Possible To Overfill Trans and Diff?

[RRMach1]

Hey everyone! I got my trans and diff fluid flushed the other day, had to take it to a local performance shop because I didn’t have access to a lift this time. I took two quarts for the diff (capacity is 2) and four quarts for the transmission (capacity is 3.3) and they needed to grab a third quart for the diff and used some of it, saying that the fluid level was too low after putting in 2 quarts. Is it possible they overfilled the diff? And if so, what potential issues could that cause?

Sponsored

 

[galaxy]

Short answer is no. Both items are fill to the bottom of the drain hole. So there’s no way a 1/2 compitent mechanic is gonna miss all the fluid gushing out of the same hole he’s trying to fill it up through. So unless the car was sitting at some steep angle instead of level or something like that, it would be difficult to overfill to the point of having problems.

Side note - if the Mach is like the 350, a lot folks misread the diff level. Is says something to the effect of 9mm below the fill hole, but that’s not the max level. The correct interpretation is fluid levels ‘between’ 9mm below and the bottom of the fill hole.

 

[RRMach1]

Short answer is no. Both items are fill to the bottom of the drain hole. So there’s no way a 1/2 compitent mechanic is gonna miss all the fluid gushing out of the same hole he’s trying to fill it up through. So unless the car was sitting at some steep angle instead of level or something like that, it would be difficult to overfill to the point of having problems.

Side note - if the Mach is like the 350, a lot folks misread the diff level. Is says something to the effect of 9mm below the fill hole, but that’s not the max level. The correct interpretation is fluid levels ‘between’ 9mm below and the bottom of the fill hole.

Yeah I’m pretty sure the Mach 1 had the same differential and transmission setup as the 350, including the coolers. Wouldn’t some of the fluid stay trapped in the coolers during the fluid flush? That was my main concern.

 

[traxiii]

It is the same as the GT350 and there is a procedure for flushing the cooler and refiling that runs the gear oil pump, if I remember. The easiest way to do it is to drain the old into a graduated container and refill with the same amount.

In my case, I ran over a pipe fitting that fell off a paving truck and hit my cooler. (see my delivery thread) It bent the cooler and caused a leak where the tube exits the cooler. It happened the day after we got back from driving it home to California from Iowa, 2900 miles and 10 days of ownership. I cleaned it with brake clean, plugged it with JB Weld to stop the dripping and disconnected the oil pump so it wouldn't pump fluid to the cooler, while I waited for the back ordered new cooler to come 2 months later.

I used one of those hand oil transfer pumps to fill the cooler, connected it up and topped the diff up to the specified level, then came back and checked it after a week of running and the level was the same, so it seemed to work for me. Needless to say, I learned how to remove the diffuser so well I could do it in my sleep. Lots of pebbles every time.

 

[spankybranch]

Yeah I’m pretty sure the Mach 1 had the same differential and transmission setup as the 350, including the coolers. Wouldn’t some of the fluid stay trapped in the coolers during the fluid flush? That was my main concern.

I used the BG kit for trans+diff from OPMustang and it comes with 4qt trans/3qt diff fluid with the instructions for the diff specifically to cycle the pump to completely drain/fill. I had it done at a shop also and there was about half-qt left of each (so 3.5qt trans/2.5qt diff).

As other said I don’t think it would be possible to overfill either to the point of causing damage like you could with engine oil since the trans/diff fill from the side.

Sponsored