Brake Booster Swap Question

[Ohmess]

So, to make space for my carbs, I have swapped in a tii brake booster. It appears not to be working, however. I swapped in a new check valve (for the new valve I had in there), and this did not improve the brake functioning. Hose and clamps are also new. Carbs do not act like I have a vacuum leak.

The booster was used, so that may be the problem, but before I remove the booster and send it off for repairs I have a question. I had difficulty setting the length of the piston rod from the pedal to the booster (I set it outside the car and had to disassemble it to install it). If I got this wrong, could this be my problem?

 

[m5bb]

Probably not.

Even if the adjustment of the rod was off a you would still have boosted
brake even if the pedal was close to the floor.
Really that adjustment has more to do with how the pedal line ups with the clutch pedal.

Boosters can be rebuilt.
I had one done a few years ago.
Can't recall the name right now.

Gary

 

[Sven]

The Tii booster, even if working correctly, will require more applied pressure to the brake pedal than with the stock CS booster. It is definitely a noticeable difference.

You should be able to feel if it is working. With the engine off the brake pedal should be depress only a little bit and then feel firm. With the engine running the pedal should depress further and feel a bit softer before firming up further down the stroke. Do you notice a change in the pedal feel between engine off and running?

White Post rebuilds them.

 

[sfdon]

Pump pedal 10 times engine off
Foot on pedal pushing very firmly engine off pedal should not move
Keep pressure on and start engine
Pedal should go down

Run car 2 minutes
Disconnect booster hose from check valve
Listen for whoosh

 

[Peter Coomaraswamy]

Thread hijack

Is there a separate way to bleed the brake master. I was getting very little grip on the brakes so I bled the 4 corners again, minor improvement only. I did rebuild the master- pretty sure I got that part right though? Any help is appreciated!

 

[sfdon]

If you use a pressure bleeder the master will self bleed by pumping the brakes

 

[Peter Coomaraswamy]

Just got my Phd.

(that would be a post-hole-digger) it seems I have the check valve from the manifold in backwards.

 

[Lotuss7]

Maybe a silly question but I am assuming the booster swap was to allow room for sidedrafts. We're are you now getting your vacuum takeoff? Perhaps there is no boost because of insufficient or no vacuum?

 

[Peter Coomaraswamy]

Hi Lotus, no- this is on the Polaris coupe which is remaining 100% stock less the springs and shocks/struts. I have the original Zeniths on there and the check valve from the forward manifold to the booster is on there backwards so not allowing vacuum to pull the booster diaphragm, at least that's the theory-

 

[Ohmess]

Maybe a silly question but I am assuming the booster swap was to allow room for sidedrafts. We're are you now getting your vacuum takeoff? Perhaps there is no boost because of insufficient or no vacuum?

Good question -- I did some of the carb prep stuff separately in advance, including the programmable distributor, electric fuel pump and the booster and tested them with the DGAVs still in the car. I was drawing vacuum from the same port previously used with the stock booster. And yes Peter -- my check valve was installed properly.


Don -- Will do, as soon as I finish cleaning the block; install the rebuilt starter Peter gave me; install the heater core block off and reassemble the cooling system (with the fan shroud); install the intake manifolds, and install the webers. Right now, she looks like this:

 

[Ohmess]

Is there a separate way to bleed the brake master. I was getting very little grip on the brakes so I bled the 4 corners again, minor improvement only. I did rebuild the master- pretty sure I got that part right though? Any help is appreciated!

Hi Peter - I believe the rod connecting the pedal to the brake master must be set properly in order for the master to fully pressurize. Apparently there is an inlet port in the master, and the piston needs to return far enough to open this port. This is illustrated in the third picture down in this thread:

http://bmwe32.masscom.net/maxf_website/booster/booster.htm

Following this reasoning, you may need to shorten the connecting rod to make sure the piston has enough travel to move toward the firewall far enough to open this port.