Still Another Healey Brake Bleeding Saga [unfinished]

[RDKeysor]

Before I head back out to the (very hot) garage, I'll share another of my perhaps tedious errant Healey misadventures. Some may recall that I installed a British Victoria aftermarket servo in my '60 BN7 a few years back. The first series 3000 did not come with servos. Since I thought that because later cars used the larger 7/8" master cylinder, I should have one. And did. While the new servo passed the function test, I found I had good braking but a pretty heavy pedal. The Forum wise men then advised that I erred, that the heavy pedal was caused by pushing more fluid. Advice was to return to the original 5/8" standard master cylinder. I had one on hand, and I recently installed it. Did not pre-bleed it, but had brake fluid in it at installation. Did the usual two-man bleeding operation and had a low pedal. Did it all around again. Drove the car with the low pedal but a nice braking feel. I've now lost track of the number of times I've bled the system. At times I found I was getting a clunking sound from the vicinity of the servo with the car at rest, but not on the road. At times I had a good pedal in the garage and a low pedal when driving (very cautiously). Having worn out my pedal pusher--and such a pity as he can now distinguish between the clutch and brake pedals--I then tried using my Mighty Vac (not recommend by Nock) with the same result. Tried a recently purchased one-man bleeder and go no result. Then, dipping deep into this Forum's fairly massive brake bleed history, I tried a new method that goes like this: Acquire several feet of slightly undersize plastic that will slide snugly inside the normal clear plastic tubing, in my case the tubing and bleeder fitting from the Mighty Vac. Then run the new tubing up over a support higher than the fluid reservoir, and then submerge the downstream end in brake fluid in a bottle. The neat thing about this system that was revealed and then illustrated in earlier Forum postings is that you can arrange this whole system so you can see it from the driver's seat. So, tap open the bleeder with tubing attached (having smeared grease around fitting to prevent the escape of brake fluid, a second choice to the better but messy practice of wrapping a few turns of teflon tape over the threads) sit in driver's seat, gently pump pedal, watch fluid climb to the top of the tubing and plummet downward into the bottle, making sure no more air bubbles are emerging, climb out, crawl behind subject wheel, snug bleeder. Top off reservoir. Repeat at other three wheels. I put a lot of faith in this system but still got a low pedal and servo clunk with brake pedal push. That sound goes away when car is running. Perhaps I should have used prop of some kind to hold the brake pedal down while I dismounted to disconnect the bleeder, but that wasn't among the instructions and the fluid did not retreat back to the bleed point. Obviously, I can disconnect the servo and reconnect the original line between the master cylinder and the four-way brake line junction--I had left it capped but in place upon installing the servo with a new line. But that would be accepting defeat. Obviously I am overlooking something that is amiss.

 

[Jack T]

I just installed the aftermarket servo from Moss on my BT7. I've observed that the pedal feel when the car is not running is completely different than when it is. I attributed this to the vacuum acting on the servo. That may be why you are hearing a clunk from the servo at times. If the car is not running and you push the pedal, the travel of the slave cylinder may be hitting its limit when there is no air pressure in the system. The pedal is higher and firmer when the car is not running, but the servo definitely lessens the amount of pressure needed to fully stop the car.

 

[red57]

Going from a 7/8 (.875) bore to a 5/8 (.625) bore is about a 28% reduction in bore size which means that for a given stroke you will be pushing about 28% less fluid. Less fluid = longer stroke to push the same fluid = lower pedal.
May not be a bleed problem if the pedal is firm but low. I have no guess on the 'clunk' since I've never had a booster.
Dave

 

[Bob_Spidell]

I just installed the aftermarket servo from Moss on my BT7. I've observed that the pedal feel when the car is not running is completely different than when it is. I attributed this to the vacuum acting on the servo. ...

Yep. In fact, that is how you test that the booster is functioning properly: hold your foot firmly on the brake pedal when starting the engine; when the engine fires the pedal should go down a bit as the booster gets some vacuum.

As for the clunk, my BJ8's booster has always clunked the way you describe and, so far, it has nearly 200K miles on it, with one--probably unnecessary--rebuild.

 

[Jack T]

Going from a 7/8 (.875) bore to a 5/8 (.625) bore is about a 28% reduction in bore size which means that for a given stroke you will be pushing about 28% less fluid. Less fluid = longer stroke to push the same fluid = lower pedal.
May not be a bleed problem if the pedal is firm but low. I have no guess on the 'clunk' since I've never had a booster.
Dave

That's great information. Just got back from a 50 mile ride with plenty of opportunity to test the brakes. It would be nice to have a higher pedal, but I can get used to it. It's worth it for the extra confidence I have in the brakes now.

"Yep. In fact, that is how you test that the booster is functioning properly: hold your foot firmly on the brake pedal when starting the engine; when the engine fires the pedal should go down a bit as the booster gets some vacuum."

Thanks Bob. That makes sense.

Jack

 

[RDKeysor]

Thanks for all of the suggestions. The test of the servo function described above is the one I used after installing mine. Of course I got that tip from this Forum. I agree that I only got my "clunk" when the car was not operating. The master cylinder I just installed is the same size I had in the car before installing the larger one. I don't think I had a low pedal with that unit, though the idea that the smaller piston will move less fluid is surely correct. I remain puzzled that I have at times gotten a good pedal in the garage but lose it immediately while driving.

