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  #1  
Old 01-26-2008, 05:33 PM
katchung's Avatar
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1982 300cdt seat-backs don't lock...vacuum question

Okay, 123 model. i understand that the blue vacuum line going into the firewall on the driver's side is responsible for the rear seat-back locks. Is this line supposed to be running through a door lock check valve? It appears that it is plugged into one side of a two output door lock check valve. The other output is plugged up with a rubber cap. Seats don't lock. Vacuum doesn't hold on trunk lock when sitting overnight. Also, if I use a hand pump to test the vacuum on the actual door lock check valve supply side, it holds between 10 and 12 psi until I lock and unlock the driver's side door...then the vacuum reduces to maybe 5 psi. Any suggestions?

Thanks

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  #2  
Old 01-26-2008, 06:13 PM
TheDon's Avatar
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vacuum doesnt use PSI.. it uses inches IIRC

experiment with a vacuum check valve for the seats.


you might also have a leak somewhere else in the system
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  #3  
Old 01-26-2008, 08:25 PM
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what do you mean experiment with vacuum check valve?

??? remove it and see what happens to rear seat-backs? Replace it? should the check valve be attached to rear seat-back vacuum line in the 300cdt 1982?
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  #4  
Old 01-27-2008, 08:31 AM
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similar problem

My problem is just the seat backs not locking at all, period. No matter what the circumstance.... (door shut, door open, engine on, etc...)

I have no problem with vacuum overnight, in fact I didn't drive my car for 6 days and it still had vacuum for the door locks.

Should I check the connections at the firewall....
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  #5  
Old 01-27-2008, 11:39 AM
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seat-backs

spug,

I am just learning about the vacuum system. Here's what I know about the nonlocking seatbacks...they are vacuum controlled. On the 300cdt 1982 model the baby blue vacuum line bundled with the yellow lines just in front of the firewall on driver's side is responsible for the seatbacks locking. Yellow lines are for door locks. Get a mityvac hand pump and test for vacuum seal on the baby blue line. No seal means you have to go downstream...into the cabin of the car...I assume you have the 300cdt? The seatback vacuum line is baby blue in the coupes. The lines run under the floorboard to the seats...I've read that you have to pull out the seats in order to get to the vacuum lines under the seats to test them...My guess is that removing the seats is a lot of work...Before removing the seats I plan on removing the underdash and looking for where the lines enter into the cabin...perhaps there's a loose connector under the dash that needs reconnecting or replacing?...Much easier that pulling the seats. If there's nothing under the dash, then next step is to go under the seats to find the leak...not sure if you can easily pull the connector under the seat in order to test vacuum seal with mityvac. From what I understand you are best starting upstream by the vacuum pump and going down until you find the leak. Any leaks that you find, you should plug with a golf tee or appropriate sized nail until you can buy new connectors or check valves, as they will not only affect the related system, but can also screw up everything else that runs on vacuum...ie, shut-off, transmission, etc...

I'm new at this, but have spent the better part of this weekend researching and understanding the vacuum line diagrams. You should find a schematic for the vacuum system and EGR either front right or front left above headlights. Vacuum systems changed regularly sometimes several times during early 80 years. Looking at somebody elses diagram of the same year car could only confuse you as yours could be different. The diagram for my car was on the front left lip just behind the headlight assembly facing up.

The fact that your car holds vacuum seal for five days likely means your vacuum resevoir is solid functioning...getting ready to test mine this afternoon.

Again, I am a newbie, and would welcome any feedback...still not sure if there should be a check valve on the seatback vacuum line...I have one and it looks jerry rigged...half the check valve is plugged...probably needs replacing...no vacuum post valve to seats...the mystery continues to unfold.
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  #6  
Old 01-27-2008, 06:41 PM
toomany MBZ's Avatar
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This is from the FSM concerning your possible problem. Check, if you can that you have a deviation. Before you start swapping things out.
There are two yellow check valves on a CD, the one with a blue line goes to the seat back, it is independent, sorta, of the door locks.
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1982 300cdt seat-backs don't lock...vacuum question-info.jpg  
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Last edited by toomany MBZ; 01-27-2008 at 06:46 PM. Reason: more info
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  #7  
Old 01-27-2008, 08:50 PM
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Thanks for the info

I figured out that the second yellow line with the grey stripe on it runs to the vacuum reservoir. The vacuum reservoir has a slow leak...I jiggled the connection into the reservoir and that seemed to help the vacuum a little bit...I've read conflicting solutions to fixing a leaking Vac. reservoir...any suggestions from the pros?

