Braking issues with triumph gt6

[arh]

Hi All

Help me out here, the brakes when bled work perfectly for about 10 minuets of driving. Then the pedal will travel further with each press, if you bleed them again all is restored for another 5 mins or so. The rear cylinders are new, the calipers reconed and all new pipes fitted. There is very little movement in fluid level.

Do you think it will be the master cylinder or servo?

It did pass an MOT though so most of the system is working, there are no (noticable) leaks

Thanks

Adrioan.

[GreenV8S]

Could be there is insufficient free play at the top of its travel, so the port from the master clinder to the reservoir isn't opening. If this is the case you may also find the brakes jam on when they get hot.

[arh]

No when bled the travel on the pedal is perfect, air is getting in somewhere. I have ordered a new master cylinder and will fit this as I don't feel safe with the old one anymore. I may bypass the servo to see if it makes a difference.

[Hasbeen]

How much fluid do you have to bleed to get them up? A little, the air is getting at the wheel end. A lot , its getting in at the master. Do you have to bleed both ends? That should give some idea, of where to look, & perhaps save some money. Some rebuilt, & even new gear, is not right.

[arh]

Thanks

each time I bleed it I have to change what appears to be all the fluid hence the master cylinder. I am still wondering how when it is bled the pedal feels perfect, but only for about 5 Miles. I am guessing that a servo being a vacuum operated device would suck fluid out rather than letting air in, is this right?

Also I am being told by people that one of the couplings could be lose letting air in but still tight enougth to not let fluid out, I can't really see this.

[Incorrigible]

arh said:

Also I am being told by people that one of the couplings could be lose letting air in but still tight enougth to not let fluid out, I can't really see this.

I'm only guessing here, but they might mean that you are generating a vacuum in the reservois whcih is sucking air in where the reservoir joins the cylinder

I can't see it myself either but you could try fitting the reservoir cap very loosely (or ensure it has a small hole in the top) this would at least eliminate this as a possibility

I'm inclined to agree with GreenV8s

[Incorrigible]

IIRC the servo is remote on a GT6 but there are also IIRC some combined units that work very well (I can't remember if they're upgrades)

What have you got

Also what happens if you pump the brakes ?? I assume you get a very spongey pedal

I also assume there's plenty of air coming out when you re-bleed the brakes

[zumbruk]

I've known this happen when the diaphragm in the servo has perished and the manifold vacuum sucks fluid into the engine where it gets burned. Did you say there was a vacuum in the reservoir?

[ARH]

Thanks again

the servo is remote, And there is a blocked up hole in the resovior lid it has a sticky lable over it, I did not consider that to be a problem. but it could well be. Each time it is bled air comes out so it is getting in somehow. The servo does not let fluid into the engine as there is no sign of white smoke from the exhaust.


If it wasn't raining I would be out bleeding them now. but it looks like i have to wait till saturday before I sort it out.

Adrian.

[yertis]

I had this problem with my GT6 and yes it was the servo. At that time they were NLA so I just bypassed it and to be honest it made hardly any difference, just a heftier shove to stop it.

[arh]

Incorrigible said:

arh said: Also I am being told by people that one of the couplings could be lose letting air in but still tight enougth to not let fluid out, I can't really see this. I'm only guessing here, but they might mean that you are generating a vacuum in the reservois whcih is sucking air in where the reservoir joins the cylinder I can't see it myself either but you could try fitting the reservoir cap very loosely (or ensure it has a small hole in the top) this would at least eliminate this as a possibility I'm inclined to agree with GreenV8s

I think this is going to be the answer, I have had a look and what I thought was a sticker is in fact a blanking grommet. It would appear someone has drilled a hole in the centre of the cap and filled the hole with a blanking grommet, this will stop the resovoir breathing and allow air past the seals in the master cylinder. Thanks I would never have realised that if you hadn't suggested it. I will still replace the master cylinder as a new one is on it's way, and I have lost confidence in the old one.


Adrian.

[IOLAIRE]

arh said:

Hi All Help me out here, the brakes when bled work perfectly for about 10 minuets of driving. Then the pedal will travel further with each press, if you bleed them again all is restored for another 5 mins or so. The rear cylinders are new, the calipers reconed and all new pipes fitted. There is very little movement in fluid level. Do you think it will be the master cylinder or servo? It did pass an MOT though so most of the system is working, there are no (noticable) leaks Thanks Adrioan.

Hi ARH,
the pressure lock up or non return valve is worn or sticking in your master cylinder.
Don't mess about with it; renew the whole cylinder.
When it sticks it allows the pressure in the primary part of the cylinder to escape and the pedal will slowly creep to the floor.
Don't wait 'til it suddenly shoots to the floor!!

[Nick_F]

My Vitesse never had a servo - unecessary complication, chuck it out!

[ARH]

well it turned out to be a lack of breather hole in the master cylinder lid. put a hole in it bled it and all is fine again. It has also taken me a while to track down a sticky needle valve in one of the carbs, it would stick shut when it got warm. Sorted that now and put about 40 miles on it this afternoon. Great fun and what a noise.

Thanks again for all your help.

[Incorrigible]

ARH said:

Thanks again for all your help.

Where do I send the bill

Glad you got it sorted keep us updated, and get some piccies up on your profile

[ARH]

Thanks and send the bill to me I do owe you one though, I have put a picture up on my profile, it was taken a few weeks ago, the wheels are painted now so look a little better.

Once you get settled with your new business I will drive it over, you can see it properly then.

[Incorrigible]

Cool, it will be good to see it in the flesh.

Did you fit the new master clylinder or just re-use the old one

[ARH]

new master cylinder is still in the post, so i used the old one, i will change it at the weekend, as the delivery was attempted today but her indoors went out so missed the guy.

It's all the other issues that now have to be sorted, paint, interier, bumpers, then I might fuel inject it.