abnormal tranny shifting

[Tonglebeak]

th125c

Not sure if it's the cold weather...

Just today, when@37 I punch it to pass. It downshifts to 2nd gear as I would expect. Usually when I'm beyond 33 1st gear will not kick in at WOT, and this is a good thing because I get the same kind of acceleration from a high 1st as a low 2nd. Anyways, the downshift occurs, and I get up to about 42, and then the tranny downshifts AGAIN into 1st for no reason. Get up to around 46 and upshifts back to 2nd. I'm thinking "WTF"

However, this is NOT the first time lately that the tranny's been acting up. Quite a bit recently, the tranny would go into lockup in 3rd and be on its happy way. For no reason at all (no speed change, no braking) lockup would disengage and never come back until the next time the car was started up.

I've also noticed other shifting anomalies similar to what I described above, and a couple times it feels like the tranny is slipping.

Could it be the cold weather just toying around with the 20 year old parts? Or is there perhaps something not nice happening :(

Note that last year (oh wait, happy new years, I guess 2 years ago then) the fluid+filter were replaced by Aamco when they had replaced the lockup solenoid.

[87Cutlass Ciera]

I have a similar problem with my th125c. It varies a bit from yours though but I can help point you in a direction. Mine during the summer months with warm temperatures (above 10 degrees C) it would take about 10 minutes of driving at about 80km/h untill my TC would lock up, and sometimes it would jump out of being locked up. Now when it's cold out I could drive around all day at 80km/h and it will not lock up. But drive around in stop and go traffic for 10 minutes and then drive at 80 and it'll lock up in a heart beat, but it is still more apt to jump out of being locked up and not lock up again untill you stop and start again. I had the filter/fluid changed this summer and had a GM mechanic from the era when our cars were brand new look at it and he told me what I needed. TCC Selonoid and TCC Pressure switch. I have both parts here if you want to know what they look like, but I believe there was a recent post with pictures of an opened up TH125C. Good luck with it!

[Tonglebeak]

Pressure...I wonder if perhaps my fluid is low for whatever reason? Come to think of it when I replaced the radiator this summer, we forgot to plug the tranny cooler line back in and out spewed a bunch of fluid, but I filled it back up afterwards...guess I can dump in some more fluid and see if that corrects it. Does kinda make sense with the colder weather, and the fact that it didn't start happening until the cold weather came around...

[turbokinetic]

Maybe it is cool engine operating temperatures? The ECM looks at the following to decide if to lock up the TCC; coolant temperature (must be above a set point), road speed (must be above a set point) and engine load (load must be light enough, depends on road speed).
Could the thermostat be weak? Stop/ go driving and warm wether might help the engine reach that magic threshold temp?
On the slipping and downshifting, have you looked at the TV cable? It is the only way that 125C knows what you expect it to do when in D (full auto) range. On my turbo car, the TV cable got on the exhaust and melted and got in a bind. Talk about messed up shifting! I was about to start ordering clutches and bearings and stuff then I found the melted cable!
Just a thought!
David

[Tonglebeak]

The tstat is not out of the question for sure, that's getting replaced when I do my top-end swap.

Which reminds me, still need to get some more parts for that. Just some hoses, a bracket and a cam.

[turbokinetic]

You going to install a 3400 top-end? How much extra getty-up-and-go is that worth? You have to do anything to the calibration?
What has fascinated me is the 3900VVT engine. It's a 60° motor with slightly modified dimensions for 3.9 L and it has a variable cam timing mechanism. If the opportunity presented its self I would love to set up a 3900VVT turbo-intercooled engine. Would take a seriously stout transmission to stand up to that, might even need a 4T80E.
Take care!
David

[Tonglebeak]

http://www.a-body.net/forums/showthread.php?t=238

[notsoslimshady76]

Shake n Bake has had fluid changed every 30k since new. And honest, the 125C isn't the best shifter in the world. It gets the job done, but its fairly sloppy compared to my 4T60

[Jamerian]

i also have abnormal tranny shifting.. It shifts extrmely late into 2nd and 3rd gear. It revs really fast till about 50 km/h and then it harshely hits second gear.. if om on a 40km/h zone, i speed up so it shifts so i can bring the noise and fuel cost down. Anbody know whats happening and if its an easy or hard fix?

[notsoslimshady76]

how's the fluid? is it bright red, or kinda brown and burnt looking?

[Jr's3800]

Sounds almost like you guys may need to adjust the TV/Kick Down cable.... The THM125c( 3T40 ) uses this TV for shift time and quality... If its off a tad you'll know it..

The 4T60 is a bit of a different animal.. The TV cable is used for shift timing and kick down, the Vac Modulator is for line pressure which in turn controls the shift feel...

[Jamerian]

how's the fluid? is it bright red, or kinda brown and burnt looking?

