mechanical throttle linkage, what's the problem ?

[bartsscooterservice]

Everybody knows the problem: it's really hard to drive away without flooring it right away and having a wheelspin. I lubed everything, I adjusted the play, even did the bellhousing modification, that helped a little, but still I have problems driving away normally. What's the problem here ?

It's driving me crazy..

[AZ-240z]

Bart,

It is a design short-coming in the geometry of the 240z throttle linkage, and plagues every car. I have heard that it is possible to solve
this problem by re-configuring some of the linkage attachment points, but I have not done any further investigation.

I'm sure someone here has attempted to do a modification to the linkage to allow for a smoother accelerator pedal application.

Dan

[siteunseen]

It is a design short-coming in the geometry of the 240z throttle linkage, and plagues every car.

Boy oh boy that makes my day. Same problem here too and was on my short list, to do very soon. Mine starts "hopping" when I try to leave out easy from my driveway.

[zKars]

The common fix involves reducing the included angle of the two bell crank arms from ~90deg to ~50deg or so. There is a thread on here somewhere about this.

Just cut the mounting tube in half, rotate and re-weld. Change length of the upper rod end to match.

You could also convert to cable throttle, the best solution in my mind. Depends on whether original look or vastly improved functionality is your goal.

[Mikes Z car]

The PO for my car bent the arm on the linkage to help with throttle jerk but it doesn't get rid of the prblem completely. I sure remember my other 240Z from 30 years ago taking off fast from every start. A passenger mentioned it to me once. (Is that why you like these little cars?)



More info here:
Throttle jerk fix - Blogs - Classic Zcar Club

[Blue]

Karl & Dan got it here: Accel. Linkage Fix

I recommend taking the slop out of the linkage and lubricating as a first step.

FYI Some of the linkage rods are threaded for doing this.

Hardway and I cut and chased new threads on his to improve performance.

[240dkw]

Here is the post

http://www.classiczcars.com/forums/f...rovements.html

[Mike W]

So unless you have an aversion to moving away from stock, which is a perfectly valid reason to stick with the OEM setup, then moving to a throttle cable is the best and only way to go in my opinion. I run with triple Webers and have for years, and constantly fought the "drivability issues" that the OEM linkage introduced. I know that some have been successful with getting the OEM setup correct, but no matter what I tried I could never get there.

So I went with a Lokar universal cable setup. It did take a little modification at the pedal to get the connection right and I also had to figure out the connection to the throttle rod for the Webers, , but enough other people had done this, I found numerous choices.

I wish I had done this years ago. My car is some much more drivable and responsive it just makes you want to drive it more as I am not constantly fighting the jerkiness, etc. And the return to idle is always perfect now.

This probably ranks in the top 2 improvements I have made to my car and could be #1. I'm so happy with it that when I had my car painted last year, I had the shop totally remove all of the brackets in the engine bay associated with the OEM linkage. Needless to say, I'm never going back.

Mike.

[grannyknot]

Bart, Lokar cable. Smooth and simple,

[Zedyone_kenobi]

I do not find this to be a fault with the Z. My Z had this exact problem when I first bought it. It was quite bad actually. When I got the SU's rebuilt at Z therapy, It came back with new linkage rods on them. The cars problem were 100% gone. All of the parts were bone stock. Nothing was cut, bent, modified or any other creative bandaid. I am just saying that if the parts are in good non worn out condition, the throttle will be perfectly OEM.

I would recommend calling Z therapy and asking them how much it would be for a complete set of new push pull rods with new ends on them

I think if you get that, and remove all the slop, you will see your problem goes away.

Moral of the story, when the car was new it did not have a sticky throttle, so return it to new....



Or you can get a lokar cable, as it work very well just as Mike said.

[bartsscooterservice]

I want to keep it Original, so cable is no option. I did the bell crank mod, and for a while that seemed to help but the problem is back. @ Kenobi : I was thinking the same way, the problem wasn't there when new ! It must be wear.. or a little sticky butterfly valves in the idle/lower part ?

[bartsscooterservice]

mm, so the problem must be in the butterfly shafts on the carbies...

