Vanishing Brake Pressure

[RDKeysor]

This past weekend I pulled the left rear brake drum on my '60 BN7 looking for a bit of grabbing I had reported here earlier. I found nothing amiss, but hand sanded a bit of polish on the brake pads. This car was restored possibly eight years ago, and all of the components appear as new. Deciding on a brake fluid change, I bled that brake with my Mighty Vac. Initially I got a lot of very dark fluid. Moving to the right rear, I was unable to get any brake pedal using the vacuum tool. I then enlisted a neighbor, and we bled the right rear conventionally. Still evacuating pretty dark fluid. At this point I hadn't done the front brakes. A day or two later I found I again had no pedal. I then used a reduced size piece of clear bleeding hose to make sure what was being expelled filled the hose so I could watch for bubbles. With another helper, we bled the left rear and got good pedal. The right front did not bleed until I removed the bleeder. Pressure on the pedal then blew out whatever the blockage was. That brake was then bled successfully with a higher pedal than I had noted in the past. However, the piston on the right front did not appear to have any movement, so I removed the pads (like new), inserted slightly thinner wooden blocks in the pad slots and had my helper pump the pedal, establishing movement. I moved the pistons in an out a bit with a tool. The left front brake was then bled successfully, but I repeated the pad removal to establish that I had piston movement. At the finish both rotors were more firmly held by the brake pads than my previous experience with disc brakes, but we had really good pedal. In fact, it was higher than I had observed previously. By now we had rather thoroughly cleaned out the old fluid, using more than a full 32 oz. Dot 3 container. I was careful to keep the reservoir, which I had siphoned early on and refilled with new fluid, full during the bleeding. The cap was left loose during the process. Today, one day after bleeding, I again had no pedal. No sign of leaking anywhere, including at the master cylinder. I hadn't touched the clutch slave during the brake bleeding. So what's going on?

 

[Patrick67BJ8]

This past weekend I pulled the left rear brake drum on my '60 BN7 looking for a bit of grabbing I had reported here earlier. I found nothing amiss, but hand sanded a bit of polish on the brake pads. This car was restored possibly eight years ago, and all of the components appear as new. Deciding on a brake fluid change, I bled that brake with my Mighty Vac. Initially I got a lot of very dark fluid. Moving to the right rear, I was unable to get any brake pedal using the vacuum tool. I then enlisted a neighbor, and we bled the right rear conventionally. Still evacuating pretty dark fluid. At this point I hadn't done the front brakes. A day or two later I found I again had no pedal. I then used a reduced size piece of clear bleeding hose to make sure what was being expelled filled the hose so I could watch for bubbles. With another helper, we bled the left rear and got good pedal. The right front did not bleed until I removed the bleeder. Pressure on the pedal then blew out whatever the blockage was. That brake was then bled successfully with a higher pedal than I had noted in the past. However, the piston on the right front did not appear to have any movement, so I removed the pads (like new), inserted slightly thinner wooden blocks in the pad slots and had my helper pump the pedal, establishing movement. I moved the pistons in an out a bit with a tool. The left front brake was then bled successfully, but I repeated the pad removal to establish that I had piston movement. At the finish both rotors were more firmly held by the brake pads than my previous experience with disc brakes, but we had really good pedal. In fact, it was higher than I had observed previously. By now we had rather thoroughly cleaned out the old fluid, using more than a full 32 oz. Dot 3 container. I was careful to keep the reservoir, which I had siphoned early on and refilled with new fluid, full during the bleeding. The cap was left loose during the process. Today, one day after bleeding, I again had no pedal. No sign of leaking anywhere, including at the master cylinder. I hadn't touched the clutch slave during the brake bleeding. So what's going on?

Sounds like the Master Cylinder to me. There's a seal at the end(internally), of the pushrod that might cause the problem you're having.

 

[healeyblue]

+1 on the master. Sounds like an internal seal works if used repeatedly, but if left to relax, the pressure is bypassed.

