I was wondering if there was anyone out there that has instructions for flushing a transmission on a 1998 Chevy Blazer LT 4x4. I'm looking for graphic pictures that will walk me step by step through the process. I got a new transmission around 56K miles and I am currently around 105K miles. I figured it was about time to flush it. Written instructions will work as well if graphic instructions are not available.

Any help is appreciated.

Thanks,

Blazin 4x4

 

You really should do more than "Flush" the tranny. With that many miles on the tranny you should change the filter to. Just doing a "Flush" will just clog up the filter and make the tranny worse....

 

I had planned on it but forgot to put it in the post. Do you have any instructions on how to flush the tranny and change the filter or is it too difficult to do myself? Better off taking it somewhere to be done?

 

Personally, I wouldn't flush it at all.

Drop your tranny pan, careful its messy. Clean the pan as best as possible, brake cleaner. Install a new tranny filter (you just introduced dirt to the system), and add tranny fluid. Getting the old filter gasket out can be fun, I use an awl, careful, do not score the metal. You will change out about 4-5 quarts of the 11-12 in there. Cost is less then $30 and can be done in your driveway. Get a really big catch container. Bigger then your tranny pan, that fluid runs everywhere. Use a cork gasket, and don't add gasket sealer. Torque the bolts to like 10 ft pounds in a criss-cross pattern. Count the number of tranny pan bolts before you go buy the filter kit. I think my options are either 12 or 16.

Some back ground in why I feel the way I do.
GM has recommended intervals for normal driving and extreme driving. Most fall somewhere in between the two. Changing it every 50,000 miles is fine in most cases, unless your more on the extreme side (every 30,000) or have overheated your engine. Although I do know a few tranny techs who never change the filter. They install a drain plug in the pan and drain out the 4-5 quarts every 20,000 miles and add new fluid. The tranny is a closed system. That means the only thing it has to filter is the fluid you add, and any debris from the clutch packs. Dirt from the outside world can only get in when you check your dipstick, and if you wipe it off everytime that ain't going to be much. If you have debris from the clutch packs, its time for a rebuild, installing a new filter won't fix that. The biggest thing to making your tranny live longer is keeping it cool. When it gets hot the fluid loses its ability to lubricate properly, no need to add all new fluid unless you really overheated it. And in that case, you might have done permenant damage. Is it worth the $100 or so for a complete tranny flush, not in my opinion.

On the flip side, the seals in your tranny get used to the fluid in there. If you replace all the fluid you can introduce problems. Its called tranny shock. Check your local parts store they sell something to combat this. I learned that when I swapped in a used tranny in my '93 Astro van. Burnt the first used tranny out in no time, glad it came with a 90 day warrenty. Made mention of it to the gal behind the counter and she recommended the Tranny shock stuff. Got another 100,000 miles out of that tranny. Could have gotten more, however I totaled the truck at 286,000 miles. Is a tranny flush worth it? Not in my opinion.

The best thing to do is add a drain plug when you drop the pan. Install a new filter, top it off with fluid. Then make draining it part of your regular maintenance program.

 

I do agree that there could be an issue with a full on flush. With only 51k miles on the new transmission, I wouldn't worry about this being a factor in your case. The problem with transmission fluid is that even though it is supposed to be a closed system, there are still vents in the transmission that will allow trace amounts of water vapor in that will degrade the fluid over time. It is a preferencial call as to whether or not you want to do a full flush. But a full flush isn't something that is typically done in your driveway.

I am on a full ultrasonic flush schedule of 40-45k miles on both my Bravada & Bonneville (as well as all of the other vehicles I have owned in the past). This involves hooking an ultrasonic flush machine up to the lines from the cooler (or radiator, but you really should have an aux cooler on there) and as it pulls out the old fluid, it puts pulses back through the lines that clean the inside of the transmission all while it is adding back in the same amount of brand new fluid. The filter is changed before the flush is done. This is because the fluid runs from the pan, through the filter, through the trans, through the cooler and back to the pan. If clean fluid is going to the pan, no dirt/gunk will make its way to the filter.

The problems arise when you do a full flush (ultrasonic or not) on a high mileage (75k or more) transmission that has never had it done before. Some of that gunk now has degraded seals and gaskets and is the only thing keeping them from leaking. If you remove it, you're going to have a problem and that is where flushes got much or their bad rep from.

I mentioned adding an auxilliary cooler. This should be everyones first priority. They only cost around $30-$40 and can extend the life of your transmission dramatically. Especially if you routinely tow anything or run with heavy loads. The benefits far out weigh the costs. Also, for the cost of a drain plug, they do make any trans service much easier and cleaner. GET ONE while you have the pan off! You won't regret it!