Harsh automatic gear changes

[reggie]

Enjoying my new pagoda very much,but when slowing down the last down shift into second seems very harsh, is this normal, I seem to remember my last one in 1990 was harsh too, Thought i better check with you guys
Reg

[Larry & Norma]

Hi Reggie, mine is not harsh up or down except a little when the engine is cold ie tickover is high (1100 rpm).
So if your tickover is about 850 rpm then changes should be smooth. There is a whole load of stuff on this site about setting up for smooth changes,
you really have to do all the engine set up tours first.

[reggie]

Thanks for that,engine seems ok to me,tick over is pretty low when i first start up,takes a bit to start after a run,but i understand that to be fuel evapoaration ? so were to go next. mmm
Reg

[ja17]

Hello reggie,

A harsh final downshift is usually caused by an improperly adjusted venturi switch. This swich is on the intake venturi and must be adjusted correctly. It lowers the modulator pressure in the transmission before the last downshift. Review the "Linkage Tour" on this site for all the details.

[reggie]

Thanks joe,i was up late last night reading all about it,trouble is i dont have a gauge to know which way to adjust it, i will come up with a plan ime sure
Reg

[ja17]

Hello reggie,

You do not need a gauge. Just unhook the linkage at the venturi, loosen the 10mm lock nut on the adjustment and back off the small slotted screw until the flap in the venturi is closed all the way. Set the screw just enough to keep the flap from binding closed. This should always be set at this point. next make sure that you adjust the linkage so that it just slips over the linkage ball on the venturi.  The "linkage tour"  goes into the fine details.

[reggie]

Thanks again Joe-the two wires that goe to that solenoid-what should be the readings and when ?. I was looking at that today but dont want to fiddle with anything until i understand what it is suppose to do.
Reg

[reggie]

So this afternoon i set the venturi flap just open without binding-then it was much better but not perfect-then it says engine warm and running the slip rod should be fully collapsed it wasnt so i did that and it didnt like changing up-so i put it back a bit at a time so its not bad but not perfect-i can here a slight popping back from the exhaust (muffler) on the over run,and it smelled a bit funny when i put it back in the garage  - flap open too much ?, I have done the tour but dont want to fiddle with any thing else until i get that bit right 
Reg

[xcashewx]

try the  vacuumm modulator in the trans. that funky smell could be ATF getting sucked up and burning in your #6 cylinder

[tel76]

Hello JA17.
You indicated that Reggies problem could be an Improperly Adjusted Venturi Switch,correct me if i am wrong but the tour does not tell us how to adjust the switch (the switch can be adjusted by slackening the two screws and turning the switch a small amount clockwise and anteclockwise).
After setting the butterfly in the closed position can you please inform us how to get the switch in the correct position.

[reggie]

HI Eric
I was wondering that myself, i took that off this afternoon, looked at it and put it back, it didnt seem to have much adjustment, but i presume you turn it clockwise the same as backing of the venturi flap ? i adjusted the slip rod to fully colapsed like it says, but then it wouldnt change up, so i backed it off a bit at a time until it was nearly back to were it was and ime nearly there, its a big improvement now, but a bit more fine tuning might make it even better, i always mark things so i can put it back if its not right, as for the smell i think it was unburnt fuel, my last test drive was ok, no popping back or smell, so i must have done something right, think that was the slip rod being too short and holding the flap open, strange set up ?
Reg

[tel76]

Hello Reg,
I saw in a previous post that your car went through its test ok,did the tester not query the side lights,i visited my test centre(government owned here) to ask if i can have yellow lenses like yours,i was told you must have white lights to the front.
Does anyone in the UK have yellow side lights as per Reggies?

[reggie]

Hello Eric The mot tester never said anything, He just walked round it saying things like WOW and BLOODY HELL, It was pretty funny really, And he waved me off when i left, Ime just a lucky guy i think 
Reg

[reggie]

Well, I have faffed and tinkered and now turned the venturi switch both ways and clockwise seems best but that last change down is still not to my likeing, If ime doing a rolling stop its ok but if i stop quickly thats when its worse, There dosnt seem to be a feed to that solenoid that lets the throttle off slowly- but i presume thats to do with emissions ? nothing to do with the auto box ,Did i say iwasnt going to play with this car, Its booked in for some paint work next week,And ive been under the bonnet-(hood) since i got it, Have i got pagodaitus ?   
Reg

[tel76]

Hello Reg,
I would have thought by know someone would have read the BBB and given us all the way to correctly adjust the switch.
Has anyone stripped it down?
Is it just an On/Off switch or does it carry out more functions?

