Brake booster vacuum tank
#1
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Brake booster vacuum tank
As some of you might know I'm installing a V12 in a Series III sedan.....replacing the old 4.2 6-cylinder. I post here at times because there is more V12-related experience.
https://www.jaguarforums.com/forum/x...roject-142259/
Anyhow.....
I wondering about the vacuum tank for the power brake system. I have the tank, pipes etc from the donor car (also a Series III V12). This vacuum reservoir system was not used with the 4.2 6-cylinder although the braking systems are the same on both cars
Vacuum Tank Assembly-Lhd - Parts For Series III Saloon | Jaguar Classic Parts UK
Is there something different about V12 vacuum characteristics than would require a vacuum reservoir for the power brakes....where the same car with a 4.2 6-cylinder did perfectly well without it?
The XJS V12 used the same vacuum reservoir set-up, by the way
It wouldn't be too hard to install. I could take it or leave it. For the sake of simplicity, though, I think I'd rather leave it
Any thoughts?
Cheers and thanks,
Doug
https://www.jaguarforums.com/forum/x...roject-142259/
Anyhow.....
I wondering about the vacuum tank for the power brake system. I have the tank, pipes etc from the donor car (also a Series III V12). This vacuum reservoir system was not used with the 4.2 6-cylinder although the braking systems are the same on both cars
Vacuum Tank Assembly-Lhd - Parts For Series III Saloon | Jaguar Classic Parts UK
Is there something different about V12 vacuum characteristics than would require a vacuum reservoir for the power brakes....where the same car with a 4.2 6-cylinder did perfectly well without it?
The XJS V12 used the same vacuum reservoir set-up, by the way
It wouldn't be too hard to install. I could take it or leave it. For the sake of simplicity, though, I think I'd rather leave it
Any thoughts?
Cheers and thanks,
Doug
Last edited by Doug; 05-26-2016 at 12:31 AM.
#2
The reason for it, Doug, as you probably know anyway, was that if a failure of engine vac occurred, or you needed brakes when the engine was not running, there was a "reserve" of vacuum to help. Basically an extra safety feature. Up to you therefore, but FWIW, I would be inclined to keep it...
Greg
Greg
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orangeblossom (05-26-2016)
#3
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Actually, no, I hadn't thought of it as a reserve supply. I thought perhaps the V12 didn't typically develop as much vacuum....although I have no recollection of that ever being as issue
Hmmmm. It might be the first time I've ever seen a reserve vac tank on a vacuum assist system.
Jaguar thought the V12 owners deserved the extra safety measure but the 6-cylinder owners were less worthy ?
Cheers
DD
Hmmmm. It might be the first time I've ever seen a reserve vac tank on a vacuum assist system.
Jaguar thought the V12 owners deserved the extra safety measure but the 6-cylinder owners were less worthy ?
Cheers
DD
Last edited by Doug; 05-26-2016 at 11:16 AM.
#4
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Interesting:
1. I wonder if there are spec's to compare V12 vs I6 vacum numbers.
probably between 15 and 20 hg's ???
2. I do know that '"souped up " engines with cams that have a ot f overlap suffer from low vacuum at lower rpm's. Cure? vacuum tanks and even electric powered vacuum pumps.
3. A lot if not most cars do well sans a vacuum reserve tank! Each of my cars have none and do well.
So, inasmuch as you have one, I vote for it's use.
Carl
1. I wonder if there are spec's to compare V12 vs I6 vacum numbers.
probably between 15 and 20 hg's ???
2. I do know that '"souped up " engines with cams that have a ot f overlap suffer from low vacuum at lower rpm's. Cure? vacuum tanks and even electric powered vacuum pumps.
3. A lot if not most cars do well sans a vacuum reserve tank! Each of my cars have none and do well.
So, inasmuch as you have one, I vote for it's use.
Carl
#5
#6
systems carry a reserve. At least you should
Thinking back to your GM days, you will recall that the reserve
was integral to the booster.
Perhaps the particular booster used on the V12 did not have
an integral reserve, or it was deemed to be inadequate.
Maybe physical packaging requirements of shoehorning the
V12 into the space forced using an external reserve.
It's not the only car with an external reserve tank. I just
can't remember a particular example to point at right now.
#7
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#8
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They did? No, I didn't know. Which models? Was it some sort of separate chamber or ?
Perhaps the particular booster used on the V12 did not have
an integral reserve, or it was deemed to be inadequate.
Maybe physical packaging requirements of shoehorning the
V12 into the space forced using an external reserve.
