News:

Location, Location, Location.
Please add your location to your profile. It will help others to help you!

Main Menu

"Control pressure rod?"

Started by JasonP, 08 January 2012, 07:28 PM

JasonP


I am getting two different stories on what this part is and what it does. I have a 1979 300SD, and this part is basically a linkage rod that goes from the top of the engine block down past the firewall to connect to the transmission.

It is loose, as you can see from this video and pic. The top bushing is loose, and I can pull the rod right off no problem, and the bottom has no bushing at all - it is just held in place by a rusty metal clamp. It has A LOT of play, too much in my opinion.

Top linkage:
http://meandmymercedes.ucoz.org/video-2012-01-08-16-28-11.swf

Bottom linkage:



Question #1: What is it? One person tells me it is the kick-down rod for the transmission (so when I floor it, it goes down one gear for higher revs and torque), and another person tells me that this is the rod that dictates shifting times for the transmission, based on how far the throttle is open. My car does have odd shifting times, as it hits 4th gear by the time I am going 35 miles per hour, so I am leaning towards the latter explanation.

Question #2: Should it really be this loose? I cannot imagine these cars leaving the factory floor with this much play in the rod. And besides, it rubs up against the throttle linkage, so they bang into each other as well.
1979 300SD
Color: 623H "Light Ivory"
1979 300SD
Color: 861H "Silver Green Metallic"
1977 280 E
Color: 606G "Maple Yellow"
-------------------------------------------

Squiggle Dog

This control pressure rod dictates shifting times. There is a separate electric kickdown switch. When I replaced my transmission I had to adjust this rod until it would shift at the correct RPM. When you replace the bushing at the bottom of the rod it helps the bushing at the top from being sloppy, but it looks like you should replace the one on top, too. When you replace the bushings, it will either put the shifting RPM back where it should be, or you'll have to adjust it until it shifts at the right time.
Stop paying for animal cruelty and slaughter. Go vegan! [url="https://challenge22.com/"]https://challenge22.com/[/url]

1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Heated Seats, 350,000+

JasonP


Thank you Squiggle Dog!

Why would a mechanic say otherwise? Are there some cars where this IS the kickdown system?

Could you help me find the right parts? So far, this is what I have found:

http://www.autopartsauthority.com/specials/mb_300SD_AT~Shift~Linkage~Bushing-sparts.html

and

http://www.redlinemotive.com/store/replacement/wizard.asp?year=1979&make=MB&model=300-SD-001&category=J&part=AT+Shift+Linkage+Bushing

Which one goes on the bottom, and which on top?

I would like to get this taken care of ASAP, on my own.

Thanks again for your help!
1979 300SD
Color: 623H "Light Ivory"
1979 300SD
Color: 861H "Silver Green Metallic"
1977 280 E
Color: 606G "Maple Yellow"
-------------------------------------------

Squiggle Dog

I have been looking for the part number for the plastic bushing on the top of the valve cover for a long time. I was never able to find it. I might bore mine out and sleeve it with a nylon insert when it gets really sloppy.

The bushing that goes on the transmission end of the control pressure rod is part number A 110 277 05 50. You can get one here: http://www.autohausaz.com/search/product.aspx?sid=bbebf3i2csk4nx45neuiyr55&partnumber=1102770550.

What you are showing in the second picture is where the shifter connects to the gear change rod. That will need a bushing with part number A 115 992 03 10 ( http://www.autohausaz.com/search/product.aspx?sid=bbebf3i2csk4nx45neuiyr55&partnumber=1159920310 ). Order two of these, because the second one will attach on the transmission end of the gear change rod. Don't try adjusting the gear change rod length until you have the bushings installed because it might be the proper length. Just make sure that when you put in park that the car won't roll away.

Some of the old American automobiles used a kickdown rod. Mercedes did things differently.
Stop paying for animal cruelty and slaughter. Go vegan! [url="https://challenge22.com/"]https://challenge22.com/[/url]

1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Heated Seats, 350,000+

Bandolero

Yes, my V8 Chrysler had a Torqueflite auto and the rod was a kick-down rod. I think most US autos are the same.
However after saying that, some models of the Torqueflite (6 cyl) had what was called "part throttle kick-down) and this meant that as you put the foot down, it would kick back a gear. The V8s didn't have this as I guess they didn't need it.

Our 116's have an electric switch under the pedal which engages the kick-down and the rod adjustment is there to alter how high the revs go before it drops up to the next gear, as "young" Squiggle Dog said.  ;D ;D
Russell Bond - (Adelaide, South Australia)
1978 450SEL 6.9 .... #5166 .... 12/78 (Sold.) [url="//www.ezycoat.com.au"]www.ezycoat.com.au[/url]

JasonP

#5
Thanks, everybody.   :)



Page 203, Chilton's Repair & Tune-Up Guide, Mercedes-Benz 1974-84:

CONTROL PRESSURE ROD
DIESEL ENGINES

"The control pressure rod can only be adjusted with a special guage available only from Mercedes-Benz dealers."



Gee, thanks.


