700R4 Issues

[CedarGrove]

The 84 C10 that I bought the other week is up and going (after sleeping for several years). New freeze plugs, radiator, motor mounts, water pump, gp controller, and some other bits. The truck is a little worn out but overall I'm happy with it. The price was right and it's a good project. Anyway...Enough backstory, let's get to the issue.

The truck doesn't shift to 2nd until something like 22 or 23. Way too high. I've fiddled with the tv cable and it's as tight as it's going to get at the top end. Guess I still need to poke my head underneath and see if there is anything going on at the other end. Loosening it, it won't ever shift to 2nd. Do these cables stretch?

Also...The torque converter doesn't seem to lock up when I'm cruising...It seems to sort of gently slip in and out as I go down the road. Cruising at 65, the motor sort of lopes around as the converter slips.

Is there any chance that these 2 things are related or or they definitely 2 different things? TV cable stretched and converter slipping? Other possibilities? Wrong converter installed. Any ideas?

After I get into 2nd and up to about 45 or 50, everything is dreamy. Very smooth shifts...Too smooth if you asked me. Nearly impossible to tell when you hit 3 and 4.

My goal for this rig is economy. I went it to shift a little early and keep the revs down. I drive like an old man. I'll tow a couple thousand pounds once or twice a month.

Cheers,

Lewis

[Subzilla]

Greetings,
If you feel comfortable with your proper adjustment of the TV cable, then you can easily change the shifting points with a governor kit. I felt that my Sub was shifting too late and swapped out springs and weights till I got what I wanted. I think the kit from B&M costs maybe $30 or $40. Very easy to do as the governor protudes outside the transmission. Just make sure the cover is securely attached after you do the work. Don't ask me why I say that!

Concerning the torque coverter, I've had my share of experience with that. On the Sub, the TC would actually slip with pedal pressure after lock-up. Short story, the idiot trans shop said this was impossible but a fellow TDP diagnosed it as a bad TC. I replaced it and 3 years later, it still works like a charm. On the Blazer, the TC would simply lock and unlock very randomly. The throttle position sensor located on the side of the injector pump was to blame. Try adjusting yours by loosening the 2 screws and rotating it. There is a proper adjustment procedure to relate the rotation percentage with pedal position written somewhere. It could be that your cruising speed is right at the lock/unlock point. I just bypassed my TPS and the TC has operated properly eversince. I'm not even sure why the TPS is needed on the older models. Maybe someone with more smarts can chime in.

[moondoggie]

Good Day!

"I just bypassed my TPS..." How? Did you simply unplug it, or dummy a signal into the wires?

Blessings!

[john8662]

So, adjusting the TV cable makes no discernable difference in the way the transmission performs?

If so, you've got a bad TV valve (from what I've been reading). There are some light shift kits out there that are more corrective in nature to help that. Transgo makes a Jr. Shift kit that does just that, and it's pretty cheap too. I'm going to be putting one in one of my tranny's and crossing my fingers as well, but what I read about it says it "fixes" these flaws.

For the torque convertor, subzilla is right, it's likely the TPS on the injection pump. The switch (not sensor) controls lockup by allowing voltage to go to the solenoid in the tranny that controls lockup. The switch is only closed when you have your foot on the throttle, as well as the brake switch being off.

When you take your foot off the throttle the TC won't lock. Try adjusting the switch position on in the side of the injection pump. The way I do it is to get it close by rotating the swith on the pump until you can lightly feel the prong on the pump contacting the nobs on the inside of the wheel on the switch. If that doesn't work, take the switch off and remove the spring and clean things up real good (it it's sticking). Then remove the two very tiny bolts on the top of the switch, this is where the SWITCH is located for the TC, verify it's not stuck and contacts are good, do not bend anything. Put it together as you found it. This has helped me in the past (dirty contacts, saves replacing the whole thing).

This was all made on the assumption that you have the 4speed OD 700R4 transmission of course, not a TH350 replacement.

On edit, one final note.. How full is the transmission? Check with engine running, level should come over the full level on dipstick. A little low, and the tranny will behave oddly (hanging late in gears, etc.).

[Subzilla]

I unplugged the TPS connector and put in a jumper wire. To go along with John's explanation, because my TPS is bypassed, my TC stays locked with the foot "off" the pedal until speed drops below that 42 mph mark, then the TC unlocks at the mechanical command of the transmission. I've always assumed this is OK as I do like that engine braking effect with the TC locked. It seems to me another advantage would be less wear and tear on the TC and lock-up solenoid since it is not unlocking every single time your foot lifts off the accelorator. Make sense?