 

[Randy Forbes]

Before I head back out to the (very hot) garage, I'll share another of my perhaps tedious errant Healey misadventures. Some may recall that I installed a British Victoria aftermarket servo in my '60 BN7 a few years back. The first series 3000 did not come with servos. Since I thought that because later cars used the larger 7/8" master cylinder, I should have one. And did. While the new servo passed the function test, I found I had good braking but a pretty heavy pedal. The Forum wise men then advised that I erred, that the heavy pedal was caused by pushing more fluid. Advice was to return to the original 5/8" standard master cylinder. I had one on hand, and I recently installed it. Did not pre-bleed it, but had brake fluid in it at installation. Did the usual two-man bleeding operation and had a low pedal. Did it all around again. Drove the car with the low pedal but a nice braking feel. I've now lost track of the number of times I've bled the system. At times I found I was getting a clunking sound from the vicinity of the servo with the car at rest, but not on the road. At times I had a good pedal in the garage and a low pedal when driving (very cautiously). Having worn out my pedal pusher--and such a pity as he can now distinguish between the clutch and brake pedals--I then tried using my Mighty Vac (not recommend by Nock) with the same result. Tried a recently purchased one-man bleeder and go no result. Then, dipping deep into this Forum's fairly massive brake bleed history, I tried a new method that goes like this: Acquire several feet of slightly undersize plastic that will slide snugly inside the normal clear plastic tubing, in my case the tubing and bleeder fitting from the Mighty Vac. Then run the new tubing up over a support higher than the fluid reservoir, and then submerge the downstream end in brake fluid in a bottle. The neat thing about this system that was revealed and then illustrated in earlier Forum postings is that you can arrange this whole system so you can see it from the driver's seat. So, tap open the bleeder with tubing attached (having smeared grease around fitting to prevent the escape of brake fluid, a second choice to the better but messy practice of wrapping a few turns of teflon tape over the threads) sit in driver's seat, gently pump pedal, watch fluid climb to the top of the tubing and plummet downward into the bottle, making sure no more air bubbles are emerging, climb out, crawl behind subject wheel, snug bleeder. Top off reservoir. Repeat at other three wheels. I put a lot of faith in this system but still got a low pedal and servo clunk with brake pedal push. That sound goes away when car is running. Perhaps I should have used prop of some kind to hold the brake pedal down while I dismounted to disconnect the bleeder, but that wasn't among the instructions and the fluid did not retreat back to the bleed point. Obviously, I can disconnect the servo and reconnect the original line between the master cylinder and the four-way brake line junction--I had left it capped but in place upon installing the servo with a new line. But that would be accepting defeat. Obviously I am overlooking something that is amiss.

I'd like to offer suggestions, based on forty (>40) years of Healey experience, but with no paragraph/topic-point breaks in your post, I can't read it.

My problem, not yours, but with posts like that, my eyes just glaze over, I lose my place and it feels like the onset of vertigo. Sorry

Though most of this forum's members are of a certain age, I cannot fathom how the young(er) generation of enthusiasts on other (BMW) forums I frequent can read that on a tiny I-phone screen! Yes, the term dinosaur seems fitting in my personal bio...

 

[RDKeysor]

I'll definitely accept Randy's criticism. It's a poor defense to say I didn't think I would go on with my blab for so long. As a retired writer/editor, my own pet peeve was text written in all capital letters.

For Randy's benefit, my problem is an inability to get a full brake pedal after installing a new standard master cylinder in my '60 BN7. I had unwisely installed the later, larger master cylinder to work with a newly installed aftermarket servo. The servo passed the function tests, but I had a pedal that required a lot of foot effort, albeit with satisfactory braking.

I was advised to return to the standard master cylinder, which I did. This was followed by repeated bleedings with the standard two man technique, a try with a Mighty Vac, and then a technique described in this Forum and favorably commented on a couple of years back.

Briefly, that means making a standard bleeder connection, fitting a long, smaller diameter piece of clear hose to the bleeder hose, and looping the small hose over something higher than the brake fluid reservoir, with the outlet end descending and immersed in brake fluid in a container. The operator then cracks open the bleeder, slowly operates the pedal up and down, expelling first air and then brake fluid.

A virtue of this is that the operator can see the progression of the bubbles and the clear fluid as it transits over the top of the hose support. I did this successfully with all four wheels, refilling the reservoir between wheels, and, getting out and snugging the bleeder before the fluid retreats back to the brake. When done I still had a low pedal.

While I have had a high pedal a couple of times in the garage during some bleeding episodes, the pedal went down when driven, stabilizing at a lower level than I would prefer. I will say the braking pressure required was, as predicted by a couple of Forum members, quite acceptable. Strangely, I found virtually no ability to pump up the pedal from its low position. That was particularly surprising to me. I think all of us have experienced that process, a sure sign of air in the system.

 

[Randy Forbes]

Thank you, and glad that it was viewed as favorable criticism

Are the rear brake shoes adjusted up? I personally set them so that I can just barely hear them touching, and 1/2 turn (two quarter turns) usually locks them solid. Any space between the shoe and drum will require more fluid movement to get a full pedal stop.

Someone on here had advised before that during the diagnostic process, he adjusts the shoes up tight to the drum; you can try that to separate the hydraulic function from the mechanical one.

Going to be kind of busy around here for the next few days (fingers crossed) but I'll check back periodically.

 

[RDKeysor]

Yes, I did double check the drum brake adjustment. I had recently replaced the shoes and brake cylinders on both sides. I clicked them one turn that brought them snug, then backed off one click. If I do another brake bleed, I'll run them up tight as a test. Understand that you are watching the weather down there because of the approaching storm. Ditto here near Jacksonville. My wife wants me to go out and start our unused generator as a test because of concern about the weather. We have been pretty **** lucky since moving down here from Northern Virginia in 2005.