BJ8 with Servo, Is the 7/8 Master Cylinder recommended ??

[rcflyer]

I am still sorting out the BJ8 I bought in August. I have discovered it has a 5/8 MC The car has a Lockheed brake servo installed. What is the opinion of all you guys on putting in the 7/8 MC like was originally on with a car with servo?? I have in my hand a TRW 7/8 ready to install. Right now my brakes work OK, but the travel each time is about 3 inches., Thanks, Lee

 

[Keoke]

I am still sorting out the BJ8 I bought in August. I have discovered it has a 5/8 MC The car has a Lockheed brake servo installed. What is the opinion of all you guys on putting in the 7/8 MC like was originally on with a car with servo?? I have in my hand a TRW 7/8 ready to install. Right now my brakes work OK, but the travel each time is about 3 inches., Thanks, Lee

I have in my hand a TRW 7/8 ready to install. Right now my brakes work OK, but the travel each time is about 3 inches., Thanks, Lee
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Using the "If it ain't broke don't fix it", you might just wait to install the 7/8" unit which was used with the servo.

 

[rcflyer]

It is broke, I don't like a 3" pedal movement. My question is really have lots of people used the 7/8 with the Lockheed servo and been happy??, Thanks, Lee

 

[Keoke]

You might read this listing----BJ8 with servo...Brake travel issue

 

[rcflyer]

Yes, that's a thread I started....I am now just looking for the experience out there to let me know if those that have 7/8 MC are happy with it. I do have a Lockheed replacement servo not Girling original in my car. Thanks, Lee

 

[Lotuswins]

Hi Lee,

I would definately go to the the larger cylinder, and set the car up as it was originally designed. I understand the Lockheed servo is a direct replacement for the Girling, so that shouldn't be an issue. 3 inch travel is way too much, and it won't take much wear in the pads/shoes until the pedal is on the floor. Not good. The change in travel should be about 1/2 what it is now since the cross sectional area is being almost doubled. The additional pressure needed should be minimal since you have the servo in the circuit.

I hope this helps out. On my Lotus I went from a 0.700 bore to a 7/8 and it improved the pedal travel immensely, and that was w/o a servo.

 

[RAC68]

Lee,

Although I do agree that the 3” peddle travel seems excessive, I can not confirm that this is consistent and attributable to your use of a 5/8” bore MC. Since others have made this tradeoff, it would be nice to here what they have experienced when making this change.

Based only upon speculation and a further reading of the Lockheed installation instructions found on-line (https://gentry.zxq.net/Remote_Servo_Installation.pdf), I would consider re-bleeding your braking system with emphasis on verifying that the servo is clear of trapped air within its hydraulics. Also, I suggest you also check that your servo’s installation angles conform to those specified within the instructions. According to the document’s bleed procedures, specific angles are identified for the servo’s installation and, not conforming, could affect the units operation and hamper bleeding all the air out of the unit’s hydraulics.

Additionally, as you will note from the specifications presented in the forward portion of the installation document, if the unit recommended for the Healey is the servo installed in your car, the unit’s internal hydraulic slave bore would be 5/8”. With this slave bore size in mind, I can only speculate that a 5/8” MC bore would move a sufficient amount of fluid and not cause your issue.

Again, although checking these facts and bleeding the unit may solve your problem, I personally would still use the new 7/8” bore MC you have as I still feel that, without the packing spacers, the installed unit’s seals may have been compromised. Either way, follow the procedure outlined in the Lockheed installation document.

Good luck,
Ray (64BJ8P1)

 

[rcflyer]

Jerry, Ray...thanks very much for the good info. I will put in the 7/8, and I will check the servo for correct install. I will also, re-bleed if I find the servo was installed wrong (after I fix that). I have done lots of bleeding and I think I'm good there (?). I received from Moss the 2 spacers for the MC and I will use them of course (PO did not used them). I will bench bleed the MC, install it then re-bleed at least the closest wheel (drivers front) to be sure if any air got into MC I will get it. Also, I will probably just run another pint of Dot 3 and bleed all again. With luck, it will be as good as new (and work like my MGA I rebuild last year). , Thanks...Lee