New Bendix (Bonaldi) brake boosters - whacky pedal feel

[drewrgs]

Hi All,
Looking for a bit of advice on very strange brake pedal feel after fitting a new pair of (Alfaholics) Bendix brake boosters to my RHD GTV 2000.
I bought the car 6 months ago and the original boosters had given up the ghost, so have been driving without any assistance. Pedal felt fine, just needed a bit of extra push, but thought I'd better fix it.
So, fitted two brand new boosters and bled all the air out of the system. Nice hard pedal, doesn't deteriorate overnight and I can now hear the telltale hiss of functioning brake boosters.
So, everything appears to function - but man is it a pig to drive!
Initial pedal travel feels unassisted, then the booster appears to kick in and you get push back through the pedal - very hard to modulate a smooth stop.
Also pretty funky when sitting at the lights with your foot on the pedal. Sometimes the pedal just moves 3/4 of the way to the floor, then hardens up and returns back to the original position.

My only guess is that there's something NQR in one/both of the new boosters and something is sticking as the piston moves down the cylinder.

Anyone had a similar experience?

Drew


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[Colin Byrne]

Sounds like there could be something funky going on with the air valve not allowing the other side of the air valve diaphragm going to atmosphere when it's supposed to.

[LaStregaNera]

Did you bleed the booster cylinders?

[LukeC]

You probably have the "new production" boosters. I suspect they are made in China. The originals were marked Bonaldi, then Benditalia and finally Bosch before being discontinued. Supply of the quality ones dried up a while back from the usual sources from what I understand.

I have fitted these "New production" boosters to a couple of cars. I have noted that they are a little difficult to modulate on light pedal pressures (you can feel the boost coming on and an increase in braking), unlike the original ones which had a very natural feel.

I have not had any issues with pedal height.

The PBR VH44 boosters are very good in action and are easier to bleed that the Bonaldi design, but do not look right.

[LaStregaNera]

I got so sick of the booster on mine needing a rebuild every 12 months that I deleted it - converted to another ATE master with my own bracket design and went dual circuit while I was there (The cylinder diameter for boosted is much larger than unboosted and requires an excessive amount of pedal pressure when the boosters are removed/bypassed).
The Alfaholics dual circuit pedal box hung too far off the rail for my liking, although it does seem popular.

[drewrgs]

Thanks for the responses everyone.
I did bleed both booster cylinders on-car and I'm pretty confident I have the air out as the  pedal is quite firm.
I'll have a closer look at the air valves just to make sure everything is working as it should. Definitely getting vacuum to both boosters and get piston movement with vacuum applied.
The units probably are new manufacture units out of China. Who knows, maybe their production tolerances aren't what they should be.
Might put some miles in the car and see if things settle down (or if I just get used to the feel)

Cheers
Drew


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