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Old 05-09-2019, 11:22 AM   #1
IansPlatinum
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Default 1973 1800es questions

1. If my master cylinder has a faulty piston, where does the brake failure warning show up in the car? From my understanding, there's a little ball in the brake octopus thing that will shift side to side if there's a pressure differential, closing the circuit for the brake warning. So where's the warning lamp? Is it the same as the brake warning lamp for the E-brake?

2. Recently had some water intrusion after very heavy rains. It seems to me that water is leaking from somewhere under the dash, which might point to windshield seal, heater box, or some other entry point. What's common on these cars? I haven't noticed any creeping rust from the windshield surround to be suspicious of...
Water dripped onto my boots from stepping on the clutch, brake, steering, etc...

3. Oil pressure reads 35 psi at idle, but isn't very linear. At 2K RPM, it might go to 45 or 50 or so. I'm thinking there's some resistance somewhere in the circuitry... Or do those values sound normal?
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Old 05-09-2019, 11:29 AM   #2
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1) It's the same light for parking brake on/brake failure. They both ground to light that bulb. you can pull the wire off the octopus and ground it to see if that lights the bulb as it should.

2) You might check the HVAC vent drains. Water falls straight into it, but there is a hose on the side (running near the fan housing) that drains to the front of the firewall. If blocked, water can build up in the vent until it pours inside. Another stealthy leak spot - those rubber bushings on the wiper shafts.

3) My '72 1800E had a mechanical oil pressure gauge - with a pressurized oil line leading straight from the gauge to the motor (with a flex line near the firewall that popped once and sprayed oil on the manifold for an amazing smoke show). In which case... nothing funky electrical to blame for oil pressure oddities. 35 psi at idle is good, as long as it's fully warmed up.
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Old 05-09-2019, 11:35 AM   #3
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1. Good to know. Should the light only illuminate while braking (assuming faulty MC), and then turn off when not braking? It stayed illuminated through my entire drive yesterday. I had noticed the E-brake switch was also screwy from previous goofing.

2. Will check both. Water seemed much more present on passenger side of the car...

3. I'll give it another look today. I thought it was electronic, but I can't remember if I'm assuming that or actually saw the sender...
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Old 05-09-2019, 11:40 AM   #4
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It's possible that they changed the oil pressure to electical between 72 and 73, but I suspect they didn't. There's still only one port into the engine block, behind the exhaust downpipe. Mine had a 'T' fitting, with the oil pressure idiot light sender on one side, and the oil gauge line leading back toward the firewall on the other.
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Old 05-09-2019, 12:30 PM   #5
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1. As John said the E-brake warning light and brake failure light use the same warning lamp. Make sure the E-brake switch isn't causing the light to come on. There's supposed to be a little piece of plastic in the channel under the handle to push on the end of the switch. They're often missing.



On the early cars the brake failure switch doesn't automatically reset. The plastic plunger in the switch drops down when the shuttle valve moves to one side. If you don't remove the switch after repairing the system you'll shear off the end of the plastic plunger when brake pressure is restored to the failed circuit. That ruins the switch and the light will stay on all the time. Remove the switch before bleeding the brakes.



2. The fresh air vents are inside the cowl, one of them directly above the pedals. If the drains are plugged water will back up in the cowl and reach the fresh air vents, especially when going around turns. If the vents aren't closed (and they rarely close completely) water will splash onto yours or your passengers feet.

3. All 1800 oil pressure gauges are mechanical.
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Old 05-09-2019, 04:00 PM   #6
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Quote:
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If you don't remove the switch after repairing the system you'll shear off the end of the plastic plunger when brake pressure is restored to the failed circuit. That ruins the switch and the light will stay on all the time. Remove the switch before bleeding the brakes.
Does it need to be fully removed or can the contact be pulled with pliers to remove the plunger from the hydraulic piston assembly?
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Old 05-09-2019, 04:13 PM   #7
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Does it need to be fully removed or can the contact be pulled with pliers to remove the plunger from the hydraulic piston assembly?
No, do not pull on the contact. It is not designed like that.

Simply unscrew the switch from the block with a socket or box wrench. Bleed the brakes. Reinstall the switch.

It's good to remove the switch anyway to see if any seals are leaking within the block.
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Old 05-09-2019, 04:30 PM   #8
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Often times they're pretty sticky, after many decades of stale fluid sitting in the system. So the high PSI of a working brake circuit vs. a dead one can budge it, but not the relatively balanced pressures of two working circuits pressing against each other.
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Old 05-09-2019, 05:46 PM   #9
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It's good to remove the switch anyway to see if any seals are leaking within the block.
I'm guessing this would be evident by brake fluid coming from the brake failure sensor/sender hole when pressurized?
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Old 05-09-2019, 06:17 PM   #10
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Yep. There are o-rings on both ends of the floating piston - the center part is supposed to be dry and no fluid or pressure.

FWIW the 'dual-diagonal' brake circuits on them work so well that you really won't notice half of the brake circuits being out without the switch.
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Old 05-09-2019, 11:49 PM   #11
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Quote:
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Yep. There are o-rings on both ends of the floating piston - the center part is supposed to be dry and no fluid or pressure.

FWIW the 'dual-diagonal' brake circuits on them work so well that you really won't notice half of the brake circuits being out without the switch.
Previous owner installed a 'centric' MC. I think the issue is a circuit not being pressurized, but yeah it felt fine, just not ideal. Took it for a ~5 mile cruise the other day, I'd really only worry about the braking power if someone were to pull out in front of me or something.
That's that 80% retained braking power that they advertised
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Old 05-14-2019, 03:35 PM   #12
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It's possible that they changed the oil pressure to electical between 72 and 73, but I suspect they didn't. There's still only one port into the engine block, behind the exhaust downpipe. Mine had a 'T' fitting, with the oil pressure idiot light sender on one side, and the oil gauge line leading back toward the firewall on the other.
My '73 ES is exactly the same way.
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Old 05-20-2019, 12:52 AM   #13
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Thanks y'all. Cowl drains were plugged with dirt and driver's side fresh air vent was open (cable broken). Cleaned and closed.
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