Master Cylinder change working

[RDKeysor]

Recently I addressed the forum about the overly long pedal throw I found on my '60 BN7 after replacing the master cylinder (MC) with a like unit with a 5/8" piston, rebuilding the calipers and installing the Moss-sourced stainless steel mesh brake hoses. Bleeding the system twice didn't help. I have now installed the later MC with the 7/8" piston, a change Healey seems to have made to work with the servos used on most later cars. I reasoned that the 7/8" piston would move more brake fluid, shortening the pedal movement. I have received the hoped for benefit, minimal pedal movement before I get strong braking. I had on hand a Victoria British servo kit purchased earlier and chose this opportunity to install that along with the larger MC. This may make it harder to assess the benefit of the larger master cylinder, and I intend to block off the intake manifold hose to the servo at some point to get a sense for how much the servo contributes to the improved braking. While I have done a minimal amount of driving with the new system, most notable is how much the front of the car pulls down under hard braking. I didn't get that with the smaller MC. Unfortunately, I still get a sense that the left rear drum brake seems to lock up earlier and skid under hard braking. Possibly the right rear, further from my ears, is also doing that. I have checked out the drum brake mechanisms, and they appear correct. An additional note on the brake MCs. The push rod yoke on the small MC is fixed, meaning it has no adjustment. The larger TRW unit has a push rod that threads into the yoke and incorporating a locking nut. It also has a longer and more elaborate rubber piece that caps the rear of the MC. So, the TRW unit is adjustable at the pedal attachment point, and I found this enabled me to make that pedal position the same as with the clutch pedal. My clutch uses the small-diameter cylinder and has the unadjustable yoke connection. I am not advocating the use of servos, knowing that they can be troublesome. One of our club members removed his from a BJ8 and is perfectly happy. My daily driver is a Porsche 968 with four-pot brakes, however, and I am accustomed to really good brake performance, making the non-servo Healey braking a bit disconcerting at first blush.

 

[Keoke]

I am accustomed to really good brake performance, making the non-servo Healey braking a bit disconcerting at first blush.

YEP!!-Not much to write home about.:highly_amused:

Can't beat the servo assist in the Healey car.-----

 

[RDKeysor]

Further to my jabber about installing a brake master cylinder (MC) of a larger diameter on my '60 BN7, I want to confirm that both MCs previously on the car were 5/8" diameter. The replacement is 7/8". The first MC was replaced after I found my brake fluid virtually black and layered when I emptied it in a glass jar after spotting the problem during a bleeding exercise. Someone on the forum suggested that the blackness was from damage to the rubber parts in the system. I hadn't noticed a particularly long pedal stroke before getting braking with that MC. I then installed a new, same-size MC and encountered the long-stroke issue. Also regards the brake fluid, which because it layered may be been silicone when I acquired the car, with some Dot 3 or 4 added by me. Shortly after the master cylinder change, the clutch MC also failed and was rebuilt. Next, I found the brake fluid reservoir empty and a drip mark on a front tire. That resulted in a caliper rebuild. The pistons I removed appeared to be chrome plated, with a lot of corrosion and plating flaking at about the point where the caliper internal rubber seal contacts the piston. Given all of the rust on the pistons, I expected the rebuilt calipers along with the previously installed standard 5/8" MC would provide better braking. All I noticed was that for some reason the brake pedal throw was longer than before. I had bled the holy heck out of it. I did one quick bleed with the larger MC and got a full pedal. I am using NAPA Dot4, which is recommended by our AH club members. I put a ton of it through the system in the course of this exercise.

 

[steveg]

Further to my jabber about installing a brake master cylinder (MC) of a larger diameter on my '60 BN7, I want to confirm that both MCs previously on the car were 5/8" diameter. The replacement is 7/8". The first MC was replaced after I found my brake fluid virtually black and layered when I emptied it in a glass jar after spotting the problem during a bleeding exercise. Someone on the forum suggested that the blackness was from damage to the rubber parts in the system. I hadn't noticed a particularly long pedal stroke before getting braking with that MC. I then installed a new, same-size MC and encountered the long-stroke issue. Also regards the brake fluid, which because it layered may be been silicone when I acquired the car, with some Dot 3 or 4 added by me. Shortly after the master cylinder change, the clutch MC also failed and was rebuilt. Next, I found the brake fluid reservoir empty and a drip mark on a front tire. That resulted in a caliper rebuild. The pistons I removed appeared to be chrome plated, with a lot of corrosion and plating flaking at about the point where the caliper internal rubber seal contacts the piston. Given all of the rust on the pistons, I expected the rebuilt calipers along with the previously installed standard 5/8" MC would provide better braking. All I noticed was that for some reason the brake pedal throw was longer than before. I had bled the holy heck out of it. I did one quick bleed with the larger MC and got a full pedal. I am using NAPA Dot4, which is recommended by our AH club members. I put a ton of it through the system in the course of this exercise.

