Vacuum tutorial-Process of elimination
Vacuum leaks are cumulative. There are dozens of connections under the dash, but you can think of the distribution as a bunch of vacuum leaks tapped off a main trunk line. Vacuum is generated in the manifold were there's a tap for the vacuum pump.
1. Bypass the vacuum pump with a piece of hose connecting the manifold tap directly to the tube that runs under the engine.
2. Hook a vacuum gauge to the end to that pipe. That disconnects every accessory that uses vacuum.
3. Disconnect and plug the large vacuum line leading to the brake booster.
This effectively isolates the engine for a basic vacuum adjustment.
1. Start the engine and bring it up to temperature.
2. Take a reading on the vacuum gauge.
3. Adjust the timing by rotating the distributor to attain the maximum vacuum at the lowest rpm using the idle adjustment screws.
Now the engine is optimally tuned for driving, but must be retarded slightly if there's pinging. A healthy engine will produce between 19-21 inches of vacuum. If you don't have that check for:
1. Soot in the choke mechanism. That's caused by a rusted-through heat exchanger under the carb. They are replaceable.
2. A vacuum leak where the carb meets the manifold and spacer.
3. A vacuum leak where the intake manifold meets the heads.
If you can't maintain a steady vacuum of 19-21" you should troubleshoot the brake booster and reserve first.
1. Hook the large diameter vacuum tube back up to the engine and start the car. If you have the same vacuum you can move to the next step, if not you have a vacuum leak.
2. Check to see if someone has replaced the vacuum line with water line, which can collapse as it was meant for pressure, not vacuum
3. Pull up on the brake pedal, if he leak goes away you've just deactivated the vacuum switch in the brake booster. That will have to be addressed. It's usually a problem with a crud ring in the booster that keeps it from fully retraction the vacuum shuttle.
4. If you still have a vacuum leak the line going to the reserve should be tested as the tanks rust out from accumulated moisture there's no provision to remove.
If you still have good vacuum you can proceed to troubleshoot, if not you can cap off the manifold tap and proceed with troubleshooting the washers.
The washers are a complicated system that should be initially bypassed to move on with troubleshooting.
1. Hook the end of the steel line under the front of the engine the vacuum gauge was tapped into directly to the metal hose attach two the frame.
2. Remove the pipe from the T next to the battery tray and hook the vacuum gauge to it to confirm full vacuum,
3. Hook up the T and install the vacuum gauge to the top of it and hook up the vacuum line to the wiper motor and check for full vacuum.
At this point you have confirmed vacuum up to the firewall. There is another rubber tube to the left coming from the water bottle, It carries washer fluid from the washer jug. Now it?s time to start using a hand vacuum pump. While the engine is warm and running activate the water valves individually to confirm that the valves function and you get hot water flow.
1. Remove panel under the dash that has the interior light switch and the vacuum switch, remove both and set aside the panel. The antenna is the first T on a non a/c car. The antenna does not fully extend by vacuum. There are two more shafts that extend manually for distant reception.
2. The switch can be checked manually, in the center-off position. Hook the vacuum pump to the center tube and apply vacuum. It should hold 21?. Opening the single-pole double throw vacuum switch will release the vacuum in either direction. Cap the outgoing vacuum tap and check the operation of the antenna.
Rehook the vacuum T. The next stop is the tap for the tiny tube to the washer switch. That has a second tube that can easily be installed backwards. You?ll hear a vacuum leak if you do.
1. Cap the outgoing tiny vacuum line at the wiper motor and attached the vacuum gauge to the T and start the engine. If you have full vacuum you?re almost done.
There is a temperature control valve well hidden in the LH heater duct. If it leaks nothing will work well. Unfortunately, a lot of the dash and footwell need to be removed to get to it.
1. Use the hand vacuum pump attached to the ?Spider? valve and a vacuum gauge to the water valve. Pump up the vacuum to see if it holds. Operate the controls to see if the valve operates. Replace if necessary.
Circle-back to the sprayer. Re-hook the T, start the car and see if the washer bottle works. It uses vacuum to draw back a spring-loaded piston to hold a charge of washer fluid. When you hit the center button on the wiper knob that sends 12 volts to the solenoid that released the spring for a shot of fluid. There?s another vacuum line that sends a signal to the wipers bottle to coordinate the spray to hit the windshield in the middle of each stroke.
The last item to check is the vacuum pump operation. With two vacuum gauges, one hooked to manifold vacuum and the other hooked to the output of the pump. Rev the engine up. The engine vacuum should go up and down while the output of the pump should be steady, eliminating the common complaint of wipers not working while accelerating.
Rubber hardens with time. Vacuum leaks are cumulative. Replacing all of the lines is the only way to insure a properly operating Mark II.
Barry Wolk
Farmington Hills, MI
C5681126
Reply With Quote
Originally Posted by Spike
