1966 FHC 2+2 - exhaust brake after overheating?

E-Type
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Hello everyone, I hope you are all doing great. Once again, I am seeking advice.

In my last post, I had issues with boiling coolant, but since the temperature gauge showed temps below 100 degrees, I assumed it must have been the expansion that caused it to spill after being too full.

Last week, I took it for a ride again, and after 30 minutes or so, I had a hard time shifting gears. They would not go in on the first 3-4 attempts, and it required quite some force, which was very stressful in that day’s traffic. Reverse would work, but it always made a scratching sound as if the clutch was not fully engaged, even though I was stepping on the clutch pedal fully. I made it to a parking lot, and again, the coolant was boiling and spilling out.

Fast forward, I brought it to a garage, and apparently, the belt of the cooling system did not run properly, causing the overheating. That was fixed, and they bled the clutch.

When I drove home, the gears shifted very smoothly, in fact, smoother than the first day I got it. However, after just 10 minutes of driving, I again had boiling coolant, and I noticed something new. I cannot say for sure if I experienced this already when the shift issue started, but I might have.

When I removed my foot from the gas pedal, the car slowed down noticeably faster than before. It almost feels as if the handbrake was engaged, or as if I was stepping on the brakes a bit.

Does anyone have a clue about what’s likely to be the issue here? I am quite concerned that it might be an issue with the engine. All of my budget went into the nuts and bolts restoration, including a complete engine overhaul, but the garage that did that is 1000km away, so it’s difficult to consult them directly.

On a side note: one of the carbs cap was off when i got home (not sure if the garage opened it or whether it came undone on its own, not sure thats relevant).

Thanks!

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I have had your problem with two of my cars in the past. Usually presented in hot weather/traffic. You will need to understand how your brake system works to see if any of my thoughts apply.
My Mk2 used to give trouble because the clearance between the push rod and the valve in the slave cylinder (remote from the master cylinder) was insufficient. As the brake fluid and the internals of the slave cylinder warmed the too small clearance would close - this stopped the fluid returning to reservoir. The effect was to keep the brakes applied even though the pedal was released. I had to remove the slave cylinder/booster combination and set the push rod clearance properly. No more problems.
My E type used to have the same issue for a similar reason. I have a 3.8 - so different to yours - but also a pushrod clearance denying fluid return. Set to factory setting (both E type and Mk2 adjusted by thread) and no further issues. Look in your service manual. Expect your car might be more like the Mk2 arrangement.

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Thanks a lot Paul - i’ll def. take a look at that. What i do wonder tho for this scenario: i now seem to have this slowing down issue when the car is cold as well. So it appears as if the overheating that caused the gearshift issue altered something permanently for this to occur. Could this still apply?

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When was the restoration? How often has the car been driven since? If these issues began just after the restoration, I’d, definitely, would be calling the restoration services.
I see three different issues; “overheating”, “gearbox engagement” and a sticking stuck caliper(s)

First address the cooling system: What was rebuilt replaced in your “nuts and bolts” restoration, regarding the cooling system? Call and have a conversation about this problem.
The same for the gearbox, slave etc. Since the gearbox seem to shift nicely just after the bleeding, it’s likely there’s a leak in the system.
As for the brakes, were all of the rubber flexible hoses replaced? Could the parking brake not being fully disengaged? Hanging up? Not releasing totally etc.
Just need more details on the totality of the rest.

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Same issue a couple of times with the XK120 tandem master cylinder and with my racing Mini: the pedal needs play at the top to allow the brake fluid to discharge. Otherwise brakes bind, which can cause overheating. Lift the car wheel by wheel or front read, and check which wheel binds.

I also think that the advice of Ken is very good: the bleeding issue can have solved permanently the clutch, but the brakes can be more tricky, hoses even new can perish as there are strange (non) compatibilities with some brake fluids, even seals could be swollen, but all in all, this is not necessarily a big deal, other than annoyance: many restorations needs trimming afterwards, so be positive.

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Furthermore, make sure that you have the right radiator pressure cap (4Psi will boil fast, I use 7Psi and avoid modern 11-15 PSI, as I am wary of the core plugs, but 7 is a must-minimum, there should be a marking on it) and do not stress out yet, it can also be something as minor as a thermostat. Have you checked that it opens - i.e. hot top hose-? Can be very simply done letting it idle 20 minutes. Is your fan fully operational and the flow free?

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S1 4.2? There’s a special problem with this cooling system, as there really are no proper thermostats available. You can read my writeup on it here:

The best available thermostat is SNG 3731/1, any alternative solution will leave the bypass wide open. The stock cap for this car was 7lbs, but there is absolutely no reason why you couldn’t use a 13 lb cap, which will give you a little more boilover protection. Did they replace the fan with something modern? A common error is to wire a modern fan backwards. It can’t happen with the original series wound motor, but modern permanent magnet motors can rotate backwards.

The brakes in this car are very complex, there’s no comparison to any other car. My opinion, which will likely draw criticism, is that heat is the least likely problem. But the diagnosis is very difficult. The booster/servo mechanism is a frequent culprit. But then so is the master. And then the reaction valve. So you have a lot to choose from.

Where I would suggest starting is with the small slave piston in the mater cylinder (I bet I’ve lost you already). To explain. When you step on the brake, you are directly engaging the master cylinder. That sets in motion a Rube Goldberg contraption of pistons and valves, which eventually results in the booster supplying pressure to the slave cylinder. The main piston in the master cylinder pushes a smaller piston forward under hydraulic pressure. This releases the air valve in the reaction capsule, which is what releases the vacuum in the booster. Sooooo…if that small piston sticks, the brakes remain engaged.

To check this small piston, remove the plastic reaction valve from the front of the master cylinder. This is just held in place with a few screws. With that out of the way, you will see a steel plate with a hole in the center, mounted to the front of the master. Insert a small tool into this hole, and hold it in place with light pressure. Have someone step on the brake while you are holding it back. You should find that your tool is pushed forward, and then retracts once the brake is released. If this isn’t the case, that’s your culprit.

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Oh, I forgot the carb cap. Screw it back in firmly, but keep it under observation. If it happens again, replace the fiber washer. If that doesn’t do it, replace the cap.

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There are a number of probably completely separate things going on here. This is why a proper “shake down” period is necessary after a complete resto.

Your cooling problem may just be the system finding its level. If you overfill it when cold it will burp out extra fluid when hot, but not boil. If you leave the level as is, let it cool and then drive it again it should stop burping out excess fluid and run at correct temperature. If it overheats or continues to lose coolant then this is not your problem.

Your gearshift does sound like there’s a problem with your clutch not disengaging properly when you press it. However I’m not sure why it isn’t there when the car is cold and then manifests when the car warms up. At a minimum I would check the presence of and level of oil in your gearbox. Bleed the clutch system; the slave can be tricky to bleed as the nipple is on the bottom. Check that you are getting full movement of the pushrod and fork. Check that the pushrod is correctly installed/adjusted/fitted with spring depending on your model.

As above the reaction valve piston can stick, resulting in the brakes sticking on. If they are doing this they will get quite hot. Feel the wheel knockoff after a drive. They should be no more than warm and certainly not hot.