissatisfied with the result of the swap. HB systems actually reduce the mechanical advantage between master cylinder and wheel cylinders / calipers by using a larger master cylinder piston. They overcome some of this with extra hydraulic assist but IME a system which requires "too much" pedal pressure in vacuum still doesn't feel right if switched to HB.

HTH

[vintovka]

Thanks, What i was thinking. Pump kit is standard one with pressure switch (18-22") and will add check valve between manifold and line. Check valve at booster will remain. You described exactly what is happening even with 18" at idle or coast. While theres a little info around on piping options (like connecting pump "exhaust" to manifold vacuum). The low vacuum problem seems like a very common issue and a pump or HB seem the common solutions. Pump makers and users, however, seem hesitant to share info. Those who use the pump seem to like the results but complain mostly about the noise. May move or enclose the pump if it works. Being a somewhat anal retentive engineer I installed a shut off switch so i can compare braking with or without the pump. Had I the funds/ resources i would have used a diesel engine with the HB systems they require. If circumstances allow i'll report back on how it went and maybe offer a diagram.

[01spirit750]

I wonder if you issue is related to the size of the booster. A small diameter booster or single diaphram booster will not provide as mush assist as a larger diameter or dual stage booster. The concern is that adding the vacuum pump may not add much to the power assist that you want.

I had a similar issue running a small diameter booster mounted under the floor. I switched to a hydraulic booster from an astro van and what a difference.

[1project2many]

You described exactly what is happening even with 18" at idle or coast.

Pedal feel is subjective, but 18" vacuum at idle is generally not low enough to be a problem. 8-10" at idle is where significant problems usually show up. Are you aware that several GM vehicles from the '80s used calipers with similar outside dimensions but different diameter pistons? If available, larger pistons would help reduce pedal effort.

theres a little info around on piping options (like connecting pump "exhaust" to manifold vacuum)

Vacuum pump exhaust probably should not be directed to manifold vacuum. It can alter manifold pressure and in some cases will alter airflow readings to a computer in fuel injected vehicles. I would direct it to the air intake tubes in front of the air filter or the air cleaner.

Those who use the pump seem to like the results but complain mostly about the noise.

I had an '82 Cavalier with a factory installed vacuum pump. For me the noise was simply part of using the vehicle. We have owned fleet vehicles which have Hydroboost and use electric assist pumps. Again, noise is simply part of proper operation of the system.

Being a somewhat anal retentive engineer I installed a shut off switch

Interesting.

As a discussion point, there are several design considerations for powering the pump. Most OE installed applications that I'm aware of allow the assist pump to operate if the brake is applied when the key is off. A brake operated switch could be wired to battery power so the pump is powered whenever the brakes are applied. This could cause the pump to operate unnecessarily at idle however it would also ensure brake assist is available in the case of an engine stall. Wiring the brake switch through the vacuum switch limits operation to those times when vacuum is needed, however it could prevent the booster from maintaining the minimum level of vacuum and would not provide assist if the engine stalled. I believe the GM and Delco based systems connect the pressure switch to battery power. The consequence of the circuit malfunctioning and draining the battery is far better than the consequence of an accident caused by insufficient braking.

[mr48chev]

You have to have a check valve between the T and the manifold or the pump will just suck air out of the manifold and not pull a vacuum on the booster. Path of least resistance.

[vintovka]

Pump is in and just got back from test drive. Text may be a bit incoherent as really tired. Test drives along the bright beautiful ocean/beach takes it out of you. Starting a mini-car show at the beach rest stop finishes you off.

I Can really feel difference when pump is on or off (via dash switch). I would say brakes are at 99% . Can't hear or feel pump when engine is running. Did put a check valve on manifold vacuum as suggested. Check valve at booster remains. Did not connect exhaust to manifold. Kit came with an "exhaust" muffler that works fairly well. At idle pump stops when vacuum is reached but does start again shortly thereafter. Will be looking for leaks. As for vacuum it runs 18" at idle 14 at cruise (OD 1000 rpm) and just under 20" at coast. Will draw a digram of wiring and piping if anyone wants to see. I like the idea of connecting power to brake switch so pump doesn't run unnecessarily.

[mr48chev]

It's always good to be able to shut off any electrical unit connected to the ignition with a switch be it vacuum pump, electrical fuel pump or ?? Some times you want the ignition on for testing purposes and don't want those units powered up.