[DmaxMaverick]

I unplugged the TPS connector and put in a jumper wire. To go along with John's explanation, because my TPS is bypassed, my TC stays locked with the foot "off" the pedal until speed drops below that 42 mph mark, then the TC unlocks at the mechanical command of the transmission. I've always assumed this is OK as I do like that engine braking effect with the TC locked. It seems to me another advantage would be less wear and tear on the TC and lock-up solenoid since it is not unlocking every single time your foot lifts off the accelorator. Make sense?
I've been operating my '85 700R4 this way for over 400K. I attribute the tranny's long life to this, and other [minimal friction] mod's I made. I have a switch mounted on the shift lever to manually engage/disengage the TC. I hardly ever disengage it. Mine will lock at about 35 MPH, and unlock at about 30 MPH in high range, and lock/unlock at about 8-10 MPH in low range. It can make for rough shifts sometimes, but a fair trade, IMO.

Also, DO NOT mess with the TV cable once it's set. If it isn't adjusted correctly, you will toast your tranny. The pressures are regulated by the TV.

[floridaboyzx9r]

sub, which wires did you jump on your TPS? i haven't looked again but i thought there were three. i think i am gonna do the same mod to mine and need to know. thanks.

[john8662]

The TPS on the IP usually has 5 wires and two connectors. One connector is for the EGR and EPR, the other is for the TC lockup, and it's only two wires. Just unplug this connector and install your shunt.

[floridaboyzx9r]

thanks, i will try that and see if i like it.

[Robyn]

Here is the trick for adjusting the TV cable properly.
If all is well go for a very light throttle 1-2 upshift and as soon asn the critter shifts mash the pedal to the mat and it should drop back to low gear. If it does not drop you need more throttle pressure. (tighter cable)
anything looser is a one way trip ticket to a toasted box.

[CedarGrove]

I like what I'm reading here. Lots of good ideas. If only I had time to get out there and work on the beast :(

I'll report back after I've tinkered.

Lewis

[CedarGrove]

[QUOTE=john8662]So, adjusting the TV cable makes no discernable difference in the way the transmission performs?

With the tv cable as tight as she will go, I get the late shift from 1 to 2. Loosening the cable does change the situation...It won't shift to 2nd.

[Lightyear]

After reading this thread, I have to jump in and piggyback on it. The 700R4 in my 1988 'Burb has the opposite problem...the TC stays locked all the time, unless I'm on the brake or REALLY hammer down on the throttle. Trying to start out like that feels like your in OD on a manual gearbox. Ichecked voltage at the TC connector on the tranny, and it reads 12.XX volts, unless the brake pedal is depressed. Will shunting the TPS help in this case, or are there bigger problems lurking deep in all that ATF? Thanks...

[ZZ]

Sounds like someone wired your TC lock direct through the brake light switch where it stays on all the time..

[john8662]

The TC stays locked all the time, unless I'm on the brake or REALLY hammer down on the throttle. Trying to start out like that feels like your in OD on a manual gearbox. Ichecked voltage at the TC connector on the tranny, and it reads 12.XX volts, unless the brake pedal is depressed. Will shunting the TPS help in this case, or are there bigger problems lurking deep in all that ATF? Thanks...

Sounds like the switch is stuck on your rig, or mis-adjusted.

Normally, no voltage exists at the transmission wire without throttle. How many wires do you have going to the transmission. I only have one.

They did change the switch on the later 6.2's, probably starting in 88, my '91 burb had a different switch, seems that the switch no longer controlled the EGR and EPR on that model, just the transmission lockup.

J

[CedarGrove]

So I poked at the TPS a wee bit this evening. Jumped the 2 wires on the TPS such that the TC would be locked at all times. I liked the feel of the tranny better that way, although it seems to me that I still have the slipping problem. I'm thinking she needs a new TC, just like Subzilla's 'Burban.

Didn't make any difference on the 1 to 2 shift and I didn't have any time to tinker with that. Long weekend in the mountains this weekend so it's looking like no tinker time 'till next weekend.

Lewis

[DmaxMaverick]

After reading this thread, I have to jump in and piggyback on it. The 700R4 in my 1988 'Burb has the opposite problem...the TC stays locked all the time, unless I'm on the brake or REALLY hammer down on the throttle. Trying to start out like that feels like your in OD on a manual gearbox. Ichecked voltage at the TC connector on the tranny, and it reads 12.XX volts, unless the brake pedal is depressed. Will shunting the TPS help in this case, or are there bigger problems lurking deep in all that ATF? Thanks...

Your problem has to be internal, in the tranny hydraulic/gov circuit, not electrical. The hydraulic circuit inhibits TC engagement below a given speed (output, not ground speed). Meaning, no hydraulic pressure, with or without electric input. Your TC should not be engaged under any normal condition from a start. If it was, it would stall the engine. From what you describe, I'd suspect an internal leak, allowing a partial (low pressure?) engagement, overcome by more input torque, or braking.

