[Healeys] overdrive problem

Sun Jun 13 18:44:09 MDT 2021

MT-90 is actually a 75W-90 gear oil, equivalent to a 15W-40 motor oil 
(motor and gear oils use different viscosity indexes, and 20W-50 motor 
oil was approved in later Healey shop manuals, like the Bentley 
version). MTL is a thinner gear oil from Redline, and equivalent to 30W 
motor oil. I've used ND 30W motor oil, 20W-50 motor oil and MT-90 and 
prefer MT-90. MT-90 is /specifically/ formulated for gearboxes, so I 
don't believe foaming is an issue, but it's well-known that synthetic 
oils are more prone to taking the easy way out of an engine or gearbox. 
I've put well over 120K miles on MT-90, and have had no issues 
attributable to the oil, and all of my gears in my 205K-mile gearbox 
were in pristine shape at overhaul a couple years ago (the layshaft was, 
typically, worn at the ends). Note MT-90 is also formulated without 
extreme pressure additives, usually used in hypoid gear (GL-5) oils, 
which supposedly can degrade brass or bronze components. Note also the 
'W' stands for winter--i.e. cold--viscosity, and not 'weight.'

https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

My guess is Jim's new solenoid is defective, assuming it was adjusted 
properly (measuring the lift of the operating valve). The solenoids have 
two sets of points: one is a 'pull-up' set that allows higher current to 
actuate the solenoid, and the other is a sustaining set, which allows a 
lower current to hold the solenoid in the activated position. If the 
pull-up points stick, you would likely blow a fuse, and/or overheat and 
destroy the solenoid in short order; this is also the reason the OD 
circuit has a slow-blow fuse, as the initial current draw would blow a 
standard fuse every time. The fact Jim's OD will operate with an assist 
on the lever tells me the accumulator is OK. I did hear there were some 
defective solenoids going around a few years ago.

Bob

On 6/13/2021 4:49 PM, Henry G Leach via Healeys wrote:
> Hi healeymanjim -there a few statements you made that trouble me about 
> your overdrive.
>
> 1-why was there 90W oil in the trans? Was there an attempt to get more 
> pressure with heavier oil?
>
> 2- if you can manually engage overdrive with the lever on the 
> right-the overdrive is working and pressure has been built up enough 
> to switch from direct to OD (overcome spring pressure). However you 
> should probably measure the pressure with a gauge and insure that it 
> is over 400lbs.(photo)
>
> 3-the mainshaft should have nothing to do with engagement
>
> 4-if the solenoid is good, and if properly adjusted, it should shift 
> into OD if the switch on the dash is in OD. My guess is that the 
> adjustment is not by the book. Measure the solenoid and if it draws 
> about 8 Amps, it is defective.
>
> 5-you can follow the procedure in the workshop manual to remover the 
> accumulator, remembering that a huge spring is pushing on the solenoid 
> case and must be eased out. You should have the correct replacement 
> parts-piston rings or o-rings and any gaskets-and a proper puller 
> before you pull it apart, as just examining it and replacing it won't 
> give you an answer, unless you see major scoring or broken piston rings.
>
> 6- I would never use 90W oil in that gearbox. It will foam and cause 
> problems in the overdrive and when cold adds additional problems with 
> gear engagement. Use the 30 ND (won't foam)
>
> Take particular care in disassembly, as this is an involved mechanism, 
> and must be handled correctly to achieve successful operation.  
> Regards, Hank
>
> -----------------------------------------
>
> From: "healeymanjim via Healeys"
> To: "healeys at autox.team.net"
> Cc:
> Sent: Sunday June 13 2021 3:33:31PM
> Subject: [Healeys] overdrive problem
>
> is there such a thing as a stuck accumulator in the overdrive? a few 
> weeks ago we changed the gasket on the side of the
> case that houses the solenoid and arm. have been unable to get o/d to 
> engage electrically ever since. the solenoid is new
> and works perfectly as long as the overdrive mainshaft is not turning. 
> it tries to move the arm but is unable. pushing on
> the right side shaft lever for a second or two will engage the o/d and 
> it will stay in o/d until the o/d switch is returned to
> normal. it is like the accumulator has no pressure and does not give 
> the boost to engage the o/d. can the accumulator be
> removed without damaging it? it had MT 90 oil in it which we replaced 
> with 30ND hoping to stop any more leaks but can
> put it back in if it would help. any assistance welcomed.
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