# [EVDL] Question about Vacuum reservoir, bigger is better?



## EVDL List (Jul 27, 2007)

The S-10 conversion that I purchased came with a vacuum reservoir made
out of 1 1/2" PVC pipe (about 3 inches long). When I switch it on it
takes the GAST pump about 31 seconds to "charge". It works fine for
ordinary driving, but re-starts the vacuum pump after every break pedal
press.

The day we purchased and towed the pick-up home I had to ride the breaks
going down a long hill (so-as to not overtake the tow vehicle and
wife...) and lost vacuum assist near the end because the pump/reservoir
couldn't keep up.

I decided that it would be nice to have a larger vacuum reservoir, to
allow me more pedal pushes before the pump starts up, and to have a bit
more "reserve capacity" if I have to break twice in a row, etc...

Not knowing much about the physics of vacuum, but assuming it was
somewhat like a compressed air tank, I figured using a one foot piece of
3" PVC pipe would give me ample capacity. So I built a larger reservoir:
http://www.summet.com/blog/2011/03/23/building-a-pvc-vacuum-reservoir/

(I also added a connection for a vacuum/boost gauge, so I could see how
things were going...)

I've just connected the new reservoir to the vacuum system (the old one
is also still in the system, as I'm testing) and I have not been
impressed with the results. In fact, I'm wondering if it is worth
mounting the new reservoir at all...

Instead of 32 seconds to charge the reservoir from empty, it now takes
around 50 seconds (which is expected). HOWEVER, as soon as I press the
break pedal, the vacuum pump turns back on! (I may have a bit more
"reserve" capacity, as it feels like I have a few extra pumps after that
before the vacuum is completely gone, but I was expecting to be able to
pump the pedal a few times before the pump turned on).

The (cheap/AutoZone) vacuum gauge shows that the vacuum only builds up
to 19 inHg and then the pump switches off, and the pump switches back on
when it drops below around 16.5 inHg. (The vacuum switch label says that
it is supposed to switch on at 16.5 inHg but according to the label it
isn't supposed to switch off until it hits 25 inHg. Perhaps somebody
adjusted it?) The system holds 19inHg for over 15 minutes when idle, so
I don't feel that leaks are a problem.

On a test drive with stop signs every block up and down hills the vacuum
never dropped below 10 inHg, but the pump also never shut off. My questions:

1. Is it worth mounting the larger reservoir? (I haven't seen a super
improvement in breaking capacity, and the pump runs longer now.) Any
comments on your experiences and how they match up (or don't) with mine?

2. Should I try to adjust my vacuum switch to have a greater range
between on and off? It is currently about 5 inHg, and I can go up to 10
inHg differential. (What is the lowest "on" point I should use?)

Thanks,
Jay

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## EVDL List (Jul 27, 2007)

Jay,

I'm guessing there is a problem with something other than the reservoir. I
have a reservoir about the size of your new larger one, and when I start my
car the vacuum pump charges it up in about 8-10 seconds. I hear it come on
maybe once or twice during my typical 6 mile commute (I drive pretty flat
terrain). My pump is a CANEv model
http://www.canev.com/KitsComp/Components/VacuumPumpKit.html

- Peter Flipsen Jr
http://www.evalbum.com/1974



> Jay Summet <[email protected]> wrote:
> 
> > The S-10 conversion that I purchased came with a vacuum reservoir made
> > out of 1 1/2" PVC pipe (about 3 inches long). When I switch it on it
> ...


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## EVDL List (Jul 27, 2007)

> SLPinfo.org wrote:
> > Jay,
> >
> > I'm guessing there is a problem with something other than the reservoir. I
> ...


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## EVDL List (Jul 27, 2007)

You can get rid of the vacuum boost brake system with a unit that is call a 
hydro boost unit which many old and new vehicles are using now.

When my vacuum boost went out, I went on line to see how these conversions 
are done. You can just type in your search engine:

Hydro Boost Conversion and many web sites will come up showing how 
to do this conversion.

I use the info from:

www.stu.offroad.com/suspension/vanco/hydroboost-1.htm

They use a Vanco for a truck that requires a high pressure. Learning from 
there mistakes and talking to a lot of people, I found that I could use a GM 
factory rebuilt unit for a 1986 Chevy or GMC truck that uses the normal 
brake pressure which uses DOT-3 oil. My 1977 El Camino uses DOT-3 oil so 
that year hydro boost which provides 800 to 1000 psi will work.

You use the power steering pump to provide pressure to this unit. You run 
the high pressure hose from the power steering pump to the hydro boost unit 
and then out to the steering rack. A low pressure line goes back to power 
steering pump.

