My 87 Series III trans is a little clunky through the low gears and sometime in reverse. I have heard that these cars required regular transmission services to keep the transmissions shifting well.

I wonder what there is to do on these except change the fluid. Is there a filter or adjustments that should be attended to on a regular basis as well? If so, how does on adjust the transmission?

 

Change the oil in it and add a friction modifier like MGC from BG products , that will do about all you can do unless you tear the box apart and replacing parts

 

Your '87 Series III is equipped with a Borg-Warner Type 66 three-speed gearbox, which does require periodic maintenance such as changing the fluid and cleaning/replacing the filter screen.

I have found the best way to service this type of gearbox is to securely raise the vehicle on four jack-stands and remove the pan, drain the fluid in the gearbox and clean or replace the screen. Check to see if there is a magnet attached to the pan since this is used to trap any steel pieces that may be in the fluid from clogging the filter. If there is no magnet, one should be added to ensure the continued health of the gearbox!

The Borg-Warner Type 66 gearbox requires type F fluid, which is slowly added through the dipstick tube with the engine off. Once fluid appears on the dipstick, the engine should be started and the gearbox run through the gears to circulate the fluid. In addition, disconnect one of the cooler lines that run forward to the radiator and divert the fluid into a suitable container for recycling. Continue to add type F fluid via the dipstick tube as the old fluid from the torque converter and cooler are flushed out. This will not take long as the fluid is under pressure.

Once the old fluid is removed, top up the gearbox level to the warm/hot position on the dipstick running it through the gears several times. Stop the engine, lower the vehicle safely to the ground and check the fluid level once more while the vehicle is at idle and all accessories off. Top up fluid as needed and you're finished!

Some additional comments and information can be found here:
Borg Warner 66 Transmission Adjustment

NBCat

 

The link takes you to a page outlining the brake band adjustment method. Unlike the modern autotransmissions, the BW uses brake bands rather than clutches to change gear. The brake material wears, and eventually the brake band needs adjusting to restore correct clearance.

Other thing to inspect is the lines to/from the transmission oil cooler for security and leaks. Note that over time, (and these are old cars now), corrosion in the engine coolant side of the tranny cooler can cause leakage between engine coolant and transmission oil, so this needs checking too.

 

I could be mistaken, but if memory serves, the BW Type 65 had bands that had to be adjusted while the Type 66 was a more modern design incorporating clutch-packs activated by a piston. Since there is less inherent slippage with a clutch-pack compared with a band, less wear on the friction material and fluid contamination is the result.

NBCat

 

It's a long time since I had a Series 3 and memory fades, but as I recall, the Workshop Manual described the BW66 as an improved 65. However, I'm wrong about brake bands, because I found this description of the box on the internet, and it seems both 65 and 66 use clutches.

http://www.automaticchoice.com/Catalogue/bw65.pdf

 

It's too early and my coffee has yet to wake me up !!

Looking at the pictures in the pdf on the web page, it shows that BW65 and 66 boxes use both clutches AND brake bands, (two of them).

http://www.automaticchoice.com/Catalogue/bw65.pdf