No, the V12 and 6-cylinder cars used identical systems, including the booster
It's not the only car with an external reserve tank. I just
can't remember a particular example to point at right now.
can't remember a particular example to point at right now.
Let me know when the bells ring
The only external vacuum reserve tanks for power brakes I've seen were add-ons....for hot rods with lumpy cams where there just wasn't much vacuum to work with.
Cheers
DD
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What size can? Single serving, or family size? If single serve, that sounds more like a vacuum reservoir for heating/air condition systems.
The Jag vacuum reserve is about the size of a small watermelon ! Maybe 8" diameter and 16" long or so
Cheers
DD
#10
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Also, never by me, used for exhaust tips!!! Termed "blooey" cans, back
in the day. At times to simulate "dual pipes". Swap to blacken the inside!!!
Exhaust tips seldom appealed to me.
I only recall a couple. One used in 58 on my T speedster project.
straight single pipe. No muffler. About 12" of 8" pipe. Open on each end. T exhaust pipe suspended in the center. Theory, In motion, air would enter the front of the 8" pipe and create a scavenge for the exhaust??? worked?? But, sounded much better. It could and did run off and hide from friend's restored T three door "phaeton"!!!
Carl
in the day. At times to simulate "dual pipes". Swap to blacken the inside!!!
Exhaust tips seldom appealed to me.
I only recall a couple. One used in 58 on my T speedster project.
straight single pipe. No muffler. About 12" of 8" pipe. Open on each end. T exhaust pipe suspended in the center. Theory, In motion, air would enter the front of the 8" pipe and create a scavenge for the exhaust??? worked?? But, sounded much better. It could and did run off and hide from friend's restored T three door "phaeton"!!!
Carl
#14
Just a thought while I'm at it, and I'm happy to be proven wrong...
The V12 can only be cranked when in Park, so unless you're stationery, there's no swinging a V12 over... The Straight 6, if I'm correct*, can be cranked in Neutral and Park. If you were to lose engine power suddenly at a low speed for any reason with the V12 you have about 3 strokes of vacuum assisted power, there after you're on your own. The Straight 6 would still be able to be swung over, generating a little vacuum to help with the braking.
Just a thought, some may disagree. I'd keep the reservoir though, no harm done.
The V12 can only be cranked when in Park, so unless you're stationery, there's no swinging a V12 over... The Straight 6, if I'm correct*, can be cranked in Neutral and Park. If you were to lose engine power suddenly at a low speed for any reason with the V12 you have about 3 strokes of vacuum assisted power, there after you're on your own. The Straight 6 would still be able to be swung over, generating a little vacuum to help with the braking.
Just a thought, some may disagree. I'd keep the reservoir though, no harm done.
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NathanDD6 (06-02-2016)
#16
#17
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, I learn something new every day.
As we all do, hopefully.
Sometimes I get lucky and learn my 'new thing' early on, before I'm even done with morning coffee. Then I can take the rest of the day off
Cheers
DD
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NathanDD6 (06-04-2016)
#18
#19
Hi Doug ,
Under Jags " vacuum verification " test procedure , the vacuum gauge should read
at 800 rpm , 14.5 (in. Hg) .
Most cars have a safe reading of 16 to 21 (in. Hg) , at best your XJ6 would be running somewhere between 20 and 24 (in. Hg) .
At only 14.5 (in. Hg) at idle , it won't take much to evacuate the booster , 2 may be 3 pumps , I can see why the V12 would need to run a vacuum tank .
Cheers ,
Sid
Under Jags " vacuum verification " test procedure , the vacuum gauge should read
at 800 rpm , 14.5 (in. Hg) .
Most cars have a safe reading of 16 to 21 (in. Hg) , at best your XJ6 would be running somewhere between 20 and 24 (in. Hg) .
At only 14.5 (in. Hg) at idle , it won't take much to evacuate the booster , 2 may be 3 pumps , I can see why the V12 would need to run a vacuum tank .
Cheers ,
Sid
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#20
My suspicion is it has to do with the injection. The XJ6 uses an air flow meter, the V12 does not, it determines engine load from the vacuum signal. There is a vacuum pipe that runs the length of the car to the ECU in the boot.
I suspect the extra vacuum reservoir is a way to separate the braking vacuum and the signal vacuum so that when you step on the brakes there isn't a drop in vacuum that would be read as extra load and the ECU then adding more fuel. In extreme cases that could give you a rich stall.
I suspect the extra vacuum reservoir is a way to separate the braking vacuum and the signal vacuum so that when you step on the brakes there isn't a drop in vacuum that would be read as extra load and the ECU then adding more fuel. In extreme cases that could give you a rich stall.
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