Borg Warner 71c Transmision Maintenance

[lancelot9898]

I've never located the drain plug on the tranny and merely use the dipstick hole to remove the fluid. Has anyone found a drain plug on the 71c? Not sure how much fluid (percentage wise) that I'm removing, but always put back in the same quantity that was removed which isn't very much. Also there is a cooler associated with the transmission and not sure if I should attempt to clean it out like I've done on the water heat exchanger on the Perkins 4-108. Has anyone performed maintenance on that cooler and it would seem like more transmission fluid would be in those coolant lines than what I'm getting out when I attempt to drain the fluid? (I assume that the cooler is for the transmission fluid rather than for the engine oil.)

[skipmac]

Hello,

Not sure about the fluid capacity but that should be in the manual. Do you have a manual? If not I think I have one in digital format somewhere I could send.

Regarding the drain, I happen to have a spare, used 71C in my shed but I'm 1000 miles away and won't be there until Oct. If you don't get an answer before I'll just roll that one over and look at the bottom.

Regarding the cooler, I was told by a factory trained BW mechanic (who wasn't trying to sell me anything) that the coolers have a finite life and should be replaced every 6-7 years. Why? If the cooling tubes inside corrode and the transmission fluid leaks out you won't know until you've burned up the clutches in the tranny. Since a new cooler is only $150-200 it's cheap insurance. I got new ones from Mr. Cool. Very helpful guy.

[bletso]

The drain plug is on the lower right side of the case just forward of the neutral safety switch. Page 29 item 88. It is on the reduction gear section. `http://69.89.27.238/~sailboa1/wp-con...ive-Manual.pdf
There are several manuals on this page; Manuals | Sailing Vessel Vigah

I have the Borg Warner AS3-71CR Velvet drive with a 2.1:1 reduction unit.

[lancelot9898]

Thanks for the replays. I'll crawl down there and locate that plug next week and that should be easier than pumping. The oil cooler is 32 years old and has never been replaced. It should have a pretty easy life being freshwater cooled and I'm not even sure if a cooler is necessary on a low power engine on a sailboat. Perkins 4-108

[bletso]

I took a picture this morning. Keep in mind that there is a spring in there as well.

[jstevens]

Here' a link to the Service Manual. The oil draining procedure starts on page 24.

http://www.svsarah.com/Sarah/Manuals...vicemanual.pdf

John

[lancelot9898]

Originally Posted by jstevens

Here' a link to the Service Manual. The oil draining procedure starts on page 24.

http://www.svsarah.com/Sarah/Manuals...vicemanual.pdf
ohn

Thanks for the service manual which has a bit more detail than what I had. I've attached a picture of the 71c transmission. I noticed that for a 2.10 to 1 ratio that no diagrams are in the service manual and that is apparently the one that I have. The other 71c shows an inlet from the oil cooler on the lower right hand side and that is also the drain plug. However the 2.1 to 1 makes the return from the oil cooler on top and there is no drain plug that I felt or saw. A couple of other pictures are attached and I see that the oil cooler is being cooled via raw water.

[lancelot9898]

One other question about measuring the transmission fluid with the dip stick. Apparently there are two marks on the dip stick....one for cold measurement and the other when hot. I don't understand why the difference. While the hot measurement is suppose to give a higher level due to heat...but is it that significant for a liquid? Plus as it cools down would not some of the ATF drain from the oil cooler drain back into the sump and thus give a higher level? A cold level should be higher than the hot, but that is not how the service manual reads. I just ran the engine up to operating temperature in gear and took a reading. Same as the cold reading, but I ran just for 20 minutes and maybe that was not enough. I'll pump out the fluid soon and measure what I pump out. The manual says 1.3 quarts with the tranny at 15 degrees and doesn't include volume from cooler.

[Diesel Bill]

I treat the two marks on the dipstick the same as on my engines. No higher than the upper mark and no lower than the lower mark. Oil will expand when heated. When we took on bunkers on the ships we used a chart of temp/volume to make sure we got what we payed for depending on the oncoming bunker oil temps.