Home » Public Forums » GMCnet » My First Vapor Lock
| My First Vapor Lock [message #175198] |
Sun, 01 July 2012 07:02  |
Luvn737s
Messages: 1106
Registered: June 2007
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We generally don't take our GMC out in the middle of summer, so the camping trip this week of 107-113F temps was an eye opener. While under way, there was no problem, but the route to the mountains required a couple of stop lights and there was the real problem. Chug, chug, and pretended to quit a time or two, then cleared out and kept on going. I made sure I had full tanks for help absorb some of the heat radiated off the roads and even switched tanks to the fuller one (if there really was a difference, it was probably all in my head).
I have an electric pump mounted, I just need to wait until a cooler set of days to plumb the lines. At least it didn't quit. With a "part-time" generator to run the roof air, it could have been a pretty bad scene.
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: My First Vapor Lock [message #175211 is a reply to message #175198] |
Sun, 01 July 2012 09:56  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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My "new" rig ran perfectly all the way back from LA, but taking it to storage the other day (about 106 degrees as I recall) led to one vapor lock episode. I had been idling at a stoplight waiting to make a left turn - I took off and the engine just quit halfway around the corner. I had enough momentum to coast into a handy parking lot, and thought to flip on the vacuum pump to make sure that I'd be able to stop. I hadn't been running the electric fuel pump, but I now make sure and have it on when driving around. I was running around a couple days ago in 110+ degree weather, and it didn't miss a beat.
So yeah, plumb that new fuel pump!
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] My First Vapor Lock [message #175232 is a reply to message #175198] |
Sun, 01 July 2012 15:18 |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
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Do you have fresh, cool air ducted to your carb?
I've never driven my GMC in that kind of heat. 100°, maybe. I did an
experiment a few years ago and took the fresh air duct off my air
cleaner and ran it like GMC intended. Sucking warm air from the engine
compartment. Worked fine for months and the first indication of
problems with the OEM setup was a 90° day and city driving with
stoplights. Did pretty much what you described.
Hooked the fresh air vent back up for the return trip and while there
was still a little hiccup or two it was totally acceptable.
I think the fuel in the float bowl just gets too damn hot. If it
vaporizes it's hard for the float to... float. So is it a problem of
too much fuel or not enough? A flooded carb would do pretty much the
same thing as a starved carb.
My 2¢.
Kelvin
On 7/1/2012 5:03 AM, Randy wrote:
>
> We generally don't take our GMC out in the middle of summer, so the camping trip this week of 107-113F temps was an eye opener. While under way, there was no problem, but the route to the mountains required a couple of stop lights and there was the real problem. Chug, chug, and pretended to quit a time or two, then cleared out and kept on going. I made sure I had full tanks for help absorb some of the heat radiated off the roads and even switched tanks to the fuller one (if there really was a difference, it was probably all in my head).
>
> I have an electric pump mounted, I just need to wait until a cooler set of days to plumb the lines. At least it didn't quit. With a "part-time" generator to run the roof air, it could have been a pretty bad scene.
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| Re: My First Vapor Lock [message #175235 is a reply to message #175211] |
Sun, 01 July 2012 17:04 |
Luvn737s
Messages: 1106
Registered: June 2007
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| habbyguy wrote on Sun, 01 July 2012 07:56 |
I had enough momentum to coast into a handy parking lot, and thought to flip on the vacuum pump to make sure that I'd be able to stop.
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I did some empirical testing in my coach and found the following: In the event of engine failure, you still have boosted brake pressure for the first application. If you take your foot off and re-apply, you get alot less boost and the 3rd pump is basically nothing. So, if you have no aux vacuum pump, don't take your foot off the brake!
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
[Updated on: Sun, 01 July 2012 17:05] Report message to a moderator |
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| Re: My First Vapor Lock [message #175243 is a reply to message #175235] |
Sun, 01 July 2012 19:01 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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| Luvn737s wrote on Sun, 01 July 2012 17:04 |
| habbyguy wrote on Sun, 01 July 2012 07:56 |
I had enough momentum to coast into a handy parking lot, and thought to flip on the vacuum pump to make sure that I'd be able to stop.
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I did some empirical testing in my coach and found the following: In the event of engine failure, you still have boosted brake pressure for the first application. If you take your foot off and re-apply, you get alot less boost and the 3rd pump is basically nothing. So, if you have no aux vacuum pump, don't take your foot off the brake!
