sidescreen Posted February 14, 2014 Report Share Posted February 14, 2014 Hi All, I need to change the oil in my A-type overdrive (and gearbox) and I reckon it's time to clean the filter which is hidden behind the large bronze plug. My question: can I without any risk remove the bronze plug? (of course after draing the oil by removing the regular square gearbox plug). Thank you! - Raymond Quote Link to post Share on other sites
Dave Satchwell Posted February 14, 2014 Report Share Posted February 14, 2014 Yes that will allow you to get at the filter and magnets, no problem, David Quote Link to post Share on other sites
vivdownunder Posted February 14, 2014 Report Share Posted February 14, 2014 Raymond, ideally the large drain plug should be removed/refitted with a tool that slots into the teeth around the circumference. I've seen them mangled as if someone has used a chisel and hammer. It's not hard to make a suitable tool for the job. You may be aware that the drain plug often leaks oil. Sometimes very thin washers are supplied in which case it helps to use two of them. Hope you find a nice clean filter which indicates the overdrive is in good shape. Rgds, Viv Quote Link to post Share on other sites
AlanT Posted February 14, 2014 Report Share Posted February 14, 2014 http://www.overdrive-repairs.co.uk/ supply the right tool to undo the plug and washers to seal it. You wont get much oil out of the OD by way of the gearbox plug because there is an internal "dam" partially separating them. Search the oil for any metallic bits. I got half a circlip out of mine? And yes I did strip and fix it. Quote Link to post Share on other sites
sidescreen Posted February 14, 2014 Author Report Share Posted February 14, 2014 David & Viv, Thank you both for your quick reply with useful advise! Cheers - Raymond Quote Link to post Share on other sites
sidescreen Posted February 14, 2014 Author Report Share Posted February 14, 2014 Thank you Alan as well! It seems, just as Viv said, I indeed need the special tool to prevent quashing the plug. Cheers - Raymond Quote Link to post Share on other sites
AlanT Posted February 14, 2014 Report Share Posted February 14, 2014 These plugs need to be tight to stop leaks. This means they can be hard to unscrew. You can make a tool. I did. But its needs to be a good fit and tough. Also the brass is soft so you need to pick up all six slots if possible. If you have a good workshop I tell you how I made mine. At a minimum you can make with a drill, saw and maybe welder. Quote Link to post Share on other sites
BrianC Posted February 14, 2014 Report Share Posted February 14, 2014 This is a timely discussion as I was about to raise this issue on the Forum myself. I have been thinking about changing the oil in my gearbox/overdrive which have now done about 25,000 miles since rebuild, but I have been in two minds as one of our local group members has had a recent overdrive failure within a few miles of changing the oil. He has been told by one of the respected TR specialists that this is not an isolated incident and they recommended avoiding oil changes on overdrive gearboxes. Sure enough, the overdrive was badly damaged and had to be rebuilt by ORS, although I believe it had been previously rebuilt not long ago and had shown no signs of problems. I intend following this up as I cannot understand why an oil change could result in overdrive failure but if anyone has any theories or experiences I would love to hear them. Quote Link to post Share on other sites
sidescreen Posted February 14, 2014 Author Report Share Posted February 14, 2014 Hmm, Brian a theory which indeed evokes questions and care to continue... Raymond Quote Link to post Share on other sites
AlanT Posted February 14, 2014 Report Share Posted February 14, 2014 When I stripped mine down it had done over 100K. The oil ways were all full of "black-sludge". This comes I think from accumulation of particles from the friction material. The thrust race and circlip on these are a bit small for the impact loads that they see. Maybe when you drain the oil it results in a more sudden action and this precipitates a breakage that would otherwise have been delayed a while. The broken circlip in mine showed poor manufacture with longitudinal marks from the stamping out process. These make the ideal start for cracks. When I rebuilt I was careful to polish the circlip to remove these marks leaving only circumferential grooves. Quote Link to post Share on other sites
RogerH Posted February 14, 2014 Report Share Posted February 14, 2014 Hi Alan, the 'black sludge' could be the break down products of 'EP' oil itself caused by very high temps on the O/D clutch. This was highlighted by the O/D manufacturers in the very early days. Roger Quote Link to post Share on other sites
BrianC Posted February 14, 2014 Report Share Posted February 14, 2014 Roger, Now you've got me worried. I'm using EP now as that's what the gearbox/overdrive rebuilders put in although I used straight SAE50 in the past. Maybe this is really is a case of "if it ain't broke, don't fix it". Quote Link to post Share on other sites
AlanT Posted February 14, 2014 Report Share Posted February 14, 2014 You can learn a lot about a OD by fitting a pressure gauge: http://flickr.com/gp/90670218@N04/5d4t1P This will show how long it takes for pressure to build up, rebuild after a switch-over and stay in the unit when its stops moving. Now you will know the stae of the pump, lift of the oprating valve and seal of the accumulator. Also you will see the top pressure achieved and hence the setting of the relief valve. If lubrication is poor there will be wear on the accumulator piston and of course all the rollers. Quote Link to post Share on other sites
Lebro Posted February 14, 2014 Report Share Posted February 14, 2014 I was told by the experts who re-built my O/D that a plain 20/50 oil was the best bet. Bob. Quote Link to post Share on other sites
vivdownunder Posted February 15, 2014 Report Share Posted February 15, 2014 Diffs are also known to fail after oil changes. The reason is unclear, but suspected of changing to a different type of oil. Sometimes the owner or service person doesn't know what they are draining out, so as to replace it with the same. Recent extensive testing here on O/D gearboxes has revealed that Castrol VMX80 gear oil is an excellent substitute for plain SAE 30 or 40 oil. It's good at protecting the countershaft thrust washers. Viv Quote Link to post Share on other sites
Don Elliott Posted February 15, 2014 Report Share Posted February 15, 2014 For 24 years, I have used Valvoline 20W50 "R" motor oil in my gearbox and overdrive. I got that advice in 1990 from Ken Gillanders of British Frame and Engine in California who is the original owner of his TR2. The "R" on the label is for "Racing". I drain and change the oil every 3000 to 5000 miles and clean the screen and magnets in the screen basket at the same time. Since 1990, I have driven my 1958 TR3A 113,000 miles. Quote Link to post Share on other sites
BrianC Posted February 15, 2014 Report Share Posted February 15, 2014 Diffs are also known to fail after oil changes. The reason is unclear, but suspected of changing to a different type of oil. Sometimes the owner or service person doesn't know what they are draining out, so as to replace it with the same. Oh...oh - that was also on the cards ('was' being the operative word). Quote Link to post Share on other sites
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