Strange Sound Like Compressed Air Escaping

[KVH]

I have a new issue to sort out.

In my TR4A, with OD, when I travel at high RPMs and then slow down and apply the brakes I'm at times hearing what seems to be the sound of compressed air escaping. Maybe something is rattling in the driver's side rear drum brake, but I've not yet been able to isolate the issue. I was even wondering if it's the pressure escaping from the overdrive unit, then building back up--but that's fluid pressure, not air (unless my fluid is low, I wouldn't think that could be the problem). Is there any reason to suspect the OD unit?

It's a bit like when you remove the air chuck from a compressed air line. A few times it seemed to be coming from my foot-well, driver's side, but then more from behind me.

This happens when the OD is not engaged. I've not even tried to listen while it's engaged.

Any better ideas?

 

[alanjohnturner]

OD does not make compressed air noises. You will see on a parallel thread that I ran mine on a test-bed so I found out what goes on with these.

Have you got a brake-servo fitted? Not original on UK spec cars but lots have em.

Al.

 

[Andrew Mace]

Is it a one-time sound? steady? rhythmic, with frequency dependent on speed?

 

[Geo Hahn]

Snakes in the Car!

 

[sp53]

I guess it could be stuff rattling in the muffler from theback pressure of letting off or a snake.

 

[TR3driver]

Just a thought: Could you make a recording of it for us to hear?

 

[KVH]

Andrew, it's a one-time pop and I hear it when I just start to brake. I'll go for a run tonight and listen closely again.

 

[DNK]

Is there an servo on a 4??

 

[Andrew Mace]

Such noises can be deceiving; any chance it's something like a loose bolt on a lever shock mount or other suspension bit?

 

[Roger]

Is there an servo on a 4??

My thought too - noisy vacuum servo.

 

[CJD]

My thought too - noisy vacuum servo.

X 4

Second thought is a vacuum leak

 

[sp53]

Does it happen every time you touch the brake?

 

[HerronScott]

Normally no brake servo on a TR4A although someone posted pictures here of a TR4A in the UK that had one a couple years ago.

Scott

 

[DNK]

Normally no brake servo on a TR4A although someone posted pictures here of a TR4A in the UK that had one a couple years ago.

Scott

Well, guess that takes that out of the answers

 

[DanB]

Does it always do it? Does pedal pressure make a difference?