Be careful when changing to silicone hoses

[njhucker]

Hi all,
Yesterday I purchased a 400se from someone in Kingston upon Thames.
Driving back on the M4 I lost my brake pedal completely, just this side of Slough.( very scary)
When the pick up truck came, the brakes were back to normal. Not wanting to risk anything he brought me back home to south wales.
The seller had just fitted new silicone hoses to everything including the vacuum pipe to the servo.
It looks like to heat soak from the exhaust had made the pipe soft and it collapsed under the vacuum, and then when it cooled down everything was fine again.
So if you change your hoses to silicone, leave the servo hose alone or sleeve it, don't replace it!

Nigel H

[Big Daft Lad]

If I’m being too subtle that’s a picture of a pair of brown trousers….

[adam quantrill]

njhucker said:

I lost my brake pedal completely
Nigel H

Errm - loss of vacuum wouldn't "lose the brake pedal", it would get harder to push but would still do something. Is that what you meant?

[njhucker]

No The Brake went all the way to the floor. If the hose was disconnected then there would be no servo, but the brakes would work, as air would still be free moving air in the chamber. If you press the pedal and then the hose collapses,while it is down, then wouldn't the pistons ( especially the second non connected one) stay in, held by the vaccum, until the vacuum is released. This can be my only explanation because when it cooled a bit, the pedal came back up, as firm as before. At the time I had just come out of a long works section where the air temp under the bonnet would have been fairly high.

[njhucker]

I'll do a test tomorrow. I will get someone to press the pedal with the engine running & clamp off the hose to see if it replicates what I believe.

[ROOODBOY]

I agree with Adam Q., no servo should not equal no brakes, just a stiffer pedal.

I would suspect a master cylinder problem if the pedal is suddenly going to the floor.

Be careful!

[benebob]

I currently have a bad M.C. Need to pump it 3 times to get a good feel. It started pretty much like you describe. Did it once or twice here and there and steadly got worse. Seemed to be worse after a long non brake period. When I got the car it had a leaky connection on the vac line to the servo. You would still have some brakes but you would need to push it nearly to the floor as was stated. Hoping the rebuild kit arrives soon although I did get my wife's X type back together from a 2 week cat. converter replacement (had to send it out to get one made like it since no one including Jag had one available for my year).

[dixiebabes]

This happened to me on the way to the BBWF 3 years ago. No brakes but worked after pumping them and a big trouser moment. I thought it was the brake fluid boiling after i found out the O/S back brake was binding on worked fine when cool. But after i took it to a garage they repaired it letting me know it was the bearings in the diff that had collapsed causing the brakes to catch resulting in new disc's + pads. Sounds uncanilly like your symptoms i would have a look at that. And its not a cheap or easy job by the way!!!


Dix

[leorest]

By the sound of it this is not an issue with the siliconeness of the hose but that the servo hose was replaced with a pipe designed for pressure not vacuum. Under vacuum the pipe gets sucked flat.

[cptsideways]

I'll second all that's said above


DO NOT USE SILCONE HOSES on BRAKE VACUUMS


I had the same issue (heat soak) at the best part of 120mph on track, luckily my car has a decent handbrake so it got lobbed in properly sideways to scrub the speed. Luckily its a drift car so am fairly used to lobbing it in like that all be it a bit more planned usually!!, even still a bit a brown trouser moment.

[rev-erend]

ROOODBOY said:

I agree with Adam Q., no servo should not equal no brakes, just a stiffer pedal.

I would suspect a master cylinder problem if the pedal is suddenly going to the floor.

Be careful!

Agree here too ..

But also agree - not silicon for servo connection, make sure the one way value works and is on the right way round.

Also - brake master cylinder when it fails can be fine then suddently sink to floor.. pump it and its fine again for a while.

As above you might have more than one isue - so be careful.

[AM400]

My monies on boiling fluid due to brakes binding,most probably the rear. If they are only binding a bit a run down the Motorway will soon heat the fluid up.

[TVRleigh_BBWR]

I run a silicone vacuum hose on the racer, and I have Griff headers so there more heat near the hose, without any problems (I did make it as short as possible though), and I think I would notice as its only used on the track.
Silicone has a higher melting point so would think it would be better, all depends on the construction though, mine is only single wall vacuum hose but its quite thick.

[NTEL]

I too run a silicone Vac hose on the race car but it has a wire helix and is quite thick. No issues at all.

[rev-erend]

Whick kind of brings us back to :

brake master cylinder when it fails can be fine then suddently sink to floor.. pump it and its fine again for a while.

[njhucker]

Still having problems with my brakes. I have changed the servo hose and fitted a new master cylinder. Have checked that all the pistons move freely, and completely flushed the system. I was driving to Cardiff today. Down the M4 and then the A4232. All was fine until I got to the tunnels. Put my foot on the brakes, and it went straight to the floor again. Stopped and after 10 mins the pressure came back as normal. Have left the car with Peter at Roath Garage to try to find out what it is. Have booked to take the car to France in a couple of weeks so need to make sure it is sorted and safe. Any more ideas?

[adam quantrill]

Are you losing brake fluid?

If not, I would suspect a master cylinder seal problem.

[njhucker]

Not loosing brake fluid, and just fitted new master cylinder which I got from TVRcarparts. It made no difference.

[rev-erend]

It can only be air in the system.

Now only the brake pipes / unions and slaves cylinders remain.

A careful inspection of all is needed .. looking for brake fluid and general gummyiness.

[adam quantrill]

Or else as mentioned above - binding and boiling? But usually that would result in some overflow out of the reservoir?

Try taking it for a run (5 miles?) and use the brakes as little as possible - slow down on the engine etc. Especially towards the end. Then park up and check the temperature of each disk by hand - you can reach underneath. Any hot ones point to the binding brake.