RPM surging between 40 and 55 MPH
 

My Blazer: 177k miles, 4WD, 2D
I'm having an issue with RPM where I'm driving along and at the point where my Blazer wants to shift into 4th it does, but if I ease off the throttle a bit trying to maintain the current speed the tach will start jumping up and down. I'm quite sensitive to the motions and vibrations my Blazer makes, and I can tell I feel a surge of power in the drive train whenever it does this.

I found this video of a guy driving his Blazer where mine is doing the exact same thing.

Is this indication of the transmission going out?
I notice it won't do this if I stay in 3rd gear or if I accelerate quickly to 65 and cruise from there.
It's very noticable in D driving through city traffic.

This started happened after I had replaced an axle seal and I needed to remove the center pin and axle retaining clip from the rear diff.
I'm faily confident I put it all back correctly, but is it possible I misaligned something?
Other work I've done that may be related is changing out Diff and Transfer Case fluid.

Some people say it's the TCC solenoid, speed sensor, or MAF sensor.
Others in the comments on that video are claiming it could be a bunch of things.

Following... mine moves +-100rpm while coasting at any speed. And I get a tick tick tick while reversing lol...

Does your surge like the video? Also have you done any maintenance on it since you got it? I did a transmission service around 250k km, its got 345k km on it now...

Probably the TCC working exactly as designed. Between 45 and 55 in 4th (especially 45-50) it doesn't take much acceleration to disengage it. Does tach go up the same amount when you tap the brake pedal when going steady 50?

Still diagnosing the issue, so I'm revisiting this thread I didn't mean to abandon.
It has felt like the surging is slowly getting worse, so I'm trying to set some time aside to work it out when I get a second daily driver.

I have not, but it is way over dur for service. It needs a fluid change. I have a new filter and gasket for the oil pan sitting in my garage. I need to set time aside to do it when I learn more about replacing the filter.

Is the whole vehice suppose to feel like it's lurching forward / braking when the tach does surge? That's what mine is doing, and it's actually more pronouced than what the video.
If I'm maintaining speed or accelerating slowly, it will surge between 40 and 55 MPH. If I accelerate fast to 65, then maintain speed, it doesn't surge.

This surging started happening around the same time I started hearing a grinding noise in the drive train somwhere.
https://blazerforum.com/forum/2nd-ge...-right-102683/

I haven't yet isolated the grinding noise to the diferentials, transmission, transfer case, or the CV axels. All of these things are suspect.

• I removed a rear axel to replace a seal. Maybe I didn't put it back right.
• The transmission has been downshifted from 4 to 3 at around 45 MPH once before (totally by accident).
• The front CV axels leaked grease before. I repacked them, the leaked all the new grease again. So they might be worn out.
• I accedentally changed the wrong fluid with the transfer. Ran it for about 15k miles on AutoTrak II when it should have been Dexron III ATF.

So when the engine surges, the tach reading goes up, you hear an increase in engine rpm and the truck accelerates? IOW, the truck acts exactly the same as if you had depressed the accelerator pedal a small amount as apposed to say the transmission is slipping or downshifting with no additional power or speed?


George

TCC is cycling in and out. Are brakes dragging? Something else robbing power from moving the vehicle forward (ie grinding, etc)?

Yes. It feels like something is dragging like a brake when it does this.

Brakes are not dragging. There is a grinding noise I've been trying to figure out.
https://blazerforum.com/forum/2nd-ge...-right-102683/

I'm having a hard time getting my head wrapped around what is happening here., So the truck surges on its own when you are not asking for a sudden increase in power from the accelerator pedal. The rpm gauge increases, the truck audibly goes up in rpm, the truck accelerates and the speed increases and then it suddenly feels like its braking, making an equally strong reduction in power and forward speed as if you had applied the brakes? What is the change in speed during all of this?


George

Oh no, it's not accelerating when the RPM surges. Actually I take back that it sounds like it's reving when the RPM spikes. It just feels more like it's going in and out of 4th/overdrive constantly and I feel it dragging the truck down when it does.

There is no change in speed.

So its downshifting and engine braking?

George

I would concentrate on fixing the noise, and not worry about the RPM surging. This is because I believe the noise is indicative of the cause, and the RPM surging is only the effect.

I’m going to leave you with Les on this, I think he has a better handle on your problem. I’m sure he will get you fixed up.


George

Okaayy. So I learned something new from a video where this guy is going over things to check when there's drive train noise.
The fluid level should only be checked when the engine is hot and running.

That lead me to this video where checking the transmssion fluid in GM trucks isn't as cut and dry as I originally thought.

This whole time I've been checking it each morning cold, not running, and saw the fluid level just above the cold range. So I've been thinking it's definately not low on fluid.
Well, it turns out it actually is low.

I drove it for about 10 minutes today averaging about 15 MPH through my neighborhood trying to get the transmission up to operating temperature. I checked the fluid level while the engine was still running, and saw the fluid level is actually just at the very edge of the dipstick.