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I heard horor stories about no brakes when the engine is off after I bought my GMC. I tested the brakes with a dead engine to see what all the excitement was about. I was still able to slide all 6 wheels even after disconnecting the brake assist and draining the vacuum reservoir. The brakes still work without assist, they just take more foot pressure. I think modern brakes on cars have made people spoiled and they don't know that they can just push harder to get the brakes to work. I grew up on a farm where we had to plan ahead, pump the brakes up, and then push like hell to get the truck to stop. Not the safest but I have a strong right leg!
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] My First Vapor Lock [message #175251 is a reply to message #175243] |
Sun, 01 July 2012 20:10 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Jerrod,
I believe what you've noted but I've got a few questions / comments for you:
1) What kind of road were you on when you conducted your experiment?
2) How fast you were going?
3) Just how strong is your right leg?
4) Do you think you're wife could stop the GMC without the vacuum assist?
I'm 6' 1" @ 250 lb and agree that I too could probably stop Double Trouble with no vacuum in the booster; however, if you're saying
your test proves that an auxiliary vacuum pump or canister is not necessary I disagree heartily.
You have to take into consideration that you KNEW that there was no vacuum assist when you went to hit the brakes and that you were
going to have to push like mad to get the GMC to stop. What do you think would happen to the individual who was sitting in the
driver's seat heading merrily down a freeway at 60 MPH when the guy in front of him in a Honda Civic slammed on the brakes? I reckon
the GMC would have a new hood ornament!
Regards,
Rob M.
-----Original Message-----
From: Jerrod Winter
I heard horor stories about no brakes when the engine is off after I bought my GMC. I tested the brakes with a dead engine to see
what all the excitement was about. I was still able to slide all 6 wheels even after disconnecting the brake assist and draining
the vacuum reservoir. The brakes still work without assist, they just take more foot pressure. I think modern brakes on cars have
made people spoiled and they don't know that they can just push harder to get the brakes to work. I grew up on a farm where we had
to plan ahead, pump the brakes up, and then push like hell to get the truck to stop. Not the safest but I have a strong right leg!
--
Jerrod
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: My First Vapor Lock [message #175252 is a reply to message #175198] |
Sun, 01 July 2012 20:18 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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Rob,
My point was not that an assist doesn't help. It was pointing out the fact that the brakes are still there, it just takes more effort. Not everyone may know that and it is worth bringing up.
The same thing goes with power steering. The steering is still there without the engine, it just takes a little more effort.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: My First Vapor Lock [message #175253 is a reply to message #175198] |
Sun, 01 July 2012 20:21 |
Darryl
Messages: 144
Registered: December 2011
Location: Northern California
Karma: 0
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I was driving a GMC at less than 25mph when the engine quit. Fortunately no traffic. When I got it pulled over I had both feet on the brake with my butt pushed against the seat and both hands at 2:00 trying to pull it to the curb with no power steering.
I'd prefer not to try it at higher speeds or in traffic.
Darryl Meyers
1978 Eleganza II
El Dorado Hills, CA
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| Re: [GMCnet] My First Vapor Lock [message #175254 is a reply to message #175243] |
Sun, 01 July 2012 20:33 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Jerrod,
Back in '06 when I ran tests on the then-new EBC yellow brake pads, I ran
repeated tests where 70 lbf was automatically applied to the brake pedal.
The distance from brake application to a dead stop was measured. The
average stopping distance from 55 mph was about 250'. At the end of the
test series, we ran one test without vacuum boost. That stopping distance
was 765' -- 3 times as far!
Granted, a stong person can apply a lot of force -- perhaps even more than
the booster can once it reaches its limit. BUT, if one were surprised to
suddenly have that need, the stopping distance would be far greater than
expected. I believe in both a larger vacuum reservoir and a vacuum pump,
though I do have a manual switch on the pump.
Oh yeah, in 14 years, I've often slid the rearmost wheels (and paid with
the flat spots). I've NEVER slid all six on dry pavement.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Sun, Jul 1, 2012 at 8:01 PM, jerrod winter <jerrod_beth@msn.com> wrote:
>
>
> Luvn737s wrote on Sun, 01 July 2012 17:04
>
> I heard horor stories about no brakes when the engine is off after I
> bought my GMC. I tested the brakes with a dead engine to see what all the
> excitement was about. I was still able to slide all 6 wheels even after
> disconnecting the brake assist and draining the vacuum reservoir. The
> brakes still work without assist, they just take more foot pressure. I
> think modern brakes on cars have made people spoiled and they don't know
> that they can just push harder to get the brakes to work. I grew up on a
> farm where we had to plan ahead, pump the brakes up, and then push like
> hell to get the truck to stop. Not the safest but I have a strong right
> leg!
