IF you can, please decipher what the hell this says;

"Downshift Timing Control"
At higher vehicle speeds, the 2-4 band apply must be delayed to allow the engine speed RPM to increase sufficiently for a smooth transfer of the engine load to the 2-4 band. Therefore, exhaust of the 3rd accumulator fluid must be delayed. However, at lower speeds the band must be applied quickly. In order to provide for the varying requirements for the 2-4 band apply rate, the exhausting 3rd accumulator fluid is routed to both the 3rd accumulator checkball (#2) and the 3-2 control valve."

This is the evidence that the dealer just gave to me that my truck bouncing off the redline when you punch it between 60 and 65mpg ir normal. As some of you know I have been having transmission issues in my 2005 Blazer 4x4 for a while now and not long ago the dealership "replaced some burnt reverse bands" in it to fix this very problem at any speed. It used to feel like it would slip a bit any time you punched it but now it is only when you punch it from 60-65. He basically said when you punch it, it comes out of overdrive, goes into 3rd for a second, then into 2nd gear to build RPMs and back into 3rd gear where it stays till you let off or are really hauling ***. I suppose it feels like that is what it is doing but it never grabs in 2nd and I cannot imagine why GM would want their vehicle to drop into 2nd at 60+mph. It feels like driving a 5 speed, pushing in the clutch holding your foot to the floor til the engine redlines and then popping the clutch in 4th. Normal says Chevy...what do you guys say?

 

Um... At 60-65mph, it should NOT go to 2nd gear. Not at that high of speed.

I'll try to do some searching to decipher that for you, but off the top of my head, I can't help you.

Ask to drive another vehicle with the 4L60E they have on the lot. They are all pretty much programmed the same. If they have another Blazer there, even better. FORCE them to show you that this is normal. They will not be able to.

Good luck and stand tall. Don't let them snow ball you. Cause that's EXACTLY what they are trying to do to you.

 

*EDIT* - Damn sorry... Again, not really applicable.

 

Thanks man. I plan to take it to another dealer and not mention what the first place said.

 

Not sure how to explain it any easier.
Accumulator is like a bottle for fluid. Once the bottle is full, the fluid moves on to the next place.
Exhaust is a checkball. When you down shift you have to dump the fluid out of the accumulator, the 3-2 control valve controls the exhaust.
The automatic tranny does an excellent job of automatically shifting gears based on various inputs; vehicle speed, current gear, trottle, load, it will even downshift/coast up/down hills without any change in the trottle.

During noraml driving, 60-65 should be 4th gear (overdrive) and more then likely you will also be in torque converter lock up. When you punch it, it will drop out of torque converter lock up, and if you go past 3/4 torttle drop down into 3rd gear. It might even drop into 2nd gear if you put your foot to the floor. Depends on vehicle speed, load, and how much trottle you have. I can jump on the trottle and hold 2nd gear well into 60mph, and 3rd well into 80mph before she drops into 4th gear. You can wrap these trannies and engines out pretty far.

 

Yeah, I just tried this today... It will go down to 2nd gear when prompted. It definitely is not normal to bounce off the rev limiter when downshifting into 2nd at 60mph though...

 

Darn, after reading the first couple of posts I was going to give you guys the true sccop, but I see everybody caught up with the tranny.

Yeah fourth is 30 percent or so overdrive. That means third is about 1-1. Top speed at 1-1 is what 120 or so? With a 373 it might be 110 or so? Yes second will make it to 60 easy. If the governor were set better it would go 65 easily. 600 or 700 RPm may well be eaten up by the mechanical governor in a 700R4 in earlier models. The 4L60 E is of course, computer governed, so it all happens in the puter. No way to go any faster.

Yes, lockup will disappear (slip away) and you gain what, 500 rpm? What actual amount is doesnt really matter , but tach goes up instantly. Then tach jumps even higher to show a slip (Smooth transistion) down through 3rd gear on its way to second, where it really jumps. At all times the actual TOP rpm's are being "governed". It never goes over red-line does it? If it does, you need mr. goodwrench AGAIN.

