The right oil for older gearboxes?

[Al Weyman]

After trouble with two of my GM Muncie 4 speed gearboxes, one at Snetterton recently when the 3rd and 4th gears started baulking prompted me to do some research and I came across this on the Chevelle forum and thought it may also be of interest to racers of older cars as I am sure its not unique to the Muncie gearbox. I thought I may share this with you although I did discuss it on Deltas Tea Break page I feel is deserves a wider audiance. In much the same wasy as some modern engine oils will not suit older cars it appears the same is true with some transmissions and is worth noting.

REDLINE Synthetic Manual Transmission Lubricants

GEAR AND SYNCHRONIZER WEAR PROTECTION
Most manufacturers of manual transmissions and
transaxles recommend an 80W or 90W GL-4 lubricant.
GL-5 gears oils which are required in hypoid differentials
are not used in most synchromesh transmissions
because the chemicals used to provide the extreme
pressure protection can be corrosive to synchronizers,
which are commonly made of brass or bronze. Typically,
the use of a GL-5 lubricant in a synchromesh
transmission will shorten the synchronizer life by one
half. The extreme pressure requirements of spur gears
and helical gears found in transmissions are not nearly
as great as found in rear-wheel drive differentials. A
GL-4 lubricant provides adequate protection for most
manual transmissions, unless a unique design
consideration requires the extra protection of a GL-5.
The reason that many manufacturers have made
recommendations of motor oils or ATFs is that petroleum
80W gear oils frequently do not shift well at low
temperatures. Motor oils and ATFs are much more fluid
at lower temperatures and they are not corrosive toward
synchros, but they provide very poor gear protection.
These lubricants provide almost no extreme-pressure
protection. In addition, petroleum multigrade motor oils
and ATFs have very poor shear stability. The shearing
action by a manual transmission on thickeners is much
worse than in an engine or automatic transmission.
Within 5,000 miles the thickeners can be rendered
ineffective and the transmission will be operating on a
much reduced level of protection, as shown in the graph
below. In hot weather these transmissions will whine
and rattle because of poor vibration dampening and
metal contact. Red Line MTL and MT-90 provide the
excellent gear protection of a GL-4 gear oil in a synthetic
lubricant which spans hot and cold temperatures and will
not shear or oxidize with use.

DIRECTIONS FOR USE
Red Line MTL may be used in transmissions which
recommend 75W, 80W, or 85W GL-4 gear oils, or SAE
30 or 5W/10W30 motor oils. If a 90W GL-4 or SAE 40,
10W40, or 15W40 is required, MT-90 may be used. If the
transmission or transaxle requires an SAE 90 GL-5 gear
oil, then Red Line 75W90NS or 75W140NS Gear Oil
may be used. In transmissions which recommend Dexron
or Mercon fluids we recommend our D4 ATF which is
very similar to the MTL, being a GL-4 Gear Oil also. The
D4 ATF will provide better low-temperature shiftability,
and the MTL would provide better wear protection for
racing use. MTL is not designed for use in rear-wheel
drive differentials. Those generally require a GL-5 lubricant
such as Red Line 75W90 Gear Oil. It is not necessary
to flush the transmission before replacing with MTL.
Remove the drain plug and drain while warm. Seal
compatibility has been designed to be similar to petroleum
lubricants, and leakage should be no greater than
any other oil of comparable viscosity. Being formulated
with extremely stable synthetic basestocks, MTL and
MT-90 will last much longer than conventional petroleum
lubricants. However, we do not recommend extended
drain intervals, since without a filtration system, there is
no way to remove metal shavings other than draining the
lubricant. The regular maintenance intervals are also
recommended to insure that the proper level of the fluid
is maintained.