Thanks for all your help!
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  #8  
Old 01-28-2008, 05:14 AM
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This may help:
use a non hardening silicone product on the line, and reservoir, making sure to not clog things up.
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1982 300cdt seat-backs don't lock...vacuum question-info-003-cropped.jpg  
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  #9  
Old 01-29-2008, 11:57 AM
KCM KCM is offline
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If it is just the seat locks you are having problems with, the first thing I would do is unhook the line under each seat and use the MityVac to apply vacuum to the diaphragms directly to see if they work and hold vacuum. There are two per seat connected in parallel, and if one leaks, they both won't work. I bet you have at least one bad diaphragm, as the rubber rots out with age. You can also use your MityVac to see if you have vacuum from the engine at the connection with the engine running and doors closed.
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  #10  
Old 01-29-2008, 02:39 PM
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seat backs

Thanks for your input. The driver's side seatback holds vacuum now, but the passenger side doesn't. the seat lock underneath on the passenger side is unreachable I think without removing the seat altogether. I just can't get in there to test the rubber connections...everything appears to be plugged in...so unless there's another way, the seat is coming out this week. I've removed the seat panels and checked those connections...they are fine...

Onward and hopefully upward...

David

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  #11  
Old 02-03-2008, 03:02 PM
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blue vacuum line to seat backs seems plugged somewhere

Trying to avoid pulling the line out completely. There is vacuum at check valve behind firewall. The vacuum doesn't make it to the passenger seat. I'm trying to resist grabbing the line and yanking it all the way out until i find the crack or leak...not sure if there is another check valve under the dash for the seat back locks or not. PO had stuck something in the connector between the line and the check valve to plug the line...once I took that plug out of the line the car wouldn't turn off till i replugged it. Anybody? Please stop me from doing something rash and aggressive like pulling the line completely out from behind the dash...very tempting.

Thanks...

David

www.mindbodylink.com
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  #12  
Old 02-03-2008, 05:07 PM
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There are a number of connectors, including at the door jams, but I don't see any check valves, in the diagram, but I can't identify where this, first pic, top, is. There are many pages in the FSM.
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1982 300cdt seat-backs don't lock...vacuum question-new-048.jpg   1982 300cdt seat-backs don't lock...vacuum question-new-047.jpg  
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  #13  
Old 02-04-2008, 04:22 PM
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spoke too soon

I spoke too soon. I parked over the weekend, and lost vacuum to open my central locks. I turned the key and it didn't actuate the passenger door..... It looks like I may be searching for vac leak threads now.....



Quote:
Originally Posted by spugeddy View Post
My problem is just the seat backs not locking at all, period. No matter what the circumstance.... (door shut, door open, engine on, etc...)

I have no problem with vacuum overnight, in fact I didn't drive my car for 6 days and it still had vacuum for the door locks.

Should I check the connections at the firewall....
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  #14  
Old 02-04-2008, 07:32 PM
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And the fun begins

I have ripped the floors out and mityvaced (word?) every last connection of hose in my 300cdt. There are many postings in this forum for the vacuum system. Check valves, vacuum elements, rubber connectors can all be culprits. Definitely get a mityvac to check vacuum seal. Some say start at the vacuum pump behind the driver's side firewall, and some say start at the vacuum reservoir in the back and go forward...Mostly still a mystery to me. Many say you should just replace all of the check valves and master switch in the driver's side door. toomanymbz sent me some great diagrams for the vacuum system...I'll try to dig them up for you.
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  #15  
Old 02-05-2008, 08:22 AM
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mess at firewall

I have an absolute mess at the firewall where the vac lines go into the cab right there at the oil filter housing. Has anyone messed around there to clean it up, or re-route stuff to be neat.....I have some bandages there from PO, so I would like to go one by one and redo...

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