It's burned looking. I havent changed it in a lonnng while. I guess its not lubricatin enough for the gears to switch?

[Jr's3800]

Burnt looking?

Would that be Brown or Black?

[Jamerian]

brownish. chocolate milk looking

[turbokinetic]

The THM125c( 3T40 ) uses this TV for shift time and quality... The 4T60 is a bit of a different animal.....

Glad someone else also appreciates the merits of the 4T60. It's stronger and has torquier 1st gear too! Have you had success making the 125C shift better with shift kits, etc?

Jamerian; If the TV cable is not binding to cause the late shift, then it is sticking valves. Something in the VB could be scored from dirty, contaminated fluid. First, unhook the TV cable at the throttle. Pull it out by hand, then slowly let it go back in. It should retract with about as much force as it took to pull it. If you have to release most of the hand pressure before it retracts, the cable is binding. It is cheap and easy to replace!
If this is not the case, change the bad oil and put some additive in the new oil that claims to clean and eliminate sticking valves. The K&W TransX works well. Change oil, add TransX to new oil, and as soon as shifting improves, change oil again.
If the oil is burned and dirty you need to change it before you have a major failure due to lubrication breakdown, regardless of wether the TV cable fixed the late shift.
Hope this helps!

[Jr's3800]

Glad someone else also appreciates the merits of the 4T60. It's stronger and has torquier 1st gear too! Have you had success making the 125C shift better with shift kits, etc?

Jamerian; If the TV cable is not binding to cause the late shift, then it is sticking valves. Something in the VB could be scored from dirty, contaminated fluid. First, unhook the TV cable at the throttle. Pull it out by hand, then slowly let it go back in. It should retract with about as much force as it took to pull it. If you have to release most of the hand pressure before it retracts, the cable is binding. It is cheap and easy to replace!
If this is not the case, change the bad oil and put some additive in the new oil that claims to clean and eliminate sticking valves. The K&W TransX works well. Change oil, add TransX to new oil, and as soon as shifting improves, change oil again.
If the oil is burned and dirty you need to change it before you have a major failure due to lubrication breakdown, regardless of wether the TV cable fixed the late shift.
Hope this helps!


I'm going to go a little off topic here..

The 4T60 in my eyes is a Good transmission... The Majority of the failures I have seen over the years was either simply clutch wear or a severely overheated trans which cooked the internals.. In general we could put an adjustable Modulator on the 4T60 and quicken and firm the shifts a little but they may be a little too abrupt.. There are some shift kit out there, but I think we'd be better off calling them shift improver's... The good thing about the 4T60 is that the TCC apply is on or off... There is no Pulse Width apply for the TCC on those units... Makes for a more solid TCC apply and is better for the converter clutch..

The 60-E wasn't a whole lot different and could also use the Adjustable tranny modulator... There is a Transgo shift improver kit for it as well..

The 3T40 is a good trans but its a 3 speed with a taller first gear than a 4T60, the 4T60 has a slightly lower first gear which does make better use of torque... But both of the transmissions have a 1:1 3rd gear, the 4T60 gets the added benefit of the .7xx : 1 4th gear...


I agree with what you have said on the 3T40 and what he needs to do with the trans..

But The Chocolate milk part scares me... This makes me think that there has been a rupture in the trans cooler in the radiator and the Trans oil and coolant are mixing..

The Fluid is simply a brownish red color right? If it really looks like Chocolate Milk than we have a real problem that could destroy the trans..

[86euro]

A little off topic, what would cause tranny fluid to turn a milky pink color? I saw it once in a 125c out of a celebrity.

[Jr's3800]

A little off topic, what would cause tranny fluid to turn a milky pink color? I saw it once in a 125c out of a celebrity.

That usually means that the Trans Fluid has taken on moisture.... 99.99% of the time that will be due to an internal failure of the Tranny cooler inside the radiator.... When that happens there is a good chance that it could destroy the friction plates in the trans..

[turbokinetic]