Healey ownership can be a character-building exercise!

 

[Keoke]

Healey ownership can be a character-building exercise!

------ -----------OR!!
An advanced introduction to cuss-sin .:highly_amused:

 

[PHulst]

Where did you source the larger MC? From Moss?

Having a similar "long stroke" issue with a 1959 BN4. It has had a replacement MC just like yours as well as new or rebuilt wheel cylinders and some new lines. In addition it has also been converted from silicone fluid to DOT4 in an attempt to improve the brake pedal and feel. None of that has worked.
While I was not necessarily planning on adding the servo, the larger MC may end up being the key, although it is only from 3/4 to 7/8 for a BN4.

Let me know your source if you get a chance, and thanks for posting your "fix."

 

[DerekJ]

A servo doesn't improve the braking on a car. It simply reduces the effort required. I run my car on track without a servo and have no problem with the braking.

 

[RDKeysor]

Per PHulst's inquiry, I bought the larger MC from Moss. It happens that most of my brake issues came up while Moss had those components on sale. I had purchased my servo earlier from Victoria British. As I said, I have much better braking now, but I continue to have a left rear brake lockup (the tire skid sound) when I test the braking system. I'm aware of that as the left rear is close to my ear. I'm going to try it with a friend in the passenger seat to see whether he hears the brake lock up on that side. I have had both drums off and find no issues there. No, I have yet to change my 10-year-old tires, but I have run older tires before and not experienced this with other cars. Of course they weren't the tires I have on this car. This issue has occurred virtually since I bought the car. Maybe I need a brake bias device. Truly not interested in doing more brake work at this juncture. One thing to note on the later MCs. They have a separate rubber band that encircles the portion that inserts through the firewall. I suggest removing this before the insertion and installing the band from the inside. Otherwise the dang thing won't go through the firewall. The smaller MCs don't have the extra band. I learned this the Healey way, the had way.

 

[bdcvg]

I had the opposite done to My BJ8 by Four-in-Tune and couldn't be happier with the results, I actually have some control over brake modulation instead of the servo being all or nothing. The beauty of old car fiddling, there is always another option.

 

[DerekJ]

You really shouldn't be running with 10 year old tyres. These could be contributing to rear wheel lock up under braking where the weight is transferred to the front of the car leaving the rears struggling for grip.

 

[steveg]

Per PHulst's inquiry, I bought the larger MC from Moss. It happens that most of my brake issues came up while Moss had those components on sale. I had purchased my servo earlier from Victoria British. As I said, I have much better braking now, but I continue to have a left rear brake lockup (the tire skid sound) when I test the braking system. I'm aware of that as the left rear is close to my ear. I'm going to try it with a friend in the passenger seat to see whether he hears the brake lock up on that side. I have had both drums off and find no issues there. No, I have yet to change my 10-year-old tires, but I have run older tires before and not experienced this with other cars. Of course they weren't the tires I have on this car. This issue has occurred virtually since I bought the car. Maybe I need a brake bias device. Truly not interested in doing more brake work at this juncture. One thing to note on the later MCs. They have a separate rubber band that encircles the portion that inserts through the firewall. I suggest removing this before the insertion and installing the band from the inside. Otherwise the dang thing won't go through the firewall. The smaller MCs don't have the extra band. I learned this the Healey way, the had way.

As a science project, maybe deflate the tires to 15 lbs or so and see if you avoid the lockup that way.

PS - reminds me of The Christmas Story movie: "...they were tires in the academic sense, in that they were round and had once been made of rubber."

 

[Gearhead_Garage]

If you want to test anything rotating on your car, rather than bungy your significant other to the hood, just use a small camera. You can buy a really good one for $100 with a suction cup for the side of your car. Go hit the brakes and you will see if it locks up. You can also use it under the car to look for abnormal suspension deflection, tire hop, or even drips.

https://www.mobius-actioncam.com/store/products/mobius-basic-actioncam-16g-2/

If you already have a small digital camera, check to see if it has an HD video mode (most do) and a tripod thread hole (1/4"-20). If so, then you may only need a suction mount

https://www.amazon.com/Fotodiox-Win...9531&sr=8-2&keywords=suction+cup+tripod+mount

With a PC (or Mac) and free video software like VLC you can go frame by frame to look for stuff.

https://www.videolan.org/vlc/index.html

Or you can suction it to the windshield aimed forward or rear and record all those blissful Healey miles after you sort your braking issues.

 

[PHulst]

Per PHulst's inquiry, I bought the larger MC from Moss.

Thanks for the reply.