'79 300TD "needs new vacuum hoses"

So if this '79 300TD I'm looking at comes with a "needs new vacuum hoses" message, what all is involved in "updating the system" with
all-new hoses? I understand that vacuum controls everything, but how accessible is it all? I suppose I need to talk to someone other than who I did about the car (talked to the driver, her husband did all the maintenance on it though), but where is vacuum routed, and how accessible is it throughout the car?
I've only ever owned GMs and one Honda, and the prospect of what might be involved in this is a bit frightening, but perhaps the vacuum system either doesn't degrade too bad outside of the engine bay (which I'm guessing is relatively straight-forward to just whack some new hoses into?) or it's all fairly accessible unlike the other cars I've had?
thanks for any tips, although maybe I should skip this car (there's a nifty Peugeot 505 turbo wagon available for sale down here for half the money, but that frightens me in other ways <g>).
-tom!
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I'd be skeptical about the car "needing all new vacuum hoses" - unless its been in a fire!
(IMHO, that sounds like something told "the spouse" to justify replacing the car.)
But it may well need repairs and these could range from:
a rebuilt vacuum pump a new brake booster repair to the vacuum powered door locks
The brake booster is the $$, the door locks just time consuming.
Vacuum aside, you should know that the climate control system on the '77 - '80 MY cars is quite expensive to repair - so much so that there's now a digital retrofit kit to replace most of this OEM system. (I installed one on my '80.)
Considering these points, and that this is a non-turbo engine, I'd look for a TD (if that's what you want) in the '82 to '85 MY as these have an improved climate control system and a turbodiesel.
Of course if this car is very cheap and you like it then.....you know.
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A 79 300TD is a 116.120......That makes it a turbo diesel.
And 'needs new vacuum hoses' probably means the ACC climate control has massive vacuum leaks......

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T.G. Lambach wrote:

Thanks for the warning, not heeded soon enough but hey the car was cheap. ;) The digital system looks like a good investment, although I'm going to tear apart other bits first just to make sure all is well and good before spending "real" money.
Would it be correct to assume that despite these being the same engines, pulling a turbo off a later MY wouldn't be something I'd want to install? I'm asking 'cause I assume that compression ratios in turbo engines are probably much lower, so I'd need to get shorter rods to make it not blow up, in which case I might as well replace the whole engine?
As it is, the engine is strong enough for me. It's not the 3.8L supercharged V6 I'm replacing, but it gets me where I'm going fast enough. ;)
-tom!
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You CANNOT add a turbo to a naturally aspirated engine.

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It's a ompletely different engine insise designed from the ground up to have a turbo. You could drop a turbo engine in but it'd probably ne easier to find another car.
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. . .
The Pug is a good car. Very soft ride. A buddy of mine had one, it's impressive.
The vacuum hoses are a stupid simple fix. You need two things 1) a supply of the hose and a few of eevry connector, end and t them make. 2) A car like yours that's plumbed correctly.
You just put on the vaccum bits till it matches exactly the other car.
You'll need new little white fingers for the things in the black box on top of the valve cover where the vacuum goes into.
Rumor has it the hose is no longer available in clear or colored and that it only comes in black so your car will look logically, not physically the same as the other car.
But that's all there is to it. Vacuum bits are cheap at the dealer and it shouldn't take you more than a half hour to put them all on.
Get a vacuum handpump/gauge. You'll need it anyway if you hve one of these cars. DO NOT cheap out and get the plastic one, they break, get a metal one.
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Richard Sexton wrote:

