So I was searching the forums and didn't happen to see this problem described, but may have missed it. If so please point me in the right direction of the thread...

Yesterday I started getting a strange sporadic vibration when the 4L60E shifted into O/D. It seemed to happen above 45 mph only, which I thought was very strange. I was on my lunch break when it first occurred, and went back and parked the truck. After getting off work, I had some errands to run and after about 30 minutes of city driving, the vibration was gone but then I noticed that after braking and coming to a stop, that the trans. started to slip in 1st gear when resuming travel. Now is where it gets stranger to me. This problem only seems to happen after the tranny has been operating at normal temperatures for about 30 minutes or more. When it's cold, I have no problems and operation is normal.

I have checked the fluid level and it is accurate, as I thought it may have been low since it slips after braking. I can tear down and rebuild a 305 or 350 with no problems, but when it comes to trans. I have no freakin clue about anything... My next step is to change the fluid and filter, but have been told that a filter change on a trans. with as many miles as mine, can actually make problems worse... I have no idea if this is true or not, but it doesn't sound right to me... I'm guessing that the fluid could be thinning and losing viscosity thus causing the slippage when the trans. heats up. Or are my bands starting to wear?

My blazer has 250K+ miles.

If any one knows of a fix, or what could be causing the issues I would greatly appreciate any help and advice...

Matt

 

With that mileage its probably due to slipping clutches, pull the pan and look for clutch material. Probably a burnt set of forward clutches and it may also be causing the vibration in OD. If it shifts decently/smoothly the band is probably not at fault. Time for a overhaul/rebuild. If the fluid is red and not burnt smelling and you dont have a transmission whine indicating a clogged filter, I wouldnt change the fluid. If there is no clutch material/huge metal pieces in the pan it would point to a valve body issue or maybe and overheating issue. Do you have a tranny cooler? Not really a simple fix for this. 250K is a s'hit ton of miles for a 4l60! Has anything been done to it before? I would imagine so.

Edit: The reason as Ive heard for not changing transmission fluid in higher mileage vehicles, Is because the the clutch material that was once on the clutch plates is now suspended in the fluid and changing will get rid of the material or the last bit of friction. If that is the case that gunk should get stopped by the filter So I dont know. Thats just what Ive heard anyways.

 

Understood Chris... The one thing that confuses me still is the fact that when it's cold it has no problems. If the clutches are worn out, wouldn't it happen regardless of temp? As for the trans. cooler it's just the factory setup of being cooled through the radiator. Don't know if anything was done to it prior to me, but when I bought it in Dec. they didn't mention anything. And the crazy thing is I drove it from OK. to MS. for about 5 straight hours and didn't have any issues then.

 

Well my worn clutch assumption was purely based on mileage factor. How consistent does it happen? It only slips in first? No other gears? Since it only happens once hot, it may be the o-rings in the forward clutch piston assembly have lost their dexterity once heated up, combine that with 250k+ mile clutch's and theres your slip.

 

I have the same truck first off. 1994 two door full size 5.7 liter 4 spd auto 4x4. Currently running at 285,000 klm. My trans ended up going around 240,000 mark. One of the things that happened on the way out that probably aggravated the last ten thou or so was the transmission computer module. If it reads something it doesn't like it will go into "limp home mode".

Maybe this is what you are experiencing. If you went to a tranny shop to get a quick diagnosis before buying/ tearing up a **** load of parts you might save some time. Just make sure you tell them that you only want the computer tested. Shouldn't cost too much.

BTW my brand new Auto tranny with the largest torque converter I could fit, cost me $3,400 with a 40,000 klm warranty. Good luck!

 

So here's what I did. I simply unplugged the battery for about 1/2 an hour to clear the ECM (computer) and I have had 0 problems since then. I also have been taking it pretty easy lately and watching my driving habits as to not put any extra strain on the tranny. Also added a bottle of Lucas tranny conditioner, and found out my tires were 20lbs. under recommended pressure for 285 75/16 LT size and thought that may have something to do with it as well. Hell I don't really know what's stopped it from acting up, but I'm not complaining at this point. So I'm considering this a closed case at this point in time.

 

Thanks for the update!
Resetting the computer is always worth a try. I will remember this if/when I run across something similar.