Hi from Germany,

I have a problem with my transmission (I think)

When cruising like 40-50mph and have the throttle open as far as the car does not accelerate nor its slowed down by the engine, I can feel the gears kinda jump back in forth.
You can also see that the rpm kine jumps around by like 500-600rpm up and down. Like the clutch is slipping.

But when I accelerate hard, i can't feel any clutch slip at all.
I already flushed the transmission and put new oil and filter in it.

Does anyone had similar problems?
(sorry for the bad english )

Car: '87 Iroc-Z 305 Automatic

 

I'm not a automatic transmission expert but it could be torque converter locking and unlocking. It could also be slipping out of 4th gear. I'd try driving it in 3rd and see if the problem persists.
Unless it's the ecm or wiring failing to tell the transmission to lock up the torque converter, you'll probably need a rebuild of the transmission. Hopefully more automatic savvy members give some input

 

I try to get more testing done and keep the post updated...sadly its like -10°C (14F) here right now...so no driving this thing on icy roads

 

Make sure your TV cable is properly adjusted too

 

lock/unlock of the torque converter is most likely cause of the slight rpm flare while cruising.

the lock up can be disengaged by the brake switch. try depressing the brake switch slightly at cruise and see if it duplicates the symptoms.

converter lock is commanded by the ECM under cruise conditions, so it depends on inputs from various sensors including the MAP, TPS and CTS

a bad sensor, faulty brake switch or just plain old, wore out or loose wiring could be the cause. Best to scan the system while operating and look for any weird readings.

 

Thanks for the suggestions, as soon as it gets warmer and less salt on the street I check all the things

 

How is everything going now, any changes?


 

Sounds like the OP was talking days/weeks before he gets to looking at it....not 3 hours.

 

yeah its going to be weeks...still freezing here

 

Hey guys,

I was finally able to drive the car.
I tested the mentioned things above.

Depressing the brakepedal didn't change anything. And the jumping/surging while cruising is in all gears.
Also I noticed that when I roll pretty fast like downhill and I break, when the transmission drops the gears you can see the jumping/surging ever so slighty in the moment the gear changes.

Except from that the car drives pretty normal, shifts somwhat smooth (sometimes you don't feel the change sometimes a gentle jerk).
Transmission was flushed 1 year ago, fluid level is normal.

Can the transmission itself get damaged when the problem is the torqueconverter and I let it get worse?(I know kinda silly question)

 

Wrong post

 

Hey,

its not like it happens when i accelerate. Its more like just enough throttle to have the car not slow down nor accelerate on a flat straight...like just cruising

 

Is the fluid level good?? And TV cable adjusted properly??

 

hey there fluid level is good.

I have to admit I had to google what a tv cable is (its my first oldtimer that I build)

But after checking the thematic and what other people here reported about it, it sounds like a reason to check it.

Never the less I check all the hints you guys give me

Here in germany the US car scene is pretty dead, so I depend on forums

 

Hey there there are a couple of new things I tried with no success...

I adjusted the TV cable...nothing changed...
I removed the plug at the transmission who appearently controles the TCC (so that it doe not try in the first place)...nothing changed...

Next step as soon as I have spare time is replacing the TPS with a new one...

Here is a video of said symptoms..when I just want to cruise all the time or after the acceleration when I let of the gas for a short time the rpm jumps...you can feel the car shake slightly (but not as hard as you would think by the rpm range, maybe the analog dial is overwhelmed by it)

 

Do you hear a difference in the engine revs? Or are you relying strictly on the tachometer? That appears to be tachometer bounce, not transmission related

 

You can definitely feel the car buck a little bit. But ever so slightly. But no way as it should as you would expect from the rpm bounce (not even sure the engine would be physicly able to do as the gauge shows). But there is definitely a bounce/buck to it

 

I would closely inspect the grounds at the back of the cylinder heads. And I agree, I don't think the engine is capable of swinging that wildly without a much more profound effect than mild bucking.

