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Old 10-17-2013, 10:22 PM
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Torque converter question 700R4

I'm running a recently rebuilt 700R4 behind a 4.3 Chevy V6 in my 40 Ford pickup.

When I first fired the truck up, I didn't realize that I needed a speed signal calibration box so as soon as the truck began to move upon being put in gear, the torque converter clutch would receive a signal from the ecm to apply. I have the speed signal sorted out now but I think I damaged the torque converter.

Here are my symptoms:

Transmission engages very harshly with a lurch from park or neutral (to drive or reverse)

The truck launches with a lurch as well. It's nearly impossible to get the truck to leave the line smoothly and it's difficult not to chirp the tires or at least make a spectacle of myself when pulling away from a light. There doesn't seem to be the "normal" amount of engine acceleration before the truck starts to move.

It's impossible to detect the engagement of the clutch while driving. The only indication that I have is if I'm driving with a scanner attached to the OBD1 port, it tells me when the clutch solenoid is activated or released.

I have had a few of these transmissions in various cars (700R4. 4L60E) and none of them act like this one. It's kinda frustrating to drive at times. All of the other cars I have with automatics will go from park (or neutral) into gear smoothly without making the car jump and there's no change in hot the vehicle idles whether its in gear or not. When I put this truck in gear not only does it bang into gear but once it's engaged, there's a vibration from the engine idling that you can feel in throughout the truck.

I would be pleased to find out that it's just a bad converter. Anyone have any ideas?

Thanks

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Old 10-18-2013, 07:58 AM
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have you checked to make sure you are at the proper fluid level ? also this motor and trans may have sat different in the donor car and giving a false reading on the fluid level. if your good their next check your fluid to see if it is burnt.
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Old 10-18-2013, 11:20 AM
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If you have checked pressures, post them, if not you really need to do that before anyone can get to far into helping you.
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Old 10-19-2013, 07:09 PM
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When I fabbed up the motor and tranny mounts, I set the throttle body mounting surface of the intake manifold to be level. That's the way I have always done it and never had any fluid level problems before.
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Old 10-21-2013, 08:47 AM
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Overdrive said it. Check pressures and post the results. One thing that occurs to me is that the TCC enable in the ECM is controlled first by the pressure switch(es) in the valvebody. There are so many variations on the factory set up for these switches that I couldn't guess how yours is setup, but all of the factory systems rely on the signal from those switches to enable the TCC. If you had lock up in anything other than 3rd or 4th gear, there almost has to be an issue in the wiring of these switches to the ECM. Otherwise you could have a hydraulic fault either in the TCC solenoid or in the TCC valvetrain. Then again, you may just have a faulty torque converter.

One method I know of for diagnosing a torque converter is the stall test. Power brake the vehicle to check for smooth action of the converter as it goes from idle to stall. If it is chattering or grabbing as you apply throttle in this mode, it is probably defective. You need to first verify that the pressures are good in the trans itself to be sure you're not just feeling the low/reverse and or overrun clutches slip and chatter due to lack of pressure.
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Old 11-03-2013, 12:36 PM
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Hello again. I have been away from the truck for a bit but this weekend I installed a tachometer, (no pressure readings yet, but I did locate a gauge that I can use).

Here's what I found out:

The truck does not go into OD nor does the TC ever lock even though the scanner says it's locked.

The racing between gears seems to be gone. The guy at the tranny shop told me to move the TV cable plunger closer to the firewall and I did, but I'm still wondering why the factory setting of the cable doesn't provide correct results. All the TV geometry is bone stock GM from the throttle body, the throttle cable/TV cable bracket all the way down to the original (albeit rebuilt) trans.

The truck idles at about 600 RPM in park and it drops to 500 in drive and as I mentioned, it "lurches" when you step on the gas, you cant ease it away from a stop sign. It goes through 1-2-3 normally but is turning at about 2500 RPM at 60 MPH. If while holding the gas pedal at 60 or so, you shift it down to 3rd, there's no change in gear or RPM, that's to say the truck was in 3rd gear even though the selector is in Drive. If you ease off the gas, the truck will go in to OD as is evidenced by the fact that if I ease off, and then down shift, I feel the truck hit 3rd, and the tach indicated an increase in RPM.

