Synthetic gearbox oil in VW Transaxle?

[NVJ157G]

Hi there, first of all great forum, I can spend hours on here just reading and reading and reading

Anyway my question is this. I have been thinking about refilling the transaxle in my 69 VW Bug with fully synthetic oil but I am worried about leaks. The Box is the original unit and has (as far as I know ) never been torn down and rebuilt. Is there a good chance synth will just leak out past the original seals? I'm particularly worried about the flywheel seal failing and contaminating the clutch. What is everyone's opinion on this? If its a big no no its OK as I have three litres of Castrol 80W90 GL4 mineral ready to go if the Castrol TAF-X Synthetic I have is no good.
Your thoughts on this are much appreciated

 

[Hethaerto]

I'd go with the mineral oil. You're right to assume the syn would breach the seals in that ancient gearbox.

 

[NVJ157G]

Ah, then its as I thought. Thank you. Shame though, I've heard so much about the advantages of Synth I really fancied giving it a go, but it seems that rebuilding the box with new seals is overkill just for that lol especially when its otherwise cherry.

 

[ddean]

For a 40+ year old transaxle conventional oil is probably the way to go unless this is a daily driver in winter and there might be an alternative.

I am not sure if you can find it in the UK, but Redline MT-90 would be the only synthetic transaxle fluid that I would recommend for an older gearbox. Nice shifting in 0 F weather and no synchro problems. On my '84 VW Rabbit (MK I Golf) 4 speed MT-90 actually stopped my gearbox from leaking on warm days and leaving a few spots on the ground. Transaxle case was still a bit wet around the leaks but I did not have oil on the ground. This is because Redline is a POE based synthetic instead of a PAO / Group III based synthetic and POE oils actually will swell seals much more than conventional oils and require additives to reduce this swelling effect. Not guaranteed not to leak but Redline may be an alternative in an older transaxle.

 

[NVJ157G]

Yes the whole Redline range is available but I think I will take your advice and stick with mineral, its just I happened to of been given the Castrol Synth to try.

 

[unDummy]

The seal conspiracy is a farce.

Use the synthetic if you want.

 

[mechtech2]

Of course you can use a synthetic.
40+ years on that transaxle is gonna leak a bit either way.
The best dedicated manual trans/transaxle fluids are full synthetics, nowadays.
There is hypoid gearing in that unit, but it is lightly loaded. The Redline MT90 or Amsoil MTG would be good bets.

 

[NVJ157G]

Blimey! Now I can't decide either way

Hate to be indecisive. I was only going to try the sythetic because I have some in stock but its not not a fluid they sell in the States so I imagine not many others here have tried it.

 

[mechtech2]

You won't get 100 horsepower more either way!
Those cars ran on dino gear oil almost 100% of the time, anyway.

It's just that the modern stuff like Redline MT 90 or Amsoil MTG are the best and helps shifting and are full synthetic. But not 100% best for that hypoid gear. Your transaxle is unusual in that it has a 90 deg power change, and has a hypoid gear in it.
Low loading makes all the difference. Low power and gear loading .

 

[NVJ157G]

I'm not after more horsepower, theres just none to be had on a stock Bug anyway. I just liked the sound of the slicker shifts that Synth offer.

 

[mechtech2]

Better shifting is more from having a friction modified fluid that makes synchros grab better. Whether or not is is full synthetic is not really the issue.
It turns out that the best modern fluids designed for good shifting are full synthetic.

Like many of us, you may narrow down your choices and have to try several to see what you like best. General advice can only get you close.

 

[Bill888]

Stay with dino, GL5. Kendall NS-MP is a good one. IIRC, the VW transaxle is very similar to the early Porsche gearbox and those do well with regular dino 80w-90. The synchros in the 901 and 915 transaxles require dino, while the later G50 does well with full syn.

 

[mechtech2]

Bil888 - Synchros that 'require dino"??

 

[Bill888]

"Designed for" is more appropriate.

 

[mechtech2]

That's only because dino was pretty much all there was available at the time!

 

[Bill888]

& that's exactly my point.