Speedometer is boggling my mind.

Ok so Ive been at this for going on 3 hours running the math and im still stumped. I just hope I can remember everything to put it here.

To start, I have a civic std. It has a 5sp and not the stock 4spd. It is running 175/70/13 tires right now.

I do not know which transmission I have in there right now, and I was trying to figure it out. Also, Ive noticed, and tested with gps that my speedo is off by as much as 5mph high at 60 (it reads 60, im doing 55 on gps), and I believe even more in higher speeds. Now the thing that is getting me is this. Lets say I have an SI transmission (boy I can hope cant I?), the stock tire size is 185/60/14. My tires will only throw my speedo off by .4%, resulting in a reading .2mph too fast.

Now, to go to the other end of the spectrum. If I have an hf tranny, which had a stock tire size of 165/70/13 I will be reading 1.5mph too SLOW, meaning I will actually be traveling faster than my speedo indicates, this is not the case.

So heres where it gets murky. To my understanding the drive on the speedometer is the same on all transmission of this family, and that its gearing is the same from one d-series cable tranny to another. (if im wrong please tell me because this is an important piece of info)

My other assumption is that the speedo pickup is driven off of the final drive on the transmission, and therefore spins in direct correlation with the output of the transmission at all times.

If these two things are true then the only thing that could possibly affect the speedometer readings are two things. The size of the tires, or the gearing INSIDE the actual speedometer. Which as far as I know are all identical, again if I'm wrong please tell me. If any one of these things happens to be false then it could change everything.

So. Moving along. I manage to figure that the rpm of the engine is irrelevant except to tell the difference in speed between two trannys at a certain rpm. Because if the drive unit is in fact run directly off of the final drive then the speedo will read right regardless of the final drive gearing or rpm. Yes one transmission will move faster/slower at the same rpm and the same gear than another transmission, but the speedo should spin faster as well.

So, I have 2 questions for you. If there are 3 things that could make my speedo be off by this, then they are tires, speedo drive unit, and the actual speedometer. I have found that to be 5mph off of an si transmission while running a 13" tire you would have to be using a tread as far off as 165/60/13. I am most certainly not running that size. So we can rule out my tires being that far off.

The second bit of info that ive found is that at the same rpm, the SI in 5th gear will run 5.5 mph slower than the DX, while the DX is running at 60mph the SI will go 54.5. And at 80, the difference is increased to about 7mph, which is almost exactly what I have noticed on the highway.

This leads me to believe that I am incorrect in thinking that the speedo is driven off the transmissions final drive, and may be on some other gear that's speed will be changed when the final drive changes.

My questions are
1. Does anybody know the gearing/final drive of the std 4 speed transmission

2. Does anyone know whether the speedometer drives are any different gearing wise.

3. Does anyone know if the speedometers themselves have different gear ratios?

I know its not my tires.

no, it's the return spring in your gauge bud... seriously... check it w/ another speedo, that's known to be correct.. I'll almost guarantee it goes to the right speed.. if that spring is worn (20 year old car.. think about it) it will throw your displayed speed off exponentially based on actual speed.

Thats a very logical answer man. I thought about a few more thingsa before I went to sleep that could help narrow it down. Things like finding out which tranny I have (crawling under the car and reading the casing) and then getting a cluster to match. That would tell me if its the drive or the speedo right there. Ill consider that idea, thanks alot. I need a new cluster anyway, one with a tach!

You should have an L7 tranny.. afaik, all cable D-series are L7, hydro D's are S20. I might be wrong, but you can always look and see..., afaik again, all the speedo's are the same, the only thing would be the diff final drive in each tranny, but that doesn't make sense, b/c I went from a DX to an HF tranny, and they're diff finals, and showing the same speed... alot of guys do cluster swaps, and don't say anything about speed differential, so the (most) logical answer (that I can think of) is the return spring on the speedo being weak... you can also rebuild it if you have a guage that's not the right one for your car or whatever, but is for a similar model... like if you have a Sedan Pod, and it won't fit in the CRX pod... but it's a pain to rebuild too.

Yeah your speedo shouldnt change with the different final drive, just the rpms that you turn in each gear at the same speed. And yeah the trannys are all the same but I mean I need to crawl under and check the diff housing to see if its an SI or not, as this is the only way ive heard of to identify them.

ah... I've usually just trusted the person that it came from... and sold it as the same.. I've never actually used an Si tranny except on a dune buggy.. and you can't tell the diff on a dune buggy between a Si and DX tranny... they feel about the same... of course, you're looking at 118 HP or so pushing (mid/rear config) somewhere close to 700 lbs.. of course you can't tell.

haha, well theres no bloody way i have an hf, and if i had a tach i could figure out which one it is pretty easy..but it still doesnt explain the speedo.

