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Old 07-01-2006, 06:38 AM
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700R4 - TV cable tension problem wont allow WOT

Hi, bit of a tranny novice here and just getting back into modding cars after a couple of decades away from it. I have a chev TPI 5.7 and 700R4 transplanted from a Z28 into an aussie made GM utility.

The problem i have is that the TV cable requires so much tension that it wont allow WOT using the pedal (can manually at linkages with considerable effort) and if it gets close it will break throttle cables. With TV cable detached the throttle is light and reaches WOT perfectly. Ive checked all the geometry against several websites with adjustment instructions and all looks dead standard and spot on. Sedate shift points are perfect but I cant test beyond about 3/4 throttle due to the problem.

The car is a recent purchase so the box build is unknown but has high stall so may have other mods also. The TV cable tension is definitely the reason so I'd just like to confirm that what i feel when pulling the cable by hand sounds normal.

If i detatch the TV cable and let it retract to a relaxed position and then pull it through its full travel it appears to have 3 stages of hardness getting progressively harder and the last stage is seriously hard, enough to explain the broken throttle cables. Heres what i find;

The first stage is very light indeed and travels for about 6mm (0.23"). The next stage is noticeably harder but nothing too heavy and travels a further 14mm (0.55"). The thrid stage is very heavy indeed but even and travels a further 20mm (0.78") until an obvious stop is hit. Total travel is approx 40mm (1.57").

This third stage corresponds exactly to where the pedal gets hard and trying to pull through it with the pedal is where the throttle cable will break or the pedal will bend.

Does this travel sound normal and its just running a heavy TV setup like a transgo or something or is it that the cable should be adjusted so that at the end of the second stage corresponds to WOT (with the cable somewhat slack at idle) rather than WOT coming most of the way into the third stage.

Thanks in advance to anyone who can offer any advice on this.

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Old 07-01-2006, 08:15 AM
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Thanks for the detail of your problem. It helps considerably.
You may have two different, but related issues. The cable for the TPI motors was longer than all the others of the same time period. I would recommend getting a cable (new GM). Specify the donor car for the correct part. After the new cable is installed, and before adjustment, remove the pan form the trans to view the TV cable bracketry at the valvebody. When the throttle blades are at WOT, the plunger in the valvebody MUST be stroked fully or bottomed out. You can push the TV linkage by hand, but there can be some effort involved. Adjust the cable so that the plunger is fully bottomed at WOT.
If you cannot depress the TV plunger fully by hand, it may have a TV spring that is way too stiff. Remove the TV cable bracketry (two 10mm head bolts) and remove the TV cable bracketry. Remove the roll pin from the that is now exposed and slide the TV plunger and bushing out of the valvebody. The spring may come out with the bushing. This is the spring to check. Find a local trans shop that fixes GM trrannies and see if they have a stock TV spring. Replace the spring, the plunger and bushing, the bracketry and see if the TV linkage will work correctly. Torque bolts to 10 ft-lb. As the TV linkage moves thru its travel, the effort to compress the spring will increase. The effort will also be higher when the engine is running (trans fluid pressure). Be sure to check the tv bracketry (when installed on valvebody) to be sure it has smooth, sweeping path thru its travel.
Remember when the TV plunger is completely depressed, the throttle blades should be at WOT.
Hope this helps...
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Old 07-01-2006, 05:20 PM
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re: 700R4 - TV cable tension problem wont allow WOT

Thanks for the advice Chaz, all makes sense. Getting a new cable will be tough here (Australia), parts for the donor car aren't stocked here as far as i know so that will be a slow one to try with international shipping etc but I can check the movement and the spring fine and will do so asap. Thanks again.
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Old 07-01-2006, 08:04 PM
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Lokar makes a fine cable assembly for the 700R4. Combine that with instructions on TV Made easy and you should be fine.

Vince
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Old 07-02-2006, 03:47 AM
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re: 700R4 - TV cable tension problem wont allow WOT

Hi ppl,

did the cable check as Chazmac specified (thanks) found that the valve was fully in at WOT and had only just got there. The first light stage of the movement i described was that the TV lever was not contacting the TV at rest, there is a gap big enough to slip your finger in between the lever and the TV (not sure if this is ok or not). The second stage was when the lever contacted the valve and the third was when the lever went passed the point where it was perpendicular to the cable, so that it got pregressively heavier as leverage lessened.

The spring felt reasonably heavy but im a fairly big fella and I could put my finger on the end of it and compress it fully without too much effort so from what chaz said that sounded ok to me so Ive left it go.

With the knowledge that all was well and ajusted right I decided it had to be that way and that i had to put up with the hard pedal and simply strenthen everything. I suspect that the throttle cable was from the original car not the transplant so I managed to get a heavier one today and I welded some re-inforcing on the pedal arm and set it all up and finally, i now (with a good shove) can get WOT (showing 4.4v on the TPS instead of 3.5).

Theres a couple more issues i want to cover with this tranny yet but I'll leave you guys to rest a bit before bugging you again with it.

Thanks heaps to Chasmac for the clear and simple instructions.

Cheers from a happy guy who now has WOT to play with instead of 2/3s
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