• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)
Tips
Tips

Brake Pedal Vary Hard to Push Down and Brakes feel like there's no Booster on my BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
I applied my brakes as usual and the pedal was very hard and very little movement plus they were less than responsive. It did this twice on a short trip last weekend.

New Master and Slave cylinders a few years ago.
Brake Booster rebuilt, twice, by Power Brake Exchange.
After running the engine and turning off I do not have the swooshing sound as I press on the brake pedal which releases the air from the Booster. I added a "check valve" per suggestion from a mechanic.
All New brake lines.
Brakes just adjusted after replacing rear wheel axle bearing.
 
Country flag
Offline
When did you add the 'check valve?' Girling boosters should already have a check valve; however, they are often missing or not functioning.
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
When did you add the 'check valve?' Girling boosters should already have a check valve; however, they are often missing or not functioning.
I installed the check valve yesterday because it was suggested that it could be that and your post comment confirms that. I made sure that the check valve "arrow" was pointed towards the boost as required.
 

RAC68

Darth Vader
Offline
Hi Patrick,

Have you been missing fluid a little at a time over a long period? I have had a similar condition a while back when the booster leaked and fluid collected in its vacuum chamber causing a hard peddle. Others may have a way to check for this condition with the booster instill installed as I found the issue after removing the booster.

A though,
Ray(64BJ8P1)
 
Country flag
Offline
Hi Patrick,

Have you been missing fluid a little at a time over a long period? I have had a similar condition a while back when the booster leaked and fluid collected in its vacuum chamber causing a hard peddle. Others may have a way to check for this condition with the booster instill installed as I found the issue after removing the booster.

A though,
Ray(64BJ8P1)


... or white smoke out the tailpipe (which doesn't indicate we have a new Pope, coming from a Healey). Sorry to say, but this does sound like a servo issue; the 'gland seal,' which keeps fluid from entering the vacuum cylinder and getting sucked into the intake manifold, is a common point of failure. If the slave cylinder in the servo, which activates the servo's MC, is stuck you'd lose boost as well. The rocker valve that is operated by the slave cylinder could stick, I suppose, but I don't think that's likely as it's a butt simple design.

Some people seem to have endless problems with the Girling servo and resort to the aftermarket replacement (I think it's made by Lockheed), others have more luck with the Girlings.
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Hi Patrick,

Have you been missing fluid a little at a time over a long period? I have had a similar condition a while back when the booster leaked and fluid collected in its vacuum chamber causing a hard peddle. Others may have a way to check for this condition with the booster instill installed as I found the issue after removing the booster.

A though,
Ray(64BJ8P1)
I forgot to List that in my original post, but I checked the fluid and it's not going down so I don't have the exhaust smoke that goes with that either. I'm thinking of taking my large rubber mallet and giving it a good swat on the large booster cover because something may be stuck, like maybe the large seal in the booster chamber?
 

RAC68

Darth Vader
Offline
Hi Patrick,

Bob may have had white smoke but my servo produced no brake fluid even in the vacuum tube. I use Silicone Brake Fluid (DOT 5) which may not produce white smoke. The loss of fluid and its built-up on the inner portion of the vacuum/"Booster" chamber must have happened over the period of more than a year and the loss was not that obvious unless the car was not used for a month or so. The build-up caused the booster piston in the chamber to become inoperative by blocking its inward movement. When finally dismantling the servo and opening the chamber, about a 1/2 quart of fluid pored out.

Your plan to bang the chamber is feasible if your piston is just stuck (Piston and seal cantered on the wall) in the chamber but will not do much good if it is fluid-locked.

Ray(64BJ8P1)
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Hi Patrick,

Bob may have had white smoke but my servo produced no brake fluid even in the vacuum tube. I use Silicone Brake Fluid (DOT 5) which may not produce white smoke. The loss of fluid and its built-up on the inner portion of the vacuum/"Booster" chamber must have happened over the period of more than a year and the loss was not that obvious unless the car was not used for a month or so. The build-up caused the booster piston in the chamber to become inoperative by blocking its inward movement. When finally dismantling the servo and opening the chamber, about a 1/2 quart of fluid pored out.

Your plan to bang the chamber is feasible if your piston is just stuck (Piston and seal cantered on the wall) in the chamber but will not do much good if it is fluid-locked.

