1994 Suburban 4L60E Transmission Questions
May 6th, 2019, 9:06 PM
#1
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1994 Suburban 4L60E Transmission Questions
1994 GMC Suburban SLE 5.7 L 4x4 4L60E, non-PWM
I got this Suburban a few weeks back with no tranny engagement at all. Last owners said it just stopped moving one day. So I pulled the pan, and it was thick with clutch material. I pulled the valve body and it was gummed up terribly as well. None of the valves moved easily. I pulled all the valves and springs except the reverse abuse valve. The plug wouldn't come out. The way I understand it, that should be a huge issue(?).
So, after I cleaned the valve body, I did get some movement out of it. But no reverse and, barely any forward. So I rebuilt it with new frictions, steels, seals, etc. As well as checking for proper clearances and air pressure testing the clutches after assembly. But to my frustration, it behaved very badly during test drives. Long story short, I discovered that the ECM isn't engaging the 1-2 shift solenoid in any case. I verified the wiring is good back to the ECM and that the solenoid works. I can manually engahe the solenoid by grounding the wire at the ECM. In fact, I put two switches in for testing, one for each shift solenoid. I can get first, second, and I think 4th, but in 3rd, I bang the rev limiter right away. I haven't verified if the TCC solenoid or 3-2 control is working yet.
1) Is there another switch or sensor that would cause the ECM to keep the 1-2 solenoid off?
2) What could cause the shift into 3rd to hit the limiter, but not 4th?
I got this Suburban a few weeks back with no tranny engagement at all. Last owners said it just stopped moving one day. So I pulled the pan, and it was thick with clutch material. I pulled the valve body and it was gummed up terribly as well. None of the valves moved easily. I pulled all the valves and springs except the reverse abuse valve. The plug wouldn't come out. The way I understand it, that should be a huge issue(?).
So, after I cleaned the valve body, I did get some movement out of it. But no reverse and, barely any forward. So I rebuilt it with new frictions, steels, seals, etc. As well as checking for proper clearances and air pressure testing the clutches after assembly. But to my frustration, it behaved very badly during test drives. Long story short, I discovered that the ECM isn't engaging the 1-2 shift solenoid in any case. I verified the wiring is good back to the ECM and that the solenoid works. I can manually engahe the solenoid by grounding the wire at the ECM. In fact, I put two switches in for testing, one for each shift solenoid. I can get first, second, and I think 4th, but in 3rd, I bang the rev limiter right away. I haven't verified if the TCC solenoid or 3-2 control is working yet.
1) Is there another switch or sensor that would cause the ECM to keep the 1-2 solenoid off?
2) What could cause the shift into 3rd to hit the limiter, but not 4th?
May 11th, 2019, 10:29 AM
#2
I’m not expert on transmissions but have worked on the 4l60E in my suburban a bit. I can’t help with specifics of
your questions but, in general, I think it less likely the ECM can go bad such that it doesn’t engage 1-2 and more likely it’s getting bad input or wiring/connector is bad. Or, of course, it could be something in trans itself where I have little experience.
You say you don’t get 1st or 2nd. Is this when you put shift lever in first it doesn’t shift into first? Or when you put in D you can tell it’s not shifting thru 1st & 2nd?
There is a membrane switch in the transmission, at least in mine, which uses pressure ported in trans from the shift mechanism to tell the ECM what gear is selected. That switch can go bad and ECM thinks the gear selector is in a position which it is not. You can check it with a voltmeter on the input lines from transmission at the ECM. I found something somewhere online or in a forum on how.
If your problem is it doesn’t go into 1st or 2nd when selected but it does shift thru them when put in D its possible that could be something to check
your questions but, in general, I think it less likely the ECM can go bad such that it doesn’t engage 1-2 and more likely it’s getting bad input or wiring/connector is bad. Or, of course, it could be something in trans itself where I have little experience.
You say you don’t get 1st or 2nd. Is this when you put shift lever in first it doesn’t shift into first? Or when you put in D you can tell it’s not shifting thru 1st & 2nd?
There is a membrane switch in the transmission, at least in mine, which uses pressure ported in trans from the shift mechanism to tell the ECM what gear is selected. That switch can go bad and ECM thinks the gear selector is in a position which it is not. You can check it with a voltmeter on the input lines from transmission at the ECM. I found something somewhere online or in a forum on how.
If your problem is it doesn’t go into 1st or 2nd when selected but it does shift thru them when put in D its possible that could be something to check