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I searched the internets pretty hard and couldn't find any concrete info on this, so I pulled out my spare 6 speed and started drilling. Only took 2 attempts!
The one by the drain plug interfered with too much so it got plugged. This one seems to work, but its very tight. Make sure your hole is perfectly centered and the sensor will just barely fit.
Sensor is an Airtex/Wells 1H9. 1/8NPT GM temp curve. Comes from a saturn SL coolant temp sensor.
This is a relatively ancient post but the title is perfect for my needs and frankly, searching this forum has sucked.
Does anybody have experience with drilling the passenger PPF side of the transmission for a temperature sensor? I'd like to keep the sensor away from the hot exhaust and I want a more permanent solution than drilling the drain bolt. Because race car.
I have the transmission out, I have a brand new 1/8 NPT drill and tap set, and Ballenger has a great sensor for 1/8 NPT.
Last edited by thebeerbaron; Aug 25, 2025 at 03:08 AM.
Reason: Edited for clarity to help readers who drive on the wrong side of the road
But the passenger side has the hot exhaust, I think you mean the driver's side.
Oh, wait ... maybe we just call it hot side/cold side?
One of the theories about 6-speed failures is (was?) case flex. If the case is prone to flex, and you are putting high torque loads into it, I'd be cautious about more holes. Why not ring Walters and see what they say, they must be pretty familiar with the insides of those boxes. I am contemplating a rebuild/C-clip mod from Neat here and will ask them, but my timing will not help you.
But the passenger side has the hot exhaust, I think you mean the driver's side.
Oh, wait ... maybe we just call it hot side/cold side?
One of the theories about 6-speed failures is (was?) case flex. If the case is prone to flex, and you are putting high torque loads into it, I'd be cautious about more holes. Why not ring Walters and see what they say, they must be pretty familiar with the insides of those boxes. I am contemplating a rebuild/C-clip mod from Neat here and will ask them, but my timing will not help you.
Ya know.. I did think about the imprecision of the terms I used for starboard and port, but I went with it anyhow because I’m American dammit and the world revolves around me and my imperial units of measurement.
So let’s get more precise.
The side of the case opposite the drain hole.
I made the mistake of looking at the service document for the six speed and a UteOob video, now I’m thinking about just pulling off the rear of the transmission and drilling it without the guts.
I’m not sure I want to bother Walters for information if I’m not buying things from them. At only 200hp, I’m not worried about case flex, but I am worried about the extra heat of the K24 exhaust cross-under cooking the trans even more than usual.
Yes, I take your point about the heat, you Imperialist Yankee!
The only ready-made options on that side are the speedo sensor and the reverse switch, both of which may be optional for the racecar situation. But how much oil they see I don't know - and that is the basic/necessary requirement. I'd spend a dime on the phone call, but then I once took a gearbox apart, and swore to never try a second time ...
Yes, I take your point about the heat, you Imperialist Yankee!
You know, I've typed a few quips here, but seeing as you live in one of the countries I've identified as potential escape routes from my current overlords, I'm just going to smile and nod in case your border agents ever review my posts…
I dropped an email to Walter, no response yet. I'm not offended or disappointed, we'll see if they reply at their leisure.Edited 9/5/25 to say that I received a wonderful personal reply from Brittany at Walter, even though they don't do any 6-speed work (I swear they used to?) she asked her tech and he (wisely) said he couldn't say without taking one apart. I mention this here to give credit to amazing non-customer support.
I took the easy way out, for now, and ordered a M18x1.5 drain plug tapped for 1/8 BSPT. It's made out of aluminum and from Amazon, so who knows if it'll be any good. What's the big deal about a little trans fluid dropped on the track and a six speed that has no oil in it?
Last edited by thebeerbaron; Sep 5, 2025 at 01:11 PM.
I don't think we do that here, then again I reckon there is A List somewhere, but I hope it is based on something more substantial that what you posted about Albo ... so LMK if/when you need a character reference or an accommodation address. We can always do with another MX5/Miata enthusiast!
The back up and speedo sensors are in the oil splash zone above the static fluid level. So not that great a site.
The number of times I run my race car over curbs I would not really want to place a vulnerable sensor on the very bottom.
But going into the tail housing, as close to the main housing as you can will work. The oil fill level does cover that area, and slosh will keep it in thermal equilibrium with the rest.
The location of the back up sensor tells you where you have clearance from the shaft and just make contact with the shifter rod arrangements. As you rotate lower down, you are out of range of the shifter rods, and into the oil level. And you can judge the static oil level by projecting from the bottom of the fill plug.
Because it curves upward in the tail housing, you could probably go in from the bottom and be protected from road rash damage too.
The back up and speedo sensors are in the oil splash zone above the static fluid level. So not that great a site.
The number of times I run my race car over curbs I would not really want to place a vulnerable sensor on the very bottom.