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: My First Vapor Lock [message #175258 is a reply to message #175198] |
Sun, 01 July 2012 21:00 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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To all
I AM NOT saying that assist isn't better.
I AM saying that the brakes are still there and will work without the engine. Trying to stop the coach after the engine dies is one thing. Nailing the brakes to avoid an accident is another. What are the odds that you have to make an emergency stop at the same time the engine dies? My point is that if the engine dies, you still have brakes, they just take a little more force. Some of the posts sound as though the brakes are gone and you're done. I just wanted to say otherwise.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] My First Vapor Lock [message #175259 is a reply to message #175254] |
Sun, 01 July 2012 21:06 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
Karma: 0
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| Ken Henderson wrote on Sun, 01 July 2012 20:33 |
Jerrod,
Back in '06 when I ran tests on the then-new EBC yellow brake pads, I ran
repeated tests where 70 lbf was automatically applied to the brake pedal.
The distance from brake application to a dead stop was measured. The
average stopping distance from 55 mph was about 250'. At the end of the
test series, we ran one test without vacuum boost. That stopping distance
was 765' -- 3 times as far!
Granted, a stong person can apply a lot of force -- perhaps even more than
the booster can once it reaches its limit. BUT, if one were surprised to
suddenly have that need, the stopping distance would be far greater than
expected. I believe in both a larger vacuum reservoir and a vacuum pump,
though I do have a manual switch on the pump.
Oh yeah, in 14 years, I've often slid the rearmost wheels (and paid with
the flat spots). I've NEVER slid all six on dry pavement.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Sun, Jul 1, 2012 at 8:01 PM, jerrod winter <jerrod_beth@msn.com> wrote:
>
>
> Luvn737s wrote on Sun, 01 July 2012 17:04
>
> I heard horor stories about no brakes when the engine is off after I
> bought my GMC. I tested the brakes with a dead engine to see what all the
> excitement was about. I was still able to slide all 6 wheels even after
> disconnecting the brake assist and draining the vacuum reservoir. The
> brakes still work without assist, they just take more foot pressure. I
> think modern brakes on cars have made people spoiled and they don't know
> that they can just push harder to get the brakes to work. I grew up on a
> farm where we had to plan ahead, pump the brakes up, and then push like
> hell to get the truck to stop. Not the safest but I have a strong right
> leg!
> --
>
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At the current price for tires, I try not to slide any of them if possible.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] My First Vapor Lock [message #175268 is a reply to message #175263] |
Sun, 01 July 2012 22:20 |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
Karma: 0
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Put that 12,000# on a hill and see if you can hold it?
I couldn't hold a 10,000# 230 on a fairly steep hill.
Personally I think what you're saying is actually a little dangerous.
Yes... you can stop the coach, just like you can turn it if the PS isn't
working. Neither work well and very likely you're going to hit
something if you're surprised by this event.
Let's not suggest that folks are worrying about this problem when it's
not something to worry about. I've experienced it. It's real.
Kelvin
'73 23' in Eugene, OR
On 7/1/2012 7:33 PM, Robert Mueller wrote:
> Jerrod,
>
> There are more than one way to loose vacuum to the booster than having the engine die. I had the accelerator fully depressed on
> Double Trouble to hold speed at the top of a hill on a freeway. Just as I got to the top the idiot in the left hand lane decided to
> pull over to the right without signaling. I hit the horn and brakes. Nothing happened with the brakes fortunately the horn got his
> attention and he stopped pulling over. After my heart rate got back to normal I pulled over and popped the driver side hood and
> found out that somehow the canon plug on the brake vacuum booster pump had come loose.
>
> I have a sensitized booster and it works great but seems to loose vacuum which is why when I hit the brakes nothing happened at the
> top of the hill.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: jerrod winter
>
> To all
>
> I AM NOT saying that assist isn't better.
>
> I AM saying that the brakes are still there and will work without the engine. Trying to stop the coach after the engine dies is one
> thing. Nailing the brakes to avoid an accident is another. What are the odds that you have to make an emergency stop at the same
> time the engine dies? My point is that if the engine dies, you still have brakes, they just take a little more force. Some of the
> posts sound as though the brakes are gone and you're done. I just wanted to say otherwise.
