Addressing your second question first, it's possible the shift solenoid(s) have been damaged by debris floating around in the fluid mix. The primary issue is still improper fluid (contaminated with coolant) and excessive debris in the fluid from wear from improper lubrication.

You need a rebuild kit for that one, at a minimum, and possible some other "hard parts" if there's unusual wear on anything in there. You can keep ruining filters, fluid, hoses and other things as much as you want, but until you find where all the excessive metal bits came from, you're not going to effectively repair it.

As for the fluids, Valvoline MaxLife and Castrol TransMax fluids are compatible, and work fine in these transmissions when the transmission is in good shape. However, both have synthetic oils in their base oil mix, and both have cleaners in the additive package. That combination can unmask existing issues that would remain masked by conventional (cheap) fluid. Basically, if your seals are old and have cracks that are filled with varnish and gunk from conventional fluids, the synthetic (or semi-synthetic), "high mileage" fluids can clean the gunk out and expose leaks. The cracks were already there, they were just masked by the gunk from conventional fluids and the new fluid "cleaned out the cracks." It's possible some of the internal seals in yours have this kind of leakage now (in addition to the other damage from coolant/water in your fluid and excessive wear from that).

Most people wait far too long before switching over to "high mileage" fluids and oils. The best time is between 60,000 miles and 90,000 miles. For transmission, that's on the second or third scheduled filter replacement "transmission service."

 

I wanted to post a quick updated to where things stand. Found a 99 Blazer about 120 miles away for $400.00 that had the tranny rebuilt 10K miles ago. Engine was making some noise according to the sale listing. Got there and it sounded like a rod was about to go through the pan. Tried to drive, but ended up calling AAA for a tow.

Got it home and cringing I drove it up my road and made sure it got through all the gears. Is seemed to be smooth with the 2nd to 3rd shift seeming to rev a little higher than I would have imagined (3100 RPM), but that could be because of the acceleration I was having to use to get it moving that fast with a motor that was about to blow up.

Anyway. Today I am on my way to pick up fluid, filter, new radiator, new radiator cooler, rear main seal, and exhaust donuts. Hoping to swap the units today and get it back on the road. I still owe pictures of what I found in the pan which I will.

Now I am just hoping the new tranny is in good shape internally. No real way to tell before I bought it, but the person I bought it from seemed on the up and up, but you never cal tell.

If not, I have a LOT of spare parts available.....

I will post an update once the swap is completed.

 

Update:


Due to time constraints I can only do a little bit of work at a time, but here is where we are:

1. Transmission is out of the 1999 4 Door Blazer
2. Getting close to dropping the transmission out of the 2000 2 Door Blazer

Some interesting observations:

1. The 1999 transmission pan is completely flat all all the way across, whereas the 2000 transmission pan has part of it that is shallower than the rest of it (rear 1/4 of the pan).

2. Exhaust is different on both of them. I am looking at swapping the exhaust from the 1999 as literally everything appear to be very new (cat, muffler, 02 sensors, etc), but the 1999 does not have a resonator on it. Should they be swappable?

And now a question as I am certainly a first time transmission swap noob. I was told by multiple sources that the transmission from 1999 4 door 4wd was interchangable with the 2000 2 door 2wd. All the electical connectors, vacuum lines, etc seem to be the same, but is there anything I should look for or should these indeed simply swap out?

Hoping to hit it tomorrow and by the end of the day be able to bolt the 1999 one into the 2000.

Thanks for any info!

 

Just to add to my last post, I have found the following info:

1. The 1999 4 Door Blazer has a Transmission tag on it of 8TAD (Assuming this means a 1998 manufacture date), however the vehicle itself has an 04/99 manufacture date.

2. The 2000 2 Door Blazer as a Transmission tag on it of 00TAD with a manufacture date of sometime in 2000.

The 1999 Blazer supposedly has a rebuild transmission in it, however I am guessing either it is a junk yard rebuilt tranny or it is just a junkyard tranny that was swapped into it. No matter, the fluid looks good (believe me I have seen plenty of it) and the only "metal" in it anywhere was a very slight film of grey (no flakes) in some that drained out.

We will drop the pan once it is back up and replace the filter, but so far so good. We are swapping the full transmission and torque converter from the old to the new one. I did find out that the 1998 an earlier tranny's used shallow pans vs the 2000 which used a deeper pan. That being said, the 2000 had a shallow pan filter in it (possible part of what killed it).

So should I use the deeper pan on the 8TAD tranny and just install the deep pan filter, or should I stay with what was working on the 1999? Does anyone see any other issues with using the 8TAD tranny in one that has an 00TAD tranny in it?

Length measures the same and bold patterns appear to be correct. We will do full comparison once we have both of them side by side to be sure before bolting up the 99 to the 2000.

Again looking for any possible helpful feedback.

Thank you!

 

So part of the process here is to determine why the old tranny failed. I have come to a couple of things that seem to have worked together to cause the failure (I believe):

1. The wrong filter was used and upon thinking back to when I dropped the pan, the existing filter was not hanging all the way up against the tranny the way it should have been. Of course I used the same filter not recognizing it should have been different, but the damage had already been done.

2. The bellhousing was missing 4 upper bolts AND the others were finger tight instead of properly torqued on. Additionally 1 of the alignment DOWEL PINS was missing. My understanding is this probably caused the transmission to shift when under stress and probably caused lots of bad things to happen in the unit.

This is a real shame too. The transmission that was in it was a real genuine GM reman from a dealer.

---------

Had to hunt around for the DOWEL PINS, but *think* I have found them at a GM dealer with part number of: 01453658 @$5.00 / each. Picking them up shortly.

So far everything between the 1998 and the 2000 tranny seems to match other than the fact someone seems to have crimped shut the vent line on top of the transmission. We are going to open it back up and flare it out so we can re-attach a vacuum line to it, but not sure what the reasoning was in doing this to begin with.

I am posting both to update the thread and am happily looking for any feedback. This is a whole new experience for me as I have always shied away from transmission replacements in the past.

 

As long as the transmissions are the same type (same engine bell pattern and 2 or 4 wheel drive) all of them from that general era are interchangeable. However, your post # 13 states you bought a 4X4 trans to put in a 2 wheel drive Blazer. If this is correct you will not be able to use it as the output shaft on the 4X4 one is shorter and made to fit into the transfer case. A 2 wheel drive has a longer shaft and an extension housing designed to take the driveshaft slip yoke. The output shaft is swappable, but the entire trans has to come apart as that is the first thing installed!

The deep pan and matching filter is what I would use on any replacement trans, adds an extra quart which is all good. Just remember to use the proper filter when changing the fluid again!

If your rad was leaking coolant into the trans, that killed it. The clutches are paper glued to metal, the water in the coolant both rusts the metal under the paper breaking the bond, and the glue is water soluble. Double whammy.

The shudder you felt previously could have been the lockup clutch in the torque converter slipping, or an engine miss. When the TCC is not engaged, the normal slippage in the converter soaks up any engine rpm change, when the TCC is locked up you have a solid connection and every little surge of the engine is felt.