TN cars should stay in TN.

__________________
daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

Well, a transmission failing on an import auto is a scary thing! Thats why Im a little worried at my hiccuping Tranny! I really hope its something simple...so I'll describe its problem as best I can!

Alright, here goes.

In the mornings, when the engine and tranny are cool...it shifts great and quick without "jerky" movements!

As it gets warm though, it jerks from 1 to 2 more often.

Recently, I replaced most of my vacuum hoses and the shifting got a LOT smoother...until I changed my tranny fluid and filter. For the first 2 days I was a little low on fluid, so it acted up a bit...but now my fluid is correct.

Its shifting can be smooth sometimes with juuuust the right throttle position.

In traffic, its weird what it does. (when all warmed up) With light throttle, it jerks into 2nd gear and seems like it goes through to 4th ASAP. With each shift, it seems like the tranny is slipping slightly...although only slightly. When I open er' up with a little bit heavier throttle, she shifts FIRMLY into 2nd and then a smoother the rest of the gears.

I thought a vacuum problem...but why all of a sudden and why conveniently after a tranny flush?

Hey, I got a MityVac today and checked some of the components in the system. I got a weird shifting tranny and I was checkin the modulator...but this question is about if Im doing it right.

Alright, I checked all vacuum lines from the pump backwards and I found a component leaking...its that thing that sits next to the injector pump...dont know the name of it...but it wont hold a vacuum. (on the 300SDL, its one of the first stops from the Vacuum pump...it goes to a TEE and splits to the modulator.)

Should this hold vacuum?

I next checked the modulator...I put the mityvac on the VAC input and gave it some vacuum...a slow leak...

so I disconnected the tranny line...slow leak

I blocked off a few other lines...slow leak

I even checked the line to the tranny...it wasnt leaking.

Did I check the modulator correctly or is there a different way?

That thing on the side of the IP varies vacuum based on throttle position. It should pretty much block vacuum at WOT but I don't know that it's an absolute block. Might just be very close to 0.

Sixto
87 300D

Hmmm, I havent actually hooked up a gauge to the lines and ran the car...mostly cause I dont know what Im looking for.

As of now, Im paying very close attention to the symptoms of this car over different conditions.

As for the the modulator, how do I test it?

Also, this may be an interesting side note...when the car is COLD...and I mean sat overnight in the COLD (30's or lower)...the brakes are HARD in the morning...like I got no brake boost! When it runs for a lil while...theyre back!

When the car is COLD...the tranny CLUNKS when I brake to a stop (from downshifting I assume).

Any thoughts?

The engine vacuum pump on these cars can be a trouble spot. The original design identified by no exposed screws on the brass front plate has a poor bearing design. There is a plastic spacer ring keeping 6 balls distributed on each side of the bearing. The plastic disintegrates over time allowing the balls to fall out of the races. It's bad enough these balls fall into the timing chain, but when the bearing gives up completely, it sends shrapnel into the timing chain. Not to mention a complete lack of vacuum.

That possibility, void of any symptoms, is enough to make folks upgrade to the later style pump with shielded bearing. You have intermittent pump peformance which is one strike. How lucky do you feel? Thus far only gsxr has managed to destroy a newer style pump and you might say he was out to do just that. I'm kidding, Dave

If it wan't mentioned earlier in the thread (I haven't read it all), vacuum modulation is key to proper shift feel. No vacuum means neck snapping shifts at low throttle. There's no point futzing with shift feel until you sort out the vacuum supply situation. If you'd like, hook up a vacuum gauge to the plastic line that goes from the TRANS port of the blue UFO thing on the left inner fender to the transmission. You should see high vacuum at low throttle and close to no vacuum at full throttle. Linear relationship in between. Actual numbers of what you should see are in the archives.

Sixto
87 300D

vstech always wants another car even though the county says he has 13 too many already in his front yard alone

__________________
commercial fisherman diesel in my blood in my boats trucks and Dear old Dad has had me drivin them since i got my first license in 1968
1986 300 SDL 427654
1999 Chevy Crew Cab Dually 225423
1986 300 SDL 287000 Dad's
1987 190 Turbo 158000 Mom's (my inheritance)

Look at the following.

1) The vacuum lines to the blue saucer on the left fender. Replace any cracked ones

2) The vacuum lines to and from the switchover valve near the saucer. This shuts off vacuum when the car is cold and opens when the car reaches 50 degrees C.

3)The wiring from the switch to the right front of the engine block. If you look down near the air fliter you will see a temperature sensor low on the block with one wire on it. Mine had collected a lot of gunk inside the connector which I blew out with WD 40. This sensor is closed to ground while the engine is cold and opens when it is warm. This opens the switchover valve.

This is how the car determines if the engine is cold or not and sets the shifts accordingly.

__________________
"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad

Okay, that makes a LOT more sense...I wasnt aware of the proper procedure of checking the vacuum...i'll try testing that this evening. In regards to the switchover valve...I'll clean that out too, see if it works.

I'll repost with my findings.

Typically, Im lookin for the high teens right at the pump...I'll look into the possibility of changing the pump.
.

...ONE more thing...that vacuum/throttle position next to the injector pump...should it be able to hold vacuum?

Not in the idle position.

Sixto
87 300D

Ahh, okay...as I was testing the vac system (with engine off, listening to the faint hiss of a leak), I noticed that it wouldnt hold a vacuum.

Well, after I got off work...I went out to my car (which had been sitting for 7 hours and cold) and started up the engine. I then pulled off the TRA line from the modulator and checked the vacuum at the modulator...it read 0. So, I revved up the motor a little bit...it then started to pull some vacuum...at about 3k RPM it was pullin about 5" of vacuum. If I read correctly, it should be the opposite (according to sixto)...I should have higher vacuum at idle and lower at increasing throttle.

Does this condemn the Modulator?

Could it just be a bad modulator this whole time?

You don't have any vacuum at the modulator.......so the modulator cannot do it's job.

Now, you need to measure the vacuum coming from the vacuum pump and going to the vacuum control valve. That's the first place to start. If you have good vacuum there (20"), then you check the vacuum from the VCV to the amplifier (blue flying saucer). The vacuum at idle should be reasonably high........15" or so. If you don't have 15", then the VCV is NG or you have a leak in one of the hoses (the most common problem).

Im sorry, what I meant to say was I removed the TRA line and replaced it with my gauge to measure what (if any) vacuum I was receiving FROM the TRA port on the blue flying saucer.

The VCV, when I would apply an outside vacuum to it (and plug one end) , would not hold a vacuum...Ive been told this is normal.

I replaced most of the vacuum lines already and the boots seem to be fine.