My truck recently hit 100k and I have decided to get my transmission flushed. I was going to do the BG Transmission flush and while calling around a few of the shops in the area one told me that they will not touch a truck over a 100k and do a full flush because of the problems (he said known problems) that will happen after taking out all the old fluid and putting in all new?? He was telling me about varnish buildup and yada yada and how adding all new fluid with detergents in it would give me problems since the transmission has never been internaly serviced and it have over 100k on it. I have changed the external several times and just figured that the BG flush would have been a good thing to get done before a long trip that I have coming up driving from MD>NY>WY and back?? Does this sound right?

And yes I have read about the HOOT meathod, I don't have time to do it myself.

Wayne-o

It's ok to do a full flush on an Allison even with 100K. This trans is different than any out there.

It's ok to do a full flush on an Allison even with 100K. This trans is different than any out there.

Thanks Mike. I tend to look at myself as a mechanicaly inclined person and it just sounded odd to me.

If you are talking about a power flush (and UIAM, BG is a power flush machine designed to clean the transmission), Allison recommends against it. Here's a post by Crafty:

There are exchange machines and flush machines. With an exchange type system the transmission pump does the pumping and the machine only collects the old fluid and puts new back in... That's what you need with the Allison. This basically automates what the Hoot method does.

What you don't want to do is try to power flush the Allison with an external pump. If they try to backflush it, the converter LU clutch will act as a check valve and close off getting no flow. If you try the other way you can damage the suction filter in the pan and force debris into harmful places causing pump failure or valve sticking.