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Triumph TR6 - Servo causing idle change?

After rebuilding the MC and bleeding my lines (at least twice) my brakes still take a lot of effort to stop. The MC fluid level hasn't changed, so at least I fixed the leak. When I hit the brakes the idle drops down considerably. I replaced the cracked vacuum hose coming out of the servo and I don't think it is collapsing, but perhaps it is. I plan on sending off the servo for a rebuild this spring.

Could someone offer some insight into why it would start to stall and how do you know if the servo is bad, short of opening it up and checking for fluid. I don't think I will be addressing this until spring but it's one of the many questions bothering me.

Thanks,
Mark 72
Mark Wright

Mark,

Pull the vacuum line off the servo and plug the line. If the idle problem goes away, it was the servo.

This sounds like a split diaphram in the servo. I had this happen to me once when I was on a trip. Plugging the hose cured it, and I didn't really notice the loss of brake boost from the servo. In fact, I drove it like that for about 2 years before springing for the money to buy a replacement servo (they are rather expensive, and not really needed).

With a split diaphram, the booster lets air into the engine intake when the brakes are applied, which seriously throws off the air/fuel ratio, causing the idle change.
Dan Masters

I got a replacement from Partco for $85 or so with exchange.

http://www.partcoautomotive.com/

The amount of brake fluid that came out of the old unit was impressive!
Brent B

Brent,
Have you been well satisfied with your rebuilt unit? I have to replace mine and have been talking with Kai Radicke of Wishbone who offers a Brake Servo rebuild for $140/Powder coated for $180. If the $85 rebuild works well, that'd be some savings.
db
Doug Baker

I am satisfied, but as Dan suggested there was not a big difference in pedal effort before & after the new unit. In your case it should stop the tendency to stall when the brakes are applied, though.

The rebuild comes painted black, and it's best to use the box it comes in to ship back the core.

BB
Brent B

Would the bad servo explain why I have to put a lot of pressure on the brakes to stop? At this time I wouldn't want to tailgate anyone or have to stop quickly.

Thanks for the suggestions as I do plan on using Partco in the spring.

Mark
Mark Wright

Brent,

I see that you are clairvoyant as I was typing my question as you were answering it. If I wouldn't see a noticable change in the brake pressure with a new servo, then could you point me in another direction to solve this problem.

Mark
Mark Wright

Hey, Mark. Perhaps the best explaination is that my servo was not as "bad" as yours, so I didn't notice a drastic before & after case. I replaced it because it was 30 years old & full of fluid. I haven't tried disconnecting it to see how much assist it actually gives - and won't be able to for a while as wet as it is here.

Another thing to check if you haven't already is for brake fluid on the pads/shoes. A bad wheel cylinder leak can really diminish the effectiveness of the rear brakes, which means you'd have to stand on the pedal hard.

BB
Brent B

Mark,
If you're having a hard time stopping it could be air in the brake fluid, it could be worn out pads or shoes,
you might be able to solve it by ajusting the rear brake shoe speader. It might be old and spongy brake hoses(the rubber hose)swelling when you push on the pedal. I replaced my brand new rubber hoses with braided steel hoses and felt a big difference, much firmer. Start with bleeding and maybe even a flush if it has been awhile since the last time and adjusting the rear shoes. If that doesn't do it then you are looking at shoes and or pad replacement and then hoses as the last weak link.
Chris
Christopher Trace

I am guilty of never doing a thorough inspection, as I rebuilt the MC, added new fuild (DOT 4), bled it, new wheel cylinders, but there's a lot of other things I should have looked at. This is definitely my first priority come Spring. I appreciate the input!
Mark Wright

This thread was discussed between 06/01/2005 and 09/01/2005

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