Notice the rpm is climbing SMOOTHLY. Thats what the description says; right?

GM does not allow drivers to actually make mistakes anymore. This is one form of restricting us from having that neck snapping feeling we actually crave.

There are many 700R4s out there that will simply never shift back up into fourth either. Camaros full of 145 MPH speedos and when you floor them they stay in 3rd. Never upshift. Top speed 105-110 with a 273? RPM and shift limiting. 4500-5000 in third. (engine model dependent)

Did anyone ever explain that a chevy four speed tranny like the 4L60 is really two/ two speeds? yup. The 2- 4 band ties these together.

Fun though, isnt it? Give me a Muncie 4 speed anytime. I like the neck action.

 

Sure doesn't feel normal guys but thanks for the input and even testing the theory. There is no smooth climb is RPMs, you floor it, it kinda grabs, then slips, redlines, and then feels like a manual when you hold the gas to the floor and slip the clutch until finally popping it at the end as if you were really trying to race someone and didn't care about your clutch.

 

Seems that the "grab" you indicate may well be a problem if it releases just as suddenly in order to continue going through its transistion downward. A suggestion was made that the dealer show you how a new one works. Seems like just the ticket. What is the "redline" on yours?

A ride with mr goodwrench driving you and testing it might also be a good idea.

Yes the tranny goes through a whole lot more than I wish it had to. But the way its designed, (upshift and lockup pattern) its the only way it can accomplish the intended downshift. The descriptions of how this works are correct. It does seem as if you describe a situation that is not as "SMOOTH" as the factory would wish it were. Keep looking into it.

I remember very well when I had a plymouth with a 3 speed auto that simply downshifted into 2nd from drive. It would do this in less than 1/3 the time that a 700r4 takes to do the same thing. But it would also snap you back in the seat and not release back into third (drive) till about 75-80. Top end with the car was about 115 with a 390 rear. It was shifting at 5800 rpm though ( In auto, drive). Drag (airflow) effects came into play in drive (3rd) even though it was the Cuda variety. This limited rpm in top gear to about 5500.

Results with a th350 would be similar. Though different (speed) by about 10% across the board. The two trannies are geared different in final drive. Assuming the governor on the th350 was adjusted properly and not interfering with its performance.

It was decided by the powers that be that in order to keep using the low quality methods of building engines, that the best thing to do was to make things last longer by lowering operating RPM. The US government had a good solid grip on fuel economy standards and only using less rpm was a simple sokution. The simple solutions were not the correct ones in my opinion. Better robotics and getting rid of the old plants while building new ones in right to work states to get rid of the union labor would have been the correct answers back in the mid 70ts' . We are now paying for the nonsense they decided to play with.

 

That doesn't sound normal. When you floor it, the tranny will downshift, grab and the rpms will jump up but the tranny will not drop out of gear, it should never slip. Slip being engine rpms climb while the vehicle speed remains the same. That is not normal. Did they do any line pressure readings to diagnose the tranny?

I am having a problem in my '87 700R4 tranny. It doesn't want to hold 3rd gear when I stomp on the gas peddle, nor does it want to downshift into 3rd properly. I could bore out the vavle body and slide in a couple of parts to fix it (new checkball and 2/3 valve, spring, and sleeve), however I can get a reconditioned valve body for less then it would cost me in tools to make the repairs. Mine is driveable, yet I have to becarefull with it. At times going through normal excelleration from a stop it works fine, and then there are times when it doesn't want to grab 3rd gear. I'll get the speed up to 30mph and it shift from 2nd into 4th then instatnly drop into 3rd gear and work noramlly again. Sometimes I have to take my foot off the gas peddle until 3rd gear catches. Parts ar eon order and should be here tomorrow.



As for 2 gears in these trannies, not so. Without going into what is happening within the tranny. The 2/4 band does grab in 2nd and 4th gears. It grabs the input carrier assmeble, however in 2nd gear you could say half the tranny is engaged. There are more things going on inside then just that. First gear is 3.06, second gear is like 2.65, 3rd gear is 1:1, and 4th gear is .70:1.