[reggie]

Eric, Well i wish somebody would its bugging me now, Why when i had that slip rod too short it was ok down and no good up the gears, Its just the last change down now, I tried to come back the other way one bit at a time but ? I dont want to mess with it incase i cause something else,The rod was too short and it caused it to pop on the over run, It must have been letting air in the intake, Thats ok now- I think its just an on off switch, I had my tester on it, Somebody must have been through all this before,
Reg

[jacovdw]

Reggie, Eric and others...

According to the BBB, you need an inspection lamp (or test lamp), a rev counter and an engine at operating temperature.
Disconnect the two wires from the throttle switch and connect one cable to ground and the other via the test lamp to the positive pole of the battery.

For transmission type K4A025 (as used in the 280SL pagodas) the maximum cutout speed for the idle switch is 1600 rpm.

Now with the engine running (idle speed) place gear selector lever in "P" or "N" (make sure parking brake is applied) and increase the engine speed slowly. The test lamp should extinguish at the latest when the cutout speed (1600 rpm) is attained.

If not, slightly loosen the two mounting screws of the switch and rotate until the test lamp extinguishes at the appropriate speed. Tighten mounting screws and recheck.

Hope this helps.

[reggie]

Jaco thanks for that, Do you mean run the test lamp through the switch-not the wires that go to the switch ?
Reg

[ja17]

Hello Guys,

The switch on the venturi actually controls part of the function of the three positiion solenoid on the transmission. The  kick down switch on the floor also inputs the three position solenoid. The three position solenoid moves a linkage rod to the automatic transmission modulator which changes pressure in the transmission to perform kick down passing gear and allow smooth downshifts.
A few things must be happening before this all works correctly. First the transmission must be functioning correctly with correct modulator pressure (assume this is correct for now), the solenoid must be functional , the transmission linkage rod from from the solenoid to the modulator must be free (often rusted and will not move), the engine linkages must be correctly adjusted, and you must have correct electrical power to the switch and the solenoid (check fuses).

The first thing to do is remove the access cover on the inside of the car and make sure the linkage rod and solenoid are functional.

When the ignition is turned on and the accelerator pedal is all the way up (idle) current is feed to and through the switch on the venturi. Current actually flows through the switch and moves the three position solenoid and a its linkages to the rear position lowering pressure in the tranmissionand  creating a nice smooth last  downshift. Soon after the accelerator pedal is moved, the switch on the venturi interupts the current to the  solenoid and it returns to its center "rest" position (no current) which raises the modulator pressure  in the transmission. When the acceerator pedal is pressd all the way to the floor the kick down switch moves the three position solenoid to the front-most position, raising the modulator pressure even more and causing the tranmisssion to shift down {passing gear).  

Yes loosening the two screws holding the switch will allow some adjustment of the switch. It is mostly used to adjust at what rpm the three position solenoid is de-activated activated when depressing the accelerator pedal. .  In most cases, improperly set engine linkages will be the cause of the venturi switch not working since the switch itself is factory set correctly.

[reggie]

Joe, done all that and set the switch like jaco said, It went off before 1000 rpm and wouldnt adjust any more, So i turned the switch 180 dg, tThen it went off at 1500 rpm, No differance,Mmmm, I was having a poke about and saw that the breather pipe from the air filter housing had an air screw on the inlet manifoild, So i turned it in one full turn and the engine sounded much better and even, I suppose that creates more vacuum in the manifold, So guess what, Perfect ghanges up and down, Whats that all about  . I have a funny rattle in the right hand door, So thats my next tinker tome, ha ha, what did i say ? ime not going to faff about with this one 
Reg

[ja17]

Hello Reggie,

The idle speed after warm up should be around 700 rpms. Naturally the idle will effect the engine vacuum which will effect the the vacuum modulator on the transmission.

I guess the moral of the story is "make sure the engine is in good tune and adjusted properly before looking deeper into running problems" (injection, transmission etc.).  

Glad to see you ironed out your problem.  Not exactly a direct route, but look at all you learned along the way!

The large slotted air screw on the air filter line is used to adjust idle mixture air, this along with the "mixture thumb screw" on the back of the injection pump is used to tweak idle for smoothness and correct rpm.

Improper engine ignition timing is another thing which can effect engine vacuum and tranmission shifting characteristics!

Happy motoring,

Joe Alexander
Blacklick,Ohio

[reggie]

Joe, Thanks for all your help, Yup never too old to learn,   
Reg

[tel76]

Hello Joe,
I am still rebuilding my transmission,before mounting it onto the engine and refitting it into the vehicle,how can i check that the solenoid is working correctly?
It would be better/easier to do this now than when the engine is installed.