I'm still planning on getting the line pressures measured and posted here but I just wanted to post this additional information. Thanks
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Old 11-03-2013, 04:24 PM
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What gears to you have in the rear? Are you using the ome ecu for the engine? Seems like it never goes into 4th gear or OD.
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Old 11-03-2013, 08:12 PM
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The rear axle ratio is 3.45:1 I'm running the stock Chevy ECM although I still need to check to see if it has the 6cyl or the 8 cyl PROM in it. The transmission is a 700R4 not a 4L60E so it's essentially a "dumb" transmission as I understand it. All the communication between the engine and transmission happens via the TV cable and the ECM tells the TC to lock up with the only input from the tranny being the switch in the valve body that tells the ECM that the transmission is in 3rd or 4th gear (I'm not clear on that yet)

So, like I said, the only time the transmission goes into 4th (OD) is when you let up off the gas once you reach cruising speed. This is evidenced by the fact that once you let up on the gas and are coasting, if you drop it in 3rd, you get engine braking as the trans grabs 3rd gear. From there, I can let it slow down a bit and grab 2nd, and then slow it some more and grab 1st.
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Old 11-06-2013, 01:19 PM
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The shift into and out of 4th(OD) in late 700R4s is controlled largely by the TV plunger and bushing(82-early 87, 700R4s, I believe, are different). The bushing has part throttle detent passages that provide 4th gear only below 1/2 to 2/3 throttle. I guess this is mostly to prevent slipping of the 2-4 band under the reduced apply force of the 4th servo. There is a modification that can be done to the TV bushing , plugging the part throttle passages, that prevents the forced downshift into 3rd at less than full throttle and allows full throttle 3-4 upshifts. Sonnax, for one, also makes a high performance TV plunger and bushing set with the PT passages deleted. Since the aluminum TV bushing wears from constant cycling, the new TV set is a good idea anyway, whether you go with just an OE style #94 set or the HP set.

I've been told that the full throttle shift mod is not recommended on higher horsepower applications unless the line pressures are very good and a larger than stock 4th servo is used. I like the Sonnax superhold dual piston 4th servo as it has the largest apply area.

This may seem like a dumb question but are you sure that the throttle itself isn't sticking? Aside from the engine itself lurching due to a sticking throttle, I can't really think of anything that would cause the lurching you describe other than the converter. The vibration you speak of and the bang into drive gear from neutral also point to an issue with the converter.

A harsh reverse engagement can be caused by the check ball being left out of the capsule in the rear of the transmission. A harsh forward engagement can result from a broken spring or other issue in the forward accumulator. When you say that both engagements are harsh, I think of the converter. Line pressure being too high due to TV cable adjusted too tight could also cause harsh engagements I suppose. Be sure to verify correct line pressure before you replace any parts.
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Old 11-07-2013, 05:38 PM
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Thanks for the additional information. I plan on going through the TV setting again this weekend. I'm more able to see what's going on now that I have installed a tach. It felt to me that the transmission was revving up between gears when shifting and the guy who rebuilt it told me to move the sliding part of the TV cable closer to the firewall, maybe I have gone too far since it is not revving up between gears according to the tach, although it still sounds like it but the tach doesn't lie, I think it's my Thrush turbo mufflers overriding my brain. I realize all of this is not a substitute for measuring the line pressures. I plan to reset the TV and try the transmission again and look at the tach instead of listening to the engine. If it does rev up between gears with the TV set according to the GM instructions, then there's something wrong because the TB and the brackets and the cable are all stock GM stuff from the donor truck, the transmission is from the donor truck only the engine is different, (same type, just from a different truck.

I hear ya on the throttle sticking stuff, but that's not the case. I even went through the return spring setup, thinking that I was just pushing and pushing and all of a sudden I would overcome the spring force and cause it to lurch but the throttle operates smoothly, it's not binding.

I know I may be comparing apples and oranges but my other GM's with the same tranny will wind up to 1500 rpm or better before the vehicle starts to move out. In this way, I can feather the car off the line and accelerate smoothly. This truck seems to lurch even before it gets to 1000 RPM or so.
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Old 11-08-2013, 04:17 AM
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This is the first thing I do when installing (or re-installing) one of these trans. Check #5 and make sure the cable is set correctly.
SUBJECT: 700R4 Throttle Valve Cable Adjustments
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Old 11-19-2013, 05:38 PM
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A little more clarity on the 700R4 situation:

I got the tach installed and did the basic TV cable setting as is explained in the GM manual. The transmission shifts without revving up between gears. But still no 4th unless I let off the gas and let it drop in.
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Old 11-20-2013, 07:48 AM
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If the trans is shifting correctly in all other ranges and only having issues going into 4th, I would really look into the TV plunger and bushing. Yours may be worn and bleeding pressure. From looking at the hydraulic schematic for the transmission, the TV bushing and plunger also affect detent down and up shifts in other gears, but apparently, they affect the 3-4 shift more. You could also look at the 3-4 shift valve train in case its sticking or worn.
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