 

[Randy Forbes]

Make it three (3) for unanimous. The "very dark fluid" is likely the result of rubber degradation throughout the circuit(s), so you're probably not far from a system overhaul.
As someone that's lived with British sportscars nearly my entire driving life (forty-three of the forty-four years since I got a driver's licence) eight (8) years is probably longer than I've ever stretched out the interval between overhauls__but for a great many of those years, they were daily drivers.

They're your brakes, and in the words of Clint Eastwood, aka (Dirty) Harry Callahan, "do ya feel lucky punk? Well do ya?"

 

[RDKeysor]

Thanks, all. Interesting that the master cylinder would crap out the first time I worked on the brakes, but then there was a lot of pedal action in the process. I recall our Jacksonville-area AH club session dealing with this issue, and the guys doing the job were unable to pull the MC innards out from inside the foot well. Not sure why. When I had to depart during this procedure, they were trying to remove the entire MC from below the air cleaners. That was also proving difficult. What are the chances of removing the guts from inside and replacing them with the rebuild kit? Otherwise, I assume one has to remove the cylinder rod clovis pin and extract the whole cylinder from inside the engine bay. If that is so, I'm thinking the rear air cleaner must come out for ease of access.

 

[rjc157]

I would try to do it from the inside first why not couldn't hurt your just going to have to remove all the oil .

 

[steveg]

Thanks, all. Interesting that the master cylinder would crap out the first time I worked on the brakes, but then there was a lot of pedal action in the process. I recall our Jacksonville-area AH club session dealing with this issue, and the guys doing the job were unable to pull the MC innards out from inside the foot well. Not sure why. When I had to depart during this procedure, they were trying to remove the entire MC from below the air cleaners. That was also proving difficult. What are the chances of removing the guts from inside and replacing them with the rebuild kit? Otherwise, I assume one has to remove the cylinder rod clovis pin and extract the whole cylinder from inside the engine bay. If that is so, I'm thinking the rear air cleaner must come out for ease of access.

A friend of mine recently installed the rebuild kit from the footwell. It can be done. Sounds like your mechanic is too fat/old/doesn't wanna.

When I recently replaced mine from the engine side, I found it necessary to remove the carbs as well as the air cleaners. From inside the car is the way to go for a simple rebuild.

 

[HealeyRick]

If you decide to replace the m/c, take a look at Pegasus Racing. Their prices are very reasonable for genuine Girling parts: https://www.pegasusautoracing.com/group.asp?GroupID=MCGIRLING

 

[blueskies]

Don't feel too bad. This happened to me with new parts. I recently installed a new brake master cylinder and a new clutch master cylinder on the BN4. Both parts had the correct part number but came from the vendor with the wrong length of push rod and the wrong end on the push rod. On the advice of the vendor, I switched in the push rods from the old master cylinders. This is on a system with all new parts, from one end to the other.

The next problem came when the brakes would not bleed properly. The reason appears to be that the seal inside the master cylinder is allowing fluid to pass by; that fluid is coming past the push rod into the foot well. My thought is that the longer push rod and the longer travel of the push rod destroyed the internals of the master cylinder.

I've been waiting for a month or so for the vendor to come up with a solution. They admitted that the fault lay with them and thanked me for pointing out the problems. They also said that they were going back to their supplier for a fix. So far I'm waiting - somewhat patiently, but less so as time goes on - for them to make it right. It's a good thing that I'm not needing to drive the car right now.

 

[RDKeysor]

I have two rebuild kits on order, one for the brakes and another possibly for the clutch (they are listed with the same number for my car). Also ordered the kit for the slave. It was so nice to get a unanimous response to my question, and I'm pretty confident the response is correct. Before I try to access the master cylinder from the foot well, I will put a doubled plastic bag under the reservoir lid and snug it down. I think that will help reduce the inevitable brake fluid that will emerge if I can pull the master cylinder innards from inside the car.