But going into the tail housing, as close to the main housing as you can will work. The oil fill level does cover that area, and slosh will keep it in thermal equilibrium with the rest.
The location of the back up sensor tells you where you have clearance from the shaft and just make contact with the shifter rod arrangements. As you rotate lower down, you are out of range of the shifter rods, and into the oil level. And you can judge the static oil level by projecting from the bottom of the fill plug.
Because it curves upward in the tail housing, you could probably go in from the bottom and be protected from road rash damage too.
If I'm understanding you correctly @Icedawg , you're referring to the following area:
Which looks like this on the inside:
It's a little hard to tell, but am I seeing that there's some open space between the case and the tower for the end of some rod, between the holes I marked as #3 and #4?
If so, that does seem like a great place to put the sensor! As you note, dawg, the closer to the mounting flange the better, maybe just a tiny touch above #4.
It also seems to me from this video that the disassembly required to get this access isn't too difficult. Perhaps I should watch the reassembly video to check my logic.
(edited to add) I think you're also right in that if I wanted to come up through the bottom of the transmission into the floor of that area, the sensor would probably be very well protected by the forward part of the transmission.
Last edited by thebeerbaron; Aug 27, 2025 at 04:44 PM.
Reason: Tried and failed to remove the YT preview because it took up too much space, so I just moved it to the end
I took the easy way out, for now, and ordered a M18x1.5 drain plug tapped for 1/8 BSPT. It’s made out of aluminum and from Amazon, so who knows if it’ll be any good. What’s the big deal about a little trans fluid dropped on the track and a six speed that has no oil in it?
This is what I would do as well. I have a 1/8" npt temp sensor in my oil pan drain bolt hole and it works fine and isn't in the way at all. Changing oil is quite simple as well. Let us know what you find out about trans oil temps. Not sure too many people log them.
If I'm understanding you correctly @Icedawg , you're referring to the following area:
Which looks like this on the inside:
It's a little hard to tell, but am I seeing that there's some open space between the case and the tower for the end of some rod, between the holes I marked as #3 and #4?
If so, that does seem like a great place to put the sensor! As you note, dawg, the closer to the mounting flange the better, maybe just a tiny touch above #4.
It also seems to me from this video that the disassembly required to get this access isn't too difficult. Perhaps I should watch the reassembly video to check my logic.
(edited to add) I think you're also right in that if I wanted to come up through the bottom of the transmission into the floor of that area, the sensor would probably be very well protected by the forward part of the transmission.
Yes, from the added help of the video I think you can put it about half way between 4 & 5, or halfway between 3 & 4, both look good. The rod is not going to come very far at all out of the spot around 4. But to be safe, a shorter T sensor than a long one may be advisable.
The post just above shows a nice arrangement for the engine oil T sensor, but it works reasonably safely because the plug is on the side of the pan, not coming out the bottom.
Well, step 1 of the process is complete. I've opened the case, found a location I like, and drilled/tapped it. Instructional photos will be coming tomorrow if, after re-assembly, I find no issues.
Remove the speedometer sensor. Remove these M8 bolts (12mm head) Remove the neutral sensor. Remove the upper half of the shift box and then remove the bolt holding the shift cup to the shaft (12mm head) Loosen, but don't remove this M8 bolt to the rear of the neutral sensor, before you attempt to separate the case.
Now that you've removed all these things, GENTLY whack the shifter box upwards with a plastic dead-blow hammer. It should only take a couple of whacks, don't go all caveman on it. Everything is cast aluminum and far weaker than you.
Last edited by thebeerbaron; Sep 1, 2025 at 04:02 PM.
This is the area I targeted for my sensor. It's actually a bit upwards (towards the cabin) from where I had planned. Showing a broader orientation picture. The fluid level, by my reckoning (proof later) should be maybe around the bolt hole to the right of the pin. Something like this. Plenty of wrench clearance. Drilled and tapped hole. I'll share measurements after I confirm there’s no interference. Here's where the hole ends up inside the case, above the boss for the sixth gear shift rod, if that's what this is.
I’m on mobile and the damn site lost the first iteration of this post. So you get a shitty, tired second version. More pics and fitment confirmation tomorrow.
Last edited by thebeerbaron; Sep 1, 2025 at 04:03 PM.
Looks very good, well done!
The T sensors come in different lengths.
Autometer makes a shorty version that matches electrical parameters with their longer one (longer is about the length of the one you are testing), for instance.
A lot of these sensors look short, but the measurements aren't very different from the Ballenger.
I'm measuring the Ballenger probe portion at about 13mm, tip to threads.
One oversight I made last night is that the 6th gear fork actually moves towards the front of the transmission (in hindsight, duh). If I had placed the hole further forward into the gap I identified above, this might have worked. I don’t know that there’s enough room to clear the flange casting though.
Last edited by thebeerbaron; Sep 1, 2025 at 04:04 PM.
Miata 6 speed trans temp location
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