1994 full size Blazer 4L60-e issues

[BlazinBlazer1994]

Hello everyone. I'm brand new here, and recently picked up the above vehicle (GMT 420) with 268K miles on it. it still looks good, but the transmission isn't very happy.
The PO said the engine has been replaced with a 1993 TBI 5.7, and the transmission MAY still be the original 4L60-e. He used it as a hunting vehicle and as an elk-tour vehicle (off road). Drove 65 m.p.h. max in third gear only and just around town (I will explain).
Symptoms are slight vibration in third with TC locked up, and severe (dashboard shakes badly) vibration in fourth with TC locked up at speeds above 65 MPH. I noticed the transmission mount is old but in decent shape (it's getting replaced soon).
This vehicle has a 3" lift, and all front end parts are new.
Shocks are rusty Ranchos, with double steering shock absorbers, with one leaking. Bounce test shows them to be OK.
Rear springs are new.
No looseness from the driveshaft.
I have not checked the TPS yet for proper operation, but I understand this is a possible source of the problem, and will be checked/replaced first.
Transmission fluid is clear, but dark.
If the TPS checks out, I figure to do a filter and fluid swap using the procedure I read about on one of the threads, and I intend to R&R the 2-4 accumulator with pin-less Sonnex parts, check/replace the servo on the outside of the case with a Sonnex replacement, and check/replace the TCC solenoid.
If all this doesn't resolve the shaking, I will continue by running the vehicle on jack stands with wheels removed, checking for vibration at 65+, then axles removed, then driveshaft removed, as I read on another thread, to isolate the vibration.
If that doesn't resolve the shaking, I'm going to guess it's a torque converter clutch issue.
I have not checked for stored codes, but I will do that before anything.
Just seeing what opinions this board will be willing to offer. Is there an overdrive (4th) gear issue? Could it be the TCC solenoid? Trans fluid and filter needs a change? Cracked or leaking plastic accumulator pistons?
What do you all think I should check in addition?

Thanks,

Joe

 

[stutaeng]

Yes, that sounds like a good idea. Don't "guess" at the torque converter clutch though. I can't imagine why that would cause a bad vibration, but I don't really even know much about them to begin with, LOL.

I would agree: jack the truck and start with the wheels. Run it, if it still vibrates, remove the rear axles...then driveshaft. You are in the right track. Also check the front driveline.

The fact that you don't have 4th and it vibrates could be 2 different problems.

There was a thread here not that long ago and the OP also didn't have 4th. I posted this table from this source:

You must be registered for see images attach

http://shop.ukrtrans.biz/wp-content/uploads/catalogs/4L60E.pdf

Perhaps the 3-4 clutch? I suppose the 2-4 band or forward clutch could also be bad, but not likely since you have seemingly have 1-2-3 gears and you obviously move forward?

I think the 3-4 clutch is a common failure on these units: Here's an article that talks about it: https://www.sonnax.com/tech_resourc...ing-4l60-e-burnt-3-4-clutches-with-confidence

I hope this helps.

 

[BlazinBlazer1994]

Today I was able to do some initial checking. First I checked for codes and none were stored. I checked my TPS voltage, and it was at 0.39 volts at closed throttle, engine off, key on, and it went to 4.55 volts at WOT. Progression of voltage was linear, so I will call the TPS good. I also replaced the oil pressure sensor because my gauge was reading as typical with a bad sensor, and had to pull the distributor to get to it. I decided to service what I could on the distributor, so I brought it to the bench and removed the ignition module to check the condition of the heat transfer paste under it. None was found at all, so I cleaned the area well, and smeared a good amount on the bottom of the module and reinstalled it. This is usually what kills ignition modules in my experience, as GM barely puts any on at the factory, then they get overheated repeatedly and die. The brand of heat transfer paste I use is Thermacote, by Thermaloy Inc.

The distributor has no play at the bushings, so I decided to look at my pick up coil since I had the distributor out. I disassembled it, took the copper shield off, took the spring clip off and slid the pick up coil off. i noticed that both the green and yellowish wire both had cracks in the insulation going almost all the way around each wire. This would be difficult to see with the pick up coil installed as the cracks are located very near the coil itself. I'm guessing that when the trigger voltage is induced, there may be a possibility of voltage loss at the cracks (the wires touch at this location), which in turn, could cause a misfire under some conditions, which in turn could be causing my lockup vibration in third and fourth.