Ray(64BJ8P1)
Hi Bob,
I think I need to eliminate the original check valve completely by removing it from the Servo and drilling straight through it (it's plastic), to make it just a "plain" fitting and see if that fixes it. I have installed a new check valve in the line but if the original one is malfunctioning it may just have to be eliminated. Here's a link with useful info: https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-vacuum-brake-booster-check-valve
 

RAC68

Darth Vader
Offline
Hi Patrick,

I must admit that, after reading that article, I didn't expect the check valve was that involved in the operation of the brake booster and could produce those symptoms. I am using a Girling MK2A which I don't believe has a check valve but one could be located in the vacuum hose adapter at the manifold. I should have realized your BJ8 Phase 2 is using a Girling MK2B which has a check valve on the booster chamber. Both units, although similar, apply the manifold vacuum at different locations within the unit and, after reviewing each diagram, can now understand why the MK2A would collect fluid in the booster chamber and why the MK2B would have it sucked through to the manifold and be smoked (as Bob stated) off.

Thanks for your direction to the article as those symptoms produced by a faulty check valve were somewhat startling. I am now going to see if I have a check valve in my intake manifold like adapter and, if no, will consider installing one.

All the best,
Ray(64BJ8P1)
 
Country flag
Offline
Couple of things:

I'm not sure what color smoke silicone produces; I answered without thinking but remembered that regular glycol-based BF does produce white smoke (as does anti-freeze if it gets in the combustion chamber). So, anyone burned any silicone BF to see what it does?

I overhauled a Girling servo once thinking it was the cause of some problems--pedal required a couple pumps to activate brakes--but found out later it was a damaged 'foot valve' in the MC. I had a plastic, inline check valve installed by a DPO; but sourced a working, used one from BCS, and removed the plastic one (it worked, but looked, well, wrong). The original valve was inop; they are just a reed valve--a little flapper that can only move one way--and its flap was gone.

AFAIK, most of the info in the article is correct, but I take exception to some of the wording (yes, I'm as pedantic as I am scientific). The check valve is not 'designed to suck out air that is trapped in the brake booster without letting additional air enter the cylinder.' The valve is passive; it allows manifold vacuum to vacate the air in the large canister but does not admit air at atmospheric pressure. And, when the valve has failed, it does not allow 'excess pressure inside the master cylinder, which the check valve is designed to regulate.' The check valve doesn't 'regulate' anything, else it would be called a 'vacuum regulator.' As the article does state, finally, the valve is there to allow one or two applications of boosted brakes when the engine quits (and there is no more manifold vacuum to create 'boost').

I do think Patrick's problem is in the servo, but it's not caused by the check valve, because he has lost boost even when he has plenty of vacuum. The only check valve failure that would cause this is if the valve somehow got blocked or became 'reverse biased;' i.e. it allowed atmospheric pressure in, but not vacuum, or if the valve has developed a leak, allowing atmospheric air in all the time (my dad's '65 Mustang had the describe problem, but it was because an elbow that connected the vacuum hose to the servo had cracked). The reed valve could stick open, or come apart like mine did, but the only symptom would be you wouldn't get the 'extra' boosted braking when you turn the engine off.

I think something is stuck inside the servo. Have you tried whacking it yet?

Edit/add: To confirm the check valve isn't the problem, just bypass the valve (but don't rely on an emergency boosted brake application if your engine quits). If the problem persists, it's not the check valve.
 
Last edited:
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Hi Patrick,

I must admit that, after reading that article, I didn't expect the check valve was that involved in the operation of the brake booster and could produce those symptoms. I am using a Girling MK2A which I don't believe has a check valve but one could be located in the vacuum hose adapter at the manifold. I should have realized your BJ8 Phase 2 is using a Girling MK2B which has a check valve on the booster chamber. Both units, although similar, apply the manifold vacuum at different locations within the unit and, after reviewing each diagram, can now understand why the MK2A would collect fluid in the booster chamber and why the MK2B would have it sucked through to the manifold and be smoked (as Bob stated) off.

Thanks for your direction to the article as those symptoms produced by a faulty check valve were somewhat startling. I am now going to see if I have a check valve in my intake manifold like adapter and, if no, will consider installing one.

All the best,
Ray(64BJ8P1)
I checked the parts manual and a part that appears to be common to all the Boisters is called "non-return valve", aka as Check Valve. It looks like a fitting used only for connecting the vacuum hose but obviously there's valve parts inside of it. Page "Plate M3. I believe you already have one Ray.
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Couple of things:

I'm not sure what color smoke silicone produces; I answered without thinking but remembered that regular glycol-based BF does produce white smoke (as does anti-freeze if it gets in the combustion chamber). So, anyone burned any silicone BF to see what it does?

