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MG MGB Technical - OD Trans. oil

With the issues rased about new oils not being good for breaking in our new engines, I had a question about what is the best to use on a newly rebuilt D. type OD transmission?

Since our B's use engine oil for the transmission, is there a recommended weight and type for use on a new transmission?
Bruce Cunha

Hi Bruce

From the Haynes manual (page 111)

Multigrade engine oil, viscosity SAE 20W/50W (Duckhams Hypergrade)

Bruce
Bruce Mills

Hello,

As mentioned Bruce, 20w50 is the MG recommandation. But I had Volvo 142 & 122S with the same OD found in MGs. Volvo had specified ATF in OD gearboxes. It is also a good choice.
Cheers,

JGC
Jean Guy Catford

Hi Bruce:

Since the Laycock O/D pump pressure is above 400 psi, a non-detergent should be used. High pressure hydraulic systems with detergents create foam, air bubbles in the hydraulic system, and can cause cone clutch chatter. I recommend 30W non-detergent oil also recommended by John Esposito @ Quantumechanics. John did a web page report regarding detergent and nondetergent oil use.

Good luck:

Rich Boris, 67 B roadster
Rich Boris

Interesting thought. With the lack of certain elements in the new oil formulas, namely zinc, I wonder if our transmissions are not being properly protected.
Steve Simmons

Bruce,
I've seen this question come up a lot. After reading the particulars on John Esposito's website (www.quantumechanics.com), I will be using 30W non-detergent in my recently rebuilt 3-synchro OD unit. Interestingly, this same recommendation was first made to me in the spring of 1966 when I picked up my first 'B.


This is the text from John Esposito's website.

Topic of the month for June 2005 – overdrive oil recommendation

Gang – I apologize for not writing an article for some time, but between the rough winter and everything else going on, it was impossible!

I want to express our experience and opinion on the topic of the proper oil for use in the Laycock de Normanville overdrive units. We constantly get into discussions( and sometimes heated debates!) with British car owners on this subject. This month’s discussion will invariably get some interesting responses as it seems to be a rather emotional (and not necessarily logical) discussion item for British car overdrive owners.

Let’s start out with history. Historically even the recommendations from various car manufacturers are confusing. Some say to use multi grade oil (MG manuals), some hypoid oil (Triumph manuals), some non detergent oil and some even recommend automatic transmission fluid! No wonder everyone is so confused!

Many years ago (in a land far, far away (OK it wasn’t that far away or even that long ago)) we ran an experiment on overdrive oil. We rebuilt an A type overdrive unit and initially ran it with 30 weight non detergent motor oil. When spun up on our test bench at 1,000 RPM, it reached a normal pressure of 400 PPSI. When shifting the pressure dropped to 300 PPSI and quickly recovered to 400 PPSI. All was right in the world of overdrives.

We then drained the oil and replaced it with 10W30 multi grade oil. When spun on the test bench, initially it tested fine. However, after a few minutes of running, the oil pressure dropped to 300 and when shifting, to 200. Upon observation of the internals of the operating overdrive we found bubbles developing in the oil pump body and oil pump output passage. We surmised that the detergents in the oil were causing the oil pump to cavitate, and develop air bubbles as it pumped.

We then drained the oil again and replaced it with 90 weight hypoid oil. This time the oil pressure jumped to 600 PPSI! When shifted, the pressure dropped to 450 PPSI, which made the shift immediate and harsh. After a few minutes of running the oil pressure actually began to climb even higher. (Which made no sense since we thought the oil would thin out and the pressure would drop). We finally shut it off at 750 PPSI as we did not want to damage the unit. Even though the overdrive unit was now in the non overdrive position (solenoid disengaged), the overdrive was now stuck in overdrive and would not come out. The higher pressure had driven the sliding clutch member so hard into the brake ring that the clutch return springs could not return it to the non overdrive position. A tap on the brake ring with a hammer (the universal overdrive release tool), shifted it back into the direct drive position. After running a number of these test with the same result we found what was happening. The oil holes in the accumulator sleeve are very small. The 90 weight oil was so heavy it could not escape from the accumulator chamber as fast as the oil pump could pump new oil into it. So even though the accumulator piston had passed the oil hole relief position, the pressure continued to build up because the oil could not leave the system as fast as it was being pumped in. The accumulator piston actually bottomed out in the sleeve (similar to coil bind on valve springs). When removed we found the accumulator spring had been compressed and was no longer useable.

