1991 R2500 suburban 7.4l uphill overdrive drive ability problem

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
While driving uphill in od I hear what seems like a rpm change for just a second, it might do this every 5-10 seconds. Any ideas, transmission, misfire. It doesn’t seem to loose power, I just hear a change in how the engine sounds
 

zora

Staff member
Joined
Apr 24, 2012
Messages
3,742
Reaction score
20
Points
38
Really hard to say with that amount of information.
I assume you have no codes?
 

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
No codes. Planning to put in a tachometer Saturday to see if rpm jumps when this happens. First time I heard this I thought trans slip, but then started thinking misfire. Checked distributor cap rotor are good. Checking plugs tomorrow. 135,000 miles
 

zora

Staff member
Joined
Apr 24, 2012
Messages
3,742
Reaction score
20
Points
38
Have you checked the transmission fluid level?
Have you ever changed the transmission fluid and filter?
When is the last time it had a basic tuneup?
 

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
Trans fluid filter changed about 1 year ago. Changing plugs tomorrow (Monday). Cap rotor wires very new. Original coil. Fuel filter maybe 3 years old. Average 5,000 miles a year driving
 

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
I notice it does same thing in drive( level surface) at 55mph. Could it be something to do with torque converter clutch, lock up solenoid going in and out. Kind of what it feels like. Thanks much. So I think this has nothing to do with hills. In drive happens at 55mph and overdrive at 72-73 mph
 

zora

Staff member
Joined
Apr 24, 2012
Messages
3,742
Reaction score
20
Points
38
Yes that does sound like the converter. Have you checked the electrical connections to the transmission/converter?
 

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
Not yet. Do I just look for any wire connections coming out of trans. Was reading about speed sensor( could that be it). Tranny shop can’t look at it for 3weeks. I’ll check underneath at trans after work (Wednesday). Suburban drives strong, I just notice those little changes at those speeds. Hope it’s not a serious trans rebuild. Thanks much for ideas
 

zora

Staff member
Joined
Apr 24, 2012
Messages
3,742
Reaction score
20
Points
38
You stated the transmission fluid was changed a year ago, was the filter replaced at the same time?
You dont appear to have slippage so I doubt you need a rebuild.
This is a general link on the topic that does not have specifics for your vehicle
 

Hawkeye12

New member
Joined
Oct 9, 2020
Messages
8
Reaction score
0
Points
1
Thanks for the link testing procedure. I’ll check that tonight. I had a hard shifting problem year ago( trans shop found bad computer voltages)replaced with used computer also changed fluid, filter. Probably 3-4 years ago I changed out fluid and added a extra trans cooler and external trans filter. Ordered and changing external filter Friday. This transmission is maybe 16 years old. Original went bad at 68,000. Had a shop put new transmission from chev dealer 2004. So this trans has about 70,000 miles on it. Thanks so much taking time helping
 
Top