Red Line Oil's MTL and MT-90 are designed to provide excellent protection and improved shiftability for manual transmissions and transaxles, having cured the problem of hard shifting in thousands of transmissions with shifting troubles. How? They have the appropriate coefficient of friction for most manual transmission synchronizers (many gear oils, engine oils, and ATFs are too slippery for proper synchro engagement). And, the wide viscosity of MTL and MT-90 allow proper shifting over the entire temperature range which the transmission will experience. The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes. MTL is a low 70W at very low temperatures and a high 80W, nearly an 85W, at elevated temperatures, providing adequate viscosity to prevent wear and deaden gear noise. MT-90 is a thicker 75W90 version of MTL. The shear stability and oxidation stability of these products are excellent, thus the physical characteristics of Red Line MTL and MT-90 will change little with use.

MTL
MT-90

The MT-90 is a 75W90 GL-4 Gear Oil that’s slightly heavier than MTL. Provides excellent protection of gears and synchronizers and its balanced slipperiness provides a perfect coefficient of friction, allowing easier shifting.


RED LINE SYNTHETIC OIL CORP.
6100 Egret Court
Benicia, CA 94510
(707) 745-6100
www.redlineoil.com

[john ruston]

Just ring Jason or Mark 01440 760960 at Motul and they will sort correct oil.

They have new product for Historics.

[terence]

Beat me to it John,Al,do yourself a favor and follow Johns advice,we ran both Griff's on Motul,never ever gave a problem through insufficient lubrication or breakdown.

[zefarelly]

Harry survived blistering temperatures on Motul at LMC as well, thats an old synchro box . . . and an old push rod motor. THe open diff ran the same as the gearbox as well.

[Al Weyman]

Who is harry? I thought it was Rob Compton who owned Harry!

[zefarelly]

Harry the Funbeam . . .come on Al, get with the program!

[Mike Bell]

Difficult sometimes to get correct advice from manufacturers or retailers- lack of knowledge of older stuff can seem to be a problem. Like a lot of machinery, I guess 'which oil?' can depend on how long you need it to last between rebuilds?

Recommending a brand is OK but most make several different oils- synth or not. As an example I tried two different synthetic from same supplier (not Motul) in a straight-cut MGB gearbox (on their advice) before reverting to good old 20W50- which I think is what the road cars use. Synchro wouldn't function on synthetic. The ubiquitous ZF as used in 70s Ford race and rally cars also appears to work best on cheap stuff- 15W40 in it's case- even when coping with 250bhp. Would be interesting to know if a GAA engined Capri requires anything different.

As a complete opposite, when the Moss-box Meister rebuilt the unit out of my Plus 4 I was told to run Red Line 'Heavy Shockproof' fully synthetic in it, which I do. This equates, according to their data, to a 75W250 oil! So far the only complaint I have is the cost. (And if it gets on your race suit, which is likely in a Morgan, it doesn't wash out!)

On the whole my rule of thumb is old fashioned oils in old fashioned gearboxes, but obviously not always!

[john ruston]

So try Motul.They are only down the road from you!

[terence]

After a few disapointments,I switched from Red Line over to Motul,like to use the same brand in Engine, G/Box and Axle. Scew Gear on the Cam/Oil Pump shaws no sign of ware using Motul,never had problems with Gear selection/synchro hubs or gears.Likewise for the Axle. I wont use anything else,expensive? not as much as a rebuild though.

[Mike Bell]

I do use various Motul oils- only use other stuff in Moss gearbox. Tend to ask engine or gearbox builders what they want me to use. Then if it goes wrong after expensive build / rebuild at least they can't blame me for using wrong oil! Engines with skew gears for ancilliaries are well suited to 300V and that is what I run.......

BTW is this thread a tenths version of 'product placement'

[Al Weyman]

No not at all Mike, I only quoted the Redline article as it was specifically about using GL5 oils with LSD additives and the harm they can do in older type boxes with brass sychros. I am certain sure manufactures like Millers and Motul have equivilances and the theory is the same, it least the Redline article may give guys the knowledge to know what to ask for whoever they finally purchase from. as I said I have purchased two literes of Halfords own brand GL4 spec oil for mine and I feel confident its probably suitable. BTW talking of Halfords own brands have you seen their 20/50 for older cars, its like the old green Uniroyal stuff and looks ok to me I did use it when I was running a flat tappet engine.