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| Re: [GMCnet] My First Vapor Lock [message #175269 is a reply to message #175268] |
Sun, 01 July 2012 23:53 |
mickeysss
Messages: 1476
Registered: January 2012
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On Jul 01, 2012, at 08:20 PM, Kelvin Dietz <kelvin@datsuns.com> wrote:
Put that 12,000# on a hill and see if you can hold it?
I couldn't hold a 10,000# 230 on a fairly steep hill.
Personally I think what you're saying is actually a little dangerous.
Yes... you can stop the coach, just like you can turn it if the PS isn't
working. Neither work well and very likely you're going to hit
something if you're surprised by this event.
Let's not suggest that folks are worrying about this problem when it's
not something to worry about. I've experienced it. It's real.
Kelvin
'73 23' in Eugene, OR
On 7/1/2012 7:33 PM, Robert Mueller wrote:
> Jerrod,
>
> There are more than one way to loose vacuum to the booster than having the engine die. I had the accelerator fully depressed on
> Double Trouble to hold speed at the top of a hill on a freeway. Just as I got to the top the idiot in the left hand lane decided to
> pull over to the right without signaling. I hit the horn and brakes. Nothing happened with the brakes fortunately the horn got his
> attention and he stopped pulling over. After my heart rate got back to normal I pulled over and popped the driver side hood and
> found out that somehow the canon plug on the brake vacuum booster pump had come loose.
>
> I have a sensitized booster and it works great but seems to loose vacuum which is why when I hit the brakes nothing happened at the
> top of the hill.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: jerrod winter
>
> To all
>
> I AM NOT saying that assist isn't better.
>
> I AM saying that the brakes are still there and will work without the engine. Trying to stop the coach after the engine dies is one
> thing. Nailing the brakes to avoid an accident is another. What are the odds that you have to make an emergency stop at the same
> time the engine dies? My point is that if the engine dies, you still have brakes, they just take a little more force. Some of the
> posts sound as though the brakes are gone and you're done. I just wanted to say otherwise.
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| Re: [GMCnet] My First Vapor Lock [message #175278 is a reply to message #175277] |
Mon, 02 July 2012 08:25 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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On Mon, Jul 2, 2012 at 6:47 AM, Stick Miller <stickmiller@gmail.com> wrote:
>
>
> I remember my first vapor lock. Back in high school I had a date with a
> good looking old girl and, in the back seat of my Pontiac...oh, wait. I
> thought you were talking about something else. Sorry! Ignore this post. :)
> --
> Stick Miller
> '78 Royale - she left me for another man
> Americus, Georgia
>
>
>
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--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] My First Vapor Lock [message #175381 is a reply to message #175269] |
Mon, 02 July 2012 23:08 |
Luvn737s
Messages: 1106
Registered: June 2007
Karma: 2
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| mickeysss wrote on Sun, 01 July 2012 21:53 |
Personally I think what you're saying is actually a little dangerous.
Yes... you can stop the coach, just like you can turn it if the PS isn't
working. Neither work well and very likely you're going to hit
something if you're surprised by this event.
Let's not suggest that folks are worrying about this problem when it's
not something to worry about. I've experienced it. It's real.
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DON'T PUMP THE BRAKES Sure a vacuum pump might be nice (although it's hard to test it regularly to know that it will work as you expect) but my experience has been that A) don't go down a hill faster than you would go up it and
B) In the event of engine failure push on the brake (it will still have power assist from the vacuum reservoir) and don't let up on it until you are stopped.
I would be more concerned that the add-on vacuum system might not be installed properly, and that if it's as vital a safety feature as folks claim, maybe they shouldn't be pulled out of a junkyard.
The larger vacuum accumulator could be plumbed exactly as the current small one it and provide more assist in the event of a failure and be a simpler system to boot.
But this is just one fat bald guy's opinion.
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ
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| Re: [GMCnet] My First Vapor Lock [message #175385 is a reply to message #175383] |
Tue, 03 July 2012 02:34 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I have a junk yard one and it has served me quite well for many years. It turns on and pumps up every time I turn the key on before I start the engine. That way I know it is functional. If it were to not run it would not affect my normal brakes but I would know to go find the problem. If it were to run forever, then I know I have a vacuum leak and to go fix it right away. The addition of a pump adds a diagnostic that was never available with the OEM installation.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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