I overhauled a Girling servo once thinking it was the cause of some problems--pedal required a couple pumps to activate brakes--but found out later it was a damaged 'foot valve' in the MC. I had a plastic, inline check valve installed by a DPO; but sourced a working, used one from BCS, and removed the plastic one (it worked, but looked, well, wrong). The original valve was inop; they are just a reed valve--a little flapper that can only move one way--and its flap was gone.

AFAIK, most of the info in the article is correct, but I take exception to some of the wording (yes, I'm as pedantic as I am scientific). The check valve is not 'designed to suck out air that is trapped in the brake booster without letting additional air enter the cylinder.' The valve is passive; it allows manifold vacuum to vacate the air in the large canister but does not admit air at atmospheric pressure. And, when the valve has failed, it does not allow 'excess pressure inside the master cylinder, which the check valve is designed to regulate.' The check valve doesn't 'regulate' anything, else it would be called a 'vacuum regulator.' As the article does state, finally, the valve is there to allow one or two applications of boosted brakes when the engine quits (and there is no more manifold vacuum to create 'boost').

I do think Patrick's problem is in the servo, but it's not caused by the check valve, because he has lost boost even when he has plenty of vacuum. The only check valve failure that would cause this is if the valve somehow got blocked or became 'reverse biased;' i.e. it allowed atmospheric pressure in, but not vacuum, or if the valve has developed a leak, allowing atmospheric air in all the time (my dad's '65 Mustang had the describe problem, but it was because an elbow that connected the vacuum hose to the servo had cracked). The reed valve could stick open, or come apart like mine did, but the only symptom would be you wouldn't get the 'extra' boosted braking when you turn the engine off.

I think something is stuck inside the servo. Have you tried whacking it yet?

Edit/add: To confirm the check valve isn't the problem, just bypass the valve (but don't rely on an emergency boosted brake application if your engine quits). If the problem persists, it's not the check valve.
Bob, good thoughts! I do not have any reserve air in the servo when I shut off the engine. Not sure what you mean or how to bypass the check valve? I guess a flag should have gone up at that point in time, but I had brakes although they just didn't feel strong. I will have to remove the servo to take off the original check valve and drill through it to make it a simple fitting for connecting the vacuum hose so when I do that I am going to pop open the vacuum chamber to check its condition to(to make sure the piston slides easy). I will the refit and check operation but if no change I will send it out for repairs. I guess Power Brake Exchange could/would rebuild a servo without replacing the check valve. It cost $300 plus $25 each way for shipping.

I did buy the check valve from BCS. I asked David what could be wrong after giving him all my symptoms and he said "check valve". I think starting at a likely culprit that's inexpensive first is good and then working to the next solution. BCS sells a replacement servo complete with mounting bracket and brake lines for about $450. Considerably more than rebuilding the servo again but if it's improved it may be better in the long run.
 

steveg

Yoda
Gold
Country flag
Offline
Bob, good thoughts! I do not have any reserve air in the servo when I shut off the engine. Not sure what you mean or how to bypass the check valve? I guess a flag should have gone up at that point in time, but I had brakes although they just didn't feel strong. I will have to remove the servo to take off the original check valve and drill through it to make it a simple fitting for connecting the vacuum hose so when I do that I am going to pop open the vacuum chamber to check its condition to(to make sure the piston slides easy). I will the refit and check operation but if no change I will send it out for repairs. I guess Power Brake Exchange could/would rebuild a servo without replacing the check valve. It cost $300 plus $25 each way for shipping.

I did buy the check valve from BCS. I asked David what could be wrong after giving him all my symptoms and he said "check valve". I think starting at a likely culprit that's inexpensive first is good and then working to the next solution. BCS sells a replacement servo complete with mounting bracket and brake lines for about $450. Considerably more than rebuilding the servo again but if it's improved it may be better in the long run.

The Girling servos are supposed to be superior to the after-market replacements. There is info in previous threads about who does a good job rebuilding the Girlings.
 

RAC68

Darth Vader
Offline
Hi All,

When I had the fluid collection problem and opened my Girling Booster MK2A, somehow I broke the air valve and, at the time, could not source one. As an alternative, I purchased a replacement Lockheed unit. I was unhappy with the assist provided by the Lockheed booster and once I finally sourced and rebuilt the Girling, went back to the Girling and now have the Lockheed on my shelf .... just in case.