It's amazing how strong "paper" clutches are until you get water on them... :-)
You mention the on/off TCC on the 4T60. That has been the only part of my turbo car that has taken repeated attempts to get right. Since you're a tranny guy here's the story, but it's long so you've been warned!
The 125C trans is simply not suited to a 'strong' turbo engine. As you mentioned it controls shift timing AND charge pressure based on TV position. The turbo engine makes almost full torque at medium throttle, at low RPM's. This was pure hell on the 125C, most noticable at the 1-2 shift. I couldn't keep a 2nd gear band in the tranny. Good thing was you can take apart far enough to change this w/o pulling the engine/trans assembly! After the third time it happened. I got a 440T4. It came from a 3800V6 car. Before installing it I freshened it up with new piston seals and clutches, and installed a 1:1 chain ratio sprocket set, and a 3.33:1 final drive.
I could tell it was exactly what I needed from the first test drive! The shift timing was excellent and the shift firmness was more correct since the modulator would essentially sense "boost" and increase charge pressure when necessary.
Unfortunately, during a a hopped-up wild Saturday night on the town, the sorry one-disk 4th clutch burned away. To help reinforce this area, I ordered 4T65E 4th clutch parts (thinner pressure plate and 2 lined and 2 steel plates). Plugged and re-drilled the 4th clutch apply oriface in the spacer plate, one size smaller to keep this from giving an excessively harsh 3-4 shift.
With a 4th gear that would hold up to my lead foot, now the weak link was the TCC clutch. I have a manual switch on the TCC because my ECM came from a manual-transmission car. You could barely tell if it was locked or not. To help alleviate this, I installed a "Gil Younger's System Correction Package" shift improver kit, and it helped tremendously. You could feel the TCC lock, but it was still weak. It would slip under any load.
I installed the "most severe duty" TCC regulator spring in the kit and still no dice. The lack of a functional TCC was overheating the tranny. On one long-distance trip with a small trailer the trans got so hot the torque converter turned blue and the Loctite melted out of the driveplate bolts. The converter seal melted and leaked profusely. I barely got home from a 9 hour drive during which I used up (leaked out) a 5 gallon bucket of cheap tractor trans oil. :-( Whole back of car including back window was oil soaked.
Out with the transmission AGAIN. I sent that converter off as a CORE (hahaha poor suckers that thought they were going to rebuild that one!!) and got a new "heavy duty" one.
Wanting to do whatever I could to make the TCC hold, I replaced the TCC regulator spring with a piece of solid copper tubing cut to a length that would hold the velve spool in the "open" position. Also glued the TCC apply blow-off ball in place with JB-Weld. When the TCC control valve shifts now, the TCC clutch gets full charge pressure! This was just the ticket! The TCC locks hard and solid, it is as firm and definite as the shifts between gear ratios. I was afraid this would ruin the converter or blow some seals but that has been 5 years ago and it is still holding strong.
My car has a "diesel-spec" A-body radiator with the engine oil cooler in the "cool" end of the radiator and the trans oil cooler in the "hot" end. This is a sorry design, as it tries to "cool" the trans oil by heat exchange with 200°F coolant! After installing the biggest Hayden air-cooled trans oil cooler I could get, I've had absolutely no more transmission problems.
Next time the trans comes out, I have an EP limited-slip final drive to install. Looking forward to seeing how well it works but have too many projects ongoing already!
Reason I origionally asked about the 125C, is my 1984 Century (getting a turbo) has one and I know it will need all the help it can get.
Sorry for ranting on and on about torn up transmissions!:D
David

[Jr's3800]

I am not that deep into the transmissions... But I do understand what you are saying... And yes there were a few weak links in the 4T60 as you found out.... The Only reason my 2.84 Trans in my 91 LE Bonneville is still alive is because of the fluid and filter changes and the Monster Cooler parked ahead of the condenser...lol

I have a 4T60-E behind an L27 and it has worn the clutches out, I'll bet $$$ its missing a Thrust washer or 2 as well and is having a hard time applying the clutch packs as all of the movement is out of spec... The Fluid is Burnt too.. So that trans is done... I am sure its not totall failure but it does need a good rebuild... I actually have everything for it except the 4th input shaft( the 60 and 65 E's seem to love to eat the 4th input shaft...lol


Just being curious, Have you ever tinkered with an Adjustable Modulator on you 4T60?

[Tuddi]

The K&W TransX works well. Change oil, add TransX to new oil, and as soon as shifting improves, change oil again.

This... : ... or that: ? Found here: LINK (http://www.midwayautosupply.com/m-201-k-and-w-products.aspx)

[turbokinetic]

Yep it's got an adjustable modulator. It's pretty sensative, there is a fine line between firm shifting and second-gear starts. With the turbo putting extra pressure on the modulator above and beyond the internal spring, it really doesn't have to be set all that high. I didn't set it with a pressure gauge, just by feel.
When I rebuilt my mom's car's 440T4, the new modulator came with the adjustment way too high and it was second-gear-start city. I did use a pressure gauge. The shift improver kit had an updated spec for modulator pressure; to use with the new springs in the kit.
Yea the 4th clutch hub seems to get "cut into" by the internal splines of the lined plates. Some aftermarket lined plates have "flanged" splines that are supposed to not cut into the hub that bad. Ever had that plastic-caged rollerbearing disintegrate between the 4th hub and RH output shaft?
The trans I have in my car was a core from a GM dealer. It was a factory SRTA that failed after 100 miles. This bearing had been broken during assembly and jammed up between the output shaft and 4th hub. Caused a neutral 4th condition.
Dealer let it go for next to nothing and it was in like-new condition other than the 4th hub, bearing, and 4th plates were destroyed.