I wouldn't characterize a major replacement of most, if not all, vacuum hoses as a simple fix. Vacuum is used in far more applications in these cars than any other car I have ever seen, including, for example, door locks, fuel fill door, trunk lock, and shutting off the engine. The reason I would say it's far from simple is that many of the vacuum hoses are in difficult to access locations, like under the dash. You can track them down and get to just about all of them, but it can be quite a task. And there are still a few, like the lines that control the center dash vents, that are very inaccessible. For those particular lines and the actuator, the only access is if you remove the entire dash.
Also keep in mind that for every application there is a small actuator somewhere that produces the desired movement, whether moving an air flap or locking a door. These have a rubber bellows that doesn't get better with age. Mine are all still original and OK, but I keep the car garaged here in NJ which isn't the worst environment. If the car has spent 25 years in say Phoenix, the results could be much different. And each of those acuators could be $100+.
On the other hand, with my exper with a well maintained 80 300SD, only a couple of the lines have actually failed. And both of them were at the same spot, where they passed through the firewall grommet. If that's all you have to deal with, then it is relatively simple, but still time consuming to track down and find the problem.
Also, I agree with the warning about the climate control system. Not sure if that model has the auto climate control, but if it does, these are particularly problematic and involve the vacuum system. MB used a strange contraption, called the climate control servo, that combines an electric drive motor, a coolant control valve, and gear driven switches and vacuum valves that serve as the master control for the heat/ac. There must be a dozen electrical connections and about that many vacuum ones going into the thing, together with coolant hoses. These fail, either by cracking and leaking coolant, or by just quitting. If this car has auto climate, I'd inspect servo for leaks and see if it works. If it doesn't, which you may not even be able to tell since the vacuum system is kaput, then you may be in for quite a repair bill, even if you do the work yourself. Last I checked, a good rebuilt one, using an aluminum housing, was going for about $600. As TG pointed out, you can get a conversion kit that replaces the whole works for good, but that is even more expensive.

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trader4 wrote:

It turns out that it's not nearly that bad, so I bought the car today. There are a few issues, but I hope they're relatively straight-forward to fix with my knowledge + some sort of useful shop manual + the local resident experts on alt.auto.mercedes.
The only vacuum problem I've noticed so far is that the passenger-side doors, fuel door, and hatch don't lock when I turn the key in the driver door. I also can't manually operate the lock on the front (passenger) door, so I'll pop the panel off and see what's binding, and hopefully the automatic actuation problem will be obvious.
Beyond that, this car does have the auto climate control. Wow, that's some system you've described. It blows a little bit cold, but it doesn't seem that I have manual control over the fan speeds. Hopefully I can just recharge the system and it'll be all dandy.
The hatch doesn't stay open by itself, but this one I'm not too worried about just yet. I also have to get a lens for one of the reverse lights. Oh yeah and the hatch lock doesn't seem to work from outside, but it operates from the button inside, manually, ok (and since it's a wagon, I /can/ climb back there even if I prefer not to, heh).
It's pretty clean, though, and even the floor mats are in nice condition with the 300TD badging on them. ...and this car really cruises on the freeway; 80mph for a half hour and it seemed really happy to be cruising. 154k miles ain't too bad for a 28 year old car.
Baby blue, and it's even got the old blue California license plates which look real nice, oddly enough. (California cars get transferred with plates, unless you specifically request new ones.)
So since I'll sell my old car for more than I paid for this one, I get out ahead even if I do have to drop some bucks into it. I just gotta get used to not locking my car. That'll be some fun. ;)
-tom!
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Tom Plunket wrote:

Yes, if the manual lock button doesn't work, then that's the place to start. Here;s the free tip of the day:
To remove the interior door panel, besides the obvious 2 screws by the latch, there is a screw near the middle of the armrest, accessible from the underside on an angle, and another screw behind the door release handle. To get at that one, you have to use a small screwdriver or similar to pry out the thin black plastic trim cover, which is somewhat flexible. The screw is behind that. You also need to remove the thin trim piece on the door that runs from the door panel in the latch area, up to the top corner of the door. It;'s held in place by one very small screw near the top corner. After all that the door panel is held in from behind with clips, so to remove it you need to lift upwards about 1/2 inch and then out.

There is no manual control, the servo controls the fan speeds. Did you check that you can get heat out of it? If you start with a room temp or below cabin and set it to max heat 85, with car running and a warm engine, the blower should go to max heat speed. I say max heat speed, because in heating mode, the max blower speed is 4, while in max cooling it's faster at speed 5. Heat should be coming out of the floor vents, the two side vents by the windows, and a little bleed air out of the center vents. If you then get the cabin nice and warm and rotate the temp setting to max cooling, 65, the blower should slowly step down through the heating speeds, then slowly step up again to max cooling blower speed. Air should now be coming out of the side vents and center vents, with the floor vents closed off. All this should work even if the compressor system is kaput. If it does all this, I'd say 95% chance the servo is good, provided of course it's not leaking coolant.
Another tip: You should periodically do this, like once a month. Forcing it to go from max heat to max cooling moves the servo gear mechanism through it's full range of motion. That helps keep it lubricated, the electric contacts from getting dirty/bad spots, etc.