[DaveGT6]

For what it is worth I use Red Line Heavy Shockproof in the 3 synch B box in the Grantura. Seems to work a treat. Box was stripped after about 15 hours to check over and it was mint condition. No problems with gear selection and it still feels like new after a full season.

[John Turner]

I'm aware that this thread sounds a bit like 'product placement' but neither Redline nor Motul instigated this, and I don't have a problem with anyone disclosing what works for them. At the end of the day if advice given on here saves wear and/or failure and therefore reduces an individual's cost to go historic motor racing, it has to be a good thing. On the other hand neither this site nor our posters can accept responsibility for anyone taking advice which ultimately fails to succeed, as it is only a matter of opinion expressed by posters from their own experiences.

[Mike Bell]

Originally Posted by John Turner

I'm aware that this thread sounds a bit like 'product placement' but neither Redline nor Motul instigated this

My comment was very tongue in cheek John but does make you realise how easy it would be for a bit of 'PP'.

I heard the recent announcement that BBC were going to introduce it. Few days later listening to R2 the multiple Ferrari owner starting going on about Subway (sandwiches) mentioning the name many times before then introducing McD into the conversation as well. (Turns out they share parent company.) Still don't know if that was product placement or not!!!!

[terence]

Originally Posted by Al Weyman

No not at all Mike, I only quoted the Redline article as it was specifically about using GL5 oils with LSD additives and the harm they can do in older type boxes with brass sychros. I am certain sure manufactures like Millers and Motul have equivilances and the theory is the same, it least the Redline article may give guys the knowledge to know what to ask for whoever they finally purchase from. as I said I have purchased two literes of Halfords own brand GL4 spec oil for mine and I feel confident its probably suitable. BTW talking of Halfords own brands have you seen their 20/50 for older cars, its like the old green Uniroyal stuff and looks ok to me I did use it when I was running a flat tappet engine.

Al,dont know for sure if its true but I was once told that Halfords are supplied by the masters of re-claimation Comma oils.

[JimW]

Originally Posted by Mike Bell

I heard the recent announcement that BBC were going to introduce it. Few days later listening to R2 the multiple Ferrari owner starting going on about Subway (sandwiches) mentioning the name many times before then introducing McD into the conversation as well. (Turns out they share parent company.) Still don't know if that was product placement or not!!!!

Bit of confusion here. Product placement is still forbidden on the BBC. The change which was agreed applies only to commercial stations already allowed to have advertisements.

Regards

Jim

[Mike Bell]

Originally Posted by JimW

Bit of confusion here. Product placement is still forbidden on the BBC. The change which was agreed applies only to commercial stations already allowed to have advertisements.

Regards

Jim

Thanks Jim, I stand corrected- that will teach me to half listen to the news!

Glad to hear it though, but makes me wonder how long a conversation on the radio about one particular make or retailer has to go before it oversteps the mark!

[Al Weyman]

I have pulled the box out of the car that was playing up and thought may have been down to the oil, it wasnt! As soon as I removed the side cover I immediately spotted the problem why the box wouldn't shift correctly into 3rd and 4th, the little dentine slipper plates on the 3rd/4th synchro hub were missing and the hub was not being locked in but being held in gear by the selectors only. Anyone ever seen that happen before there didnt appear to be any further damage whatsoever and why would they slip out?

[terence]

Originally Posted by Al Weyman

I have pulled the box out of the car that was playing up and thought may have been down to the oil, it wasnt! As soon as I removed the side cover I immediately spotted the problem why the box wouldn't shift correctly into 3rd and 4th, the little Dentine slipper plates

Isn't that Chewing Gum?

[Al Weyman]

yeah detent (I think) sorry I wish I was as bright as you Terence

[graham bahr]

did they just slip out or did they age, break in two then slip out?

[Al Weyman]

I am not sure as havnt checked yet, i was doing some fast changing around the new 300. I recon one may have brck taken the tension away from the others and they may have slipped out.