 

a bad pick up coil in the dist will cause the tach to bounce like that

the resulting mis-fire can be more pronounced at low rpm loads.

might be time to replace that distributor or it's pick up coil.

inspect your dist and if it's rusty worn-out looking you may want to replace the whole unit

 

Would definitely be looking at ignition components
Cap, rotor, wires and plugs.

 

sadly I already replaced the whole ignition a couple of months ago and it ran fine (complete distributor assembly, wires, plugs) timing is correct...

But i will check the timing again for good measure after i replaced the tps...I mean it has to run good at some point when everything is new

 

timing isn't causing this. I'd leave it alone.

the pick up coil is where the tach signal originates. a misfire caused by other components, plugs/wires/cap/rotor, won't cause the tach to jump like that.

don't assume your 'new' distributor is good

if you have the old one, try sticking it back in and see?

 

good hint and yeah i have the old one still. will switch it and check the other components as well as soon as i got time....(i have to replace the steering rack of my '16 stang first )

 

Hey there,

its been a long time where I had no chance to tackle the problem properly.

But just for maybe others that struggle with it I keep the subject alive

I had a little oopsie while troubleshooting the problem.
I replaced the old torque converter (and trannie seals)with a new one. In the process after pulling the trannie and replacing it...i also swapped the transmission oil. (Dexron VI, wich was in it before)
We prefilled the torque converter as far as possible, poured a couple of quarts into the trannie, run the car up to operating temperature then shiftet the trannie trough and added oil until it hit the mark on the dipstick...

After that I drove the car to my garage and left it there...couple day later and there was a puddle of like 2 quarts under the car....the dipstick showed a level a nodge over the area it should be when hot...I drained another quart just in case...
I thought I've done the fluid change correctly what am I missing? (I guess the oil spilled out of the dipstick or where the dipstick meets with the transmission housing, but cant confirm it right now)

I want to take the car on friday again and get the whole system to operating temperature while actually driving and adding/draining oil during that....but I'm skeptic

 

what seals did you replace on the transmission? and how did the old fluid look? was there metal glitter or was it brown or red? Transmission fluid is a good indicator of whats going on in the trans. i may have missed it up in the thread but how did the car drive when you drove it in manual 3rd? although my transmission is a TH350 its almost the same as a 700r4 but a bit different, i had a similar issue but more pronounced. when i pulled the transmission apart to rebuild it 3rd gear was burnt up and the car was shifting in and out of 3rd.

 

From which part in Germany are u from?
I'm from Berlin and
I rebuilt my 4l60/700r4 a couple years ago on my own. With clutches bearings, bushings

Maybe I can help with informations

Gern auch auf deutsch

 

I replaced the front and rear seal of the transmission itself. so the one where the tq sits and where the driveshaft is located.
It happens in every gear so far. the fluid was actually close the new because I may drove like 1000 miles after I changed it. but no glitter or discoloration what so ever

 

Hey

I am from saarland, so quite a trip...I send u a pn

I plan to drive the car now for 20-30 minutes and check the fluid level that way...when we had it on the lift we ran the car up to temp but I think it may messed the level up because the transmission was not at temperature at all.....so I drive it check the level whilest the car is "hot" all around"

 

Ah and btw the torque converter didn't fix the problem at hand with the surging while coasting/cruising...

 

Try driving with the trans lockup plug disconnected, if the problem goes away its something in the lockup circuit causing it to slip in and out of lockup, if the problem continues it could be slipping in and out of 4th gear if its the 700r4, the 4l60 will be a bit different with testing. be sure to always check the trans fluid while it running, if you fill the transmission with fluid while the engine is off the level will be incorrect. Could you show a picture of the TV cable setup on your throttle? A improperly adjusted TV cable can mess the transmission up in a very short time. maybe try adjusting the cable to be safe? there's some good videos on you-tube for them.