Transmission flush a bad idea?
 

I guarantee there are guys out there in the forum who have more experience with me,so I'll see if I am wrong. The haynes manual and various sites all around the web say that if it is an older car that has been sitting around and the transmission is a little sticky, give it a flush.

However, from my time working at tire kingdom, and from word of mouth from other people who work on cars, I was told not to flush a transmission if the car has more than 100,000 miles on it, becuase the valves have probably expanded with all the contaminants in the fluid and now accomodate said fluid that is dirty, and changing it to clean fluid will make the transmission slip.

Is this true? Have you guys had any problems when changing transmission fluid? I'd just like to make sure before I screw up and have to blow a grand and a half on a new transmission.

I have heard of people changing to synthetic fluid and having leaks and some having no leaks. I am not sure how many miles were on the trannys in question.

If the fluid is so bad that it is thicker than it should be, then it should be changed. Flushing just gets all the fluid out of the tranny. This is normally not possible because some remains in the passages and valve body. Some MB transmissions even have a drain plug on the torque convertor so that can be drained. Getting all of the old fluid out of the tranny is a good thing.

There is alot of bad information out there about automatic trannys. I think the tranny shops want everyone to be afraid of them. Search some of the posts on this forum to see different peoples experiences.

Even before Haynes made a manual for any of those cars it suggests that for... the original owners manual and the shop manual for every auto trans car ( and manual too ) give very specific change out intervals... and often the first full change out with filter is sooner than the later ones... this is due to wanting to get out any particles produced from the initial wear in process... just like in engines...
Lots of times the change out schedule is ignored until problems already exist... then the trans gives up soon after a change out....and the change out gets blamed...
Every new to me car I get I use Trans-X in it at the recommended rate... which , on a car which has been neglected is about twice the amount that is recommended for leaving in the transmission.
If you use something like that... you have the potential for dissolving the varnish which builds up over time and from heat in the tiny orifices which control the hydraulics which move the clutches in the auto trans...
You will want to change out the filter also of course... and you do want to drain the torque converter when you do this cleaning/change out...
The miles per trans fluid change rate is shorter on MB than most American cars of the same age. Most people are shocked when they see the actual recommended change out mileage... There is lots of discussion about all this and in the archives...

2 examples:

my 1978 240D @ 205K, changed filter and all fluid (spill-n-fill). two days later front pump locked up and took the torque converter along with it (at idle!!).

my 1987 300D @ 235K, added cleaner and flushed the entire system with the BG trans flush machine (using 16 qts). been 2K miles since and no problems, still shifts as harsh as it did before, but still no leaks in using this synthetic fluid.

Should it be done before a long trip?
 

I just got this car running, and it has sat in a yard for over a year. it runs, shifts, and drives great. I am planning a trip of about 400miles and I was going to drain and change filter, then replace with mobil 1 Synthetic atf. good or bad idea before a long trip?
John

I would never try anything NEW just before a long trip...
" Shake Down" trips to test new stuff are short for a reason... the cost of towing back to the house...

Yeah, that's what I was thinking as well, but the trip is over 2 weeks away, and I will be driving it every day until the trip. I was planning to dump fluid, pull filter and refill with the M1, then test drive it for the next two weeks, I have a spare vehicle to drive if problems occur before then.
what do youse guyes think?
John

so basically, if I understand everyone correctly, a transmission flush only alleviates smaller problems, and not necessarily bigger ones.

However, complications can arise sometimes if you flush a transmission that is very poorly taken care of.

I was about to do a spill and fill, but now that I started reading some posts, I'm not sure that is such a good idea.

When was the last time you changed the fluid AND the filter ?

Those holes being stopped up can keep the trans from moving from one gear to another.. so that seems pretty important if it happens....and the Trans-X can take care of that if you don't let it get completely clogged with vanish... You seldom have a varnish problem if you change out the fluid and filter at the recommended mileage... but few do that... so sometimes a more drastic measure is needed to get back to ' even'....

Have you done a search in the archives on ' trans-x ' ? Lots of good info...

What is the recommended milage for say, a 1987 300D?

Mine had 220,000 miles on it when I bought it this May/June. 500 miles after purchase I carried the parts and fluid to a oil change shop that I trust and they changed out the filter, gasket, and put in synthetic fluid. Mobile I think. Since then I've put about 11,000 miles on it with no problems. The level is steady, no leaks. I've had no problems. 80% of my driving is 4 hours at a time at highway speeds. The rest is in town/city driving. I can only assume that this is good for the transmission.

The only issue I have with the transmission is that it rolls about a foot or so after you stop on a hill, put it in park, and then take your foot off of the brake.

In my case I don't see the need to do a transmission flush. It seems to be working just fine. I just need to know when to change the fluid & filter out again. (You do change both at the same time, don't you?)

torque converter fix
 

I've always noticed a slight slippage in my 300D engine speed/road speed when at 1/2 throttle and full throttle. It seems that more torque being sent through the transmission at the same road speed always increases the engine speed by about 200-300rpm in 4th gear. My other 300D that has less miles and has been treated far better per the service records doesn't slip at all under the same circumstances. Is this a problem with the torque converter or the transmission? Maybe a sign the previous owner did some neutral drops or something?:mad:

Is there a way to eliminate this with special fluid? I changed the fluid/filter about 9k ago when I bought the car.

Use your parking brake. It is hard on the parking pawl of the transmission to have the weight of the car pushing against it. If you set the parking brake before you put the car in park, there will be no load on the parking pawl and the car will not roll.:D

Thanks, I knew there was a reason to use the brake. I have been using it as you described because it seemed like the right thing to do, but that does not change the fact that there is some play in there.

With winter coming up fast I am a little reluctant to use the parking brake for fear of it freezing in place.

-Jim

I'm planning to drain the pan and refill with Mobil 1 ATF, then drive a while and do it again. Then I plan to drain the pan and converter, put in a new filter and refill with Mobile 1 again. I have no idea about the age of my fluid, but at least it looks nice and clean on the dipstick.

See, there in lies the problem. I recently bought this car from someone else and have no idea when he bought it and he said he never flushed it. Probably better off that way if he didn't know what he was doing, but bad in that I have no idea what kind of shape this car is in.