I have an 1989 5.0
around 175,000 miles
Fluid really dirty but ive been told not to change it as it might screw up my tranny by clearing out all the sludge that is keeping it together.
Any merit to this?
Thanks in advance.

 

Best thing for it is to drain the old crud out. Only thing sludge could prevent it leaks around the tranny pan but thats nothing a new gasket can't fix. Drop the pan, change the filter, new gasket and fill back to spec.

 

The "don't drain old fluid" saying is a myth. Get that old fluid out as soon as you can. Make sure you use a quality fluid, though. I have drained too many transmissions with burnt fluid and they performed well afterwards. You might want to use Seafoam Transtune prior to draining.

 

X2 on the seafoam, Ford trannies like fresh fluid or they dont work too well.

 

There is also the myth about not having it flushed. But again, a myth.

Fresh fluid is always good.

 

The myth is don't flush. Changing the fluid and filter is always a good idea.

 

Thanks guys. That moves up my list now.

 

if you do it order a new pan with the plug like your oil pan. itll allow you to hold more fluid. (ie better lubrication and cooler tranny temp) and make draining it ever again much easier