Locking brakes 1963 S1 FHC 3.8

[jago2002]

Good morning,

I have a 1963 Series 1 E Type FHC and experienced my car locking its brakes yesterday for the first time. The car is standard with the bellows servo and two separate brake master cylinders.

After around 15 mins I was able to restart but within a few hundred metres the problem re-occurred and I ground to a halt. I managed to get the car recovered to my home as I couldn’t risk driving any further with this persistent issue.

I am unsure how to fix this beyond assuming it is a problem with one of the two brake master cylinders but which one and how do I distinguish if the whole car simply locks up?

I would appreciate any words of wisdom please.

Many thanks.

[Simonpfhc]

Hi there,

Whats your name?

If your brakes are not releasing, it’s usually one of the brake masters sticking. The easiest way of checking is driving your car up and down a quiet road until the brakes start binding. You should be able to feel the wheel spinner getting warm on the offending brakes. Otherwise, jack the front of the car, and with the engine running, apply the brakes a few times then spin each front wheel to see if they are Try do the same for the rear if the fronts are ok. If only one side (either front or rear) then it will be a caliper piston sticking.

You can test the bellows by pressing the brakes with the engine running - you should see the bellows contract and then expand again when the brakes are released.

[jago2002]

Thanks Simon for the advice. I guess if it’s the rear brakes (master cylinder) the spinners might not be hot given the discs are inboard but by deduction if the fronts aren’t warm then it must be the rears!

I’ll try that and report back.

Much appreciated.

Jago

[Allrand]

I had the same problem after rebuilding my 3.8. I eventually traced the problem to adjustment of the top (rear) mc push rod. There has to be some slightly detectable play in the balance link between the two mc's. Any heat build-up, even mild, from braking doesn't allow the non-return valve at the front of the mc to open again thus locking the whole system because it pressurises the other mc via the balance link. Turns out my new top push rod was slightly too long, even when screwed right back. After the fluid cools off a bit the brakes unlock.

[jago2002]

Hi,

Just an update on the locking brakes issue.

I have established that the front brakes are locking on(by getting the brakes to lock and jacking up the front of the car to confirm the wheels won't turn) but how can I be sure it's the brake master cylinder rather than the servo?

Does the servo only act on the front brakes or does it act on all four wheels?

Many thanks

Jago

[Simonpfhc]

Jago,

You can eliminate the servo (bellows) by just disconnecting the vacuum hose (remember to plug the hose!). The brakes will require more effort but will still function normally. I still think it will be the brake master at fault that operates the front brakes.

[jago2002]

Thanks Simon I’ll try that in an attempt to eliminate the servo which I note is expensive to replace!

Many Thanks

Jago

[mxke]

I had the same issue and as Randal did, resolved by shortening the master cylinder rod. It was a new master cylinder from one of the usuals. I believe I shortened it by a 1/2".
Mike

[mxke]

From JL archives

Thank you to Alan Grossman and Jerry Mouton!

I don’t think it’s a booster problem, it should have cleared up right away. 45 minutes says it’s a brake
temperature problem.

Typically with a hydraulic problem, the masters don’t back off quite enough to fully open the relief valve at the end of the master (one master, usually the rears but not always). When the brakes are applied, the fluid heats up and expands and holds the release valve at the end of the master closed, so pressure can’t escape. When the fluid cools and contracts the valve finally opens and bleeds off the pressure.

Right now release the lock nut on the top master and screw it into the fork a little. Feel the movement in the
master, the shaft should not move much if at all before moving the piston. Same with the bottom master (front
brakes). Now screw the top rod into the fork until there is no play – careful that the pistons are not pushed in at all. Then screw the shaft into the fork exactly 1 1/2 turns for 1/16’’. You should be able to feel the movement very clearly. Hold everything and tighten that locking nut. Now you can be sure the clearance is good.

Then go drive it again and see whether you can repeat the lock up.

Hope this helps as it did solve my issue.

Mike

[Allrand]

Just to be sure, if they lock again jack up the rear & check if they're also locked, which was the case with mine.

[jago2002]

Update on S1 locking brake issue. Disconnected the servo and same thing happened after driving the car up down the road for 5-10 mins. I working on the hypothesis therefore that it’s the brake master cylinder. I’ll update once a new one has been fitted. Given that the two circuits (front & back) are independent, can I get away with just bleeding the fronts post installation of the new MS?

Many thanks

Jago

[Allrand]

Yes you can bleed the fronts independently, but please first check if you have a bit of free play in the balance link between the two masters. Are you sure the rears didn't lock as well?

[jago2002]

Hi Randall,

I’m not sure that the rears didn’t lock also but if it’s not the servo and I know the fronts are locking up then it has to be the MC controlling the front brakes, right. To double check I released the brake pipe in the housing of the front MC and immediately the front wheels freed up. I’m therefore assuming it must be front MC unless by an amazing coincidence the rear MC has failed also at exactly the same time. Not impossible, of course, but most unlikely I’m thinking.

I’m ordering a new front MC and will see how we go once fitted.Fingers crossed.

Thanks for the assistance so far.

Regards

Jago

[Allrand]

If there's no free play in the balance link, pressure from one mc can lock up the other, and thus the whole system.

[TGN]

Irritatingly my car has now started not releasing the front brakes after 5 mins. It hasn’t recently had the master cylinder rebuilt. It appears to do it once shortly after it’s started, if it rests a few minutes it releases and I’ve been able to continue my journey without it repeating for the rest of the day. Both times it has been relatively quickly after I’ve got up to speed on a dual carriageway.