I hope you pulled them out and looked underneath. One of the main failures in this car is rusting and this is one prime location. Part of the problem is that at this age these cars can develop rain leaks and that's where the water accumulates. Left unfixed it's a disaster. I recently pulled some parts off a similar car, where the front floor area was completely shot. In fact, I suspect that may be what sent it to the scrap yard. My suspicion is many of these may rust out from the process above, rather than from salt/etc on the outside. Once those mats get wet, with a rain leak, they can stay that way forever.

If it was in CA all those years, that is real good news!

Good luck and hope it works out well for you!
Chet
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trader4 wrote:

Great, thanks for the tips. Chilton's didn't tell me what I actually had to do with the "switch plate," so this was helpful. Pretty wild setup there, but I guess it keeps it all nice and tidy.

FWIW, my '79 back doors at least have two screws as the armrest meets in two places with a gap in the middle. ...the manual lock 'peg' wasn't attached, so I took the panel off to reconnect that and now at least I can lock up the car. ;)
Oh, and the front passenger side door lock can be manually operated for "a while" after the car's been on. Ugh, and the key doesn't work from the outside on the passenger door; guess they had a new ignition lock put in and didn't bother re-keying everything (discovered that the key doesn't lock the glove compartment either).
I'm still feeling ok though 'cause this car was 1/4 the cost of many of the other 300TDs I've seen around, so this sort of stuff is not unexpected. :)

It was 80 in LA yesterday and I didn't think to check. Alas, it does not now appear to control the temperature at all. If I can find useful information anywhere I'll see about taking that apart, but it may be that the drop-in replacement option may be desirable as well.

The fan does crank up, it just doesn't warm up in the compartment. Maybe the coolant lines are clogged or something? When running, the engine heats up to 175 and goes no further, so I guess it's got a 170 'stat in it, which appears to be functioning at least.

No problem, living in southern California gets one into a state where if it drops much below 70 you crank up the heat in your car and wear mittens. :)

I looked at it today, and now I'm thinking this'll be a major PITA to fix, but it's a good excuse to look for 300TDs at the wrecker and practice taking things apart. ;)

I have looked under the floormats. The floors are in good shape.

Thanks a bunch.
-tom!
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BEFORE you remove the passenger door panel: Your central locking system is single door only. By this I mean that ONLY the drivers door locks and unlocks the whole car. The passenger will only be able to be unlocked IF the door is locked from the drivers door. You cannot lock the pass door if the drivers door is unlocked.
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Sorry if I'm being a pest. :) I really appreciate all y'all's help. The mechanical bits are more up my alley, this vacuum stuff is all German to me.
Karl wrote:

Thanks, I actually discovered that today while playing around with it.
If I lock the driver's door, I can lock the passenger side doors manually; the front goes down easily and the back feels like it is getting /some/ vacuum assist. If I unlock the driver's door, the passenger side doors unlock as they should. ...which means that in order to lock my car, I need to turn the key in the driver's door lock, then go around the car to lock the other two doors! (Driver's side back door operates properly, and I'm not 100% positive but I think the hatch auto-locks properly. Fuel door will not lock automatically, and manually operating the mechanism doesn't 'stick' in the locked position like the doors do, i.e. it just releases as soon as I let go.) Is the "can't lock passenger door if driver door is not locked" mechanism vacuum-driven as well? I can't imagine a mechanical solution to this that wouldn't be really ugly, but if it is a fact that as long as the driver door is unlocked the passenger door is unlockable, then I must have some good vacuum functionality. I know there's a leak somewhere, though, since if I leave the car locked overnight, turning the driver door lock doesn't unlock the other doors, but they'll pop open soon after starting the car.
I haven't taken the door panels off yet (except to reconnect the back door plunger knob thinger, after which I forgot to reconnect the window switch ugh), and I have discovered that Chilton's is amazingly useless on vacuum issues, are there two lines going to the lock, e.g. a 'lock now' line and an 'unlock now' line, or is it one line with positive and negative pressure that causes the lock to operate? Would the behavior I'm seeing be automatically indicative of bad servos, or do I really need to get in there and test the vacuum with the door apart? Might there be another 'tap' to test the vacuum operation, say in the engine bay? I have a decent vacuum pump, and certainly the more I can diagnose before taking it apart, the more likely it is I can get the right parts before doing so.
Oh- when I open the doors, there's that plastic sheeting in there. Clearly I need to remove it to do any meaningful work; what should I use to reattach it to the door when reassembling?
Oh again, it typically takes a second or two for the engine to shut off, which is not the behavior of the old lady's '85 300D, so I figure that's also a vacuum issue that's hopefully pretty easy to rectify. Today the car failed to shut off entirely, but I discovered if I operate the windows it will shut right off (and I do know about the STOP lever under the hood). Fun times, I actually don't mind all of these issues 'cause I used to spend a lot of time working on cars when I had 'simpler' ones, and this seems like all stuff that one can figure out without needing to attach the vehicle to a computer. (...says the software developer!) Maybe I'll go dig out the vacuum pump and try to diagnose the shut-off issue in the morning.
Thanks, -tom!
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Tom Plunket wrote:

Is it relatively straight-forward to test my reservoir? Is there somewhere I can hook my vacuum pump, give it a few pumps, and see if it's ok? When I first saw it, I had no idea what it was, but then browsing here and there something had a picture and it clicked. I don't remember seeing any easily-accessible ports on it for testing, though.
-tom!
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Once you get a mity-vac you'll find all sorts of interesting places to probe and test. Get the metal one not the plastic one which is a short lasted false economy.
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Richard Sexton wrote:

Heh, I've had one of those for 10+ years. Yes, amazingly useful for all sorts of crazy things. ;)
-tom!
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Tom Plunket wrote:

Yes, only vacuum driven. One vacuum line moves the piston one way, and another vacuum line moves it the other way. What MB calls the vacuum switch, which is really a valve, is in the drivers door and linked to the lock. When the driver's door is locked/unlocked this valve connects the incoming vacuum vac line to either the lock or unlock line that goes to the other doors.
I can't imagine a mechanical solution to this

I think someone was selling DVD's or books on how to fix MB vac on Ebay.
are there two lines going to the lock, e.g. a 'lock

My guess is it's probably not related to the servo. First place I'd look is on the driver's side firewall, near the brake booster, where a bunch of the vacuum lines go through a rubber grommet. Try pulling those lines back and forth a bit, work them around. The only two leaks I had were right there and the lines just snapped when I tried to move them to find the problem.
Might

The vacuum originates from a pump on the front of the engine. You should see a hose, about 3/8 coming from it and then getting split off. Keep in mind that there are check valves along the way to keep one segment seperate from another. You'll see those in the lines at various spots.
The line for the driver doors goes from the engine compartment, through that grommet at the firewall, under the dash, and on to the door via the hinge area. The hinge area is another areea to check.
I have a decent vacuum pump, and certainly the more I can diagnose

Clear package sealing tape works well. If the sheet is shot, you can just use a clear poly sheet of the stuff these use to cover things when painting.

That could be due to either a vac leak or bellows problem with the shut off circuit, or there could be other leaks on whatever is shared with that line. I'd work on the obvious vac problems, like the door first, as you may cure this in the process.
Today the

The shutoff works via a vac line that runs to the ignition switch, where a valve turns with the key. From there a line goes back to the rear of the injection pump, where it works a bellows.

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Well that's true, I was thinking about the underdhood ones really they're the only ones exposed to the heat anf vibration of the engine and seem to go first. The long runs in the door seem to last forever. The diaphragms go on the door and heater flap actuatros but they're not too bad to replace. The underhood ones can be done in a leisurly afternoon though.
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Could you tell me how much is m-b s600's price in your country. In our country,It cost me about 1700,000RMB(about $250,000). Thank you.
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