High RPM, doesn't shift into next gearUPDATE: 4/12/06

[slick94prix]

Finally have all my electrical problems fixed, and have really been cracking away at getting better gas mileage, so my car is running pretty good right now, except for one thing: Anytime i'm above 6000 RPM, it will not shift into the next gear. If I would let it, it would bounce off of the rev limiter all day long. Basically, I have to let off of the accelerater and let the RPM's drop before it will shift itself.

I have a few ideas, probably not near what is wrong though.

No codes are being thrown.

BTW, this is a 93 Z34, 95 Crate, 93 ecu and wiring, rebuilt 4t60e tranny.

Thanks.

[HisCar]

If it does that in every gear, IE 1-2, 2-3, 3-4 then its prolly a fluke in the ecm or the shift kit. If thats the case it might be waiting for you to go higher than the rev limiter to shift for the best power, which would explain why you have to back off the throttle and decreace the load for it to shift in a more reasonable fashion. Kinda like-too much shift kit. The only other thing I can think of is at those engine speeds the line preassure might be holding the shifting solenoids from moving?

[SappySE107]

Is the ffp chip and adapter or the memcal itself? If its an adapter, try it without that on there. If you bought the chip in your name I can look it up though it may be labeled as your name or your screen name. I can see what the shift points are though I don't recall setting any much higher than stock.

[slick94prix]

The chip was bought originally from 4spdz34, as he was the one that did the engine transplant.

I inspected the tranny fluid, looks a bit dirty and somewhat low, so that is probably the problem. Guess i'll find out Sat. when I change the filter and fluid out.

[Mach10]

Sounds like something's clogging up a valvebody passage. Fluid/filter change, and maybe a power-flush.

[slick94prix]

Wow, totally forgot to update this.

Changed the fluid and filter. Fluid was much dirtier than I had originally thought. No significant flakes or anything, so that was good. New fluid and filter helped the shift a little.

But no fix.

Bought a new adjustable vac. modulator, and it came with the small amount of soft vac. line as well. When I pulled mine off, my vac. line was completely cracked through. Put the new one on along with the line, and went for a drive. The shift was improved.

But no fix for the high rev shift.

[Mach10]

I don't know if the 4t60E trannies have a throttle cable (aka kick-down, detent) etc... But this sound exactly as if it were a vacuum/detent modulated transmission with the cable out of adjustment.

Without knowing too much what goes on in THIS particular tranny, I would think that something is out of adjustment, or else there's a solenoid in the valve-body that isn't kicking in.

From what I remember (and feel free to correct me if I'm wrong) but the 4t60E uses Throttle position data from the ECM to set it's shift points? Or does it use a combination of electronic data and a kick-down cable to do it?

If so, the "kick" solenoid that engages the shift passages might not be engaging properly?

If it DOES have a cable, tighten it in 1/8" increments until it starts shifting normally.

Otherwise, sacrifice a kitten under it and burn some chicken feathers.

If it's a "rebuilt" transmission, seriously consider pulling it out and heaving it in through the front window of the shop that did it.

[slick94prix]

No kick down cables (or atleat I don't believe so, i'm not the greatest at transmissions). I believe they are all electronically and vacuum controlled.

I am going to adjust the vacuum modulator for a little firmer shift here within the next day or two. It could be that I was losing enough vacuum that it would not shift properly?

Yes, it does use throttle position data from the ecm.

If the adjusting the modulator doesn't work, I'm going to take it for a trans flush, which definately won't hurt to get done anyways.

If that doesn't do it,

[Mach10]

Dunno man... It sounds a lot like what the tranny doing on my old nissan van (also a 95) was doing when a solenoid bit it.

And it also sounds like what my Jag used to do when I didn't have the throttle cable set right.

I'm assuming (since you didn't say otherwise) that normal operation to about 75% throttle works fine?

Does the tranny kick down if you hammer it at cruise? A vacuum leak might make it kick down too early, or try and hold a gear longer... Vacuum drops initially at WOT (almost atmosphere) until you start getting near redline, then it starts to pick up as you move out of VE range.

If it otherwise shifts fine at normal operation, I'm not so sure that it would be the modulator. You mentioned you had an aftermarket ECM installed? Any possibility the shift-points were altered and are now higher than your rev-limiter?

I still think it's a solenoid that's not firing properly (maybe not letting go?), although I am a little surprised that whatever is happening in there is not being overridden by the governor in the transmission.

[slick94prix]

Anytime under 6000 rpm, the transmission will shift fine. It's when I go above 6000, it will slip outta gear, until I fall back under 6000 rpm again.

When I go WOT from a roll, the transmission will down shift as normal.

It's just wierd that the transmission has been fine for well over a year until about December when it started doing this.

[Mach10]

Hang on... It's SLIPPING after 6000rpm?

Or is it just holding the gear to rev-limiter?

If it's slipping, does it do the same thing if you use the manual select?

If it actually SLIPS out of gear at high RPM, you've got a shift-valve in the valve-body leaking for sure.

[slick94prix]

It feels as if it slips or falls outta gear, yet it will go right up to the rev limiter and bounce off of it without shifting into the next gear. Basically, for the vehicle to shift into the next gear, I have to fall back below 6000 rpm and for it to go back into the gear it was in.

I'm going to adjust the vac. modulator today, as the shifts do feel a bit softer than before. I may go ahead and try a new vacuum line I picked up to see how that feels as well, because I'm sure 13 year old vacuum lines cannot be the greatest things in the world.

[Mach10]

Hmm, that might not be a good sign.

The transmission is hydraulically actuated. The front pump (right behind the torque-converter) supplies the high-pressure oil needed to keep the clutchpacks engaged around the planetary gears. Now, it's possible that one of your check-balls is leaking. It's sounding like the transmission is trying to shift, but is not able to actuate the brake bands. This is usually what causes the engine to "lug" while an auto is shifting.

It could be that your bands are out of adjustment, or that they came apart (does happen).

If it's doing it in all ranges, (and I'm going on the assumption that the torque path is the same in most transmissions) it will likely be the rear band thats slipping.

The fact that the tranny is a year old since rebuild, and that the oil was "dirty" already suggests that you've burnt out the brake band.

The reason it's letting you shift at lower RPM is that it doesn't have to work against the torque of the engine to halt the planetaries.

I'm willing to bet that your tranny will start slipping in OD very soon as the brake band wears further.


Sorry

[slick94prix]

Ouch, that sucks. But, very well may be true.

I'm going to take it to a few different trans shops and see what they all think. I can hope it's something simple, but it very well may not be.

[Mach10]

Forgot to add: I'm not 100% sure if the electronic GM hydramatics have a brake-band adjustment. But you can certainly check.

Find a factory service manual for this transmission (not a haynes or chiltons etc). You can probably scrounge one up at a local GM dealership. Look for the directions on how to adjust the front and rear bands (usually adjustable externally via set-screw. The dealerships around here have never had a problem with me photocopying a few pages. There's usually a specific torque that they need to be set at. Though small, there is the possibility that they just went out of adjustment.

I'll caution to add that you usually don't see trannies that "fall out of adjustment" like this after a year's worth of service. I'd believe it if it were within 1000 miles of the rebuild...

But there's nothing to lose except an hour or so of your time, right?

Good luck!