Brake Booster Repair/Troubleshooting

[VaCat33]

Hello All

I would like to follow up on the topic posted by “pfreen” about the brake booster. I have an early MkI with the stock Girling Mk2A booster. It was completely rebuilt 10 years ago.

I recently had my brake pedal go to the floor while driving (nothing too serious as I was moving very slowly in stop and go traffic.) I immediately suspected the Brake master and sure enough, upon removal and disassembly it needed to be completely re-sleeved and rebuilt.

I got all that done and got the MC back in the car. During the test drive the brakes did not seem to be getting any help from the booster.

Since the test drive, I performed Randy’s “old School” test and when I started the car with the brake pedal partially depressed it DID NOT move forward at all. Conversely, with the car off I pumped the pedal several times and the pedal strokes never shortened and continued to travel the full range which I interpreted as evidence it is NOT holding Vacuum.

I tested the manifold vacuum and got 12-13 inches @ idle (700 rpm.) The fluid level in the reservoir does not appear to be dropping, so I do not think it is blowing by bad seals in the booster.

My question…is there any intermediate repair (check valve, gasket etc) short of a complete rebuild of the unit?

Thanks

 

[0neoffive]

First, measure the vacuum at the booster end of the hose. If OK, then remove the banjo bolt (7/8"wrench) and make sure the check valve functions. If you can suck air thru it, it's fine. It is also possible there is enough contamination in the valve body or vacuum can to prevent function. In which case, it's time to break it down and do a go-thru. just sayin'

 

[VaCat33]

First, measure the vacuum at the booster end of the hose. If OK, then remove the banjo bolt (7/8"wrench) and make sure the check valve functions. If you can suck air thru it, it's fine. It is also possible there is enough contamination in the valve body or vacuum can to prevent function. In which case, it's time to break it down and do a go-thru. just sayin'

Randy

Roger on vacuum test.I measured vacuum at the booster end of hose.

Once I get the bolt off the banjo fitting I can use a vacuum pump to suck air through the check valve, correct? Thanks.

 

[VaCat33]

Randy

Roger on vacuum test.I measured vacuum at the booster end of hose.

Once I get the bolt off the banjo fitting I can use a vacuum pump to suck air through the check valve, correct? Thanks.

Randy

Pardon my ignorance …but Just to confirm…this is the bolt (green arrow) we are talking about.

Thanks.

 

[Austin Healer]

there can be several issues to check. on the side of the booster assy is a cover with 4 screws and a pipe which connect to the vacuum reservoir. behind that is a rocking valve assy with either black or clear plastic seats. these can crack making the unit inoperable, second issue would be that the vacuum piston, inside the black portion of the booster, has has it's sponge ring (under the leather seal) fit improperly which will not allow the piston to move freely inside the reservoir. lastly, the check valve that the rubber vacuum hose connects to could be faulty.

I don't know who sleeved your booster and what material they used for sleeves (stainless or bronze).. I have had nothing but problems with the bronze sleeved units.

when assembling the vacuum piston in the chamber, you should be able to push it into the reservoir and hear the air being expelled through either the vacuum port (check valve), or the air filter assy. The piston should freely rise back out of the reservoir. if it doesn't, the sponge seal isn't fit correctly. These have a flat side and a rounded side. the rounded side faces the leather seal. these seals are supplied overlength and if you didn't trim it, that could well be the source off your problem.

to test that the servo is holding vacuum... place a rubber cap (like a vacuum cap) over the end of the check valve (where the hose connects). with the back of the vacuum chamber removed, push the vacuum piston fully down. Place your thumb over the rubber grommet for the vacuum pipe. Let go of the piston. it shouldn't move. ease your thumb off of the grommet and it (the piston) should slowly rise.

I always lubricate the leather seal with moly grease. you could also use sil-glide. Do not use lithium grease as it tends to get gummy over time and will cause the leather seal to drag, or bind up.

Never use silicone brake fluid with a Girling type booster. if the system is not perfectly virgin the seals will swell as dot 4 and dot 5 have different swelling properties. I had this problem and the brakes stayed on... I had to open a bleed screw in order to move the car.

 

[65beam]

there can be several issues to check. on the side of the booster assy is a cover with 4 screws and a pipe which connect to the vacuum reservoir. behind that is a rocking valve assy with either black or clear plastic seats. these can crack making the unit inoperable, second issue would be that the vacuum piston, inside the black portion of the booster, has has it's sponge ring (under the leather seal) fit improperly which will not allow the piston to move freely inside the reservoir. lastly, the check valve that the rubber vacuum hose connects to could be faulty.