1979 300SD
Color: 623H "Light Ivory"
1979 300SD
Color: 861H "Silver Green Metallic"
1977 280 E
Color: 606G "Maple Yellow"
-------------------------------------------

Bandolero

Haha. Of course they'll say that. They don't want to get sued over a trans "blowup".

I'd flatten the accelerator to the floor then adjust the rod till it hits the stop, (still with the foot flat) then test drive it. If it stays in gear too long just start to back off the adjustment till it works as it should.
This is how some of the US autos seem to be adjusted.

Don't sue me if you blow your tranny......mmmm. Maybe I should've rephrased that.... :o :o :o :o
Russell Bond - (Adelaide, South Australia)
1978 450SEL 6.9 .... #5166 .... 12/78 (Sold.) [url="//www.ezycoat.com.au"]www.ezycoat.com.au[/url]

koan

#7
Don't know what the linkage setup is on diesels but on petrol engines opening the throttle pulls the control rod forwards, suppose with the same basic transmission diesels would be the same.

Adjusting the rod longer so it is pushing further back makes the gearbox see/think the throttle is less open than it really is and will change gears at lower RPMs. Making the rod shorter does the opposite, gearbox sees the throttle more open than it actually is and will change at higher RPMs

EDIT: corrected the above when I realised I had the actions reversed,

koan
Boogity, Boogity, Boogity, Amen!

JasonP

#8
My shifting is all too soon, and I think it goes from 2nd to 3rd within the space of 5 mph. I also have too much transmission fluid, so these two adjustments should make it better.

The rod bumps against the throttle rods as well, it just lays on top of them, which I can't see as the way Mercedes wanted it.

By the way, I looked online for at least a half an hour, and nowhere did I see a transmission fluid dipstick for this car: not on blogs, or available for purchase. If anybody has an original 1979 300SD transmission fluid dipstick, share a pic! It is possible that mine is not the original.

Checklist:

  • Get transmission fluid to proper level
  • Purchase and insert rod bushings
  • Adjust control rod to proper length (shorten it, apparently)
  • Convince my mechanic, without offending him, that this rod controls shift timing, and is not a kickdown

Kent Bergsma said he was gonna focus on adjusting the rod/cable in his Part II video, but then decided to talk about the VCV valve for five minutes. Bummer.


http://www.youtube.com/watch?v=XjqwrnisV9s&list=UU7Kz01PM-xoDnqsiuwTn5og&index=1&feature=plcp

1979 300SD
Color: 623H "Light Ivory"
1979 300SD
Color: 861H "Silver Green Metallic"
1977 280 E
Color: 606G "Maple Yellow"
-------------------------------------------

ptashek

Moving my discussion from http://forum.w116.org/mechanicals/control-pressure-rod-for-what-a1170701475 :)

OK, so if this thing detaches from the throttle linkage entirely my transmission will shift at a much lower RPM than it's supposed to, right? Apart from likely affecting mileage, are there any other long-term issues this may cause? I have no idea how long this was loose on my 450.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

ptashek

To answer my own questions:

1. OK, so if this thing detaches from the throttle linkage entirely my transmission will shift at a much lower RPM than it's supposed to, right?
Sort of. Shifts happen much later, and much more abrupt. Acceleration suffers. After fixing this properly, on a warm engine/tranny, I can't really tell no more when my transmission shifts. The fact that it's been treated to a full re-build 10k miles ago probably helps too.

2. Apart from likely affecting mileage, are there any other long-term issues this may cause?
Affecting mileage? Yep. Positively though.
I've gone from 17l/100km to 18.3l/km, for now.

3. Any other long-term issues this may cause?
I'm inclined to say: unlikely.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

carl888

Quote from: JasonP on 08 January 2012, 07:28 PM

I am getting two different stories on what this part is and what it does. I have a 1979 300SD, and this part is basically a linkage rod that goes from the top of the engine block down past the firewall to connect to the transmission.

It is loose, as you can see from this video and pic. The top bushing is loose, and I can pull the rod right off no problem, and the bottom has no bushing at all - it is just held in place by a rusty metal clamp. It has A LOT of play, too much in my opinion.

Top linkage:
http://meandmymercedes.ucoz.org/video-2012-01-08-16-28-11.swf

Bottom linkage:



Question #1: What is it? One person tells me it is the kick-down rod for the transmission (so when I floor it, it goes down one gear for higher revs and torque), and another person tells me that this is the rod that dictates shifting times for the transmission, based on how far the throttle is open. My car does have odd shifting times, as it hits 4th gear by the time I am going 35 miles per hour, so I am leaning towards the latter explanation.

Question #2: Should it really be this loose? I cannot imagine these cars leaving the factory floor with this much play in the rod. And besides, it rubs up against the throttle linkage, so they bang into each other as well.

1. That looks like the upper section of the gear selector gate to me.  The nylon bush is missing, replace it.

2. Control pressure rod is easy to adjust.  Adjust the length of the rod (Just to avoid confusion, we are speaking of the rod that travels from the throttle linkage to the side of the transmission and "Tells" the transmission the throttle position) until the part and full throttle upshifts and downshifts without kickdown co-incide with the specifications in either the data book or the workshop manual.