I was always told, don't add things like Slick50 to an overdrive, it causes the O/D clutch to slip.
Surrey AO and Triumph Hoover, Location: Guildford - Surrey, Spitfire 2.5PI - 1967 having surgery, PI Saloon- 1969 RBRR x 3, PI Estate - 1969 (to restore), Stag - 1971 RBRR x 2, PI Saloon MkII - 1971(stalled project), Sold some cars!
Another possibility is the small bearing between the input and output shafts. It only turns when not in 4th gear; and was making noise (worse than just a whine) in my first Stag when I bought it. If that is the problem, be sure to check the "dowel bolts" that locate the gearbox to the flywheel housing, and the dowels that locate the housing to the rear plate and the rear plate to the engine block. If any of those are missing or have the wrong piece installed, it can allow the gearbox to be out of line with the crankshaft and put a lot of pressure on that little bearing. I couldn't find a source for the "dowel bolts" (which have a precision full diameter shank, not the slightly undersize shank found on normal bolts), so I made my own by threading a section of "drill rod" (precision ground steel rod) for nuts on both ends.
I agree about not trying to quiet the noise with additive.
Thanks for the quick replies. To add another variable, the engine is an RV8, so the adapter plate to the bellhousing could create a risk of misalignment. My understanding is that older manual boxes for Stags are noisier than newer boxes. The car is 1975, but the age of the gearbox in unknown.
The whining noise in neutral does disappear when I dip the clutch.
I probably need to fit the carpets to see if that helps.
Additives in an OD box is a definite no-no. Just use a decent quality gearbox oil of the correct spec.
HCR 2006 & 2007 finisher 1972 Dolomite 1850 auto (The rolling restoration) 2008 Citroën C4 Grand Picasso 2.0 HDi Exclusive (the modern) Former stable of 5 Acclaims, 1 Toledo, 2 1500fwd, 1 1300fwd, 1 Dolomite 1300 & 1 Dolomite Sprint (that's just the Triumphs!) I've still got some parts for sale... Check out my Blog on http://triumphtoledo.blogspot.com/
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Braking 1972 triumph 1500 fwd,engine and box,and she'll gone.everything else available,at fair price,scale tom 07505731012.
Red convertible 1967 Triumph Herald 13/60. Good condition (not perfect..). Runs well. 20294 miles (unverif). 10 month MoT. No rot. Reluctant sale!
1970 Triumph 1300 Blue 53,000 miles. unused in dry
garage 26 years. No rust plastic still on doors
some spares, workshop manual, handbook. Offer
for good home wanted. For more information