[madkaw]

I'm with the crowd that says the linkage is NOT a bad design, but these are old cars and will have issues. I stuck with rods on my Mikunis and they work flawlessly, better then I ever expected. So I am saying there is a fix for the rods, just need to find it. I'm almost sure you can buy all new ball ends and that's where I would start. I would also look at the long main rod that has the fork end hooks to the balance tube.

[bartsscooterservice]

Maybe the butterfly axles in the carburetor are just sticking in the closed position due wear overtime, i'll have a look next week.

Because it's the heavy point I need to overcome then suddenly it goes, I can't see how this got to do with even a linkage with play.

[Mikes Z car]

I notice my DD uses a cable that feeds to a round "pulley" on the butterfly shaft so the mechanical advantage is very close to the same throughout gas pedal depression meaning the rate of rotation of the butterfly shaft is linear. Pedal action is very smooth and the car uses a carburetor. I don't know if linear action matters for racing. Does vacuum pull on the butterfly to make it stick? Maybe unhooking the return springs and the linkage to the pedal when the car is running would answer that. Maybe compare that linkage friction to the friction when it is not running. Just ideas.

[Blue]

Dang now you got me interested in this... I'll have to take measurements, draw the linkage, model it in excel then do what-if's....curses for taking my toys apart and an interest in applied physics.

I'm thinking what Mike says as well as Karl and Dan's findings...maybe an eccentric wheel is the way to go... maybe an adjustable eccentric is even better.

[Mikes Z car]

Blue, I just figured if we could get you dragged into this discussion we would get another valuable point of view. heh heh

[z boy mn]

Hi Mike (and all), I also have triple Webers and there's a point in the linkage movement that sticks a bit. I was going to replace some of the linkage points with Heim joints, but I'm thinking now a cable might be easier/better. Do you have any pictures of your set-up? I'd like to see what I'm getting into as I'm still learning the basics!

[Mikes Z car]

z boy mn.
I only have cable on my daily driver which is an old '83 Toyota SR5 wagon though I am also curious about using cable on a Z if anyone has pictures of their setup.

For Blue, I'd love to see how linkage modeling might be done with excel. I saw some two dimensional (in a flat plane) linkage modeling using a microsoft office product (might have been excel or powerpoint) a year ago somewhere on the net but couldn't see how to make it work for a Z multiple link setup. It might be possible to do 3D dynamic linkage modeling in sketchup, but is the output desired a graph showing gas pedal linear mm input movement VS rotational degrees of butterfly shaft movement? A goal might be your eccentric idea with a slow take off that gets faster at mid pedal depression and then tapers off at maximum gas pedal depression? I don't know what might be ideal for street driving other than slow or linear butterfly movement as the pedal is pushed off of idle.

[Reverend]

I'd personally love to see dozens of pics of triple linkages.

[Travel'n Man]

http://www.classiczcars.com/forums/c...questions.html

[Mikes Z car]

Another one (mentions a cable that does not require grinding off anything on Datsun gas pedal):

Throttle cable setup - Lockar & custom bracket - Drivetrain - HybridZ

[z boy mn]

Great pictures everyone, thanks for the link. Installing a cable seems much simpler than trying to get the linkage worked out, especially for me. My linkage needs a "repeater" of sorts because the linkage to the carbs doesn't line up with the stock one on the firewall. It binds right when the mechanical advantage is worst/best and the first axle grabs the rubber washer inside the stock firewall bracket. Makes for slop and stickiness. An upgrade sounds like a good winter project!

[jfa.series1]

I'd personally love to see dozens of pics of triple linkages.

Carburetor porn??? Sounds a bit kinky!

[Captain Obvious]

Check out the venturis on that beauty!!

[240Z240Z240Z]

It's understood that the mechanical linkage isn't ideal, but I can't believe they would have sold the cars new with the linkage as jerk inducing as I've experienced or a lot of people wouldn't have bought them after a test drive. Do any of the early Road and Tracks or other publications talk about the jerky throttle problem ? Not sure, but I don't recall having ever read about it. I don't think that worn linkage is the problem, like most people I've over lubed every friction point in the linkage path and still no joy.

