The Triumph Dolomite Club - Discussion Forum

Posted: **Sat Sep 16, 2023 8:40 pm**

sprint-revival wrote: ↑Sat Sep 16, 2023 6:12 pm Just an update with the locking up rear brakes.

Over the last couple of weeks I have replaced the rear brake hose and fitted a new rear load sensing valve (Hyundai H100 van part), thoroughly bled the system and went for a spin this morning. All was going well, filled up with fuel and got just over 5 miles, until I could feel the car holding back, and started to smell that all to familiar burning smell, pulled up in a layby after about 300 yards. The brake pedal was solid with no travel at all. This time however both front and rear brakes were smoking. Checked master cylinder fluid level which was unchanged. Let the car cool off for 20 minutes and nursed it home.

I am a bit stumped now with this. The system is all but new. Club single line master cylinder, rebuilt brake calipers, new brake lines front to back and back axle, new load sensing valve, brake hoses all round, and wheel cylinders. The only parts not replaced are the engine bay brake hard lines (as were in good condition) and the brake servo. I am slightly suspect of the servo as a whistling noise can be heard in this area that goes away when pedal pressed. Is it possible that the servo could lock the brakes up intermittently.

Any advice welcome.

Thanks,

Olie

I've never experienced this symptom on a Sprint, but on half a dozen or so other makes, mostly Peugeot, including my own Pug Expert van, it's turned out to be the servo to blame. Some servos have an adjustable length pin that goes in the back of the master and adjusting it (shorter) can alleviate the problem. If the rod is fixed length, there's nowt to do but swap out the servo.

Steve

Posted: **Sun Sep 17, 2023 9:25 am**

If the internal piston in the servo has broken, it can sometimes be held together by the rubber diaphragm which wraps around it, but due to the fractures the whole assembly can distort and therefore being a fairly tight fit inside the plenum no longer freely floats with the variance in depression; the spring is also quite weak. This might mean that the piston can stick in the brakes on position, possibly? giving rise to the symptoms you're finding. It might be worth gently tapping the servo plenum case to see if that allows the piston to return...

A cheap diagnosis would be to temporarily fit a known good servo from a smaller engined model to see if that removes the symptom before committing to the cost of a Sprint servo.

Club spares do have two reconditioned Sprint units in stock at the moment, but if your piston is broken it won't be a cheap fix for you as the exchange surcharge would be forfeit.

Have you checked the operation of the one way valve? Though I don't think this would give you your symptoms...

The Triumph Dolomite Club - Discussion Forum

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