In the process of installing a 4L60E transmission, I was going to install the TPS from Compushift and found two problems. First, on my '80, the throttle cable support bracket interferes with the placement of the TPS and it's bracket. The second problem is that the "ratio arm" which is designed to bolt onto the throttle linkage using the hole where the kickdown cable would normally hook on cannot be bolted on because on at least my model Q-jet there is no hole for the kickdown to attach. It attached to a boss. If anyone has dealt with these issues before and has a solution short of hacking the throttle cable support bracket and drilling out the riveted boss on the throttle linkage, please let me know.

 

curious
why the 4L60E and not the 4L60 / 700r4 ?

 

Frankly, in my case if I were to do it again, I go with a well built 200-4R. The reason I opted for the 4L60E was that I plan to swap the engine in a couple years and figured this would allow me to easily optimize the shift pattern for whatever the new engines power curve was and not have to play the game of swapping springs and gears to set up the WOT shift point. However, after committing to the 4L60E, as I was looking at SBC's in the 400 hp range (e.g. a 383 stroker with a mild cam) and I found they all have basically the same RPM at peak HP, typically 5300 to 5500. This is mostly because how "hot" a cam is depends mostly on duration. So cams with comparable behavior generally have similar duration. I like my L82 behavior, nice lope at idle but not needing some throttle to avoid stalling when stopped in drive with the brake on, good street manners, but a nice spirit when punched and it peaks hp at 5200 RPM. Getting this same behavior in a new engine means very little change in RPM for shift at WOT. So, in my case, I really wouldn't care if I was loosing a couple tenths of a second to 60 because my shift point was 100 RPM too low or high to be optimal

For me then, this was a mistake and now I'm into all this extra effort and cost for the "E". As to why I would go with the 200-4R vs a 700 or the 4L60 - The 200 fist better, it can easily built to reliably handle over 500 ft-lb of torque and hp, and it's 1st gear is not as low as that in the 700. The 700 and 4L60 includnig the E have a big step between 1st and 2nd. As I already swapped my rear gears from 3.07 to 3.54, I don't need that low first in the 700/4L60 family and the closer ratio between 1st and 2nd of the 200 would result in less RPM drop during the 1st to 2nd shift.

Basically, I thought I had done enough research, but I was wrong.

 

If all you need is a hole drilled into the carb linkage arm (at the correct place), then just do it. Making room for the TPS will require some modifications; but you know how 'stuff' needs to be set up, once those mods have been made to get the room you need for TPS installation. Again, just do it. The throttle cable isn't going to act any differently if you move the mount point away from the carb. You will just need to adapt something to fill in the shortened length of that cable once it is re-positioned.

You're a creative person (must be, if you own a C3 ); you can figure it out.

 

Since the day it drove off the lot and it's still running

The problem on the throttle cable bracket is that it attaches to the back to carb bolts as can be seen in the photo. So all that would have to move somewhere.

But I'm in negotiations with Compushift. They have an alternative set up with a box housing the sensor and a cable allowing it to be mounted off the manifold. It appears the cable is identical to the original kickdown cable mounting, and thus may plug right into supporting bracket. That leaves getting it attached to the linkage as it still is designed to attach to the ratio arm.

 

I went with the 4L60E - currently installing same kit as Vince. No TV cable to mess with. Easy to program shift points. Changes can be made via an app on my cell phone. Can have two shift programs (such as one for normal driving and one for aggressive driving) and switch between them by the press of a switch. Although I would never tow with my Vette, one of the program options could be set up as a tow mode. Paddle shifter is actually an option for our C3s. I won't have the same issue as Vince with the TPS because my Edelbrock EFI controller can talk to the TCU via the CAN bus and report the throttle position so no extra TPS is needed.

Vince - I wonder if the guys at SST have seen your TPS issue before and have a better solution?

DC

 

Hello DC,

Good to hear from you. I didn't want to downplay the benefits of the 4L60E. I'm glad you noted them and I fully concur with the benefits in your build with the EFI heavily tilting the scales toward the 4L60E.

I've been in touch with SST and actually we have a three way email exchange going. Both SST and Compushift have been very responsive. I just heard from Compushift that there cable sensor kit comes with an attach with a threaded base that can be directly mounted to the linkage negating the need to drill out the existing KD cable attach. The whole point of the ratio arm is to easily mount to the linkage and them be rotated to put attach point at a location which will get the proper cable movement length. If attached directly to the KD cable attach it would have excessive movement. The ratio arm essentially moves the attach point closer the pivot point of the linkage, thus reducing the distance of movement. But since it is not easy to attach the ratio arm in my case, then the simpler option is to drill a hole where the attach point should be and use the attach with the threaded base. The question now is if the proper point is on the linkage.