Instead of using the belt driven power steering pump, I use the CanEV 
electric power steering pump. I use a small plastic fill reservoir that is 
tee in the low pressure return line. The reservoir is place high next to 
the vacuum boost which eliminates air bleeding of the air in the brake 
lines.

I found the re-manufacture units at the GMC dealer cost $800.00 +

So I went to my independent auto parts store which can get any thing you 
want. I ask them about a 80 something hydro boost and the clerk pick one 
off the floor that just came in, like it was waiting for me.

Looking the installation specs. It said you must retain the push rod that 
goes between the master cylinder, from the old unit. This unit which 
includes the master and hydro cost $250.00 without the core. But I needed a 
push rod, so I went down the road to a junk yard to see if they had any. 
Yes they do, they had a 1986 hydro boost like it was waiting for me. I got 
it for $50.00.

I could have bought a rebuilt kit for it which would cost about $100.00, so 
I remove the push rod and a retainer guild and use it as a core against the 
one at the auto parts store. The master cycle core credit was $50.00 and 
the hydro boost core credit was $100.00. There for the total cost to me is 
($250.00 + $50.00)-($150.00) = $150.00 which was about the same cost to 
replace the vacuum booster.

The mounting plate on the hydro boost that bolts to the firewall is a large 
steel plate which I had to cut smaller and drill four bolt holes which use 
the same firewall bolts that was use on the vacuum boost. The brake push 
rod that goes to the brake peddle swing arm can go to several holes that are 
on this swing are which did not match up exactly.

So I cut off the clevis eye off this rod and threaded it for a adjustable 
rod end that has a bearing in it. I then could adjust it to length and bolt 
it to the brake arm.

Fill up the unit with DOT-3 oil (do not not mix different DOT brake oil 
together). Started up the power steering pump and I have brakes that feel 
just like the vacuum booster unit, except I do not need a vacuum pump. I 
was using a GMC belt driven vacuum pump that works very good, still have to 
use it for my heating and A/C system.

If you has a S-10, this should be a simple installation for any future 
modification.

Roland




----- Original Message ----- 
From: "Jay Summet" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Wednesday, March 23, 2011 9:28 AM
Subject: [EVDL] Question about Vacuum reservoir, bigger is better?


> The S-10 conversion that I purchased came with a vacuum reservoir made
> out of 1 1/2" PVC pipe (about 3 inches long). When I switch it on it
> takes the GAST pump about 31 seconds to "charge". It works fine for
> ordinary driving, but re-starts the vacuum pump after every break pedal
> press.
>
> The day we purchased and towed the pick-up home I had to ride the breaks
> going down a long hill (so-as to not overtake the tow vehicle and
> wife...) and lost vacuum assist near the end because the pump/reservoir
> couldn't keep up.
>
> I decided that it would be nice to have a larger vacuum reservoir, to
> allow me more pedal pushes before the pump starts up, and to have a bit
> more "reserve capacity" if I have to break twice in a row, etc...
>
> Not knowing much about the physics of vacuum, but assuming it was
> somewhat like a compressed air tank, I figured using a one foot piece of
> 3" PVC pipe would give me ample capacity. So I built a larger reservoir:
> http://www.summet.com/blog/2011/03/23/building-a-pvc-vacuum-reservoir/
>
> (I also added a connection for a vacuum/boost gauge, so I could see how
> things were going...)
>
> I've just connected the new reservoir to the vacuum system (the old one
> is also still in the system, as I'm testing) and I have not been
> impressed with the results. In fact, I'm wondering if it is worth
> mounting the new reservoir at all...
>
> Instead of 32 seconds to charge the reservoir from empty, it now takes
> around 50 seconds (which is expected). HOWEVER, as soon as I press the
> break pedal, the vacuum pump turns back on! (I may have a bit more
> "reserve" capacity, as it feels like I have a few extra pumps after that
> before the vacuum is completely gone, but I was expecting to be able to
> pump the pedal a few times before the pump turned on).
>
> The (cheap/AutoZone) vacuum gauge shows that the vacuum only builds up
> to 19 inHg and then the pump switches off, and the pump switches back on
> when it drops below around 16.5 inHg. (The vacuum switch label says that
> it is supposed to switch on at 16.5 inHg but according to the label it
> isn't supposed to switch off until it hits 25 inHg. Perhaps somebody
> adjusted it?) The system holds 19inHg for over 15 minutes when idle, so
> I don't feel that leaks are a problem.
>
> On a test drive with stop signs every block up and down hills the vacuum
> never dropped below 10 inHg, but the pump also never shut off. My 
> questions:
>
> 1. Is it worth mounting the larger reservoir? (I haven't seen a super
> improvement in breaking capacity, and the pump runs longer now.) Any
> comments on your experiences and how they match up (or don't) with mine?
>
> 2. Should I try to adjust my vacuum switch to have a greater range
> between on and off? It is currently about 5 inHg, and I can go up to 10
> inHg differential. (What is the lowest "on" point I should use?)
>
> Thanks,
> Jay
>
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## EVDL List (Jul 27, 2007)

