NH Gary Posted May 28, 2020 Report Share Posted May 28, 2020 I have a 1976 TR6 transmission without overdrive. Should I use 85/90 GL 4 or GL 5 gear oil? Quote Link to post Share on other sites
RobH Posted May 28, 2020 Report Share Posted May 28, 2020 This was discussed only about a week ago...... Quote Link to post Share on other sites
HSM Posted May 28, 2020 Report Share Posted May 28, 2020 Always use GL 4 but never GL 5. Quote Link to post Share on other sites
Andy Moltu Posted May 28, 2020 Report Share Posted May 28, 2020 Some GL5 oils have ingredients that damage the yellow metal parts in the gearbox. Not all, but some and GL4 does a perfectly adequate job so reducing the risk of an expensive gearbox rebuld! I have to say I have become a convert to Penrite Gearbox Oil 40 of late. Since the 6 box was rebuilt I could occasionally beat the synchro in 3rd using 80/90 multigrade but since swapping to that I haven't beaten the synchro. I had a similar experience with the Stag which again was rebuilt when good quality synchro's were not readily available and after the experience with the 6 I swapped the gear oil and the synchro is much more effective. A bit stiffer to get into 2nd when cold. (Reminds me of the the 6 back in the 1980s running in EP90 on frosty mornings - the first shift into second sometimes required a firm hand) Quote Link to post Share on other sites
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