2500M Solid Pedal

[Finn2500m14]

Afternoon Gents,

Following a complete overhaul of the brake system, refurbished calipers, new braided lines, master cylinder and servo i have not had an end to my troubles.

The issue presents itself after moderately fruitful driving but nothing too strenuous on the brakes. The pedal gradually gets harder and harder until there is no travel in the pedal what so ever and the brakes are bound on, thus making the problem even worse.

I've had the MC stripped and found a load of blast media hiding inside but despite the removal of that the problem still remains.

I am pointing now towards the servo as it feels as though the push rod is in contact with the MC and activating the brakes.

Is this an over vacuum / collapsed silicone hose ?

Great to hear your thoughts.

Best, Finn

[plasticpig72]

There must be a gap between the Servo and Piston Rod of the Master Cylinder. This is to let the Master Cylinder Piston to fully return and open the oneway Valve. This releases the pressure after braking.
You can measure gap using "bluetack or plastercine"
Alan

[Finn2500m14]

Thanks,

I will ensure there's a gap although initially when the problem started my first response was to wind the push rod in. I hope by doing so i have created a gap. There is certainly some free play in the pedal before the brakes begin to engage.

Worth a double check tonight.

[Dollyman1850]

knackered servo.... Or the seals in the M/C are not correct and are causing the piston to seize in the bore and not return after brake application. From your description of the M/C it doesn't sound to have been properly refurbished and if their is swarf etc in there then that could be your cause!

Neil.

Edited by Dollyman1850 on Monday 8th April 16:43

[GAjon]

When you say the brakes are bound on, is it both front and rear?

[nwarner]

As Alan said, also I had the same problem on my Scimitar after I fitted a new brake light switch. It wasn't allowing the pedal to return fully, after adjustment all was OK again.

Nige

[Finn2500m14]

Thanks for the input everyone.

I’ve just been out for a drive and it may well be the pushrod adjustment after all however if I wind it in much more I’ll be through the bulkhead.

The blast media was discovered when the brand new MC was stripped (thinking that was the problem) and all new seals reinstalled so I hope I can rule the MC out.

In terms of binding on, I think it’s just the fronts. I may be wrong / should really check.

It seems the vacuum hose is NOT collapsing which is one thing eliminated.

Getting there 👍

[Adrian@]

What is confusing here, is that you are not describing the method of adjustment, you need to grip the servo nose shaft and turn a minor bolt. A@

[Adrian@]

Pinched a picture from the net... to get at the centre shaft it may require someone pressing the pedal, a pair of grips and a 5/16 spanner. Measure the gap without doing the M/C nuts up with bluetack stuck onto the minor nut (1/16 of an inch). A@

Edited by Adrian@ on Monday 8th April 20:31

[Finn2500m14]

Hi Adrian,

Agreed on the method of adjustment, sorry for the confusion. I’ve heard it’s best to make the adjustment with engine running ?

I am concerned that by winding in the minor bolt head I will increase brake pedal travel / bite point to beyond what is practical. Will have to wait and see however.

Best, Finn

[njhucker]

I had this probkem on my wedge after fitting a new mc. I would drive for about 5 miles and the brakes would come on. Increasing the gap slightly solved the problem

[Adrian@]

Finn, I would use the blue tack method, and 1/16 of an inch ...that era car has a spacer that sets pedal height. However, your servo is 'ballooning' and bringing on the front brakes (IF you get caught out with brakes binding, removing the one-way valve will vent the servo and as a 'reset' the servo as a get you to the next 'balloon' point) BUT that you are 100% correct, the very minimum you can get it to will give you better 'feel'.
A@

[Finn2500m14]

That’s this evenings entertainment sorted, thanks chaps. Hopefully blue tack will be the answer to my troubles.

@Adrian, by pedal spacer, do you mean an item in the pedal box ? This is a ‘72 car, ‘letter box’ front end. So if I run out of pedal travel with pushrod adjustments can I compensate with pedal spacer adjustment?

Best, Finn

[Adrian@]

Finn, the spacer under the servo sets the pedal height inside the car, BUT, this only relates to the whole operation moving to/away from the bulkhead, not in taking up play within the system. There is no adjustment on that version of the pedal/servo (later cars have a threaded clevis on the inner servo to play with). Getting the gap right and it relating to near perfect is in the 'art' and not damaging the brake pad materials whilst you are testing the 'gap'. In the past I have 'shimmed' (using slotted washers of various thickness) the master cylinder from the servo as a temporary 'suck it and see' method to find that optimum gap prior to resetting the nose (trackside, not road) A@

[Finn2500m14]

Finally getting somewhere

Managed to run the car last night with no binding issues. Now to slowly wind out the push-rod to see if i can reduce pedal travel.

In terms of the spacer, is there any reason apart from protecting the bulkhead why i can't remove it completely to raise the pedal ?

Cheers, Finn

[Adrian@]

Finn, it will change the pedal height but not 'feel'...and then you will need to reset the clutch pedal and accelerator pedal to get a happy relationship as you move your foot across the pedals... I have changed pedal boxes in and out of cars, all my TVR life (I am pretty sure that I have had the same 'long' pedal box in 20 odd different M series cars) and have to change pedal boxes regularly.

Check for the rear shoes being set up incorrectly, and feed back on it (find a safe place to do this)...find an slightly upward hill and drive along and pull up, pressing the brake pedal ('feel' the point of the pedal limiting out) stop...allow the car to roll backwards and press the brakes (then 'feel' the point of the pedal limits out) stop, go forward and press the brake pedal again (again 'feel' the point that the pedal limits out) stop. It should limit out all at the same point. A@

[Finn2500m14]

Finally solved with excellent results.

Thanks for the help !!