[turbokinetic]

It's the metal can on the right, the Stop-Leak and Tune-Up.
Unless your transmissin looks like THIS http://68.209.87.173/Temp/MVC-005F.JPG inside; it will help! :D

[Tuddi]

It's the metal can on the right, the Stop-Leak and Tune-Up.
Unless your transmissin looks like THIS

inside; it will help! :D

Thanks for the advice. I will try and locate it here in Peru, if not possible, I will order it from up north.

Regarding the picture; it looks as if someone decided to use the tranny as a piercing pin and ring treasure chest....

[Jamerian]

lol sorry, i made a bad example, its not milky looking, just cholocolaty brown.

I read an earlier post about TV cables and i was confused so i consulted my text and now it makes sense to me. So what your saying is the governor valve is still functioning, and its the shift valve thats gummy, vice versa, or both?

[Jr's3800]

Yep it's got an adjustable modulator. It's pretty sensative, there is a fine line between firm shifting and second-gear starts. With the turbo putting extra pressure on the modulator above and beyond the internal spring, it really doesn't have to be set all that high. I didn't set it with a pressure gauge, just by feel.
When I rebuilt my mom's car's 440T4, the new modulator came with the adjustment way too high and it was second-gear-start city. I did use a pressure gauge. The shift improver kit had an updated spec for modulator pressure; to use with the new springs in the kit.
Yea the 4th clutch hub seems to get "cut into" by the internal splines of the lined plates. Some aftermarket lined plates have "flanged" splines that are supposed to not cut into the hub that bad. Ever had that plastic-caged rollerbearing disintegrate between the 4th hub and RH output shaft?
The trans I have in my car was a core from a GM dealer. It was a factory SRTA that failed after 100 miles. This bearing had been broken during assembly and jammed up between the output shaft and 4th hub. Caused a neutral 4th condition.
Dealer let it go for next to nothing and it was in like-new condition other than the 4th hub, bearing, and 4th plates were destroyed.

Never have had that one happen... Just about every one I have seen came out in good shape.. My Buddies 4T60-E that we rebuilt we had come to find out that it had been rebuilt before, but the rebuild was done poorly.. And a lot of parts were reused... We found the pump vanes to be in good shape so we were able to reuse them, but somewhere along the line the pump had been starved for fluid and had galled the Pump cover... We were able to use a 4T65-E Cover on the 60-E due to the updated( some 95 Models and all 96+ iirc ).... We found the trans to be missing the Thrust washers, and this did some damage.... But my buddy had enough good parts to replace the destroyed parts..

The funny thing is that there is not as much inside these front wheel drive transmissions as people think... But you have to pay attention to detail..

And I always say this... It takes a certain someone to be able to rebuild a GM FWD trans and have it function as it was intended... I can't begin to tell you how many times I have seen a shop rebuild one only to have it fail right away or a few months down the road...

I actually love the GM FWD Transmissions... I think GM has done a better job on them than most... And look at the abuse these transmissions contend with... My 4T60 is 17 years old and at 137k.... It still functions flawlessly


Now as for the Brownish fluid... That means the trans has been overheated.... This can happen with these if you don't change the fluid once in a while...I like to change the fluid before a hot summer...

I'd tell you to do a fluid and filter change and see how the trans acts...

How many Miles are on this car/trans?

[Tuddi]

I went hunting for the TCC and the Trans-X Stop Leak today. Went every place possible, and the TCC solenoid is not to be found in this country... not even a used one (I asked several places).

And the Trans-X does not exist in the market either. So rather than go emptyhanded from this long and hot weathered walk'n'search of mine, I bought Bardahl's Transmission Stop Leak (http://store.bardahlstore.com/transtopleak.html) which should be similar to the Trans-X. According to the bottle, one should allow 300-400 miles of driving before expecting results.

I poured it in the tranny, drove off.... and I am in total disbelief. Even the lockup of 3rd gear seems to have vanished. The shifting from 1-2-3rd and down was beyond perfect.

The result was so instant that it simply can't be true.

I look forward to starting the car tomorrow morning and see how it will react. I'm sure the seals will need a lot more time before they are revitalized.... but damn... the shifting is so smooth that it's unbelievable.

Thanks for the tip on using this kind of an additive... I truly hope the effects last beyond today :)

[Tuddi]

Looks cheap... http://www.transmissionpartsusa.com/ProductDetails.asp?ProductCode=609%2D00K84856U

[Jr's3800]

Its possible that you could have had sticking valves and or check balls in the valve body and the additive may have freed them up.... Git it a little time and then you may want to do a trans service on it and smile as the 3T40 just keeps going:)