The distributor with a new OEM pick up coil, new cap, rotor, wires and distributor gasket will be reinstalled later this weekend, and I will let everyone know if the original issue has resolved.

 

[Schurkey]

While you have the distributor apart, verify the magnet near the pickup coil.

Broken magnets are very common on TBI distributors.

 

[tayto]

did you pop the transmission into neutral at these speeds to confirm the vibration went away? hate to say it but sounds like out of balance/bad tires to me and/or deathwobble. have you actually checked out the front end?

 

[BlazinBlazer1994]

While you have the distributor apart, verify the magnet near the pickup coil.

Broken magnets are very common on TBI distributors.

Found at least two cracks. See attached.

I managed to swap magnets and shafts to form a functioning distributor with a GM module. Set timing and runs good. I have not had the chance to check for shudder.

What is a good recommendation for a new distributor?

 

[BlazinBlazer1994]

did you pop the transmission into neutral at these speeds to confirm the vibration went away? hate to say it but sounds like out of balance/bad tires to me and/or deathwobble. have you actually checked out the front end?

I will bring the vehicle to a local alignment shop for their free suspension check. Will report back later with findings.

 

[Schurkey]

Found at least two cracks. See attached.

I managed to swap magnets and shafts to form a functioning distributor with a GM module. Set timing and runs good. I have not had the chance to check for shudder.

Good work. Magnets + pickup coil is about all that goes wrong with the distributor; of course there's occasional problems with modules. The GM gears and bushings on the TBI distributors seem to be very reliable. (Gears and bushings on Vortec distributors are a mess.)

What is a good recommendation for a new distributor?

Unfortunately, there's "no such thing". Almost all "New" replacement distributors are Communist Chinese bottom-feeders. The modules are junk, and the rest of the thing is suspect including the gear at the bottom. If there's a premium replacement, I don't know about it. I buy every Delco HEI I can lay my hands on at my favorite Treasure Yard.

I also bought a bunch of new TBI distributor shafts still in the boxes on eBay. They're branded "Standard Motor Products" but I suspect they're reboxed GM parts. As long as the original distributor housings aren't cracked, and the bushings aren't wiped-out, I can put a new shaft into a Genuine GM housing and be reasonably certain it's going to work right.

 

[BlazinBlazer1994]

I appreciate everyone's help in this matter.

Today I replaced the 180 degree thermostat with a 195 degree t-stat and new gasket. Added one bottle of Dura-Lube synthetic ATF protectant (red 10 oz. bottle) and took the vehicle for a 25 mile drive. The shudder issue is still present, and eventually noticed the transmission does not slam into 2nd, 3rd or 4th gear as badly. The shudder is definitely from the torque converter slipping. I tapped the brakes as it was happening and it stops immediately. I also noticed a rise of between 200-400 RPM during a shudder.

I'll keep driving this vehicle and hope the magic fluid will do something. I'll report back after I drive a few more miles.

Alignment shop says I need a rag joint, and the rest of the steering/suspension is great. The vehicle doesn't tire or suspension vibrate at all with 33" tires all the way up to 75 MPH.

My next step is to replace the transmission mount. I will also drain the ATF with the engine running via the trans cooler, drop the pan and inspect (The transmission is the original and has 268K miles, may have been overheated, and some plastic parts may have become brittle and are not controlling pressure. I also fear the torque converter clutch may have had enough and is worn out, along with the valve body components.), change the transmission filter, do a running flush with the cheap Dexron, and fill to the proper level long with a single tube of the Dura-Lube shudder fix.

Can anyone confirm the use of pulse width modulation for the TCC in a 1993 or 1994 4L60e?

Thanks!!!

 

[Schurkey]

Alignment shop says I need a rag joint,

You need the C3500(HD?) steering shaft, that has a U-joint instead of a rag joint at the bottom. That and the longer bottom bolt that goes with the shaft.

Part numbers are in the sticky "Jeep steering shaft" thread. This shaft / bolt is way better than the Jeep shaft, it fits perfectly and is a Genuine GM part.