Flush trans before new MTF?

[Auto-Union]

What do you think? Obviously, a trans with a lot of miles on the fluid is more likely to benefit from a flush before new MTF, but I only have 7k on my car. I'm thinking not to bother, unless my fluid looks dirty, but I doubt that. So, say a trans with like 75k on the original fluid....flush it for a 5 miles drive with plain motor oil in it to flush it clean? I think so, especially if you are going with a fancy fluid.

Any reason not to? I know the adds are different, but cleaning and clearing the trans seems more important than a few drops of leftover incorrect fluid.

 

[Big Jim]

If you want to "flush" it, don't use motor oil. Just do another manual transmission fluid change in a few days.

I think you are overly worried. Just change it once and call it a day.

 

[Kestas]

I agree. You've probably been reading too much BITOG.

 

[IslaVistaMan]

You won't "clear" any significant amount of metal from a manual transmission with a short change interval, Auto-Union.

Magnets inside manual transmissions pick up virtually all the large stuff, leaving it inside the transmission indefinitely -- safely secured, presumably -- regardless of the fluid change interval. Side-mounted drain holes don't allow bottom-dwelling silts and debris to evacuate all that well, either.

Differentials are a different animal, though, since vertical drain holes (and some with magnetic plugs besides) let gravity take care of metals flushing to a greater extent.

The biggest benefit changing manual transmission and diff fluids provides is a reduction of fine-particle slurries that degrade bearing and teeth faces. This is why early change-outs are recommended, as SAE studies have supported.

 

[Gary Allan]

I don't know about now ..but normally ..the old 90 weight hypoid and motor oil would foam when mixed. Now you're probably going to drain most of it ..but still ...why leave the residuals of the oil for the newer fluid to have issues with

 

[Auto-Union]

Hmm. Is there such thing as a cheap GL-4 fluid for flushing? I only ever see dino GL-5 stuff. I guess a flush is not as much needed as an engine, since there are no blow-by and real contaminates.

 

[The Critic]

Honda used to recommend 10W30 or 10W40 mineral oil for their transmissions, prior to the release of Honda MTF. Thus, I see no reason why installing a 10W30 mineral oil and operating it for a short distance to generate a "flush" effect would do any harm.

 

[Gary Allan]

You're probably right. The fluids have changed so much since I've had to play with them. My Pukeout 504 (1980) spec'd motor oil for the trans ..but the dealer said it was because of the availability of gear lube in France/Europe

..or so he imagined.

I think 90weight hypoid went out of vogue because it's a 40 weight. About that time you started to see transmissions spec'd with ATF and lighter visc oils

I've seen no "cheap" GL-4 fluids, relatively speaking. They're all pricey compared to motor oil and standard gear lube.

 

[Auto-Union]

My Honda MTF came out really grey and yucky. Some sparkles in the drain pan, very small ones and not a lot. Needless to say, I'm glad I changed it. I was going to re-use the Honda stuff in an old pick-up, but yuck, probally not.

 

[Mr Nice]

How does it shift with the new MTF ?

I changed the MTF in my wifes Honda at 97K miles and it was black like motor oil.

 

[Auto-Union]

I only drove a 1/2 mi up the road, but the shift and power delivery were much better. Funny, the shift was so smooth it was like "air". It's RL MTF 70w-80. If I can master putting the stuff in, I'll redo it at 50k. BTW- ANY trans with over 50k, I'd say flush with Dex first. It's a minimal cost 'feel good' thing. Seriously, cleaner is better in a trans where there is no filter.

 

[Auto-Union]

Dexron at least has minimal additives, seems the safest cheap MTF flush.