Why does my throttle valve require more cable distance than the TV cable will allow?

[greyT]

I am looking for suggestions on why the TV cable on my TR is only allowing the throttle valve to open ~70% of the way.

Likewise, my TPS sensor only provides a maximum of ~3.5v (this was the tip off that something was wrong at the throttle valve). When I disconnect the TV cable, the throttle valve will achieve it's full stroke along with 4.8v from the TPS. I believe the transmission was rebuilt or at least a shift kit was installed by a previous owner. The throttle lever is not bent, or damaged and the cable connection is at the correct spot on the throttle valve. I have performed the TV cable adjustment procedure provided in the service manual and it only yields that 70% max. throttle opening.

After reading the TV MADE EZ article, I took a look at the transmission end of the cable. I will use the names referenced by the article to try and describe what I see. When the throttle valve is opened, the TV plunger is pushed into the bushing until it is flush with the end of it. A curled tab on the TV lever assembly (that pushes on the plunger) stops it on the end of the bushing. Also, I can not manually push the plunger in any more from the edge of the bushing.

The TV bushing sticks out about .090" from the edge if the valve body casting. I was not able to get a measurement to the counter bore depth. Is this correct or is the bushing not supposed to stick past the edge of the casting?

The TV lever doesn't appear to be bent in any way. IMO, the parts inside the transmission look like the original parts (this is the only THM200 trans. I have to reference), but will not allow the throttle to open all the way.

Does anybody have any comments or suggestions of what may be wrong here?

Thanks,
Don

 

[chris718]

if you leave the initial tv setting 1/8 lose before it pulls the cable does it get wot?

 

[Nordbert]

It sounds like the throttle valve plunger and bushing are OK. The bushing does stick out of the valve body a little so the spring pin can be pushed into the retaining groove of the bushing. The curved part of the lever should stop against the face of the bushing as you noted. Does the throttle open fully with the cable unhooked at the valve body? I would unhook the cable and lift the lever at the valve body until it
touched the tip of the TV plunger, then I would check how far the hole for the cable moved as I lifted the lever until the curved tip touched the bushing. It should be able
to move as far as the lever on the throttle body. I would check for a problem with
the lever assembly on the valve body or possibly a frayed cable.

 

[greyT]

Thanks for the quick responses. I am really still baffled by this problem. It really seems like a simple mechanical movement issue but may be turning into a can of worms.

Nordbert, The throttle does open fully with the cable unhooked at the valve body. I removed the TV lever assembly, and did not notice anything broken or out of place. It was assembled properly. I also pulled on the TV plunger to the end of the TV bushing. I do notice that there feels to be ~ 1/8" of play from the full out position of the TV plunger to the end of the TV spring.

Chris, I do not completely understand your question. Could you please clarify? Did you mean to pull the slider out 1/8" and see if it gets to WOT.

I did manually readjust the slider so that at the same moment it gets to WOT, the curled tab on the lever assembly stops at the end of the TV bushing. The slider is about .200" further out at this setting, than with the service manual adjustment procedure. With this setting, when the throttle valve is at the idle position, the curled tab on the TV lever pushing on the plunger is only just touching the uncompressed TV spring. There is no real pre-load on the TV valve at idle, but there is also no play between the plunger and the spring. Should this be a cause for real concern?

Right now, I think that the original TV spring may have been exchanged with a shorter one from a shift kit. Is this one of the first items to be changed when upgrading a THM200?

I am going to put it all back together and see how it feels. If it shifts too violently, I will be pulling the valve body out to take a look at the TV valve and internal components. It will be a few days though.

Don

 

[Nordbert]

In your second paragraph you state that there is about 1\8" play between
the plunger and the TV spring when you pull the plunger to the end of the
bushing then push it in until it contacts the spring. I think you would benefit from
this slack being removed by replacing the spring with a slightly longer one, or by adding a spacer of the proper thickness. Don't preload the TV valve with a spring or spacer that is too long or other problems may appear. Check out chris718's post at the bottom of this thread:http://www.turbobuick.com/forums/showthread.php?t=68670&highlight=valve+body+experts+read