I'm guessing low fluid is the cause for both the in/out of overdrive and the noise.

Another thing I notice was steam coming out from the transmission filler tube. Not a lot, but noticeable. Is that a bad thing?

Was the steam before or after adding fluid? Wondering if it was burning clutches from being dry, or cooling clutches from sudden cooler fluid hitting the hot plates.

Not sure if its a bad thing or not. But those are my none educated guesses lol

Before. I haven't added more yet because I'm planning to change the fluid and add a new filter. That's on my to do list before I drive it again.

Hopefully the transman will see his calling on this...

I have had the same RPM increase at 40 - 50 mph on my 2000 ZR2. At first thought the the engine was missing as it kind of felt like it was lurching forward and back. But eventually noticed the RPM surge. Each time it was the start of the transmission going out. Eventually mine started slipping in all gears. The original trans. and 2 add'l. rebuilt did exactly the same thing. I finally had a trans. installed with a lifetime warranty and all has been good so far. Paid about $800 more than than the others but at least I have more than a 90 day or 1 year warranty if there's a problem. Hopefully yours is something simpler and less expensive.

I heard recently on a Saturday morning car talk radio show that the ATF filter really doesn't need to be changed because it generally doesn't clog up. If you find it clogged up, that indicates that there is something seriously wrong with the transmission. IOW it needs more than a simple ATF fluid and filter change. Meaning the clutch plates are wearing out and clogging up the filter. I do want to qualify this by saying that one of this show's sponsors is BG Products, Inc. One of their big services is the automatic transmission complete fluid flush. Their machine flushes 100 % of the fluid out of the transmission without removing the ATF pan. They use the trans cooler lines to flush all the fluid out and don't drop the pan. When you drop the ATF pan and replace the filter and gasket, you are only replacing about half of the ATF fluid. A lot is left in the torque converter.
I do want to say it is hard to remove the filter seal from the GM 4L60E auto trans. This seal is actually a 'O' ring and is way up in the aluminum housing of the transmission. You are using a steel flat blade screwdriver to pry out a small O ring embedded in a aluminum tube. You don't want to scratch that tube and cause leaks. If you don't remove it and put the new one in there and put it on top of the old one, you are causing a problem, You now have two seals installed and it won't seal well and will cause leaks. By leaks, I am referring to air leaks, not transmission fluid leaks. I do think the ATF fluid should be changed regularly.

jim - I have never heard of this filter seal in the 4L60E trans. I have changed the trans filter twice on my '92, once on my '95. Both of these had an O-ring on the filter neck that pushes up into the trans....is this what you are referring to? If so, the O-ring has always come-out with the old filter. Applied some new trans fluid to the new filter O-ring and it easily pushed into place.

Let me know if I have missed something for all of these years.....


Oh and RedValor...be sure to have the Blazer level, trans warmed-up and then with engine running at idle for 2-3 minutes before checking fluid level.

So I did the first tansmission fluid change on this Blazer at 178k miles and installed a new fluid filter. Certainly needed it. The fluid was really dirty, but it didn't feel gritty, so I'm confident the clutch packs aren't worn out.
I drained out about 4 quarts. The maintance seciton in my Chilton manual says it needs 5 quarts for a fluid change. So I was terribly low on fluid. Now that I know how to properly check it, that won't happen again. I thought "cold" on the dip stick litterally mean't cold.

I've been out on a few test drives with 5 quarts of clean transmission fluid, and the truck is doing alright. Shifts are smooth and there's no slippage. Also, the RPM isn't doing that weird surge/spiking behavior it was doing before trying to go into 4th gear but it felt like it wasn't staying. I now know the hard way that's what these transmissions will do on low fluid.

Last thing: I'm concerned about what the max fluid capacity is for these transmission. After each outting when I return home, with the Blazer still running, in the garage, on level surface, I check the fluid level on the transmission. I added 5 quarts after the fluid change. Today after driving it, I still don't see fluid on the dip stick (doing the procedure for a hot check). I added another cup of transmission fluid, so now it's at 5 1/4 quarts of added fluid. I gave it another test drive this afternoon, did a hot check, and still don't see any fluid on the dip stick. I feel like I'm going to be at 6 or 7 quarts of added fluid before I see a hot check result. Does this seem normal?

I found this reference that does support 5 quarts after a fluid change, but it also claims 11 quarts after a complete overhaul.

Chevrolet Blazer 2002 oil, coolant, transmission fluids capacities and cars specifications.

So I guess my assumption on adding 6--7 quarts, or even more, to see fluid on the dip stick seems valid.

So just to put the final nail in for this thread, I did end up about close to 7 quarts of fluid after a change. Learned that this 4L60E transmission takes up to 11 quarts entirely.
Also turns out this "RPM surge" I was describing seem more like a torque converter shudder due to low fluid.

https://itstillruns.com/diagnose-aut...s-5357959.html