Transmission Problem at 45-50 MPH

[Ravenhurst]

Greetings.

I've got a 2000 Blazer 4D, 4WD with AWD Feature, the standard 4.3 Vortec V6.

All in all its a good truck, which high maintenance issues that I've repaired in the past without problem. It's got approximately 78,000 miles on it and I decided to bring it in to the dealership to have all the fluids flushed and replaced. Basically the 90,000m tune up. Got a new cap, wires, plugs, fluids for brake, tranny, coolant, oil, and steering. This was about two weeks ago.

Now here's the problem:
Starting yesterday, at 45-50 MPH cruising, the truck constantly slips on itself. I watch the coolant temperature gauge nearly drop to 100, its lowest reading while it is acting "jerky." (Update: The temp guage drops and returns to normal a whole second before the *clunk* sound from the tranny and then the vehicle jerks. Sometimes the temp guage will drop to 100 and nothing more will happen. Again, only at sustained speeds between 45-50mph)
RPM's do not change, nor does any of the other guages. If I stay between this speed, the truck will repeat the jerk every 5-10 seconds. Accelerating past that speed range yields normal driving, and under that speed range everything works fine as well. Its hard to tell, but appears to be getting worse the more I test it.


I'll be checking the tranny fluid at hot idle when I get home tonight.
(Update: Fluid Levels check good.)


BlazerLT, if you got an answer for this one off the top of your head, I owe you a beer.






Ravenhurst

[starla3366]

Have you seen the check engine light come on, when this happens? Possiblly a code 1840 if you have OBDII.

Transmission Valve Body

When you got the tune up did they change the Trany filter, or did they just flush the system like most places do?

[Ravenhurst]

According to the receipt, no filter was replaced, just the fluid.


No check engine lite has come on... yet.

[starla3366]

Originally Posted by Ravenhurst

According to the receipt, no filter was replaced, just the fluid.


No check engine lite has come on... yet.

If your going to pay for that extensive of a tune up, they should have included the Tran. Filter at least. Those, greedy basterds are always out to get ya.

I'd replace the Filter, ASAP.

blazerlt, Do you got my Back on this one?

[starla3366]

Oh, one more question.

How much did you pay the dealership to have this done?

[Ravenhurst]

It was about 700$, but also included a replacement driver side window motor as well.

[Mikado14]

Ok, here's a start:

Do you get this problem when you are driving in "D" or just "OD"? (assuming that you haven't tried this)

Since you have the AWD, Are you in AWD or 2HI?

I will assume that you don't have a "Service 4WD" light on?

When the dealer changed the tranny fluid, Does the receipt show how much fluid was replaced? (I would look under the vehicle to see if the pan was dropped, you could tell by looking at it. If it wasn't dropped, you can't change the filter without doing it)

You mentioned the phrase "slips on itself". Does this mean that the tranny acts as if it is between shifts and then goes into gear with a clunk? (This is why I mentioned driving in "D" vs "OD")

If the "clunk" is gone when you drive in "D", I would check for a poor ground from engine to tranny and frame as well as from the firewall to engine. The overdrive solenoid lockup could be hesitating due to this. The fact that the temp guage is the only guage that goes down is the dilemma. A poor ground would affect others as well. However, seeing as the amount of electronics are in the tranny and transfer case a poor ground is possible and the temp guage might be the most sensitive guage to show this condition.

Conclusion is: If the problem goes away in "D", look for a bad ground on the firewall in the vicinity of the distributor cap. Since the dealer changed this and then the problem surfaced, a ground( I believe there are 2) might have come undone or disturbed. If this looks good, go under the vehicle and check the connections to the tranny. Let us know before we go further. Good Luck!

[Ravenhurst]

Originally Posted by Mikado14

Do you get this problem when you are driving in "D" or just "OD"? (assuming that you haven't tried this)
Since you have the AWD, Are you in AWD or 2HI?
I will assume that you don't have a "Service 4WD" light on?

No, OD is not installed on this vehicle.
Driving in 2HI.
No light is on.

When the dealer changed the tranny fluid, Does the receipt show how much fluid was replaced? (I would look under the vehicle to see if the pan was dropped, you could tell by looking at it. If it wasn't dropped, you can't change the filter without doing it)

Will check ASAP.
Update: This is what the receipt says when dealing with tranny:
Button/AiP Filter Tffd (The dot matrix printer f*cked up here and its hard to read)
Trans Fluid Exchg dextron Pkg
Transmission filter not included
DEXTRON/MERCON III Fluid With QTY listed at 14.

You mentioned the phrase "slips on itself". Does this mean that the tranny acts as if it is between shifts and then goes into gear with a clunk? (This is why I mentioned driving in "D" vs "OD")

Its very hard to tell. Going at a slow acceleration, it seems it is attempting to get into final gear but doesn't quite make it untill after 50mph. If I accelerate more aggressively, it goes right into gear without hesitation or problems. If I cruise at 45-50mph it is a continuous problem.

