[Mgs] Overdrive Diagram

Sat Jan 19 07:28:12 MST 2019

 Hi Barrie.  I can only speak from my experience, not any formal technical training.  When synthetic oil became popular (sometime in the mid-80's) I decided to try synthetic gear oil in my race car transmissions.  With this oil, the transmission was very hard to shift.  After speaking with some experts, we finally concluded that the synthetic oil was so slippery that is was not allowing the synchro rings to grip onto the cones, therefore reducing the effectiveness of a synchromesh transmission.  When I switched back to straight 50 Wt. Valvoline Racing oiI, it shifted just fine.
That's my experience.
Jack

    On Friday, January 18, 2019, 4:23:48 PM EST, Barrie Robinson via Mgs <mgs at autox.team.net> wrote:  

    Hello folks

  I know not if his helps but in matters of transmissions I would use synthetic.  I had a new Maserati Biturbo and when cold had a very sticky 2nd gear and "running it in" was not my idea of fun.   Dealer said Alfa Romeo had had success with synthetic as they also had a sticky 2nd.  So synthetic went in - HUGE success - never had tough 2nd gear again.   

  On 1/17/2019 6:41 PM, Max Heim via Mgs wrote:

Are you sure it isn't the gear oil? 
  The factory has always called for engine oil. There has been a lot of ridiculous debate over precisely what grade of engine oil (personally, I don’t think it matters, but let’s not start that), but there is certainly a large difference in viscosity between say 20W50, and 85W90. The overdrive, unlike the rest of the transmission, uses oil in a hydraulic function, not just as splash lubrication, so viscosity is probably very important. 
   -- Max Heim mvheim at sonic.net 

 On Jan 17, 2019, at 11:13 AM, Jack Wheeler via Mgs <mgs at autox.team.net> wrote: 
   Does anyone have a good exploded diagram of the overdrive unit used in a 1971 MGB, that you could send to me?  I am particularly interested in the pump assembly.  I changed the oil in my gearbox this week, using EP 85/90 GL-4 gear oil, as recommended in a recent article in the MG Driver magazine. 
  While the car was up in the air, I noticed a leak around the plug which holds the pump assembly in place.  So, I removed the pump, careful to keep all the pieces in the order in which they came out.  I cleaned everything up, and reinstalled the pump assembly and plug (part number 466-315 in the Moss catalog), with a new gasket.  I thought I had all of the pieces of the pump assembly (items 62-66 in the Moss diagram) in the right order when I reinstalled it,  but when I took the car out for a test drive, the overdrive would not engage. 
  In addition to trying to keep the pieces in the order in which they came out, I also used the exploded diagram in the Moss catalog (Page  41) as a guide.  The Moss diagram, however, is different than my overdrive unit.  Moss says their diagram is for cars from 1968 to 1980, but apparently, some things were changed during that time frame.  I can't believe the engineers would let anything go unchanged for 12 years!  It looks like the plunger (Moss part number 466-305) shown in the Moss catalog diagram has a roller on the end of it.  My plunger does not have a roller on the end of it.  Maybe this will give you a lead to which diagram I am looking for.

  So, that leaves me looking for a good exploded diagram of the unit used in a 1971 model.  Can anyone help with that, or does anyone have any suggestions as to what I might have done to make the overdrive not work, when it has always worked fine.  Thanks. 
  Jack Wheeler
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