Good luck with this one. Be sure to let us know what you find.

[Lightyear]

Wow, I was afraid if something like that. John, the connector that plugs into the tranny has four pins, but only two have wires on them. The truck is an '88, but I'm not sure of the build date. DMax, could it be that the last shop to 'rebuild' the tranny missed something, or is this more likely a mechanical failure internally? All this started after I had the tranny rebuilt in OK. One of the driveshaft U-bolts (shaft to rear axle input) failed. Result: one cracked tranny case and a rebuild out of necessity 700 miles from my destination. Four or five months later, it started acting up...out of warranty and driving distance to the shop, naturally. A local place drove it, and unplugged the TC connector. They wouldn't take my money unitl I had everything else checked first. Well, I tested it once myself with the results I've already written. Replaced the TC solenoid once also. I would like to get everything functioning properly again in the interest of tranny longevity and fuel economy. I will check the TPS, all voltages, and brake pedal switch to rule them all out this weekend. More to follow in this saga...

[DmaxMaverick]

Hard to say. It could be something as simple as an omitted poppet spring (or just installed backwards). I doubt it's mechanically failed, since it's done it since the rebuild. The 700 has only one electric circuit....The TCC. Most of the control is hydraulic, internal. The electric control only prevents lockup under specific conditions (braking, throtle position, etc.). Once the calibrated speed is reached (determined by the gov circuit), pressure is routed to the TCC solenoid. If the solenoid has juice, it will allow a lockup. How your TCC behaves with electrical input is determined by the TPS/brake switch, and the pressure switches on the valve body. How many switches does your tranny have? (early models had only one, later as many as 5) Could be one missing/bypassed, or even the wrong valve body??? Some older shift kits had plugs/shunts to replace/bypass some switches. Many tranny shops set up the 700 valving just by counting the switches (they don't actually look at the application, and 700 model).

I think in your case, your solenoid is irrelevant to the problem. For whatever reason, hydraulic pressure is available to the solenoid at all times. At idle, the lockup pressure would be just enough to engage the clutch, but not enough to hold it under torque. Or...The TPS is working properly and preventing lockup without throttle input (confirms hydraulic pressure isn't bypassing the solenoid). That would explain why it isn't stalling the engine, but bogs down as soon as you start to accelerate. Have you tried accelerating with slight brake pedal pressure? It should give the same result as having the harness disconnected from the tranny. If you have, and it allows normal low speed acceleration and shifting, it will confirm my suspicions.

[Lightyear]

I must have failed to mention that with the plug disconnected from the tranny TCC port, it behaves 'normally', that is smooth starts and acceptable shift points without bogging. Now I really see why an old car-nut buddy called them auto-magic transmissions.

[CedarGrove]

So I've had some time to tinker today and I've come up with a couple of things. First, it came to me this morning that the shifting problem wasn't that it was slow to shift to 2nd, but rather that I don't have a 2nd gear at all. It's just not there. It shifts from 1 to 3 at around 22 to 25 mph.

Also...I took the truck to a friends house today so he couls give it a gander. He's telling me that the slipping at cruising speed is not the torque converter slipping, but it's actually the OD slipping. It makes sense to me now that he's said it and I've thought more about it.

He's telling me it's time for a new tranny, and I think he's right.

So, before I do that...Are there any simple solutions to my problems?

1. No 2nd gear.

2. Tranny slipping in OD.

Thanks y'all.

Lewis

[ZZ]

I'll say that you're in for a complete rebuild

[CedarGrove]

There is a used 700R4 advertised around here out of a 91 Camaro. Any reason why I shouldn't try to install that? I'd put the diesel torque converter on it of course. It's 200 bucks or best offer for the tranny.

[DmaxMaverick]

There is a used 700R4 advertised around here out of a 91 Camaro. Any reason why I shouldn't try to install that? I'd put the diesel torque converter on it of course. It's 200 bucks or best offer for the tranny.

It'll work, but you'll need to replace the governor as well. The gov. from your old tranny will work, but that may be the problem you are having with your current tranny. You should't be able to shift from 1 to 3 under any circumstance. 1/2 and 3/4 share bands. If the 2 clutch is gone, it should just fly away when it tries to shift from 1. I'd suspect a sprag/roller, or a seized planetary.

[ZZ]

There is a used 700R4 advertised around here out of a 91 Camaro. Any reason why I shouldn't try to install that? I'd put the diesel torque converter on it of course. It's 200 bucks or best offer for the tranny.

I don't really know your financial situation, but I advise against buying a used tranny. I've been down that sad road one or two times too many.

I just had to spend almost a grand on my truck getting another rebuilt one. I borrowed the money from the bank against my truck to pay for it.

[CedarGrove]

Thanks y'all. I'm still sleeping on it. I'll let you know where and how it goes.

Lewis