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TR6 Tech Forum

Both Front Brakes Locked

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TR5-2085 Jim Fitzpatrick
Allen, Texas, USA   USA
Hi.

I'm working on a barn find and I've got to the point where I'm driving around the neighborhood. But I've found that my brakes start binding and, not surprisingly, the engine starts laboring. Today I just drove 1/4 mile and when I pulled into the workshop the both front wheels were seriously binding. I examined master cylinder and couldn't see a problem, (its new), removed servo vacuum pipe but that didn't solve the problem. Then ! unscrewed the master cylinder a few turns off the servo and the brakes released! So I assume I've got a sticking servo. So here are my questions:
... Does it sound like I have a faulty servo? I thought if a servo was failing it would just lose its effect, I didn't expect it to cause the wheels to lock.
... My front brakes were seriously binding but the rear wheels weren't. Is that a surprise?

Thanks for the advice
(servo is the only brake component I haven't replaced. MC is new, new flex pipes, front calipers professionally reconditioned, new slave cylinders).

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barcalude Dave B
Baldwinsville, NY, USA   USA
Hi. I'm guessing your problem is caused by the front rubber brake lines when they get old, they will internally degrade to the point that they don't let the brake fluid return to the master cylinder. Fluid will flow to the caliper as its under pressure when you brake. The degradation basically can make the brake line act like a check valve. Even if this isn't your problem, I would replace both front and rear rubber brake lines....it's cheap and easy piece of mind.
Good luck with your barn find.

rrblizard Bob Blizard
MA, Acton, USA   USA
1972 Triumph TR6 "Archie Da Triumph"
I had the same problem as you, and finally discovered the source was inadequate clearance between the master cylinder pushrod and the "button" in the brake servo. The button needs to be 0.011-0.016" recessed from the face of the servo mounting surface. The shop manual says to set with engine running, but I think I did mine with the engine off.

At any rate, retract that button a bit and I bet your problem will go away.



Bob Blizard

'72 TR6 CC782xx

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
+1 on pushrod.



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

TR5-2085 Jim Fitzpatrick
Allen, Texas, USA   USA
Bob, certainly something I should check out. How did you fix the inadequate clearance? If I need more clearance between servo and MS could I just use washers/spacers to maintain the necessary clearance? Or is the button adjustable?

Thanks for the advice.

rrblizard Bob Blizard
MA, Acton, USA   USA
1972 Triumph TR6 "Archie Da Triumph"
Once you separate the master cylinder and the servo, you will see that the servo button is actually a threaded shaft with a lock nut. I don't remember exactly how you adjust it, but it will be obvious.

I seem to recall that I sweated bullets on the first adjustment cycle to get the clearance correct, and then had to fudge it a little after testing. A bit of a bother, as you have to separate the two pieces each time, but the results are good, and it's pretty easy. Just be sure to test away from heavy traffic.



Bob Blizard

'72 TR6 CC782xx

TR5-2085 Jim Fitzpatrick
Allen, Texas, USA   USA
Bob, great advice. Thanks.

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poolboy Ken D
Sandy Hook, Mississippi, USA   USA
The adjustment procedure and the spec is in Bentley and in Haynes..."Brakes" chapters

TR-PI Lee Cunningham
Sardis, BC, Canada   CAN
Check for free movement of pedal linkage in pedal box, also look at the adjustment/ operation of brake light switch, may be holding the pedal down

Cheers Lee

TR 5 PI
TR 6 PI

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TR5-2085 Jim Fitzpatrick
Allen, Texas, USA   USA
Gents, thanks for the feedback. I've made the adjustment and I'm ready to retest the brakes. All I need to work out now is how to sort out a couple of CD175s. A different post I suspect...

Thanks again.

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