vacuum hose location

[willrev]

Hello again,
Been working on the 82 300sd. Got the first two new glow plugs in without taking off the fuel lines. Knuckle buster. Needs some wratchet box wrenches. Will go purchase some before I finish the job.

Trying to run down the problem with the clunk sound with each successive downshift in the transmission. I checked all my vacuum lines under the hood. All were connected well. Is the dark black line that comes off the front of the engine and goes to the brake booster the main line???

Right in front of the brake booster coming off that big black line is a rubber fitting. Out of that fitting comes a small diameter vacuum line that goes to the hookup on top of the IP. It was plugged with soot. I cleaned it the best I could and cleaned the black T fitting with an ice pick and lots of soot came out. But I still have the noisy downshift, but it definitely does not seem as "rough" when it shifts down. I think this helped. Are there any other possible areas that the line could be clogged??

I was referred in an earlier post to the T fitting coming off the pump before the line goes to the tranny. I hope this one right in front of the brake booster is the one. Please advise me if you can.

willrev@earthlink.net

[Pete Burton]

Originally Posted by willrev

Hello again,
Been working on the 82 300sd. Got the first two new glow plugs in without taking off the fuel lines. Knuckle buster. Needs some wratchet box wrenches. Will go purchase some before I finish the job.

Trying to run down the problem with the clunk sound with each successive downshift in the transmission. I checked all my vacuum lines under the hood. All were connected well. Is the dark black line that comes off the front of the engine and goes to the brake booster the main line??? YES

Right in front of the brake booster coming off that big black line is a rubber fitting. Out of that fitting comes a small diameter vacuum line that goes to the hookup on top of the IP. It was plugged with soot. I cleaned it the best I could and cleaned the black T fitting with an ice pick and lots of soot came out. But I still have the noisy downshift, but it definitely does not seem as "rough" when it shifts down. I think this helped. Are there any other possible areas that the line could be clogged?? There is a colored plastic orifice( or vacuum restrictor) between the line from the brake booster to the Tee on the vacuum control unit on the IP. Make sure that's not clogged, but don't drill the plastic hole out, either. The other side of the Tee should be connected to the modulator on the transmission

I was referred in an earlier post to the T fitting coming off the pump before the line goes to the tranny. I hope this one right in front of the brake booster is the one. Please advise me if you can. If you haven't done it already, I would bypass the EGR's vacuum control. This eliminates any leakage in those crossover valves from affecting the transmission shift

willrev@earthlink.net

hope that helps

Easiest way to trace the vacuum line to the trans modulator is to follow it from the left side of the tranny up to the tee.
You have the right vac line, as best I can tell. That line is subject to getting sooted up over the years. Use a drill bit to clean it all out if there is any doubt.
The soot comes from oil in the lines that dries out over time, or oil that carries dirt into the lines, then gets sucked away. That soot can get carried a long ways down the line. Only way to check is to disconnect and blow through it.
Those three way tees are a problem also. They get leaky and any loss of vacuum will change the hardness of the shift. Clean them with soap and should get better. Then on top of the valve cover there are a couple of vac switches, one of them controls the EGR, the other the vacuum to the modulator. They get worn and either leak, or will not open. Cheap switches to replace. Check them. They are mechanical and open and close with throttle.

[willrev]

How do I disable the EGR vacuum control.

I know those egr valves go bad. No way to check mine. Dont have a vacuum gauge. Where are the replaceable switches on top of valve cover? Is that the little black box with the vacuum lines coming out to the EGR?

What's the part number???

[dannym]

Hey,
You should really consider getting a mityVac to troubleshoot vacuum lines.
I bought mine at Sears for about $40. It's a purchase you won't regret and it can save you lots of time and trouble.

Then on top of the valve cover there are a couple of vac switches, one of them controls the EGR, the other the vacuum to the modulator. They get worn and either leak, or will not open. Cheap switches to replace.

My EGR, 1984 300SD, is controlled by a temp switch on the engine block right next to the Thermostat housing.
Those 3/2 way vac switches you mentioned are roughly $45 each. I had to replace both of mine because they both leaked.
As I understand it, and I could be wrong, those switches simulate the vacuum you would normally get from a manifold vacuum setup. They open on throttle position and send a signal to the modulator or IP?
either way it runs a lot better after I replaced them.

That main vac line runs from the Vac pump on the engine block. You want to make sure that's working properly. I just rebuilt mine last weekend, the intake valve was clogged with crap. If it's not pulling enough vacuum try testing the check valve. It's the piece the vac line screws into.

Danny

[willrev]

Hey, pipe cleaners are perfect for cleaning soot out of vacuum lines.
The fit right in there and pull the soot right out better than a drill bit.

You can fold them in half and double the size for bigger orifices. Works great.

I will go to sears and get the mityvac and the wrenches for the glow plugs.

How do I test the EGR?? Does anyone have a good reference for what type of vacuum each switch should be pulling???

[Pete Burton]

Will, on a 82SD, both switches on top of the valve cover operate to control EGR. No EGR at idle or full throttle, and variable EGR at partial throttle. Because at one time I thought that these switches also control transmission shifting, I was hesitant to fool with them. Now, after studying the vacuum/EGR diagrams, I know that they are purely for EGR. Removing the cover and looking at the cams variably opening these valves will help in understanding. It's confusing though, because many people have reported fixing leaks in this area and getting better shifts. That's true, but not because they control vacuum to the trans. It's because a leak is being fixed, and that leak affects the transmission shift. The switch next to the thermostat simply opens up vacuum to EGR. Here's a siple way to test the EGR: engine off, connect miti-vac directly to EGR valve's vacuum port. Pump, release. Pump release. You should be able to hear some movement and see some too, probably with the aid of an inspection mirror. Does it move back and forth? If so, good, it's not stuck. You can remove the vacuum lines leading to the valve cover and cap them off. If it doesn't move, you can spray penetrant in there and maybe get it to move. A stuck open EGR will cause crappy idling and some high end power loss

[dannym]

Hey,
Thanks for clearing that up. I thought those switches did something else.

I agree 100% that the shifting is better as a direct result of the leaks being fixed.

Danny