The Triumph Dolomite Club - Discussion Forum

I travelled a few hours and the brakes just didn't feel right. Harder than normal and it started to spit and pop on braking at times at lower speed. I found what I thought was a faulty valve and luckily had another 2nd hand one in the boot . Unfortunately it still doesn't seem right and still spits and pops on occasions. I can probably get it home like this and assume it just means hard pedal but not sure about the popping. It runs 45s with fast road cam etc.
Apart from the pedal dropping test, how can I tell if the servo is ok ?. The old valve had nothing in the hole as shown. The spare has a cross that drops down and I can blow on the inlet to make it rise again. Is that normal ?

I had similar symptoms once when the vacuum pipe between servo and manifold had rubbed through on the underside of the bonnet strengthening gusset; insulating tape effected a temporary repair which lasted many months!

As for the one way valve, you should be able to blow from the servo side, but not suck, and suck from the manifold side but not blow and I've found they can show fault in one direction only so do test from both ends...

Original one is definitely faulty. Spare seems ok but brakes are not the same as before and I am still getting the pops etc. Pipe is thick and in good condition but as it's a bit long I will cut down each end just in case. Can any other checks be made on the servo ? Maybe both have developed a fault. Valve and main unit.

Sorry you have already done the pedal drop test, so ignore my reply.

The pop and spit suggests the manifold depression is being interrupted, the question is is it a fault with the servo/valve which is causing it, or did a fault elsewhere which also causes the spits and pops cause the valve to fail?

You could try disconnecting the servo hose and blocking the end to see if the spits and pops disappear, though you'd have an exceptionally heavy brake pedal whilst trying this. If the spits and pops sustain, then you can perhaps rule out a servo fault? The pedal drop test seems to suggest it is doing what it should though.

Internally in the servo, it could be a broken piston, a ripped diaphragm or a holed casing (they can rot out on the back part which faces the bulkhead) which could cause the vacuum to be lost...there's also a concentric foam filter under the rubber boot on the back of the servo which might need replacement, but I can't see how that would cause the problem you're experiencing...

It drove home ok. 2hrs on the motorway but the issues remain. Left it a few hours and started it to put it in the garage and took a look under the bonnet and found fuel pouring out of one carb. I am assuming that may be rated and I may have pressure going back to the carb. Looks like I need to do lots of investigating.