Chimaera Brake Problem

[TVR Andy]

I have a problem with my Chimaera 450 that I need some help with.

Engine not running brake pedal feels firm with a small amount of travel, with engine running pedal goes all soft and brakes hardly work at all. Fluid level all ok. Any ideas? Could a faulty servo do this?

Many thanks

Andy

[Sam_68]

Yes, that's the servo.

The pedal should become softer when the engine is running, because the vaccuum from the engine 'powers' the servo, which 'helps' when you press the brake pedal.

The brakes should work much more effectively with servo assistance though (ie. less pedal effort required to stop), so if you're not getting much braking response, or the pedal is going right to the floor, then you have a problem (not necessarily a problem with the servo itself - though it could be - but possibly a fluid leak or air in the system somewhere).

Obviously, do not drive the car in such a dangerous state. Stop asking questions on internet forums and get it recovered to a brake specialist immediately!

[TVR Andy]

Thanks Sam,

Yes will get her booked in for repair. I was just interested in what the likely fault was to gauge how big the bill might be!

[Sam_68]

OK. Worst case is cost of servo + fitting + bleeding system.

Best case just that the system needs bleeding...though you then need to worry about how the air got in there in the first place. I assume you reguarly check your fluid level and that it hasn't been losing fluid? Have you done any track days recently, where the fluid might have boiled?

[TVR Andy]

Fluid level all OK & have not been on any track days.

[HereBeMonsters]

Servo? Sounds more like master cylinder to me...does it get better if you pump it a bit?

[Sam_68]

Several things could be the cause of the poor braking, but only the servo could result in the pedal going soft with the engine running, but being hard when the engine is switched off.

The master cylinder and the engine aren't connected in any way, shape or form!

For what it's worth, the normal symptom for a dodgy master cylinder is the pedal sinking slowly to the floor under constantly applied pressure.

[GreenV8S]

Sam_68 said:

Several things could be the cause of the poor braking, but only the servo could result in the pedal going soft with the engine running, but being hard when the engine is switched off.

But that's the characteristic of a correctly working servo, not an indication of a problem. If the pedal goes to the floor but only with the engine running, I would look for a hydraulic fault occuring when the pressure exceeds some limit. A problem of this sort at the slave would inevitably cause fluid loss, so the fact there is no loss would point to a possible m/c problem. But I think it's likely to be a problem in the m/c exposed by the normal behaviour of the servo, and not a fault in the servo.

[Sam_68]

GreenV8S said:

Sam_68 said:

Several things could be the cause of the poor braking, but only the servo could result in the pedal going soft with the engine running, but being hard when the engine is switched off.

But that's the characteristic of a correctly working servo, not an indication of a problem.

Agreed... which is what I tried to explain (probably not very well) with my first post.