The Triumph Dolomite Club - Discussion Forum

My late 1850HL auto has always been fond of it's workshop time, needing plenty of regular TLC over the years. More recently it's been running roughly and down on compression and power. To deal with that, the head has been off for extensive valve seat work and to deal with a 5 thou warp.

It's back together and sounds fine, but it idles badly when cold, frequently cutting out. When it's idling, applying the brakes makes it cut out instantly - like flicking a switch. Can anyone please offer any advice/suggestions? Thank you

Simple, the brake servo is shot!

Steve

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'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.

Vacuum leak? Why does pressing the brake pedal open up the leak more?

Try blocking the vacumn line to the servo off first, isolate it before you condemn it.

I assume you mean block the vacuum line to the inlet manifold and see if that stops the rough idle. If he blocks the feed to the servo and leaves the feed to the manifold open, it may not idle well at all.

There's also that old trick (with the vacuum pipe connected) of pressing on the pedal with the engine not running, then starting the engine to see if the pedal falls as the vacuum gets to the servo. If the pedal don't move, it's a good indicator that the servo ain't working.

Graham

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The 16v Slant 4 engine is more fun than the 3.5 V8, because you mostly drive it on the upslope of the torque curve.

Factory 1977 TR7 Sprint FHC VVC 697S (Now all of, but still needs putting together)
B&Y 73 Dolomite Sprint UVB 274M (kids!)
1970 Maroon 13/60 Herald Convertable (wife's fun car).

You can check the diagnosis by clamping the servo hose off with a brake hose clamp (or a mole grip and a bit of cardboard) and see if that fixes the running fault. But i'm pretty certain i'm right!

You've almost certainly broken the bakelite ring in the back of the servo and vacuum is leaking from the car cabin, letting more air into the manifold and ruining the mixture. Pressing the pedal just makes it worse.

Even leaking like a sieve, the servo will supply a modicum of assistance, all the ones i've had fail have been the same.

Steve

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.