 

Can it go in front and make the linkage push instead of pull?

If you're OK with programming and like experimenting you'll be glad you did it. With the e you can adjust all the whole shift curves, not just the WOT shift point. You also get better TCC control than any vacuum switch setup can give. I'll never put a non electronic automatic into a vehicle I build again. Check out BlueCat if you haven't seen it before.

 

I like the USS Computer kits , they have several styles of TPS’s , maybe one would work better for your application?

https://www.usshift.com/tps.shtml

 

In theory it could push, but it would need a new linkage set made. Not terribly hard to do I guess. But it's just wearing on me that every little thing ends up taking hours of effort and we'll be in July tomorrow.

Thanks for the pep talk on the tranny though. I feel a little better about it. I did take a quick look at BlueCat some time ago. I'll have to go deeper into it if I ever get this thing installed.

 

I'll have to drop them a line and see. They didn't specifically list a Q-jet that I found. Did I miss it?

 

while mine is for data logging I did mount a TPS on the pass side on a Holley, not sure if that's possible on a Q-Jet

Neal

 

Well, it's done, kind of. I bit the bullet and modified the original throttle support bracket, cutting out a section that interfered with the placement of the sensor. I also pulled out the kickdown cable attach boss from the throttle plate. That took a couple hours on the carb with the carb on the engine. I had to hand files the rivet on the back of the throttle plate until I could begin to rotate the boss. But it was still tight and I risked bending the linkage if I pulled too hard. Eventually with plenty of penetrating oil, a lot of turning, and some quick hits with behind the head of the boss with a chisel it separated.

When I fit everything the attach point on the TPS was way further out from the carb than the attach on the "ratio arm" that came with the kit to replace the old KD cable attach that had to be removed. The ratio allows the link to the TPS to sit closer to the pivot point of the throttle linkage in order to reduce the range of motion from what it was with the KD cable to something appropriate for the TPS. With the TPS attach so far out compared to the ratio arm attach the linkage between them was at quite an angle. The Compushift instructions specifically said to ensure this was aligned straight. I dropped a note to Compushift asking if it was OK to put a spacer in to move the ratio arm further out. They gave me the OK on that stating there is enough tolerance in the attaches to deal with some misalignment as long as nothing was binding.

So I added some washers to just get a sens of where I was. That's all shown in the photos. I still need to get the ratio arm out further for my peace of mind, so it will need a longer screw. That may cause the screws holding the link between the TPS and ratio arm to interfere with the throttle return springs, so they'll need to be cut. Also, cutting out a section of the throttle cable support bracket made it too flexible for my taste. So, I'll need to make a support bracket for the support bracket. Fortunately, the bracket for the cruise control vacuum drive (whatever it's official name is) is in a good place to run a brace between it and the throttle cable support bracket. And, fortunately, the cruise control died sometime in the mid 80's, so nothing lost there.

The summary, yes it appears the compushift TPS sensor kit can work on a Q-jet. But it's no 15 minute job an, as 7t1Vette said "You're a creative person (must be, if you own a C3 ); you can figure it out."

And now, roll the film.


Note angle between sensor and ratio arm. Screws in linkage appear to interfere with spring but don't yet. Will cut them once linkage is better aligned.

Already added two washers. Need about two more. Will get a longer screw and use jam nuts to replace the washers.

The section cut out of the throttle support bracket to make room for the sensor made it weaker. So, I have to support the support.

 

Reshape that arm (two pieces screwed together) so that the piece attaching to the TPS has a lateral offset in it, to accommodate the dimensional difference between the two attachment points. (Jeez, I wish I could just draw something in the REPLY box). The 'rear' piece will need to be longer by the amount of that shift, but then that arm will work with linear action (instead of being angled like it is).

 

I see what you mean. But I may instead need to reshape the piece on the ratio arm. If I bring the linkage toward the carb on the TPS end I may interfere with the secondary linkages. Maybe I'll see if Compushift will donate another linkage to play with given that this really doesn't fit a Q-jet as provided.

 

I created a hybrid solution between your offset (with a twist) and my spacers to move the ration arm out. I did move the arm out, but didn't want it too far out. Then instead of bending for the offset, I just put a couple nuts as spacers between the two links. See photo. It needs a few minor adjustments yet, but it appears to get the job done.