BJ8 with servo...Brake travel issue

[rcflyer]

Guys.....I did a pencil impression today of the Brake MC..it is 625 (a little hard to do but I did it!). Does not seem right...If I'm looking at this correctly that is 5/8!!! Wholly crap. That's way too small......Yes??, Also I am going to look at the Clutch MC as I think it is exactly the same size (And it should be 3/4 right?????)Thanks, Lee

 

[RAC68]

Lee,

I seem to remember that some felt the Girling servo did not provide enough of an assist to overcome the use of a large 7/8[SUP]th[/SUP] bore MC. To gain an easier peddle, they installed the MC used in a non-servo Healey as the smaller 5/8[SUP]th[/SUP] bore would produce this result. This may be why your car has the smaller bore MC.

Others with a better memory could verify this fact.

Ray (64BJ8P1)

 

[steveg]

Lee,

I seem to remember that some felt the Girling servo did not provide enough of an assist to overcome the use of a large 7/8[SUP]th[/SUP] bore MC. To gain an easier peddle, they installed the MC used in a non-servo Healey as the smaller 5/8[SUP]th[/SUP] bore would produce this result. This may be why your car has the smaller bore MC.

Others with a better memory could verify this fact.

Ray (64BJ8P1)

Especially with modern ceramic pads, it would seem like a good idea to return to the stock 7/8" size. There must be a lot of BJ8 owners on this forum who are satisfied with their pedal pressure.

 

[rcflyer]

I'm using standard pads, not ceramic as they need to warm up each time to be effective (I have heard) so I have the regular semi-metallic pads sold by Healey Surgeons. I do not plan to use ceramic pads...Now with that in mind should I be using the 5/8 or 7/8's???,Also, My servo is a newer replacement Lockheed type if that matters. Lee

 

[healeyblue]

If you want the brake travel issue fixed, then most definitely go with the correct 7/8 master. It will move more fluid per stroke than the 5/8 reducing the amount of pedal travel required.

 

[rcflyer]

OK, I will install the 7/8 MC. I can always go back to 5/8 if I want...I like the way my MGA 1600 brakes work ...about an inch or so and you have great brakes. No servo there...but pressure is fine, very easy to stop the car on a dime!. When I got the car it had set for 26 years in a garage...so I replaced every single part of the brake system and used Silicon fluid. Lee

 

[RAC68]

Lee,

I hope I am not beating a dead horse in saying that the added peddle pressure required of the Lockheed Servo applies to standard brake pads and shoes as I have experienced. As Steve commented, this condition is further amplified when using ceramics. The difference in peddle pressure may be a null factor in your decision if you have not had the experiences of both to compare.

Also, I don’t believe the smaller bore MC is the cause of your inconsistent brake travel issue and that moving more fluid is not the resolution. Although I can not be absolutely sure and as I have said before, I feel the deterioration of a slightly miss-positioned end seal, from the lack of packing spacers, resulted in a deteriorated end seal allowing a small amount of fluid to seep back into the reservoir when applying the brake. The effect seems more apparent on the first application as reasonably-immediate follow-on applications would benefit from the already close positioning of the pads/shoes to their destinations.

All that being said, good luck and all the best,

Ray (64BJ8P1)

 

[rcflyer]

Ray, Thanks for the interesting help. Are you saying the Lockheed requires more pressure to do the same work vs the old original Girling unit??? If that is so and everyone says use the 5/8 with the Lockheed unit...I could order one...otherwiase... I have the 7/8 here so I'll put it in and see if it 1) cures my issue, 2) I like the pedal feel. I'll OK with a harder to press pedal as I have a MGA 1600 with front Disc brakes, no servo and it's kind of nice to have to push it a little harder. it is smooth and responsive and I use Silicon fluid. If it cures my issue but I don't like the feel I can always order a 5/8 to swap in. The inconsistent pedal travel (1st vs others) I think has pretty much been solved by the shoe and EM brake issues I fixed. To have a slightly better pedal after the 1st press does not seem all that big a deal. I'll see what the new MC does/does not fix soon.....Thanks, Lee

 

[RAC68]

I seem to remember that some felt the Girling servo did not provide enough of an assist to overcome the use of a large 7/8[SUP]th[/SUP] bore MC. To gain an easier peddle, they installed the MC used in a non-servo Healey as the smaller 5/8[SUP]th[/SUP] bore would produce this result. This may be why your car has the smaller bore MC.

I apologize for the confusion but my earlier comment should have read Lockheed and NOT Girling. The Lockheed servo provides less assist and therefore requires more peddle pressure than the originally equipped Girling servo. For this replacement to provide a similar peddle feel, some have chosen to change their MC to the smaller unit found on the non-servo equipped BJs.

The tradeoff Peddle Pressure for Peddle Travel
To clarify my understanding, for a smaller bore MC to achieve an equivalent level of peddle pressure as the previous Girling servo required while providing the Lockheed with the increase in fluid force it needs in order to develop the proper level of assist and still move the volume of fluid required by the braking system, an increase in peddle travel is needed. Although I would expect the increase in peddle travel would not be excessive for this situation, it is one of the considerations when deciding on whether to use a 5/8” bore MC.

Lee, I believe your plan to change to the new 7/8” MC is what I would do. If nothing else, it will give you a better feel for the tradeoffs when comparing the two MCs for this application and the added confidence in knowing you are using a new unit.

Ray (64BJ8P1)

 

[rcflyer]

Ray, Very well said...now I understand. If I don't like the pedal feel/control... I will order a 5/8's to pu tin and take out the 7/8. Anyone here care to comment on what to expect with the 7/8?? Have a lot of people tried it and gone back to 5/8's???, Thanks, Lee

 

[steveg]

Ray, Very well said...now I understand. If I don't like the pedal feel/control... I will order a 5/8's to pu tin and take out the 7/8. Anyone here care to comment on what to expect with the 7/8?? Have a lot of people tried it and gone back to 5/8's???, Thanks, Lee

Lee,
I've had excellent pedal pressure with my 3/4" master cylinder (no booster), Toyota 4-piston calipers and ceramic pads. I attribute this to the ceramic pads.

IMHO would suggest you try Moss' classic gold ceramic pads before you go to a smaller MC. Be sure to follow the break-in procedure which is easy.