Peugeot 406 1.9TD 1996 Brake Servo

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Thu 7 Jun 2007 17:17
Peugeot 406 1.9TD 1996 Brake Servo - Canuck
Hi all, first all some thanks
The first time I consulted this board on this car was in a panic in 2003. I received some excellent advice back then on how to fix a battered pulley keyway on the crankshaft caused by failing crankshaft pulley. I had visions of scrapping the engine at 87,000 miles when I posted. I was given some advice that the keyway could be repaired by rebuilding it with metal epoxy and Loctiting a new pulley on. I glad to report that this advice was excellent and (knock on wood) we have now done 40,000 miles on that repair with no trouble.

Anyhow- to today's challenge, I want to change the brake servo as the brake pedal sinks slowly to the floor with the engine running and I have heard in a few places this is a likely cause (I've redone all of the brakes and checked most other things). I'll do a few more checks this weekend (it's off the road 'til I'm sure it is OK) but I'd love to hear from someone that has changed a brake servo on a 406 diesel. The Haynes manual gives it its most difficult rating due to lack of access, but I'd love to get some first hand experience.
Thanks

Canuck
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Thu 7 Jun 2007 17:49
Pug 406 1.9TD 1996 Brake Servo - Number_Cruncher
Why do you think it's the servo? If it's a direct acting suspended vacuum servo (which I'm fairly sure it is), then apart from a small rubber disc, the pedal is connected straight through to the master cylinder - it can't fail and give those symptoms.

It sounds more like a leak in the hydraulic part of the system, possibly even within the master cylinder itself. Are you losing fluid?

Number_Cruncher


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Thu 7 Jun 2007 17:51
Pug 406 1.9TD 1996 Brake Servo - RichardW
Hmm, pedal sinking to the flooe doesn't shout servo to me. That's shouting master cylinder, or failed rear wheel cylinder.

Either way for the MC or servo you may well need to remove the engine mount and push the engine forward to get a bit more room. Some of the awkward turbo pipes might need to come off too? Check it doesn't say in the instructions in Haynes somewhere "Remove engine as per chapter 1" or "Remove facia as per Chapter 13" before you get in too deep....
--
RichardW

Is it illogical? It must be Citroen....
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Thu 7 Jun 2007 18:07
Pug 406 1.9TD 1996 Brake Servo - Canuck
I have replaced both rear wheel cylinders and replaced the front pads so I've looked at everything, but I will go and check again. The thing that leads me to suspect the servo is that the pedal is as hard as a rock with the engine off. I had also found a post when I was worried about this in the past that suggested it was the servo.

"Peugeot 406 Sinking Brake Pedal - Tony.H
Hi, I've had the same fault on my 406 peugeot.
I put in another master cylinder because it felt like a master cylinder fault. (I only paid £10 for it from a salvage yard). It was cured by putting on a new servo. Lots available from salvage yard.
The master cylinder is simple to replace, just make sure you have the proper brake pipe spanner. The servo is more difficult to fit cos you need to remove the master cylinder first.
good luck Tony.H
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Thu 7 Jun 2007 21:14
Pug 406 1.9TD 1996 Brake Servo - scotmech
I would say definitely master cylinder ... if you are not loosing fluid ... the fluid bypasses the worn seals or damaged bore and returns to the reservoir ...
The servo gives only two faults it either looses vacuum, when the pedal is held down you will hear a hissing sound or the pedal goes hard with no assistance ...
The test for the servo is ... switch off the engine then pump the pedal a few times till it exhausts all the vacuum ... then press the pedal then start the engine the pedal should drop app. 1" if it does the servo is working ok ?
Would agree with NC the pedal is connected directly with the master cylinder ... and the servo cannot cause the brake pedal to have excess travel ...
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Fri 8 Jun 2007 12:19
Pug 406 1.9TD 1996 Brake Servo - Canuck
OK, I accept the advice and will change the master cylinder. I'll let everyone know what transpires. Thanks!
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Thu 5 Dec 2013 17:05
Pug 406 1.9TD 1996 Brake Servo - jono75

Hi scotmech5

i have a similar problem but on a 2.0 hdi 2000.. but my brake pedal is hard with the engine off as soon as the engine is on the pedal sinks slowly to the ground,

iv changed the master cylinder, front brake calipers cheeked the vac pump bled all the brakes the only thing is the servo witch im hopping its not...could it be the master cylinder letting by from were it bolts onto the servo (the 'O'ring) or something else?

thanks jono

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Thu 5 Dec 2013 22:44
Pug 406 1.9TD 1996 Brake Servo - Peter.N.

I would agree with the majority and say master cylinder. If it is not leaking fluid externally the only way the pedal can go down is by fluid leaking internally past the seal. When the servo is operational the pressure on the cylinder is much higher.

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Fri 6 Dec 2013 13:37
Pug 406 1.9TD 1996 Brake Servo - Gibbo_Wirral
It could be the rubber seal in the servo, or the check valve. What you describe is exactly the same as on my 1998 306 diesel.

Edited by Gibbo_Wirral on 06/12/2013 at 13:37

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