Bob, if the check valve is stuck closed and does not allow vacuum to move the booster piston (only atmospheric air in the chamber) there will be no boost and the peddle will definitely become harder. Keep in mind that the booster now becomes an impediment to the flow of brake fluid from the MC to the brakes. Since the MK2A has its vacuum connection on top of the body of the unit and not at the bottom of the booster chamber, collection of the fluid within the chamber would most likely not be sucked in to the vacuum tube. However, since the MK2B has its check valve and vacuum connection on the bottom of the booster chamber, any fluid leaking from the booster's brake cylinder into the booster chamber could be sucked into the vacuum tube and would be sucked into the intake manifold and into the combustion mix.

A vacuum tank between vacuum source and booster was mentioned with a check valve installed between vacuum source and tank (the seemed to indicate the booster check valve was also in place. The document indicated that this was a common configuration on most Girling booster installation on other cars and provided some boost assistance after the engine was turned off as well as an even, non-throbbing vacuum source to the booster. Although they did not provide sizing for such a vacuum tank, I would expect it should not be that large...any ideas?

Ray(64BJ8P1)

Patrick, you are probably correct but it didn't appear in the diagrams of the MK2A I was reviewing. I will find a way of checking before adding another (as you had).
 
Country flag
Offline
Ray, WRT:

"Bob, if the check valve is stuck closed and does not allow vacuum to move the booster piston (only atmospheric air in the chamber) there will be no boost and the peddle will definitely become harder."

Agreed, but it's atmospheric air--which is admitted when the brakes are applied--that moves the piston. The 'bottom' side of the large vacuum/air canister should always have engine vacuum--the 'top' side will have vacuum in normal running--and when brakes are applied the 'top' of the canister has air admitted. The pressure differential between manifold vacuum at, say, 10 inches of mercury vs. atmospheric air at, say, 30 inches of mercury--applied to the top of the large piston--is what gives boost. A check valve stuck closed could definitely be the problem.

To answer Patrick's question, I gave it some thought and bypassing the check valve--I don't recall if Patrick has the original valve, mounted on the booster body, or an aftermarket valve mounted somewhere else--might be a little difficult. If Patrick has the original valve, you'd have to take it out and connect the hose from the manifold to the booster some other way; if it's an aftermarket valve he could just bypass it with another vacuum hose. On my car, the original valve was still in place, but the little flapper had apparently failed and someone had removed it, and installed a large, ugly, plastic valve to the passenger side footwell (inline with the vacuum hose). The check valve can be, er, checked by removing it and blowing through it--it should allow air passage from one side but not the other.
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Ray, WRT:

"Bob, if the check valve is stuck closed and does not allow vacuum to move the booster piston (only atmospheric air in the chamber) there will be no boost and the peddle will definitely become harder."

Agreed, but it's atmospheric air--which is admitted when the brakes are applied--that moves the piston. The 'bottom' side of the large vacuum/air canister should always have engine vacuum--the 'top' side will have vacuum in normal running--and when brakes are applied the 'top' of the canister has air admitted. The pressure differential between manifold vacuum at, say, 10 inches of mercury vs. atmospheric air at, say, 30 inches of mercury--applied to the top of the large piston--is what gives boost. A check valve stuck closed could definitely be the problem.

To answer Patrick's question, I gave it some thought and bypassing the check valve--I don't recall if Patrick has the original valve, mounted on the booster body, or an aftermarket valve mounted somewhere else--might be a little difficult. If Patrick has the original valve, you'd have to take it out and connect the hose from the manifold to the booster some other way; if it's an aftermarket valve he could just bypass it with another vacuum hose. On my car, the original valve was still in place, but the little flapper had apparently failed and someone had removed it, and installed a large, ugly, plastic valve to the passenger side footwell (inline with the vacuum hose). The check valve can be, er, checked by removing it and blowing through it--it should allow air passage from one side but not the other.
Ray, I don't know if I have the original check valve installed for sure. It also serves as the connection for the hose from the intake manifold to the booster. I will have to take the booster off to remove the check valve to drill through it to open it up permanently. The check valve I purchased from BCS is a replacement and I have it installed in the vacuum hose next to the T fitting for the valve cover. The leather strap that ties the vacuuum hose and valve cover hose together mostly hides it. I hope to start work on the booster problem this upcoming week.
 
OP
Patrick67BJ8

Patrick67BJ8

Darth Vader
Silver
Country flag
Offline
Update: I removed the booster and removed the original check valve and drilled straight through it making it a connection fitting instead of a check valve. I still have the new check valve installed inline. I checked for vacuum after the new fitting and there's vacuum. I checked vacuum at the Intake manifold and Gauge says 14in HG.

