TR4/4A TR4A with Overdrive - fluid replacements?

[DrinkingWhisky]

Hi all - n00b mechanic here

I'm looking to do some fluid replacements for my TR4A IRS. I'm hoping to get it all planned out rather than having to have the car sit. A few questions:

1. Is 80/90W gear oil sufficient for the diff and transmission or is there a preference here?

2. The overdrive unit has a big old drain plug with little teeth. It looks like Moss motors has the tool for removal here. Where is the filler for the OD unit? I'm not seeing it on Bentley's exploded diagram. Any advice on this?

3. What weight motor oil is everyone using? The lubrication charts are outdated based on today's multi-grade oils. Any advice is appreciated.

Thanks all!

 

[TR3driver]

'Proper' oil for the OD has been a long-debated topic, with still no clear consensus. Personally, I prefer Redline MT-90 for the gearbox (which is a synthetic oil, rated GL-4 but specifically formulated for use in synchronized transmissions). For the differential, I prefer Valvoline full synthetic gear oil, which is rated GL-5 (but doesn't use the additive that can corrode yellow metal parts).

The OD shared oil with the gearbox, so it is filled through the plug on the side of the gearbox. You may need to wait a few minutes for the level to even out, though.

Personally, I don't like the tool shown in your link, as it only grabs one tooth and may distort the soft brass plug (leading to leaks) if it is stuck. I made this one myself (that grabs all 6 teeth) from a big socket ($10 on eBay), but I believe someone is selling them commercially.

In the background you can see my previous tool, which is just a heavy piece of flat iron (Home Depot sells it as stakes for concrete forms) with two holes drilled and tapped; plus two bolts filed down to fit the notches securely. It works OK, but can be kind of awkward under the car.

I use 20W50 motor oil, mostly, but used 10W30 at my last change and haven't seen any ill effects (except somewhat lower pressure at hot idle).

YMMV

 

[Geo Hahn]

...I made this one myself (that grabs all 6 teeth) from a big socket ($10 on eBay), but I believe someone is selling them commercially...

To wit: Triumph Overdrive Tool

You can select from several choices for filling the gearbox/OD... you can pump oil in from below, fill it from above snaking a line down past the fuel pump and into the hole or you can cut a hole in the tunnel to allow access to the fill plug from inside the car (left hand hole in this pic):

Hole is cut to take the same size rubber plug as used on the tunnel cover above the forward U-Joint.

Rearward hole is to allow R&R of the solenoid. As expected, having cut that hole I have never had any problemm with the solenoid.

 

[TR3driver]

To wit: Triumph Overdrive Tool

Thanks, Geo.

Some more tips:
Most tool stores (eg Sears) sell an 8-point socket that is the hot setup for removing the original square-head pipe plugs. They round easily if you try to use an open end wrench, or 12 point socket/wrench.

I'm not fond of the square heads myself, so I've replaced all my square plugs with socket head plugs (magnetic for the drain plugs) from MMC

A little "PTFE pipe paste" (available from your local hardware store) will both help the plug seal, and make it easier to remove next time. IMO the more common "teflon tape" has no place on a car as it can sometimes form tiny strings that break off inside and potentially clog small oil passages.

Most auto parts stores sell a small hand pump for gear oil, that I find works well enough.

 

[Geo Hahn]

...I'm not fond of the square heads myself, so I've replaced all my square plugs with socket head plugs (magnetic for the drain plugs) from MMC...

I am also a big fan of the magnetic drain plugs. I got the square headed magnetics sold by the Big 3 suppliers and thought the magnet pretty wimpy so I dug it out and replaced with a rare earth magnet with some serious gripping power. Why?

A friend had a piece of a tooth break off a gear in his TR3A. When he looked at the gear it appeared it had broken off long ago. He found that gear on the highway along with most of the other internals from the gearbox. They searched the roadside but never found the driveshaft. Best guess is that the tooth lounged around in the oil until one day (at speed) it found its way into trouble. Good thing the TR3 has a metal tunnel. Needle bearings make nasty shrapnel.

 

[TRMark]

I fill mine this way, use minimal pressure otherwise you will have a terrible mess.

 

[TR3driver]

so I dug it out and replaced with a rare earth magnet with some serious gripping power.

Probably a good idea. It might have prevented this:

Fortunately the car was sitting in the driveway when I noticed all the oil running out.