Dear All,
I have just installed a new brake servo/booster to my 1961 Mark 2 3.8l: Powertune RLE10117. It’s mechanically very similar to the removed Lockheed servo. I reused the clamp on the valence inner wall holding the servo hydraulic slave cylinder body. Instead of fixing the servo air cylinder body to the cowl mounted inside the wheel arch, I used a bracket between one of the screwed bolts on the air cylinder and one of the top cowl to valence bolts. The obtained servo orientation in the car is similar to the old unit but not fully matching the wishes in the fitting instructions “to assist bleeding”...
I have already bled the system at all 4 brakes using the ‘furthest to closest’ rule. The brake pedal has no resistance.

The new servo instructions suggest bleeding also at the servo hydraulic cylinder output connection. I have not tried this yet.

I’m looking for recommendations how to complete a full bleeding process and also be reasonably certain it’s correct and there are no leaks before remounting the wheels and removing the car from the lift. For example, run the engine to activate the vacuum servo?

I would be grateful,
Dave

 

With these cars.

Bleed at booster as suggested. Longest to shortest is correct.

One question having had this trouble before. Did you pressure bleed the system? Don't!!!!

Use the tried and tested one pumping the pedal and one opening & closing bleed nipples.

Alfa's could be chronic in this regard with twin Lockheed Bonaldi boosters/servos. You would get low pedal with pressure bleeding.

The other issue could be modern rubbers. Ensure that your master cylinder valve is closing & not just pumping fluid back into the reservoir.

Good luck.

 

Bleed the servo unit first as suggested. Otherwise, it will hold air and you can pump forever and not get pressure.
Just ensure you check the brake fluid reservoir regularly as it is a very small capacity compared to modern brake systems.
Another option is to use vacuum draw brake bleeders, but I have never had to use them on a MK2

 

Thanks. I used a Gunson Eezibleed with a tyre at about 12psi to pressurize but avoid over-stress. I did the same a couple of years ago and it worked a treat.
Is there a technical reason to prefer pedal-bleeding?

I believe the rubber seals and master cylinder are ok since the brakes were working before I replaced the servo. I had the problem that the brakes were blocked for some minutes after a drive, hence I decided to replace.

Are there any opinions on running the motor to activate the vacuum servo?

Bye for now

 

Not necessary to run the engine but you can try ~ maybe putting vacuum on your choice of booster/servo will help. DON'T pressure or suction bleed. It causes issues on many cars. Especially older cars. Pressure bleeding seems more inclined to cause the issue.

And check that the master cylinder is not pushing fluid back into the reservoir. Never mind what it was doing. Many modern rubbers are slightly undersized and don't close the input port requiring slight trimming of the piston. Many used rubbers after disturbing the system do not close the input port. I wrote a thread on it or in a thread here on the subject.

The technical reason for pedal-bleeding is that it works every time (call it experience ~ a well respected brake shop had my car for a week & still had a low pedal. I fixed it for them in 5 minutes with conventional bleeding). There are warnings in many car manuals not to pressure or suction bleed e.g. Alfa. You don't get all the air out of the system. A pocket gets trapped and you can pressure bleed to your hearts content & not remove it. Caliper over return can be another issue if you changed pads at the same time. I wrote a thread here on that too. Did you change your pads?

Worst case you got a bad booster.

 

I've pressure bled my system and it worked very well, but that is with the old style booster _ maybe that's the difference, I don't know ?
I can't remember if I bench bled the servo first.

However fluid is now filling the main vacuum booster in the drum, but I don't think that is because I used the Gunson E-Z Bleed, I think that it's seal incompatibility at the end of the slave cylinder in the booster, or something else has gone wrong there with the DOT 5 brake fluid.
I used my air compressor with a disposable moisture trap set at less then 10 Lbs.

I ordered a bunch of new seals, and have had them soaking in DOT 5 for months, and they are fine, just haven't got to it yet.

 

I like to see how far I can get with gravity before going to slow pedal pumping. Obviously that might be optimistic after a servo swap. Like Glyn, I prefer to treat the rubber seals, old or new, as gently as possible until they're full baptised in brake fluid.

 

Yes Peter. Some people think that because they got away with a certain practice that all will. Unfortunately life is not like that! e.g. elastomer compatibility.

 

Would the servo unit be similiar to that on my 1959 Mark 1 ? I have a similiar issue of no pressure at the pedal whatsoever and have assumed it is the MC that is faulty . Also, from the looks of things I believe that all four disc brakes were rebuilt. But I don't know if the servo was taken off or not. I don't kown the history of the car's recent "overhaul" as it was ongoing when the previous owner passed away . I bought it from the widow.
So how do I bleed the servo ? ( and WHERE is it located ? ) Thanks guys .
Schmitty

 

Bleed Servo here at this junction on RHS inner fender.

 

I too have found brake bleeding on my Mark 2 to be frustrating. I normally use a pressure bleeder on my other cars and it is a good reliable method for them but on my Jag, not good enough. I would really like to understand why.
My system is standard except for Wilwood calipers on the front and stainless flex hoses.
In the end I rely on my wife to drive the pedal while I operate the bleed valve. I use a long plastic tube, end held high, so that I can see the bubbles as the fluid emerges from the bleed screw.
When it's all done I do have a hard pedal and can lock the wheels on a dry road.
I tried but rejected the use of a vacuum bleeder ages ago because the bubbles never ceased for me - air must have been getting in via the bleed screw threads I surmised.
When all else fails FOLLOW THE SHOP MANUAL INSTRUCTIONS.
I do wonder how they did the bleeding on the production line - I can't believe they did it with pedal, bleed screw, plastic tube and a jar - it would simply take too much time I think.

 

Thanks, Glyn ! I had been wondering just what that little junction was .

 

"I can't believe they did it with pedal, bleed screw, plastic tube and a jar - it would simply take too much time I think."

That's exactly what they did. We have an old B&W movie in our club showing them doing it.

 

Schmitty the only problem is there is no bleed nipple there, You do it by loosening pipes. So protect your paintwork with plastic & give it a good flush with water when finished, Brake fluid is Hygroscopic so a flush with water will do the trick. Don't use any exotic fluids DOT 4+ maximum. Servo rubbers etc are seldom compatible with the silicones etc.

 

Glyn, just took a closer look at my unit and strangley it has a good size housing holding an electrical connection ( two wires) attached vertically to this unit. Any idea on what that might be ?

 

Must be the brakelights activation switch . ?

 

Brake light switch.

 

Success! After (low) pressure bleeding at the servo output (using rags to absorb the dripping brake fluid) and repeated pedal bleeding at all brakes, the brake pedal finally showed good resistance. Just to be sure, I will repeat the pedal bleeding tomorrow...

What is the reason for wetting the servo wire air filter with brake fluid rather than simple oil? I’m always concerned with potential damage to paintwork.

I got quite a shock seeing that the outer end of the Panhard rod is missing the nut, outer washer and rubber bush. They must have recently fallen off during driving. The previous owner replaced the leaf springs and may have not tightened fully up. I will start a new thread about the exact configuration of the Panhard rod parts.

Thanks again!

 

Glad to hear you resolved the servo / brake issue !!! gives me some hope ...did you bleed all output lines at the servo or just the one ?

 

Simple light oil will work just as well without potential paint damage. (Singer Sewing Machine Oil) ~ I would not put brake fluid anywhere near that filter.


Panhard Rod. (ensure no mounting point damage ~ they are famous for that, Many bulletins on reinforcement required. Used to just pull out of the body). Early Panhard rods were not adjustable.










Delighted the lack of pressure bleeding worked for you. ~ not surprised at all.