Advice Please: 308 master cylinder/booster problem..

Glad the air is gone. There may well be an issue related to the different sizes of the MC. Somewhere I recall reading that different IDs of the MC effects travel and pressures.

 

Hi Greg
There is one adjustment that is not shown. Between the MC piston and the pin there is also clearance adjustment. They don't provide a spec for that unfortunately. (Ferrari expect you to replace the booster and MC as a preassembled unit.) When I checked that gap on my setup, there was almost .25" gap. This translates to a lot of pedal travel with not enough MC piston travel for effective pressure. I measured the protusion of the pin from the booster housing and the distance from mounting face of MC to piston end. I then adjusted the pin to have a slight air gap instead of .25". I don't think the actual setting is critical, just that it not be a large gap and that it not pre-load the piston. (This is my opinion, it might not be the right thing!) Of course the other travel and gap (as shown in H10) should be set first to avoid preloading the booster as well.

One other thing to measure since you will have access to both MC's. Measure from mounting face of MC to piston face (where the rod pushes against piston end). This should be the same on both, if not then it explains a lot of your current situation (after all the air pocket issues).

Gerrit

 

If you are compressing a column of fluid the pressure achieved should be a function of the diameter of the bore of the fluid container as well as the compression distance. With a larger diameter bore the travel or stroke required to achieve the same pressure would be increased. Therefore, consider that you are using a MC with a larger diameter bore. This would require a longer piston stroke to achieve the same force exerted on the fliud i.e a longer brake travel.

 

Hi Greg
On my (modified) booster the rod is threaded. So it is adjustable. And my guess is that the rod end should be very close to touching the piston end.
While you are correct that nothing should need to be adjusted with the replacement MC, something is obviously not correct with the replacement fit. Thus the need to verify those measurements. Making the measurement is a bit challenging, you need to make a sketch of the relationship of the bits, then devise how to measure the gap wioth the MC separated from the booster. Not a huge challenge, just a small puzzle for a Saturday afternoon.
I can't speak for the other topic of more travel due to increased piston size. But I have read that elsewhere on Fchat.

Gerrit

 

While a larger diameter bore would move more fluid at equal pressure, it would take more force i.e. piston travel to achieve the increased force (pressure equal to the that created by the smaller bore MC) since it is acting on a larger surface area. As a retired psychiatrist, perhaps you need to ask the brakes why they are being resistant to change and to the resolution of their " issues."

 

First, you have the patience of Job. If demonic possession has been ruled out, what if you removed the line from the caliper ( 1 at a time)- better yet both the flex line and caliper -and tightly capped the hard line to that caliper . Press on brake and see what the pedal does. Do this 1 at a time. It might isolate/or rule out the calipers and flex lines as an issue.

 

It is always the simple things alright. I didnt know about the Wilwood calipers having 2 bleed screws mate. HOW could you have not seen them after all the time spent around the calipers bleeding them? Glad to hear you finally had a win. Get out there and drive the wheels off it now Greg.

 

I did mention it.

.

 

Oh well. Its done now. Have you driven it yet? How do the brakes pull up now??

 

It's never painless gaining "experience"

And what about the change? Does the 25mm diameter MC make a noticeable difference in the pedal stroke needed to engage?

 

speaking plainly here :

if you don't know that your four pot calipers have bleed nipples on both
sides , you really don't know enough about working on brakes to be
doing it yourself.

its dangerous.

no offense , but brakes are no. 1 on my list of stuff that must work.

 

sorry , greg , pls don't take in the wrong way.

when I started out messing DIY , I installed my brake pads the
wrong way round , ie , metal towards disc. Then I wondered
what the hell was the noise ....

my mechanic laughed so hard that he almost fell into the drain in
front of his shop.

just be careful with brakes.

cheers.
.

 

Greg,

Congratulations in solving the mistery.

I have been working on cars for over 30 years, and didn't even thing about the possibility of 2 bleed screws on the caliper. Don't feel bad about an honest mistake, it happens to the best of us.

The most important thing is that you knew to work on the problem until solved, no matter how long it took.

Once again, congratulations.

Milton

 

Sorry I just didn't think to ask earlier when we were talking.

Chalk it up to 'Experience' which is what you get when things don't go the way you think they should have... We've all been there, & will always remember the lessons learned that way. Once spent over a year off & on chasing a problem with an Rx7 TurboII ECU when I pioneered dropping a TII engine into a 1st gen GXL. Long story & I fixed it by installing an extra ground bolt for the ECU just to shut up a buddy who insisted it needed it even tho we'd just ohmed out 18 ground wires in the ECU harness! I'd designed computer power systems, where you learn early to never trust chassis ground. Again, a case of wrong assumption.
;*)

I'm just used to 4-piston calipers having 2 bleed screws. Some of them even have upper & lower bleed screws on each side & since you'd been running the calipers for almost a year, assumed you knew the all the tricks of bleeding them.

Interesting that you didn't run into this when you first installed the Wildwoods tho. But then I've never run into a MC with a trapped air bubble problem either.

 

Greg,

I got your message. Sorry I did not get back to you. Soccer games, football, dinner guests....I just sat down.

But I see you got it yourself.