Weak Braking After New Servo Installation
 

I recently installed a new Lockheed type brake servo in my 1965 1800S. The stock servo had failed. I bled the brakes on the weekend and tried it out last night in the driveway.

The brake pedal feels solid, doesn't have a lot of travel, but there is very little braking pressure being applied. At say 5mph the braking distance was about 10-15 feet. Kind of a gentle, pulling up motion rather than anything resembling a brake being applied. I did notice a few times that with my foot hard on the pedal it would kind of rest, then had a tiny bit more give after that.

I'd read that fully depressing the brake pedal can damage the master cylinder by causing it to travel further than it should. And there were a number of times I had the pedal to the floor before I installed the new servo.

So something's not right. Any ideas, could this be damaged cylinder related?

Hi Ya Neil

im very sure the cylinder should be fine i would make sure there is no air in the system with a good bleed nice fresh brake fluid being added should help lots , then if that still does not help cure your problem check for any bad hose`s that may have gone internally if after those two checks you still have not a good pedal then replace the master cylinder .
naturally if any parts you feel are of an age or chance of wear then play it safe and fit new in them areas where required brakes is a must ! Have in times of emergency so never worth the risk ;)

hope you have luck and keep us posted
kind regards
robert

Have you got a non return valve in the vacuum pipe?
if so, is it the right way round? thus creating no vacuum

I wonder if you have successfully bled every last bit of air out of the system. I had this recently on my old estate and it wasn't until I took the advice of others and raised the back of the car really, REALLY high and bled lots of fluid through that I noticed the difference

Might be worth a little try

All the best,
Adam

Hi,
The non-return valve could be the issue, I actually didn't install it. Must have read the instructions wrong - or interpreted them wrong anyway, eesh. So it should be in the hose per the attached image I guess. I think one of these shipped with the unit - I'll have a look later. Thanks for that - hoping that does the trick. Not loving the thought of bleeding the system again!

if its not installed then there would be no issue with it as its not in the line so result cannot be at fault due to missing in action as in fitted wrong way round so i would count that out from fault ;) here

summary ----- > NO firetrap fitted in system = SO no Fault with the fire trap
the firetrap is nothing more than a non return valve ;)

kind regards
robert

I went through a brake servo learning curve recently. See this thread:

http://www.volvoforums.org.uk/showthread.php?t=200859

My understanding is that the one way valve that connects the brake servo to the manifold is required. Happy to be proven wrong.

Adam's point re bleeding is well made.

Ed

lots of handy info on that thread ;) explaining stuff

kind regards
robert

Well it's only June 3rd, but I think I might have scooped idiot of the month award. Looking at the directions again, I have the inlet and outlet brake lines reversed from where they should attach to servo unit.
I'd been looking at photos of other folks' instalations and somehow got the wrong idea on how to it hook up.
Regarding the non-return valve though, doesn't like one shipped with booster.
I guess need to pick one of those up too.
Thanks for the replies!

As you can see from the picture there is usually a non return valve as part of the hose to servo connection. I don't know if they work any better by having an extra one fitted. I'd think not if the servo mounted one is working properly. A bit of suck and blow using the hose should prove that. In other words, check that your problem is solved by swapping the lines before buying an in line valve. Lockheed (Adelphi) say in the instructions that the outlet "nose" should point upwards a bit (20º?). This is to help get the bubbles out when bleeding. Many servos get fitted without the tilt and still work OK.
Frankly, the Lockheed type servo install in "our" Volvos is impossible to do neatly as everything is the opposite way round to the original Girling fitment.
If your install (photos?) uses a hose directly from the manifold it will give the best vacuum, but if T'd into the hose that goes from the side ear to the manifold it will need the PCV valve fitted just above the ear. It's a bit of a minefield what combination of valves and open or restricted fittings at the manifold are needed to give good vacuum to the servo without causing what the carbs see as a big air leak.