Didn't we cover this already? lol

The speedo cable is driven off its own gear on the ring gear, the trans has nothing at all to do with it.

All D trannys are L7's. To figure out what tranny you have you have to remove the trans and turn the input shaft 360 degrees and then watch how the diff has turned. If I wasn't busy now I'd pull up the diagram telling you what trannys are what.

You can check the serial number on the tranny to see what it came from too, it's like a tranny VIN. It's stamped on the case just under the L7 Identifier...

That came from my service manual. It's a Chilton... so it's pretty much worthless for anything other than basic info.

THERES some info I was looking for, thanks hybrid.

Will this method of finding the stamp on the diff not work? Id really hate to get the tranny off to change the clutch only to find its not the one I want anyway.

Dude, couldn't you do that w/o removing the tranny?

I'm pretty sure you could just have someone turn the engine 360* and that would do the same thing...

:thought: and logic prevails again :thought:

Yeah I suppose you could do that but the difference between the ex and the si
isn't very big and it could be easy to read it wrong.

do it in 5th gear. the rotation will be less.. compare the final drive of the EX to the Si, whichever one is a longer drive, it will rotate the tire less... mark what part of the tire is on the top, w/ a paint marker, jack up the p-side front tire, rotate the engine once, measure the distance it moved, and do the math.. (you seem to like doing math, after 3 hours of it :P) the only tire that will turn is the one in the air (obviously) and it will save you the time of taking everything apart...

I still think you can track the serial on the tranny to find the model it came from tho.

Unless I lift both tires it will rotate too much, because of the open diff.

nah, it shouldn't... when one tire is on the ground, it should turn exactly the same as it would w/ both tires up, since you're doing it from the engine.

if you had it in neutral, and you were turning the tire, you'd be right, b/c then the diff slips 1/2 turn per full rotation, unless you had them both off the ground, in which case they'd turn equally, but one would go backwards.

Dude, couldn't you do that w/o removing the tranny?

I'm pretty sure you could just have someone turn the engine 360* and that would do the same thing...

:thought: and logic prevails again :thought:

Fuck your logic. I'd rather do it with the trans off to know you did it right. They aren't THAT different with movement.

Anyway.

I did some research for you.

http://www.norcalcrx.org/tyson/pics/4gtrannyID1.jpg

look above the oil fill, there is a stamp that will say PL3/####
PL3/A### = small bearing case - DX/HF/STD
PL3/B000 = large bearing - SI/ZC
PL3/3000/6000/9000 = large bearing - SI/ZCas for clutches (http://www.honda-tech.com/zerothread?id=1551508#), as long as you have a 90-91 flywheel it will use a 90-91 SI clutch. unless the trans is an '88(21 spline input shaft)




http://img.photobucket.com/albums/v203/ryan89crx/trans_id_1.jpg



http://img.photobucket.com/albums/v203/ryan89crx/trans_id_2.jpg

If you still have a gold sticker on your old cable transmission, which you do in this case, then you can tell the year for sure.It's like this...
88/89 cable transmissions (http://www.honda-tech.com/zerothread?id=1551508#) will have a L3-1 gold sticker..
90/91 cable transmissions will have a L3-2 gold sticker..

Dude thats the link I posted on the first page, but thanks for looking. Thats the info I needed. I just wanted to double check whether or not the stamp above the fill plug was true.

where did you post a link? i went over the whole thread again and still don't see one.

Oh shit sorry, I guess I didnt get the link in there and thought I did. My bad

It was on this post.
THERES some info I was looking for, thanks hybrid.

Will this method of finding the stamp on the diff not work? Id really hate to get the tranny off to change the clutch only to find its not the one I want anyway.

Hey, the logic works if you're not into pulling the tranny for someting like that... if you were going to pull the tranny anyway, I'd do it your way, if I wasn't already planning on pulling it, I'd just mark the tire, and do it that way, it's the same thing.

So I guess it turns out I have a dx tranny. Which is not cool, because I cant put an lsd in it because of the small bearing case. I jacked it up and checked the case to find the stamp "PL3/A100"

I think tony has some Z6 tranny's, you could ask about it.

Hydro... need a different pass mount plus a conversion setup. I found the conversion for about 165 but I have no idea where to find the right d series hydro mount. I can find em for b series but not d. Even then, thats alot of money to ship a transmission then convert. I found a guy sell a full y8 setup with 50k miles includes tranny axles and ecu with the engine for 450. I dont really need anything but the longblock. He hasnt gotten back to me on seperating them.

ah... well, i could find you a hydro mount, but the conversion I can't help with, other than to say it's easier/safer to just change the entire pedal assembly and mount the master cyl where it goes.