To make my vacuum reservoir fit in the space I had I cut the 4 inch diameter
PVC pipe to 8 inches in length. I put a plumbers test cap on both ends to
seal. It would take about 15 seconds to pump up and I would get about 2
pumps of the brakes. After about a year the wife and I were going to church
and when we started out there was a loud bang. Once of the thin test caps
imploded. When I went to build a new one I happen to see the rubber style
cap that uses a hose clamp to secure at Home Depot and decided to try it.
My thought was that it would suck this in allowing more vacuum in less
space. It worked... However the pump time is longer but I get about twice
the pumps on the brakes. This way the pump does not come on at every stop
light making people wonder what that noise is and where it is coming from.
Plus when I am showing it off the reservoir is still full (I mean empty) so
I don't have to explain the noise and why it is needed so often.


Buddy Mills
[email protected]

Look mom, no gas. http://www.evalbum.com/2887

Disclaimer: No animals were harmed or killed in the process of writing this
email. Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated. =








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## EVDL List (Jul 27, 2007)

The noise you hear is the check value in the vacuum pump. This prevent the 
vacuum to come out after every pumping cycle. After you apply the brakes, 
the vacuum will drop and this check value may open if your vacuum drops too 
low.

To prevent this action, I had to use three more vacuum check valves which is 
the same type that plugs into the vacuum brake booster. Install one check 
valve on the vacuum canister between the pump and the vacuum pump. This 
prevents the vacuum in the canister to bleed back into the pump.

Install another vacuum check valve on the outlet port. Make sure the vacuum 
check value is pointed in the correct direction, so when the vacuum in the 
tank pull it open.

I install a 3/8 ID vacuum line between the canister and the vacuum brake 
booster. (which I later change out to a brake hydro-booster which does not 
any vacuum).

This main vacuum line has a tap off to control the heating and A/C systems. 
A vacuum check value should be use on this tap off.

Without these check valves, except for the one on the brake booster, I could 
only get two brake cycle before my vacuum would drop to 10 in.hg. With the 
check values, I could stay between 15 to 22 in.hg. where the noise can 
barely be heard.

I am not use a electric driven vacuum pump. I am using a belt driven vacuum 
pump which is normally use for a GMC diesel engine. I belted off the pilot 
shaft of the motor with a industrial V6 cog belted. The pulleys should be 
the same size because you do not want to over rpm the vacuum pump. The pump 
is place on a adjustable aluminum bracket that is bolted.

I am using a vacuum canister that is 4 inches in diameter and 6 inches long. 
On your 4 inch PVC pipe, it is best to glue on PVC pipe caps. These test 
caps do not glue down good. I had them leak while doing a water pressure 
test.

Roland




----- Original Message ----- 
From: "Buddy Mills" <[email protected]>
To: "'Electric Vehicle Discussion List'" <[email protected]>
Sent: Wednesday, March 23, 2011 2:35 PM
Subject: Re: [EVDL] Question about Vacuum reservoir, bigger is better?


To make my vacuum reservoir fit in the space I had I cut the 4 inch diameter
PVC pipe to 8 inches in length. I put a plumbers test cap on both ends to
seal. It would take about 15 seconds to pump up and I would get about 2
pumps of the brakes. After about a year the wife and I were going to church
and when we started out there was a loud bang. Once of the thin test caps
imploded. When I went to build a new one I happen to see the rubber style
cap that uses a hose clamp to secure at Home Depot and decided to try it.
My thought was that it would suck this in allowing more vacuum in less
space. It worked... However the pump time is longer but I get about twice
the pumps on the brakes. This way the pump does not come on at every stop
light making people wonder what that noise is and where it is coming from.
Plus when I am showing it off the reservoir is still full (I mean empty) so
I don't have to explain the noise and why it is needed so often.


Buddy Mills
[email protected]

Look mom, no gas. http://www.evalbum.com/2887

Disclaimer: No animals were harmed or killed in the process of writing this
email. Any stories to the contrary are, for the most part, either fictional
or greatly exaggerated.







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## EVDL List (Jul 27, 2007)

Thanks for all of your comments.

I ended up adjusting my Square-D vacuum switch to make the differential
(between off and on) larger. I am now able to use the breaks for 1-2
full stops before the pump turns on (or multiple small slowdowns when
coasting).

My reservoir is a 12" long 3" round PVC pipe, using full end caps, plus
I have a few more cu in of tubing. I concur that "test caps" will not do
the job, go with full end caps.

Jay

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