I don't know who sleeved your booster and what material they used for sleeves (stainless or bronze).. I have had nothing but problems with the bronze sleeved units.

when assembling the vacuum piston in the chamber, you should be able to push it into the reservoir and hear the air being expelled through either the vacuum port (check valve), or the air filter assy. The piston should freely rise back out of the reservoir. if it doesn't, the sponge seal isn't fit correctly. These have a flat side and a rounded side. the rounded side faces the leather seal. these seals are supplied overlength and if you didn't trim it, that could well be the source off your problem.

to test that the servo is holding vacuum... place a rubber cap (like a vacuum cap) over the end of the check valve (where the hose connects). with the back of the vacuum chamber removed, push the vacuum piston fully down. Place your thumb over the rubber grommet for the vacuum pipe. Let go of the piston. it shouldn't move. ease your thumb off of the grommet and it (the piston) should slowly rise.

I always lubricate the leather seal with moly grease. you could also use sil-glide. Do not use lithium grease as it tends to get gummy over time and will cause the leather seal to drag, or bind up.

Never use silicone brake fluid with a Girling type booster. if the system is not perfectly virgin the seals will swell as dot 4 and dot 5 have different swelling properties. I had this problem and the brakes stayed on... I had to open a bleed screw in order to move the car.

Another note to the use of Syl Glyde brake lube is not to use it on any other parts of the booster or on any part with rubber seals because it is a silicone based product that would not be compatible with natural rubber. It's use is primarily for use on caliper sliding areas for pads or for lubrication of other parts of the disc or drum brakes with seals that are not natural rubber.

 

[Austin Healer]

one other possible cause for a brake booster to be inoperable is assembly error. Some time ago I sent three boosters off for rebuild. One came back inoperable. I tore it to bits and found the gasket between the vacuum chamber and hydraulic body was install backwards blocking off the vacuum supply to the vacuum chamber.

 

[Austin Healer]

Another note to the use of Syl Glyde brake lube is not to use it on any other parts of the booster or on any part with rubber seals because it is a silicone based product that would not be compatible with natural rubber. It's use is primarily for use on caliper sliding areas for pads or for lubrication of other parts of the disc or drum brakes with seals that are not natural rubber.

While Girling brake parts kits were originally supplied made from natural rubber, they are not now. All of the currently available rebuild kits are made from synthetic rubber. You can use dot5 (silicone) in a car that has had the seals and hoses completely replaced, BUT, you can't just drain all your old dot 4 and refill with dot 5. The 2 brake fluids have different swelling properties and a mix of fluid will either cause rapid seal wear, or the brakes locking in the "on" position.

 

[0neoffive]

Randy

Pardon my ignorance …but Just to confirm…this is the bolt (green arrow) we are talking about.

Thanks.

View attachment 17667

Well, you can always send it up for a tear down, deep clean and diagnosis.

 

[65beam]

While Girling brake parts kits were originally supplied made from natural rubber, they are not now. All of the currently available rebuild kits are made from synthetic rubber. You can use dot5 (silicone) in a car that has had the seals and hoses completely replaced, BUT, you can't just drain all your old dot 4 and refill with dot 5. The 2 brake fluids have different swelling properties and a mix of fluid will either cause rapid seal wear, or the brakes locking in the "on" position.

There are still a lot of original very old kits still out there for sale. There is also a lot of junk made off shore that are just a waste of money. I ran across a lot of old repair kits for various uses for sale at the Carlisle Import swap meet last week. Owners buy this stuff and use it as well as listen to folks that say "use this" during assembly. Why take a chance of using a product that will result in a problem possibly in a short period of time. As far as brake fluid goes I always used Castrol LMA but production of the product ceased over a year ago so we're stuck with what ever you can buy. Silicone brake fluid seems to give a spongy feel to the system.

 

[pfreen]

Well, know I am wading into a minefield but here goes.
After every 3 years of rebuilding the two Girling boosters on my Lotus, and dealing with leaking master cylinder, brake cylinders and front Girling brake calipers, I made the switch. This was in 1999.
I replaced or rebuilt every component except the brake lines, which I flushed with alcohol and blew out. I changed from Girling to Lockheed bosters.
I put in Cartel silicone brake fluid. I did not notice any difference in brake pedal "spongeness". I did however replace the two Girling boosters with Lockheed units, which may have an effect compared to the Girling boosters
I have not had any leaking issue since 1999. The only issue I had was with the girling master cylinder which decided to start not releasing the brakes. I found this out when I was bedding in the Greenstuff front pads. The bridge in Fort Lauderdale was up so I was stuck at the gate. After the gate opened with 7000 cars behind me, the brakes would not release. So, I went forward over the bridge and by the time I had to give throttle to go down he bridge, I pulled off just after the bridge. Smoke was rolling off the front brakes. The only way to release them was to crack the brake lines at the master cylinder. I was not happy.
Anyway, I put in a Japanese master cylinder and never looked back. That was 7 years ago.
Anyway, based on my experience, On my Tiger, I replaced or rebuilt everything (including the 7" Girling booster) and have used Cartel silicone brake fluid. I just got it going. As stated in another post, the brakes work fine except for more pedal force than I expected. I can lock the brakes. I have no Tiger experience so I asked the group.

