Rebuilding the D-Type Overdrive Part 4

[@shawndavis1720]

We’ll done, thanks for this!

[@midwestmotoring]

Happy to help!

[@tjm3900]

Great video ! I fully agree with using an MTL oil like Redline in these Overdrives and syncromesh gearboxes. Even GL4 gears lube (if you can find it) risky as modern anti wear additives are like Kryptonite on syncro rings and O/D clutches.

[@midwestmotoring]

Great point! I love when people are adamant that you only use 30w oil because it's thinner. It's actually not. 90 weight gear oil is very similar in viscosity--it's a different scale.

[@jabberwockytdi8901]

Any good GL4 EP90 is good and can't per specifcation contain anyhting that will damage brass synchro rigs etc. GL5 usually contains sulphur based additives that will damage synchro, so that's what you have to avoid, GL4 is easy to find, Redline is usually a more expensive option at least outside of US and plenty of good cheaper alternative brands, depends what you use the car for and mielage vs how often you change oil if a synthetic is worth the extra.

[@tjm3900]

@@jabberwockytdi8901 For the last 20 years or so Gear oil manufacturers have almost universally used buffered Sulphur as an EP additive in gear oils The GL4 specification is nothing to do with corrosion resistance of yellow metals, it is a rating that indicates the degree of the oils Extreme Pressure protection, in fact, some modern GL5 formulations offer better compatibility to yellow metal than some older GL4 products. But that is NOT an indication that the oil is suitable for use in a syncromech manual transmission, let alone one that is close coupled to an Overdrive using a wet clutch ! Many modern Gear Lubricant formulations utilize additives (such as Molybdenum) that make them very unsuitable (too slippery ) to allow syncro rings or wet clutches to grip. It is for this reason that Manual Transmission Lubricants or MTLs were developed. As a requirement all MTLs will meet the GL4 level of EP protection, but will also employ friction modifiers to help syncro rings grip. There are many MTLs available on the market, especially in Europe where manual transmission vehicles have always been more popular. But take care to check the viscosity, as many brands tend to be lower than the 80-90 weight optimal for older transmissions.

[@midwestmotoring]

This is great information--thank you! You sound like you have a background in lubrication technology?

[@tjm3900]

@@midwestmotoring I trained as a mechanic, but I only really became interested in lubrication about 25 years ago after experiencing a product related lubrication issue. A friend in the oil industry was unable to answer my questions, but put me in touch with a soon to retire, senior Tribiologist. We corresponded for many years after his retirement. I am by no means an expert. But I understand the basics of, at least, automotive lubrication. Particularly as it relates to 'our' cars.

[@jabberwockytdi8901]

Laycock designed these overdrives originally to run on straight 30W lubrication oil, often the OD's were stand-alone at first. Later Laycock needed to certify their use with EP oils since most manufacturers started to do what Triumph did e.g. MG Volvo etc. as well, and have the OD share the lube with the gearbox rather than have their own oil - Those gearboxes were mostly designed for EP oils and won't last on straight engine oil.

[@midwestmotoring]

I believe 30w motor oil is similar to an 85w gear oil. You're good to use gear oil these days, especially after a rebuild, but stick with a gl4 for sure.

[@awakeningthesleepingb]

Awesome video series. This gives me great confidence in tackling my OD. Where did you end up sourcing your parts?

[@midwestmotoring]

Glad I could help. Most of my parts are from Moss Motors these days. There are less expensive sources, but I'm finding they often are low on stock or it's not always easy to see if the part is the correct one. That said, they're short on some overdrive and GT6 stuff when I'm shopping for that. Rimmer Bros or Spit Bits usually do a good job filling in the gaps.

[@kurtwegner4749]

What sealant did you use between the case halves and the clutch ring? I am resealing a D-type due to leaks and wondering if you used the Permatex Indian Head? Any thought about using a RTV type sealant?

[@midwestmotoring]

Honestly, I don't recall, but I feel like it was something by Permatex. RTV is okay, but you need to make sure that 1) you're using something that can withstand the temperature (the gearboxes in these get hot and also run right by the exhaust), and 2) don't go nuts with the application. It's very easy to have silicone sealant squeeze out inside the gearbox, which can clog passages and make your overdrive inoperable.

[@jabberwockytdi8901]

The overdrive gasket kit should contain gaskets for both sides of the annulus plate.

[@midwestmotoring]

Do you mean the brake ring? No, I don't believe that's the case. Perhaps with some overdrive applications or models, but not the dtype as fitted to a Spitfire. At least there isn't one in the parts diagrams or kits I've used, nor have I removed one from a unit on disassembly.