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Discussion Starter #1
Hi All,
Seems the Prelude conversion has brake troubles. I have a vacuum pump and PVC pipe reservoir set up and for the past 4 months it's been working great, even through a bitching hot summer. But lately it's not working.
The owner of the car was driving along and found she had no brakes (she did, just needed to really stomp on it) and I've since determined that the vacuum pump isn't coming on when it's supposed to.

It could be the vacuum sensor switch on the side of the reservoir - if so, it's likely to be opening the pump circuit when vacuum is achieved, but not closing when the vacuum is lost. Hopefully that's all it is, because removing the vacuum pump is a massive PITA given its location.

However another observation lately - it only seems to really pay up in hot weather. This morning it was a fairly mild 20'C, and never faulted. But last night it was playing up because the evening was well over 30'C. The other times its failed were also hot days.

If this is the case, it might suggest the pump needs to be better cooled, either by ducting airflow past it or finding a better spot for it.

I have attached an image of the pump in its location.

Does anyone here have any experience with these?
 

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The schematic on the website doesn't show the sensor or identify how the current switching to the motor is done inside the controller.

An intermittent connection that varies with temperature makes me think there is a cold solder joint on the control board, or some sliding or spring-loaded electrical junction in a connector or current-carrying device.

The good news is that the motor and pump are likely okay since it works when cold; the bad news is that thermally-induced intermittents can be a real pain to find. Maybe a hot air blower and a can of cold-spray can be used to reproduce the failure and narrow in on the culprit.
 

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Discussion Starter #4
Unfortunately I can't do any of that without putting the car on a hoist first. I really doubted the engine bay would get that hot with a 60 kW peak motor in front of it. It's not like there's no airflow in there, but sure, it's not in a wind tunnel.
But at the same time we had some 41'C days and it never faulted, until now.
It's very strange.
 

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Quick follow-up on this problem. The pump stopped working again, but this time it wasn't a warm day. I drove the car (carefully) to my workshop and while the brakes worked for the first 5 km they stopped and never returned.

At the shop I disconnected the pump and tested it with an independent 12 V supply - ran just fine. Maybe it was the vacuum sensor switch?

I removed the sensor switch and set it up on the bench with a known-good vacuum pump and reservoir. It fired up, stopped when the vacuum was reached, then when I let air in, it fired up again. So the sensor was fine :confused:

Then I tested the 12 V supply - seemed fine. I reconnected everything, the pump ran for a bit, then stopped. I checked it again - 7.0 volts! Ahha! It must be a poor power supply.

The fuse supplying the brake vacuum pump was a bit warm to touch, but critically there was a kind of poor contact between the blade fuse and the holder. I replaced the 5 A fuse with a 15 A fuse (all I had lying around) and it seemed to wedge in pretty tightly. The pump ran beautifully for ever after.

So there you go - dodgy blade fuses were the source of the trouble!
 
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