I've noticed that the accelerator pedal resistance problem occurs only when the engine is running, if the engine is off the throttles open easily. With the engine running it takes more force to crack the throttles open than it does to rotate them from there on, even when you use your hand to move the linkage at the carbs. I think this is just a function of the throttle plate design in that the manifold vacuum is trying to hold the plates closed at idle, so it stands to reason if you reduce your idle speed the problem should be reduced since less vacuum is being created and therefore it will take less force to overcome it. I currently have my carbs off for a servicing so I can't try it myself yet, but I think idling your engine down should have a positive effect.

[SledZ]

Here is what I did and it is as smooth as can be.
http://www.classiczcars.com/forums/t...html#post85160

[Kennymonster]

In my opinion this whole jerky acceleration issue is very subjective on the driver & feel.

My '72 started out on bone stock SU / linkages, I never once felt the needed to increase the linkage angle or desensitize the throttle sensitivity. I personally didn't think it was that touchy compared to other cars I've been in, but then again it all depends on preference too. I don't feel right telling someone to get used to it if they don't like the feel, it's your car after all.

I converted to triples and kept the 100% linkage set up on that too, from pedal to the carbs... until one day a socket arm came off on the freeway leaving all other linkages completely useless, all it takes is one.

The Lockar kit in post above, I had it laying around and decided to rig it with my interpretation of it. I wanted ALL the linkages gone (minus the signature 3 arms on the carbs).

Removed:




Drilled out the pedal to mount the hook side, backwards from what other write ups said:




Completely eye balled this boat bracket on ebay, the mounting holes lined up perfectly on my mikuni carbs. Bent it slightly to my desired angle, and drilled out the top portion to sandwich between the kit lock nuts.






The threaded end of the Lockar kit, I found a plastic socket with the right pitch so it can thread on to it, effectively making it very simple and direct without having to fab any custom brackets and shenanigans. The slight curvature embracing my fuel line was a bonus.







And the end result, is very short and responsive, yet controlled throttle on my triples. My foot may as well be on the carb arms themselves. The difference in response is very apparent on throttle blips on down shifts / heel toe, and take offs as well.

[Captain_Zeros]

I'm running SUs with the bone stock linkage and I've never experienced any sort of jerk or difficulty in modulating throttle at all.
Now I'm real curious what everybody is talking about.

[SledZ]

Have you ever play that game Shoot the Moon? It's almost like that. You put pressure on the pedal and it's hard to get it to move and then all of a sudden it lets go.

[Zedyone_kenobi]

This is 100% a worn throttle linkage thing. I would bet the house on it. After I replaced the linkage (with new Ztherapy SU's) my car drove exactly like any new OEM car on the market, engine running or not. I had the smoothest pedal I ever had. NO sticking ever. It may not be about lube as much as it is about suble angles and worn ball and sockets. The first thing I would do to a new to me Z car is replace all those linkages with new ones or at least new ball ends.

[bartsscooterservice]

I've noticed that the accelerator pedal resistance problem occurs only when the engine is running, if the engine is off the throttles open easily. With the engine running it takes more force to crack the throttles open than it does to rotate them from there on, even when you use your hand to move the linkage at the carbs.

yeah when engine is running, it feels like engine vacuum is pulling on it
my dad had one in the 70's and he said didn't have it, so must be a wear problem. Still thinking the carburetor axle and the linkage on the manifold cause to much resistance due wear.. but didn't have time to check it yet, will do saturday

[Blue]

I wonder if the edges of the throttle valve are the culprits and they embed a little into the aluminum wall under vacuum due to wear? Can vacuum do more than this?

[SledZ]

I would believe it was wear if after I did the "old throttle fix" and the symptom stayed the same.

[Mikes Z car]

Blue,
I was wondering if dirt in the four butterfly shaft bearings as they go through both sides of both carbs would cause friction that would cause the jerk? Maybe spraying the bearings with carb cleaner would help? I haven't seen a clear picture of what the butterfly bumps into at its top and bottom when it is closed. Maybe wear on the shaft bearings would let the butterfly contact the carb wall in a way it didn't when it was new?