 

[LarryK]

Make sure you use DOT 4 fluid not domestic DOT 3. The synthetic DOT 4 does not degrade the rubber where the domestic DOT 3 will eat rubber. Domestic older cars had a silicone style rubber and could use the harsher fluid. The British cars use a more pure rubber cones and take a synthetic fluid like Castrol LM fluid DOT4. Only use DOT 5 when replacing full system as it will not mix with other fluids.

 

[RDKeysor]

Does the objection to "domestic Dot 3" also exist for domestic synthetic Dot 3? Even though the Castrol Web site listed its products as being available as most of the usual chain auto parts places, none of those I checked actually listed Castrol as available, and I now have the Dot 3 synthetic in the car. I will be rebleeding the brake system, so I can go to Dot 4 synthetic if I can find it.

 

[LarryK]

Do not know. Have only used Castrol LMA DOT fliud in 30+ years in my British cars and Eurpoean cars. I have used DOT 3 in many domestic cars over the years, but changed to Castrol for a higher temp fluid and less inventory. If I want higher temp fluid I go with Ford big truck fluid synthetic. All British cars used DOT 4 in my manuals. Firestone makes a DOT 4 synthetic available at AZone, Advance and ORielly. Castrol I pick up on line or at my local family owned old fashion parts store.

 

[HealeyRick]

I would go with DOT 4 unless you're doing a full conversion to DOT 5 (silicone). The LM in Castrol LMA is "low moisture" as is DOT 4. I wouldn't use DOT 3 in the system. Even with DOT 4, you're going to want to change it every two years at a minimum. Also, don't confuse "synthetic" with silicone fluid. Synthetic fluid will not give you the advantages of long change life and no paint blistering that silicone does. I've been able to find DOT 4 at the local NAPA store.

 

[Patrick67BJ8]

You will need to flush out ALL brake/clutch lines before putting in new fluid and rebuild kits. I am one of the "founding members" of the JAX club and we had numerous problems with the wrong brake fluid being used when we started doing "tech sessions" after the club was formed(1974). Bill Young can probably remember that!

 

[Randy Forbes]

As an alternative brake fluid, I've been have pretty good luck (a few years now, and no rubber degradation) with annual or 2-year flushing intervals, is the ATE 200 fluid. It's the only fluid I use in BMWs, and always have several fresh cans on the shelf, so I decided the try it.

I still have a sealed (never opened/seal intact) "can" of Castrol GTLMA in the Healey's trunk; maybe somebody else will need some on a drive sometime...?

 

[longbridgehealey]

If your supplier is one of the "usual suspects" they've been aware of the rod problem for at least two years. You can guess how I know this.....

 

[mikephillips]

Even on original Girling masters there seemed to be an early and late style piston which used pushrods with different lengths inside the captive washer. I've noticed this among the Sunbeam parts I have. Same part number and the whole assembly will swap with no issues, but they cannot mix parts since the sort pushrod is too short with the late piston and the late pushrod is too long for the early piston.

 

[blueskies]

Even on original Girling masters there seemed to be an early and late style piston which used pushrods with different lengths inside the captive washer. I've noticed this among the Sunbeam parts I have. Same part number and the whole assembly will swap with no issues, but they cannot mix parts since the sort pushrod is too short with the late piston and the late pushrod is too long for the early piston.

Maybe I should have started a separate thread on this, as I did not mean to hijack the thread. My apologies to the OP.

Mike, what you say may support what I guessed - that mixing the parts can cause problems. I suspect that the seal inside the MC was damaged by the longer stroke required for the application. This is on an early BN4, without a separate brake fluid reservoir.

On the issue of what brake fluid to use - I see that pretty much everyone seems to agree that one should not use DOT 3. I will take that advice, but am wondering why DOT 3 is not compatible with the seals used in the new master cylinders and wheel cylinders. DOT 3 seems to work fine in all kinds of vintage American cars. What is different about the rubber used in the new Healey/British parts?