This might be a dumb question but....

[cl_miata]

Where is my gearbox fill plug at? I am replacing the slave cylinder this week, and since I do hear a bit of whining while in first and second, I figure it's time to try to get as many miles left out of this gearbox that I can and throw some good oil in it. Only, I couldn't figure out where the oil fill for it is when I gave it a quick look-see. and also, is the standard 73W-90 a good selection? maybe something a bit thicker for the 40 years of age its had?

 

[Trevor Jessie]

look under the tunnel carpet on the drivers side. There is an access plug there.

 

[2091351]

Where is my gearbox fill plug at? I am replacing the slave cylinder this week, and since I do hear a bit of whining while in first and second, I figure it's time to try to get as many miles left out of this gearbox that I can and throw some good oil in it. Only, I couldn't figure out where the oil fill for it is when I gave it a quick look-see. and also, is the standard 73W-90 a good selection? maybe something a bit thicker for the 40 years of age its had?

Transmission uses motor oil as lubricant.

Steve

 

[bugimike]

The plug can be accessed through the plug on the driver's side of the tunnel as stated above. About a 6" socket drive extension will allow you to reach it with a socket (and a universal on the socket can help with the angle of attack :wink: ). Anything over 30wt oil will be too heavy for these transmissions, which take the same weight oil as you put in your engine. :thumbsup:

 

[cl_miata]

Alrighty thanks guys... and wow okay thanks, wasn't expecting the gearbox to take standard motor oil, just curious, since it does use a 30W motor oil, does this mean the intervals for maintenance are around 10k miles?

 

[Brian_James]

It is suggested that you use non-detergent motor oil. The cheapest stuff you can get. Fill through the shifter hole, and fill until it reaches the fill hole on the side. Takes just over one quart to fill.

Brian

 

[jvandyke]

I refill through the plug under the access hole but sounds a lot easier to full through the shifter extension housing, I guess you remove the boot, the shifter (watch out for the spring loaded detent thing shouldn't move out that much but might?) and dump in from there?
I have found getting the plug back in to be a major PITA, hard to start straight with a socket and not enough room for fingers, I've spent way to much time trying to thread it on. Wonder if you can't get from underneath? Hopefully I don't have to bother this season.

BTW, apologies to those who are sick of this story, bought my car, test drive good, got it about 10 miles on the way home and 4th gear went bad. Drove the rest of the 90 miles or so in 3rd. Got home had to TEAR the carpet (that had been glued down in 1987, this is 2008 when I bought it). Couldn't see anything, drain plug and NOTHING COMES OUT. Refilled and nothing leaked out so the box had likely been dry for 20 years. Only 1995 miles and short pleasure hops in that 20 year span so I guess it's conceivable it was oiless that whole time. I had to swap boxes, found the old box had lost a bearing and the 3/4 slider was completely destroyed. Rest is good though. Oddly enough it shifted and sounded fine for those 10 miles.

 

[walwal63]

Do the 1500's use motor oil as well? I couldnt find a definative answer on this.

 

[bthompson]

Nope...the 1500s use 90wt. gear oil, same as the diff uses. Castrol Hypoy recommended, I think.

 

[scott_74]

Just to be sure...should I be putting motor oil in my '74 1275 Midget?

The paperwork that came with my rebuilt transmission stresses to use 90wt. gear oil (the warranty is voided if anything else is used)...but Hayne's tells me to use the motor oil.

Scott

 

[HAN8L1965]

I don't know what year your car is but the earlier 1098 cars use 20w50 in the gear box and for engine oil.

Mark

 

[Sarastro]

The data in Haynes is just a copy of what's in the factory service manuals. My understanding was that all Spridget transmissions before the 1500s used engine oil. In fact, I've been told that gear oil is harmful. It is a bit odd that these transmissions use engine oil while almost everything else uses gear oil, but that's the case. If anyone can explain the reason for this, I'd like to hear it.

Is the paperwork for your transmission specific to the Spridget ribcase, or could it be that it's just a set of general instructions, which may have missed the fact that our cars are different?

 

[ecurie_ecosse]

I think the reason might be that the gears are brass.

Stuart.

 

[scott_74]

Steve, the paperwork reads:

"All non-overdrives (except TR7 5 speeds) should use standard 90-wt. hypoid transmission gear oil. (All right, for you purists, the MGA and MGB gearboxes can use 30-wt. or 40-wt. non-detergent too.)"

They make reference to Midgets in other areas of the notes, so I assume they're not accidently dismissing the model under the exception here. I don't think oil misuse is the cause for the problems I've been having discussed in my recent thread, but the discrepancy is peculiar.

I'll call them and see what they say. But I'm gathering here that I should stick with the motor oil?

Thanks.
Scott

 

[bugimike]

I do believe that ALL Spridget trannys (smooth case & ribbed case) use motor oil, while the newer 1500 (Spitfire) trannys use the gear oil!

 

[DrEntropy]

ALL BMC boxes use oil. Small diameter needle rollers in the layshaft, brass/bronze baulk rings. Gear lube is too "heavy" to properly lube the needles, too "thick" to allow the baulk rings to grab correctly. TR/Standard boxes are a different animal.