[bartsscooterservice]

yeah something like that, I checked between work today but couldn't find anything odd. But if the butterfly valve was contacting the throttle body, then wouldn't it also be when the engine is not running ? It's only when it's running...

[bartsscooterservice]

It's understood that the mechanical linkage isn't ideal, but I can't believe they would have sold the cars new with the linkage as jerk inducing as I've experienced or a lot of people wouldn't have bought them after a test drive. Do any of the early Road and Tracks or other publications talk about the jerky throttle problem ? Not sure, but I don't recall having ever read about it. I don't think that worn linkage is the problem, like most people I've over lubed every friction point in the linkage path and still no joy.

I've noticed that the accelerator pedal resistance problem occurs only when the engine is running, if the engine is off the throttles open easily. With the engine running it takes more force to crack the throttles open than it does to rotate them from there on, even when you use your hand to move the linkage at the carbs. I think this is just a function of the throttle plate design in that the manifold vacuum is trying to hold the plates closed at idle, so it stands to reason if you reduce your idle speed the problem should be reduced since less vacuum is being created and therefore it will take less force to overcome it. I currently have my carbs off for a servicing so I can't try it myself yet, but I think idling your engine down should have a positive effect.

If you found a solution let me know ! My dad also said something about idle speed, but setting it back to 800 rpm didn't have any effect

[bartsscooterservice]

took the gas pedal off, and cleaned/lubed the rotating part, it helped again in anything above 1500 rpm , but still not the heavy part in the beginning for driving away

[Blue]

you could try wiring just one return spring for an experiment

[240Z240Z240Z]

If you found a solution let me know ! My dad also said something about idle speed, but setting it back to 800 rpm didn't have any effect

I was thinking lower than that, more in the 500 - 600 rpm range. Not sure what the manual says is correct but I don't think there's any harm from idling "too" low.

[bartsscooterservice]

That's really to low imo , I've set it just under 1000 rpm, like most cars do here. But I tried with the linkage unhooked, and feel how the butterfly valves operate on a running engine when turned by hand, and they still operate heavy, so.. problems with worn shafts then ? I can't seem to think of anything else at the moment. There's no play in the linkage.

Could a to heavy damper oil, or a shortage of incoming air cause this to ? Altough I can't see a direct connection

[bartsscooterservice]

I asked a professional carb rebuilding company from Belgium ( not so many around here ), and he says he doesn't understand why the gas pedal operates smooth when engine is off ( only on the pedal, because direct @ carbs you can feel the tensions of the springs ), but heavy when engine is running.

[Captain Obvious]

I've got something similar with my FI throttle body:

http://www.classiczcars.com/forums/f...ging-idle.html

I think I have traced the issue to wear in the throttle plate shaft. The shaft is chrome plated for wear resistance and the plating is worn through in spots. The softer gummier steel underneath gets sticky against the soft steel bearing inserts that are pressed into the throttle body casting.

I've "temporarily" fixed it by increasing the return spring force. Addresses the symptom, but not the cause. Eventually I plan to come up with a better solution that addresses the cause instead of just the symptom.

[Blue]

It is interesting it is on TB's and Carbs. Bearings/Bushings, linkage and TV are common to both so no elimination due to EFI change.

btw my 2004 Rav4 has electronic throttle and it is jerky and insensitive at low speed... I think it is the programmed curve or lack of fine digital granularity at low pedal travel region.

[bartsscooterservice]

I bounced up a topic in the carb section, that guy has exactly the same problem i'm having, curious if or how he fixed it..

[Captain Obvious]

it is jerky and insensitive

Same thing has been said about me at times.

[240Z240Z240Z]

I asked a professional carb rebuilding company from Belgium ( not so many around here ), and he says he doesn't understand why the gas pedal operates smooth when engine is off ( only on the pedal, because direct @ carbs you can feel the tensions of the springs ), but heavy when engine is running.