 

[65beam]

My later cars all have early Alpine Series 1 & 2 rear wheel cylinders and the 700 Girling brake master used on the same cars along with modified boosters. I have no problems with my brakes

 

[pfreen]

I would find rusty pistons and bores with Castrol LMA. I probably didn't flush it enough I guess. This is certainly not a critique of what people do. It's just my experience.

 

[0neoffive]

Part & parcel of maintenance is a good flush now and then. Make-up air enters the system by design. Air has moisture in it. Unless you live in the super dry areas, water contamination gets in the brake system and basic chemistry occurs. No matter how much you love and care for it, the critter still ages. Amen

 

[65beam]

I would find rusty pistons and bores with Castrol LMA. I probably didn't flush it enough I guess. This is certainly not a critique of what people do. It's just my experience.

Most brake fluids should be drained and flushed every two years. The Castrol is a DOT 4 product made using glycol ethers and borate esters just as most brakes fluids are. Castrol did use a Low Moisture Additive as do others with Castrol using it as a marketing tool.

 

[Austin Healer]

Well, know I am wading into a minefield but here goes.
After every 3 years of rebuilding the two Girling boosters on my Lotus, and dealing with leaking master cylinder, brake cylinders and front Girling brake calipers, I made the switch. This was in 1999.
I replaced or rebuilt every component except the brake lines, which I flushed with alcohol and blew out. I changed from Girling to Lockheed bosters.
I put in Cartel silicone brake fluid. I did not notice any difference in brake pedal "spongeness". I did however replace the two Girling boosters with Lockheed units, which may have an effect compared to the Girling boosters
I have not had any leaking issue since 1999. The only issue I had was with the girling master cylinder which decided to start not releasing the brakes. I found this out when I was bedding in the Greenstuff front pads. The bridge in Fort Lauderdale was up so I was stuck at the gate. After the gate opened with 7000 cars behind me, the brakes would not release. So, I went forward over the bridge and by the time I had to give throttle to go down he bridge, I pulled off just after the bridge. Smoke was rolling off the front brakes. The only way to release them was to crack the brake lines at the master cylinder. I was not happy.
Anyway, I put in a Japanese master cylinder and never looked back. That was 7 years ago.
Anyway, based on my experience, On my Tiger, I replaced or rebuilt everything (including the 7" Girling booster) and have used Cartel silicone brake fluid. I just got it going. As stated in another post, the brakes work fine except for more pedal force than I expected. I can lock the brakes. I have no Tiger experience so I asked the group.

I rebuilt my Girling booster 20 years ago. works just fine, no leaks.. two things kill braking systems... not regularly driving the car never build up enough heat in the system to get rid if moisture, and not regularly replacing the brake fluid, at least every 2 years...

Spongy brakes are common with Silicone fluid because it is compressible. I believe I did warn about the about the possibility of the brakes locking on when using Dot 5 fluid. With older kits or original brake parts with natural rubber seals, this is a very real problem. You could revert back to the original master cylinder if you buy a new (not NOS) kit. The Japanese master would definitely have synthetic rubber seals. I'm not a huge fan of the Lockheed type boosters as they are progressive and have a completely different feel that the original Girling units... However, rebuildable Girling units are getting harder and harder to find. Not so much due to the hydraulic side of the unit, that can be sleeved... I find that the hardest parts to source are good vacuum canisters, and good vacuum canister pistons. If the tip of the piston is corroded it cannot be repaired and if the canister is heavily rusted, it too, is toast.

 

[VaCat33]

After some more tests and giving this some thought, I am not convinced my booster is the issue. It has good vacuum at the banjo fitting and I could see no evidence that fluid was getting past the seal. In a test drive I easily locked up the brakes.

My subjective feel was more focused on the pedal travel before brakes engaged. I checked the pads and they have little wear. I adjusted the rear brakes according to instructions in the WSM and that seemed to help…again totally subjective.

So for now, I am going say issue resolved and start enjoying the excellent driving weather.

The bad news is…I broke the sardine clamp during Re-installation.

Thanks to all.

 

[mr55s]

After some more tests and giving this some thought, I am not convinced my booster is the issue. It has good vacuum at the banjo fitting and I could see no evidence that fluid was getting past the seal. In a test drive I easily locked up the brakes.

My subjective feel was more focused on the pedal travel before brakes engaged. I checked the pads and they have little wear. I adjusted the rear brakes according to instructions in the WSM and that seemed to help…again totally subjective.

So for now, I am going say issue resolved and start enjoying the excellent driving weather.

The bad news is…I broke the sardine clamp during Re-installation.

Thanks to all.

What part of the sardine clamp did you break, the band?

 

[VaCat33]

Mr55

Yes it was the band that broke.

 

[pfreen]

You can get new banding here. https://restorationstuff.com/. I bought heir band clamp but it is slightly different. The banding itself looks the same.