After replacing the spring, we then tried automatic transmission fluid. We saw the same results as we did when we used the 30 weight non detergent oil.

We then tried synthetic oil and the unit also worked OK although it began to leak from all sorts of places it had not leaked from before.

Based on these tests we have since and continue to recommend the 30 weight non detergent motor oil as the best oil to use in the overdrives.

Some other experiences with customer overdrives over the years have reinforced this choice. For example, we found a Jaguar compact overdrive with a broken accumulator piston and bent spring when it had been used with 90 weight oil by the owner. When the piston and spring were replaced and the unit filled with 30 weight non detergent oil, it functioned normally. A customer LH overdrive unit that was filled with 90 weight oil "pulsed" between direct drive and overdrive without even being switched on electrically. When the oil was flushed and replaced with 30 weight non detergent oil the unit worked normally.

Other noted problems with overdrives filled with 90 weight are excessive wear on the oil pump plunger wheel and the eccentric cam, probably due to the higher pressures developed. Also the clutch lining seems to be more deteriorated in units with 90 weight oil than those with 30 weight oil.

The use of non detergent 30 weight oil does not seem to affect the transmission parts or function. Bearings, synchros, gears and hubs do not seem to function any less effectively with the non detergent 30 weight oil as with 90 weight gear oil.

So there it is gang, our scientifically based rationale for using and recommending 30 weight non detergent oil in Laycock overdrives. I welcome further discussion and feedback on this topic by anyone interested. As always, thanks for reading this article!
Steve Buchina

I've used atf fluid in my o'drive and it worked smooth and shifted fine with both regular shifts and o'drive in and out.

The problem with non detergent oil is that it is usually a lower quality base oil then a detergent oil. -- And it has no ep additives.

As discussed in a thread re cam break in, modern engine oil is missing zinc and other extreme pressure lubricants to keep it from fouling cat convertors. Gear loads are point and shear loads that require ep lubricants.

Back when these cars were built there were ep lubricants in engine oil. The modern ep additives are much poorer than zinc. Part of the reason modern engines have roller lifters. Gear oils - such as atf fluid is designed for shearing lube and extreme presssure lube requirements.

If you feel the need to use engine oil, use a diesel engine oil. That oil still has zinc and other ep additives, because they don't have cat convertors to foul.

Barry
Barry Parkinson

I seem to recall that MG recommended a heavier weight oil for the MGBGTV8 - I used 90 without any probs but I daresay the O'drive was suitably modified.

I recognize some names from the V8 Board here.

For the record

Roger
RMW

Diesel oils have more detergents!

There is only 1 Zinc free oil on market as far as I am aware
http://www.opieoils.co.uk/performance_lubricants/pdf/fuchs/TITAN_GT1_SAE_5W-30_BMW_LL04.pdf

The US 20W50s do appear to have reduced ZDDP but this should not apply to UK or Australia. Penrite also make a suitable oil and also specify the base oil
http://www.penrite.com.au/html/s01_home/home.asp?

Oils have moved on since the manual was written and I would consider specific gear oils such as Castrol SMX as the additives are designed for a box rather than an engine.
Paul Wiley

The V8 uses the same basic OD and gearbox as the 4-cylinder, but the OD uses a higher hydraulic pressure - 510 to 530 psi as opposed to 400 to 420 psi and the gearbox uses a different casing. Hypoid oil is recommended for the V8 gearbox and OD because of the higher mechanical pressures between the gear wheels generated by getting on for double the power and torque. Personally I think there is far too much worrying about what oil to use in engine and gearbox and what additives they may or may not contain, especially for the 4-cylinder.
Paul Hunt 2

Its the additives that really make the difference between engine, box and diff oils and a 20W50 may well start of thicker than a Hypoid oil. Modern EP additives are a lot safer to use in a box than in the days when the manual was written. ATF a 5W20 was often used in the SD1 box with V8 torque without issues, because it allows easier cold shifting.Although this appears to be low viscosity by the time a 20W50 mineral has sheared, which will be very quickly in a box, for most of the time is probably a 20W30, so little cold performance and not much more hot in viscosity terms.
Paul Wiley

This thread was discussed on 20/10/2006

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