I still believe the problem is that the manifold vacuum is helping hold the butterflies closed at idle, its just the nature of the design. The carbs have a mechanical advantage over your foot so it doesn't take much resistance on their part to increase the effort it takes to press down on the pedal. What makes it worse is the force of your foot and the resistance of the butterflies causes the linkage to bind in-between, especially at any dry rotating linkage points. You should be able to test this with the engine off by having someone hold the butterflies close right at the carbs and see if the pedal doesn't get a lot harder to press down.

My 2 yen.

[Zedyone_kenobi]

If that is the case, then this problem would be apparent on brand new Z cars with brand new carbs. Which it is not and was not. I still hold that this is a worn part problem, either in the ball and sockets or in the carb bushings

[240Z240Z240Z]

If that is the case, then this problem would be apparent on brand new Z cars with brand new carbs. Which it is not and was not. I still hold that this is a worn part problem, either in the ball and sockets or in the carb bushings

I agree with you that it does get worse with worn or dry bushings (I think I said that), but I'm guessing many folks here also set their idle RPM higher than they did at the factory. If you're setting the idle to 1000 RPM its too high IMHO, even the E-Type guys with tripple SU's and a 4.2L set their RPM down around 600-700. Also, I think the bushings used in several places are Nylon which is known to produce stick-slip behavior when dry. So combine dry nylon bushings, with higher than necessary idle RPM and you get an initial sticky throttle press. Before I took my carbs and linkage off recently I had the sticky throttle issue. Now I'm in the process of putting my carbs back on and plan to do some experiments and see if what I've been thinking is true.

[bartsscooterservice]

Let's wait and see, I do agree with Kenobi, he has a point there. I bought the ztherapy rebuilded carbs from Grannyknot, and will put them on when they arrive, and see what happens...

[Zedyone_kenobi]

If those are fresh rebuilds inlcuding the linkages, then I predict your problem will be a think of the past. I am eagerly awaiting an update buddy;

[bartsscooterservice]

Yup, they are practically new, he had them on for a few hundred miles, let's hope the problem is solved with it... then we also know the answer to the problem.

[bartsscooterservice]

Problem is GONE. To confirm: it was in the carburetor butterfly axles ( to much drag/wear ). Pedal feels so smooth now, it's even to sensitive !

[Zedyone_kenobi]

HUZZAH!

Good for you man! Way to work through an issue!

[240Z240Z240Z]

As I indicated earlier, I took my carbs off and have been going through the linkage bits to ensure everything is working properly. Besides discovering that my carb heat tube was completely plugged I found that the Nylon bushings of the bell crank were super snug on the support shaft. I had to pry the bottom one off, its like they shrunk down over the years. I ordered some new ones from MS and they turn like butter.

[bartsscooterservice]

I guess there could be different reasons for the problem. But i'd recommend anyone to look @ the carbs first. I also tried everything else, but it came back to beeing the carbs.

[2fiddyz]

I remember back in the day I worked in a Z car junk yard, and I had every make an model at my disposal. So I mixed and matched pieces from 240's 260's, 280's and Maybe even 280ZX's and solved it 95%, but it seemed that the last pivot above the throttle linkage had the most amount of resistance. If you can duplicate that last item with a set of teflon lined heim joints (spherical rod end bearing) that makes a BIG difference. Also, if you have the resources to press the factory bushing out of the intake manifold boss and bore it out to accept a needle bearing and seal from a parts shop, that might solve all of your problems.

But many above are correct, the beginning of the travel for the factory linkage is a bit over-center and it makes the initial depressing of the throttle abrupt if the pivots are not lubed properly.

I 100% stock is your goal, I remember graphite on the bronze bushing in the manifold/carb helped. A filling each nylon cup with synthetic lube helped quite a bit.

Also you could have an oilite bushing machined by a local machinist pretty cheap, then pres it in the factory location. The raw bushing material can be purchased from McMaster Carr.

[bartsscooterservice]

HUZZAH!

Good for you man! Way to work through an issue!

Yeah..it really works perfect now. It was like new carbs mounted...and when I pressed the pedal with running engine my jaw dropped to the floor on the difference it made...