If the "clunk" is gone when you drive in "D", I would check for a poor ground from engine to tranny and frame as well as from the firewall to engine. The overdrive solenoid lockup could be hesitating due to this. The fact that the temp guage is the only guage that goes down is the dilemma. A poor ground would affect others as well. However, seeing as the amount of electronics are in the tranny and transfer case a poor ground is possible and the temp guage might be the most sensitive guage to show this condition.
Conclusion is: If the problem goes away in "D", look for a bad ground on the firewall in the vicinity of the distributor cap. Since the dealer changed this and then the problem surfaced, a ground( I believe there are 2) might have come undone or disturbed. If this looks good, go under the vehicle and check the connections to the tranny. Let us know before we go further. Good Luck!

I will examine all the wires today, and try to find a loose connection. I'm not very good with cars, so I'll do my best.

[BlazerLT]

Originally Posted by Ravenhurst

Greetings.

I've got a 2000 Blazer 4D, 4WD with AWD Feature, the standard 4.3 Vortec V6.

All in all its a good truck, which high maintenance issues that I've repaired in the past without problem. It's got approximately 78,000 miles on it and I decided to bring it in to the dealership to have all the fluids flushed and replaced. Basically the 90,000m tune up. Got a new cap, wires, plugs, fluids for brake, tranny, coolant, oil, and steering. This was about two weeks ago.

Now here's the problem:
Starting yesterday, at 45-50 MPH cruising, the truck constantly slips on itself. I watch the coolant temperature gauge nearly drop to 100, its lowest reading while it is acting "jerky." (Update: The temp guage drops and returns to normal a whole second before the *clunk* sound from the tranny and then the vehicle jerks. Sometimes the temp guage will drop to 100 and nothing more will happen. Again, only at sustained speeds between 45-50mph)
RPM's do not change, nor does any of the other guages. If I stay between this speed, the truck will repeat the jerk every 5-10 seconds. Accelerating past that speed range yields normal driving, and under that speed range everything works fine as well. Its hard to tell, but appears to be getting worse the more I test it.


I'll be checking the tranny fluid at hot idle when I get home tonight.
(Update: Fluid Levels check good.)


BlazerLT, if you got an answer for this one off the top of your head, I owe you a beer.

Ravenhurst

Hehe, people are asking for me by name here now, I must know something.

Alright, so these symptoms happen all at the same time?

Tranny slips or does the engine lose power?

Coolant temperature dives.

Ok, does any of the other gauges go like this?

[Ravenhurst]

Originally Posted by BlazerLT

Hehe, people are asking for me by name here now, I must know something.

Alright, so these symptoms happen all at the same time?

Like I said above, they happen in an almost sequential order... I'll break it down so it'll be easier to troubleshoot.

1. Accelerate to about 45-50 mph.
2. Once at or above 45mph for about 10 seconds, the coolant guage starts to fluctuate.
3. After a few minor fluctuations, it dives to 100 degrees and then returns to normal, at which time the tranny clunks and the vehicle jerks. Speed and Engine RPM remain the same.

Tranny slips or does the engine lose power?

It feels like the tranny is attempting to get into final gear but can't make it at 45-50mph speed range. If I acclerate PAST 45-50mph the tranny shifts gears, the RPM drops, and everything works as advertised.

Coolant temperature dives.

Ok, does any of the other gauges go like this?

Yes, just the coolant guage. It will go all over the place after a few cycles of this mystery. No other guages move. The RPM's will drop about one notch if the clunk is a violent one.. but I figure that is to be expected. Usually the other guages remain steady.


There's alot of information and details in the above posts.. so read carefully..

[BlazerLT]

Ok, I read it. Just needed clarification.

First, check your coolant for contamination and the same with the tranny fluid. The only time they both come together like this is in the rad.

BUT, hear me out on this.

The clunk is the Torque convertor solenoid trying to lock up the torque convertor.

It will only do this when the engine is up to temperature at 50mph or less.

What you are seeing is the coolant temperature dropping rapidly which tells the tranny's computer to unlock the torque convertor.

What needs to be checked:

Both Coolant temperature sensors.
Thermostat.
Torque Convertor solenoid.

Let us know.

[Ravenhurst]

When I looked at the fluids, there was no contamination.

Both coolant temperature sensors.
Thermostat.
Torque Convertor solenoid.

Damn. I thought it'd be easy. I don't know enough about these to really look and check and be able to identify if they are bad. But, I'll be bringing the vehicle to a real car mechanic in 2 weeks to get these checked out. I'll come back here as soon as I know.
I'd do it sooner, but I'm getting deployed for 2 weeks.

Thanks for the help, and I'll get back to you guys asap.

[BlazerLT]

Don't drive the truck too much in this condition. You are doing damage.

[starla3366]

Where are you stationed?

I'm stationed in Brunswick, ME with patrol squadron eight.

Valve Body -- I'm absolutely positive

[Rbraczyk]

My truck did this to me, and it turned out to be a bad torque converter.