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  #1  
Old 06-25-2003, 09:00 PM
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more tranny questions-I.P. bleed off valve

This is for an 83' 300 TD sedan.

My tranny used to flare during the 2-3 shift. I've followed every article I could find here and have replaced the two white vacuum switches on the valve cover and the bleed off valve on the injection pump. All seemed good for awhile but it has been shifting way too hard, especially on 3-2 downshifts.
I've got 25" at the booster hose and 14" at going to the modulator. I've tried backing off the modulator several times, going only one notch at a time but it hasn't helped.
So, I'll continue backing off the modualator, but I'm wondering if maybe the modulator is bad.

Lastly, the new injection pump bleed off valve I got doesn't have the adjustment nut under the cap, there's only a crimped on type of nut that won't adjust. When I took the part top the dealer they said it was the only part available. Any ideas?

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  #2  
Old 06-25-2003, 10:30 PM
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Your vac valve for the tranny is shot. You must have 19-20" vac with throttle closed, immediate drop of 2" or so when throttle is lifted off the stop, then progressive drop to 0 at full throttle.

Adjusting the modulator for softer shifts will result in a burned up tranny if the vac valve isn't working -- 14" will give you a firm shift at the very best. Set the modulator back to where it was and fix the valve. Usually just the fingers inside are worn, but you may need to replace the whole thing.

Are you referring to the ALDA when you say bleed-off valve (since there is no such thing on the IP)? If so, make sure the line from the back of the intake manifold to the ALDA isn't plugged anywhere, inlcuding the banjo bolt, and that the pressure isn't being vented off by a bad overboost switchover valve on the firewall (the hoses are connected to it). The whole thing should hold pressure if you disconnect at the manifold and blow down the hose. If not, fix it.

All the ALDAs I've heard of have an adjustment, but you may have to remove the thin metal seal to turn the nut to release the screw.

If you are refering to the shutoff solenoid (on the back fo the IP on yours, I think), there is no need to adjust.

Peter
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  #3  
Old 06-26-2003, 12:40 AM
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Sounds like the IP valve, while 20" to 0" may be ideal, anything from 15" to 2" is acceptable. I'm not sure why it wouldn't be adjustable, are you sure? He is refering to the white valve on top of the IP which bleeds the vacuum off, normally under that dome it is fully adjustable. What kind of vacuum does it have if you go WOT for a split second?
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Old 06-26-2003, 07:10 AM
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What's the vac valve your refering to?

If I hit WOT for a second the vacuum drops to just about zero. My range going to the modulator is 14" at idle and drops to just about zero at WOT. While driving I"ve got somewhere around 5" or so during moderate pedal, drops to just about zero when I floor it and jumps to 14" when I let up. I've also got well over 20" at the vacumm booster line.

It seems to me that the modulator isn't doing anything when I adjust it. Just backed it out one full turn and still hammers into gear. Is the madulator shot? I'm going to go get a mitivac tonight and put vacuum on the line to the modulator to see if it's holding. Will this help? Thanks!
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Old 06-26-2003, 07:15 AM
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I'm thinking the vac valve is what I'm calling the bleed off valve , the white plastic thing on the back if the injection pump with the vaccum line that feeds the modulator?

If so, it's brand new, but it doesn't have an the same type of adjustment as the old one did.
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Old 06-26-2003, 12:29 PM
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That is interesting that it doesn't have the adjustment, the reason your getting the hard shifting is the range of the bleeder valve. You need higher vacuum to get rid of the clunk on the downshift and the hard shift on the upshift. However being your valve isn't adjustable I suppose next you should try getting as much vacuum as you can there. Get some brake cleaner and take off all of those hoses and plastic fittings (mainly the dampner) and clean them all out, you'd be suprised the amount of carbon crap in there. That should help the shift a little bit, let's try leaving the modulator alone (turn it back that full turn) for the moment until you get the vacuum a little higher at the valve on the IP. See the modulator is simply another bleeder valve, you probably have it most of the way closed but being it isn't getting vacuum in the first place you have no way to improve the amount of vacuum the tranny sees.

As for the modulator line holding vacuum, if the line doesn't hold 15" of vacuum for a period of time it will also make harder shifts. If it leaks start with a new rubber cap, then if it still leaks either replace the modulator seal or modulator itself.
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Mercedes W123 DIY pages are now located here.
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2005 Avalanche 4x4 ~66k
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  #7  
Old 06-26-2003, 09:20 PM
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Alright, got myself a mityvac and tested the modulator line. Seems fine, however everything I tested with the vac seems to have a slow leak, even if I test a plugged line off the car anything under 20" slowly looses the vacuum but if I pump it up to over 20" it holds. Could the mityvac be faulty? I hope not as I just bought the thing!

I found a big leak, as I couldn't even pump it up over 5", at the switch over valves on top of the valve cover, replacing the vacuum lines there fixed that. The next big leak was at the EGR itself and the switch that is just before the EGR. I plugged the line leading to the switch and test drove the car. Much better! Downshifts are much smoother. I'm going to replace the rubber "t" fittings and get some new plastic vacuum line from the dealer. You're right about them being full of carbon. Is it O.K. to run the car with the line to that switch plugged? I assume it's a switch for the EGR valve? Thanks!
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Old 06-26-2003, 10:18 PM
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That is quite a common leak. I hope it is, because that is the way my 83 is. I don't think it does anything other than control the EGR so it should be fine.

I really doubt the MityVac is faulty. First put your finger over the end to seal the MityVac and pump it, does it hold? How about with the hose and fitting? More than likely it is from the rubber fitting on the end of the MityVac going to the other line (if going to a plastic line I use another piece of hose to couple the two), or possibly everything may leak.
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Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k
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Old 06-27-2003, 07:09 AM
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It won't hold if I put my finger over the end unless I pump it up to over 20"? I'm thinking it's just not getting a tight seal at the lower range. I'll keep playing with it.

So what's the deal with the EGR and this switch? I'm going to test the one's on my parts car and see if they leak. Is there any reason to fix them, or are they really not necessary. Thanks for all the help!

As far as the vac valve not being adjustable. When I ordered it I just ordered it by part #. Fastlane has two valves listed under that part # for two different transmissions. Perhaps I've ordered the wrong valve?
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  #10  
Old 06-27-2003, 12:17 PM
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Even if you put your finger on the plastic part? If so I'd take it back to wherever you bought it and show them that.

Pretty much that black box has two switches inside of it, they are there to tell the EGR valve to open under certain throttle. If/when you take it apart or replace the switches do NOT USE GREASE on it as that will accelerate the wear on the plastic exponentially.

I'm not sure why that'd be, it still seems like it would be adjustable no matter which tranny you had but I don't know. I know there are different modulators out there, but i thought the IP valve was the same. Actually I have some from a W126 and W123 and they look nearly the same so....

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Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k
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