T5 gearbox

Technical advice Q&A

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TheDampMan
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#1 T5 gearbox

Post by TheDampMan » Fri Mar 01, 2019 7:52 am

Hi all,
I have a T5 5 speed gearbox fitted to my car from searching it appears the correct oil is Dexron II or III ATF just want to check this is correct as both are oils designed for auto box’s?
Steve
1969 Series 2 Roadster
BMW Isetta

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ChrisC
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#2 Re: T5 gearbox

Post by ChrisC » Fri Mar 01, 2019 4:28 pm

Personally, I was advised to use MT75 manual transmission fluid for the first 5000 miles as its a bit thicker and to them move to the ATF because "the gearbox gets a little notchy". I am a little beyond the 5000 miles and yes it is a little bit more snick-snick between gears than the standard 4 speed so I will be changing to ATF shortly.
1964 FHC 4.2
Etype restoration blog http://connor.org.uk

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TheDampMan
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#3 Re: T5 gearbox

Post by TheDampMan » Fri Mar 01, 2019 7:31 pm

Thanks Chris
Steve
1969 Series 2 Roadster
BMW Isetta

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abowie
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#4 Re: T5 gearbox

Post by abowie » Fri Mar 01, 2019 10:37 pm

From the Tremec factory bulletin TRSM-T5-0510:

2-4. APPROVED LUBRICANT. Most T5
transmission models use Dexron II automatic
transmission fluid.

In one instruction sheet Paul C says he prefers Mobil One ATF but that any Dexron 11 or 111 fluid will do.

In another "We recommend DEXTRON III type oils. We prefer and like Mobil One ATF or Royal Purple Synchromax. Do not use conventional 80w-90w gear lube."
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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chuffer
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#5 Re: T5 gearbox

Post by chuffer » Sat Mar 02, 2019 5:20 am

I run ATF in my T5 but I just found this interesting item on a TVR forum posted in 2015:

“I've been in the ATF camp for years, there are three very good reasons why ATF works well in our T5 boxes.

1. Its free from corrosive sulphur

2. Its light enough to lubricate the needle roller bearings in the World Class T5

3. Its proven safe with the paper lined synchros we have in our World Class T5 boxes

The T5 is proven to last well on regular ATF and let's not forget the box was designed for that oil in the first place so why deviate?

Well its easy to forget the new breed of synthetic manual transmission fluids simply didn't exist back in the 1980's when BW designed the T5, at the time ATF was the best there was and to be fair its still a remarkably good oil.

But it is thin and this isn't always ideal for synchro function because synchro rings are essentially a wet clutch system, so definitely stick to regular ATF and avoid fully synthetic ATF as its just too slippery.

Unlike traditional hypoid gear oils the new synthetic manual transmission fluids do not contain sulphur which is known to attack brass synchro rings (5th in our boxes). Its also thin enough to lubricate needle rollers but being slightly heavier than ATF in theory should give improved synchro function.

On my T5 it was always possible to beat the 5th gear synchro if I rushed the shift under full power. I'm aware 5th is a weak point on this box and I know I shouldn't be abusing the box in this way but hey its a TVR so to nurse it is completely missing the point.

So against my own historic promotion of ATF only in this box I decided to try one of the new breed of quality 75w/85 synthetic oils specifically designed for manual transmissions, but I do accept there is a risk the paper syncho linings on the 2nd, 3rd & 4th could de-laminate.

Essentially the long term effects synthetic manual trans fluids have on the adhesive used to bond the paper to the sycro ring is inconclusive, some say its fine but some say over time you will suffer de-lamintion.

Here's what I went with:

( photo of Penrite SIN was inserted here but hasn’t transferred)

I've been running this oil for over a year now and just as I'd hoped it completely removed the ability to beat the 5th gear synchro when shifting under hard acceleration, no more graunch biggrin

What I wasn't expecting was the overall improvement in shift quality in all gears which was really very noticeable indeed.

Over a year later and the box is smoother and quieter than ever so the experiment has worked a treat (so far) and even gave additional benefits I'd not expected.

I've only covered roughly 7,000 miles on the Penrite SIN manual trans but so far there are no signs of any issues, only benefits.

Obviosly ATF is proven beyond question so if you're happy with the way your T5 shifts then there's really no reason to switch to a synthetic manual trans fluid.

But after making the change & witnessing the improvements myself I'll not be going back to ATF in a hurry nono

Unless that is the paper linings bonded to the synchros start to de-laminate, at which point I'll be living in a world of regret cry

So far so good though wink

The paper lined syncho rings aren't available anymore so anyone rebuilding a World Class T5 these days will be using the newer carbon fiber synchros that can not de-laminate like the paper lined ones we have, so a fully synthetic manual transmission fluid becomes a no-brainer.

The real question is "will the Penrite SIN manual trans fluid attack the adhesive BW used to bond the friction paper to the synchros over an extended period?".

I appreciate I'm taking a risk but I would have thought if it was going to happen it would have done so by now?

If there's anyone out there who's done big miles over many years with synthetic manual transmission fluid in their World Class T5 (with the paper lined synchros) I'd be interested to hear from them.

Until then let me take the risk & do the experiment on my box, for everyone else I'd still recommend a standard (non-synthetic) ATF.

I'll update this post if I ever do experience the de-lamination problem.”
S1 FHC 3.8, XK Convertible

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JerryL770
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#6 Re: T5 gearbox

Post by JerryL770 » Sun Mar 03, 2019 6:09 pm

If that was posted in 2015, has there been any update? If there was I guess you would have posted it.

Can you request an update?
Jerome Lunt
1970 S2 FHC - Dark Blue, Red Interior, MX5 Seats

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