Hey guys I have a 1988 IROC,
A couple of years ago I had my 700-R4 rebuild through a local Trans shop and they put in a Pro-built kit I got from Dana that boosts the H.P. up to 600. My question is in overdrive cruising between 47-52 mph. The trans seems to be shifting or locking/unlocking. The rpms seem to change from 1800-2200 when it does this. I do not notice this problem if I'm cruising up to 45-46 mph or above 53 mph. Someone suggested it could be my torque convertor, and I talked to the speed shop I purchased the convertor from. But the owner there said hes sold dozens of those torque convertors (Big End Convertors) and has never had any complaints/issues with them. He even called the manufacturer for me and they said they never have had issues like that.
So I'm wondering if there is something internally wrong with my trans!

Something is telling the torque converter clutch to lock and unlock at that particular speed. I am not an electronics expert, so you will have to find the answer. I would call TransGo and talk to Dave about this. 626 443-7451

The ECM is told when to lock and unlock the converter at a particular speed. Check your electrical connections from your VSS on the transmission to the ECM. Question, is your speedometer malfunctioning by any chance? Meaning, does the needle fluctuate as your driving, or does it stay steady...

Thanks for the reply's!
I do know one of the plastic clip retainers has broken off on the plug in to the trans, although it looks like it stays in place. I figured since it seems to seat ok it would not cause any problems.
I can't say for certain if the mph needle is fluctuating but if it is, it moves very little from what I remember but I'll have to double check. I use to have a 2:77 9 bolt which was the original rear end. I then traded the rear end for a 10 bolt 3:73. A couple of years ago I replaced the speedo gear in the tail section as I got tired of trying to estimate my speed. If by changing the speedo gear possibly did create a problem is there someway I could check and verify this?

Hey Street Lethal,
when you asked if my Speedo Gage needle was fluctuating, what would that tell me if it is?

That the vehicle speed data (pulses) sent to the ECM may be skewed, and although you may be cruising at 65-mph, because of the skewed data the ECM may be reading 30-mph, then 45-mph, then back to 30-mph, then 50-mph, then back to 30-mph, etc, which is why your torque converter keeps engaging and disengaging over and over again...

So does that mean my ECM, speedo cable, or speedo gear is bad?

If that were the case you should see the speedo needle flutter at a constant speed. Also check the break light switch. This will cause it to lock/unlock as well.

you could always just disconnect the four prong connector for a short test drive and see if it cures it. you will still have all four gears, just the lockup will be inop while disconnecting. that would isolate it to the torque converter or the related wiring system. hope that helps

Thanks for the info. guys.
If i disconnect the 4 prong connector from the trans will it hurt the trans at all, and would this for sure narrow down my problem?

700r4 in 1988 does not use a ecm or trans controller for lock up signal..it is controlled by vacume switch mounted on drivers side firewall,,check for cracked vacume line.or faulty acctuater.as posted earlier also check break switch.

mine is doing the same thing its an 85, would it be vacuum also? or ecm

Depends on the powertrain and yeah in U.S. sold Camaros, it does use the ECM.

I was not aware of this, what would I look for like any pictures or links to identify this vac. switch?

like i said in my post my 85 is doing the same, and now the speedo stopped working and the engine check light came on. any ideas?

Hmmmm, I'll wait for an expert to comment but I think all Camaro and TAs 82 and up used the ECM to control lockup of the converter. The truck versions are different and are mechanically controlled either hydraulically or by vacuum not sure which.

To the OP, you have had the trans rebuilt, did you get the Transgo shift kit in it? It has a hydraulic controlled lockup for those of us that have cars converted to carb with no ECM. TCI make a lockup controlled by vacuum, they can go in and out of lockup at certain speeds but can be adjusted at the vacuum switch.

Transgo kit came with the kit from Dana, and my IROC always was a TPI.

here is what lock up your TQ convertor.................it a thin cork type gasket. it take very little power to wipe it off the face of your convertor.


By scotiapilot at 2012-01-09

Wow thats crazy!
I don't really hear about TQ. convertors going bad, but I take it when they do thats usually the cause?

many times when you here of the lock up not engaging or slipping this is the cause.

I am not a tranny pro. so I imagine there is some better experience on the board that can give you more indepth view

But you can kinda understand how fragile they can be under load.

i'm not an expert but on all 700r4/200r4/4l60's use the ecm to lock up the converter, but they can be changed to mechanical (check ball), but you can use the electric setup by changing a pressure switch on the valve body and 12v to the plug. now Americanmouse i have experienced your prob and fixed it for others,if it was a bad clutch in the converter it would slip, not lock up and unlock.
(lockup shutter) first possible prob. the small Oring on the input shaft (it's for lock up) sometimes gets nipped when the converter is installed and can allow it to build pressure to enguge but then it builds up to the 45~psi and it blows off past the oring and over and over again it's weird but i had it happen, also make sure your tv valve is adjusted right low pressure will make it do the same, kinda like the 1-2 shift shutter the 700's can have. also if you read a gm manual it said "if you have a lock unlock lock problem while driving in town below 45 shift to Drive." this happens because of low pressure. if you think it could be the ecm use a volt metier and check to see if the ecm is switching it on off but that is less likely, under low load the ecm will send a signal to lock up even in 3rd but the trans will not allow it to lock until 4th, well unless you make a small change in the valve body. but i would bet on the TV cable needing adjusted, i like to make them a little tight so it shifts harder and has more line pressure. it helps the trans live longer. sorry that was so long

Whoa. Let's establish a few things first.

Canadian models and some other exports used the vacuum switch system to establish lockup. All US models used the ECM.