The disconnected brake line at the stop lamp switch managed to drain the brake fluid out of the cbrake guild reservoir and I topped it off but I have no one to help me bleed. I checked the brakes and still the same gard pedal feeling. I also smacked the Booster a few times to see if it would loosen anything locked up.

I did not open up the Booster chamber on the bench to check the big piston because if I did and everything started working I wouldn't know what I did to fix it. Yes, it was a half hour to take it off and 3 hours to get it back on and I get to do it again, I can't wait!
 
Country flag
Offline
Since it's free to enter this contest, I'm going to take a SWAG: The large vacuum/air piston is stuck. The canister has a thin dry lubricant coating and if (when) it wears through ... well, you get the picture.
 
Similar threads
Thread starter Title Forum Replies Date
S Receding Brake Pedal Austin Healey 32
K Midget Brake Pedal Question Spridgets 2
D TR2/3/3A clutch/brake pedal question Triumph 4
steveg "Sticking" the brake pedal Austin Healey 3
Michael Oritt Brake pedal contact or mercury switch Austin Healey 19
H BN1 Brake Pedal Hitting The Downpipe Austin Healey 9
Gearhead_Garage Brake Pedal Feel Austin Healey 24
R Low Brake Pedal Austin Healey 9
Joe_Healey Brake Pedal Rod Painted or Natural Austin Healey 14
T TR2/3/3A soft brake pedal on TR 3 Triumph 5
I TR2/3/3A Clutch and brake pedal assembly problem Triumph 4
PatGalvin TR2/3/3A Brake and Clutch pedal to MC adjustments? Triumph 4
H TR4/4A Soft Brake Pedal Triumph 3
PatGalvin TR2/3/3A Brake MC Bracket and pedal assembly install Triumph 24
A TR5/TR250 Brake Pedal return spring Triumph 2
K TR2/3/3A Brake and Clutch MC pushrod/pedal bolt stops? Triumph 2
eschneider machine gun brake pedal Other Cars 3
T Soft brake pedal on BJ8 Austin Healey 3
V TR2/3/3A TR3A Brake Pedal - Too Much Travel Triumph 6
W TR6 TR6 brake pedal drip Triumph 12
C brake pedal to the floor Austin Healey 6
R TR2/3/3A TR 3a brake/clutch master cylinders/pedal movement Triumph 4
CJD Brake/Clutch pedal adjustment Triumph 29
K Brake pedal doesn’t move mcylinder didn't fix Triumph 7
J Brake pedal cover removel? Triumph 5
J Brake/clutch pedal frozen Triumph 18
livinginthepast Disc brake conversion - soft pedal Spridgets 8
TR4 Brake Pedal Travel Adjustment Triumph 18
S BN1 clutch and brake pedal bracket Austin Healey 3
go_inbroke Brake pedal Triumph 12
N Brake pedal to the floor Austin Healey 13
Thor Brake light, do you have to remove pedal box? Spridgets 2
LuckyLuke 100-4 brake / clutch pedal seals not available Austin Healey 3
D No play in brake pedal - what a drag? Triumph 7
Randy Harris Brake Lights Work Only With Heavy Pedal Pressure Austin Healey 12
B gas, Brake, Clutch Pedal covers? Spridgets 8
saabmp3 weak brake pedal Spridgets 5
J Newbie - Soft Brake Pedal Spridgets 14
B XJ12L 1975 SOFT BRAKE PEDAL Jaguar 11
AUSMHLY brake pedal push rod adustment - YIKES ! Austin Healey 9
tr6web TR6 TR6 leaking at brake pedal Triumph 12
W Mystery of the re-occuring soft brake pedal Austin Healey 10
TomMull TR2/3/3A The ABCs of Brake Calipers Triumph 2
T TR2/3/3A Has anyone designed a hand brake warning light for the TR3? Triumph 3
F Girling Brake Fluid Reservoirs Leaking Austin Healey 12
D TR2/3/3A Why it is important to change brake fluid Triumph 4
C TR2/3/3A TR3A clutch/brake cylinder rebuild Triumph 4
D TR2/3/3A Brake fluid identification by colour. Triumph 4
K TR2/3/3A Brake Restrictor valve? Triumph 9
G Adding a Brake Booster / Brake Calipers Austin Healey 3

Similar threads

Top