Converter clutch failure is pretty uncommon and would not cause intermittent lockup like the OP is experiencing.

Probuilt in post #2 pointed to the electrical system to trouble shoot. Go back there.

One of either two things is most likely:

1) The ECM is commanding intermittent lockup for one reason or another
2) There is an intermittent open circuit somewhere

Rule out (or in) the ECM by jumping the A and F connectors at the ALDL to override the ECMs command. If the problem goes away, look at #1. The most likely culprit here in my experience is a bad TPS, but the MAP sensor or speed sensor are other possibles. A scan tool that shows you what the ECM is seeing while the lockup goes in and out is invaluable here.

If the problem remains with the pins jumped look at the wiring. The most likely culprit is probably the brake switch (it may NOT be the same one that commands the brake lights- definitely not the same switch on most models but MAYBEEEE there's one out there that uses both). Jump the brake switch out, see if it goes away. Check the connector at the trans. If you haven't found it yet, try another pigtail at the trans and trouble shoot the lockup ground (the ECM controls the lockup by GROUNDING this wire through the brake switch).

Stay in the same ball park as your problem and deal with it systematically. It will be behind you in no time.

I thought I remember someone telling me that my reverse lights would go on and then off last summer, so since I rarely backup anyway I just took the bulbs out for the backup lights. Could that tie into the brake light issue mentioned? Also I did re-check my TV cable. I also tried to use Drive only, but the problem still persists.

No. Quit guessing at random, unrelated, things and start troubleshooting.

My 88 truck does it. The tranny shifts into od around 50. I just keep it in drive when I drive around town and when I get to 55 on the highway I kick it into od. Have done it for years.

its your Tourque converter and its perfectly normal i just had my 700r4 Rebuild and the guy i took it to say that around 50-60mph if u lightly touch the brake that should happen and if it doenst there is an issue.

No it's not your torque converter. When you lightly touch the brake you are interrupting the ground circuit for the converter clutch at the brake switch and electronically disengaging the clutch. This reaction with the brake switch is normal, but is not what the OP is experiencing.

Resurrecting a old thread! (PER STREET LETHAL'S QUESTION)
The weather was nice enough this past weekend to take the IROC out. I did notice while cruising around that the MPH needle does flutter, its not rapid though its like it bounces up and down several times a second. I would guess it showing about a 2-3 mph difference from its lowest point to its highest point.

Take the speedo cable out and lube it.

As old as the cable probably is, would it be better to just replace it? Or are they hard to find new?

Pull it out and check it. It'll likely be fine after cleaning and some oil.

Thanks!
and I assume that this is the cause of my problem?

Yes. That should fix your bouncing MPH needle.

Actually I was referring to my original post.
But I guess I'll try and see what happens.
Thanks!

So I finally pulled out the mph cable on the trans side. I'm assuming I can leave it on the gage cluster to lube it up so I don't have to take apart the gage cluster. Anyway there appears to be some kind of seal and I've tried to punch it through with a small screwdriver and put a little wd-40 in it. Then using a drill to get it to flow into the cable, but it won't go down just sits in the threaded cap that goes on the trans.
Any suggestions?

There's a spring clip that easily releases it from the rear of the guage cluster. Disconnect it there and pull the steel cable out. Lube the cable and re-install it.

There may be two sections to the cable with a threaded connector near the framerail below the brake booster.

Ok!
I take it I don't need to remove the gage cluster, but just reach up from under neith and remove this clip?

use graphite lube.
WD40 is useless in this application.
If you can reach the clip to release it, that's great. Might be challenging and thus easier to pull the gauges.

Thanks
and any recommendations on what name brands are good and where I can get this graphite lube at?

So I ended up replacing the speedo cable and I finally took it for a spin this weekend. And I can't believe it its fixed!

Right on.

not to hijack a thread but im having serious tc issues i cant figure out. i swapped a l98 tpi in a 92 rs 305 tbi changed ecm harness kickdown cable the works but my speedo does not work at all rest of guages fine it starts idles revs great put it in gear instant kill adjust tv cable still nothing then today i unpluged the 4 prong sensor towards the front of trans and it finally goes right into gear with out slamming in and shutting off is my speedo related to this issue and is my torque converter staying locked up when sensors hooked up? any help really apriaciated i have no isea what i should even try to do to fix this and is it safe to drive like this? thanks

Sorry to bring back and old thread, having the some very similar problems as AmericanMouse.
Lockup keeps engaging, disengaging under 40MPH. Ironically, my speedo needle bounces horrifically between 0 - 40 MPH also... coincidence? I think not!
Just ordered a speedo cable, hope it works!

If the throttle cable doesn't fix the lock up issue, looks like you need one anyway. Feel free to come back if you still need help.

So workin on the camaro is never one step forward, two steps back. I like to think of it as one step forward, one step on black ice that leads to you wrenching your groin but the pain goes away in a couple days...

I got my new cable and installed it! VOILA!! fixed my lockup problems!
I also took the liberty of attemping to adjust my TV cable (which I'm still not sure if i did it right because of all of the weird azz instructions people give).
Issue im seeing now is shifting RPM's. Seems like it shifts early and doesnt pull all the way through like it used to. Seems to be shifting now around 4000 RPM's.

Can anyone give me some SIMPLE instructions for a 5.7L TPI engine of how to do this? People are talking about some freaking metal "tang" and shiz... and pullin back on some black hose...? seriously? Pictures?

Thank you SO much!
time to get this right...

EDIT:
After kinda forcing it back and forth a couple of times and pushing in different spots on the "D Clip" it finnaly started clicking and all that good stuff. Car shifts great now, 1-2 around 4200, pulls clear through 4500 from 2-3.
Thanks for the help.