Speedometer showing much to high after W58-R154 swap..

[scotty]

Hey,

The speedometer is showing a much to high speed compared to actual speed. If it shows 50mph, I'm only going 40mph..

Can it be any resistors that need a different value? Or what can be causing this?

Scott

 

[te72]

Mechanical speedometer buddy, shouldn't be any resistors. What's your setup? Tire size, rear end ratio? Plug those into this:

http://akb.norbie.net/Public/Gearing.aspx

Not too hard. Take for example your car. If one assumes it's a stock 87 turbo with 225/50/16, 3.91 ratio, then at ~3000rpm in 2nd gear, you should be doing ~30mph. This is why you need to put in your own info into the calculator, as I don't know your car...

 

[Jeff Lange]

What was the W58 from, what was the R154 from? What rear end do you have?

You'll need to get your speedometer gearing in the transmission to match your rear end and tires. If you still have the N/A rear end with a turbo transmission, your speedo will definitely be off.

Jeff

 

[scotty]

W58 stock from my 87' Supra. R154 also from MK3, it had however a digital speedo converter on the gearbox that I took off.

It's got a N/A rear end yes. How do I get my speedometer gearing to match? Is it just to put a turbo diff on and it should be good?

Got 225/40/18 on, diameter is 637mm. Stock diameter is 631mm, so shouldn't be very much off.

 

[Jeff Lange]

Putting the Turbo rear end in will fix it, however you need the correct turbo rear end to match it. I'd suggest pulling out the speedometer driven gear and on the end of it, it will have 2 numbers stamped into it. 33 & 10 or 32 & 10 means you need a 3.91:1, 33 & 11 means you need a 3.73:1.

I think most Turbo Supras over the pond your way have 3.73:1.

Jeff

 

[iwannadie]

Putting the Turbo rear end in will fix it, however you need the correct turbo rear end to match it. I'd suggest pulling out the speedometer driven gear and on the end of it, it will have 2 numbers stamped into it. 33 & 10 or 32 & 10 means you need a 3.91:1, 33 & 11 means you need a 3.73:1.

I think most Turbo Supras over the pond your way have 3.73:1.

Jeff

This has been discussed many times before but I don't remember there being a definitive outcome so I'll ask while it's on topic ha.

I have an r154 from an unknown supra in my 87 na with 4.30 rear end and my speedo reads about 10mph fast when going 50mph. Is there a speedo gear to match the r154 to the 4.3? I remember reading that some trucks used that combo but are pretty rare, is it a part that can be ordered? I don't want to give up my 4.3 rear end or get a speedo gear box, so I would like to just be able to replace the speedo gear if possible...

 

[Jeff Lange]

4.30:1 gearing needs 35:10 speedo gearing on the A70.

Speedometer Drive Gear: 33481-14080 (10 tooth - Same as 87-88 Turbo)
Speedometer Driven Gear: 33403-19235 (35 tooth - Same as All N/A)

Jeff

 

[iwannadie]

4.30:1 gearing needs 35:10 speedo gearing on the A70.

Speedometer Drive Gear: 33481-14080 (10 tooth - Same as 87-88 Turbo)
Speedometer Driven Gear: 33403-19235 (35 tooth - Same as All N/A)

Jeff

Thanks hopefully my speedo will be accurate soon now ha.

 

[myothersupra]

Okay, not to jack this thread but I've got one for y'all and I could really use some help with it...

I just picked up another MkIII last night from about 40 miles away from here.
A friend brought me there and then followed me back home in his 89 Turbo 5-Speed MkIII that became my speed and tach references by a phone call within a minute of merging onto the interstate when I realized this Supra's speedo and tach and traffic flow weren't in agreement with each other at all and I had no clue which one to trust...

Facts:
91 Turbo Auto MkIII (U.S. Model)
Stock 91 5-Spoke wheels with proper stock size tires

Problem:
The Speedo reads about 80mph while at 70mph actual speed and a little over 90mph at 80mph actual speed

Knowns:
The Tach matches up perfectly with a buddy's 89 Turbo 5-Speed MkIII while running down the interstate which as I recall also matched up with my old 92 Turbo Auto's tach at the same speedo readings as his 5-speed
So in my mind based on the matching tach readings at matched actual speeds this car's still got the normal U.S. Turbo MkIII 3.73LSD diff, or is that not a correct assumption?
The car got a JDM engine and new head gasket 2 owners ago

Unknowns:
I'm wondering if it possibly also got a JDM Turbo Auto tranny which I assume would have the speedo gear for the JDM 4:10 Torsen LSD instead of the U.S. 3.73 LSD or would the 4.10 speedo gear with a 3.73 diff make the speedo read low instead of high?

Or maybe is the tranny's speedo gear correct for the 3.73 diff but the speedo possibly out of a U.S. N/A that's set up for the W58 and 4.30 diff instead or are the N/A and Turbo speedo's the same part?
It's definitely a 91-92 speedo but I have no clue if it's the original cluster for this car and neither does the previous owner although the mileage seems to agree with carfax so I'm guessing the speedo's probably original

I can never remember what makes the speedo read high or low with correct stock tire sizes when swapping rear end ratios but I need to figure out what's screwing up this car's speedo reading so I can plan the best solution asap.

Any help would be greatly appreciated!

Thanks in advance!!!

 

[te72]

Sounds like your trans has a speedo gear for a lower geared rear end. My 89 has the trans from the JZA70 the engine came from, which had a 4.10 gear ratio. My speedo reads about 11.5% slow, I.E. 67mph speedo display = 75 mph actual speed.

All our car's speedo is the same, but the gear that drives the cable differs depending on drivetrain configuration.

 

[myothersupra]

So you've got a tranny geared for the JZA70's 4.10 rear end but have a MA70 Turbo's 3.73 and yours shows slower than your actual speed?
That's the opposite of mine's behavior which is why I'm confused. Are you on stock tire size?

 

[te72]

Yes, yes, yes, and no.

JZA70 R154 (speedo output geared for 4.10 diff), car has MA70 3.73 diff, and speed shown is about 11.5% lower than actual speeds. I was until recently on a tire 3.2% taller than stock, so that plays into that a little as well.

Sounds to me like you have a trans from a car with the 4.30... err... wait. You have a 91 Turbo? Stock 91 turbo diff? If so that shoots my theory down real fast. Nevermind man, the only way I can see your speedo shown being HIGHER than actual is if your trans has a speedo gear for a LOWER differential ratio (what are Mk4 TT autos geared at?), or your car has a higher geared diff than we think here.

Might wanna start crunching some numbers here: http://akb.norbie.net/Public/Gearing.aspx

 

[myothersupra]

Well I know it tachs identical to a 3.73lsd MA70 89 Turbo 5-Speed on the interstate rolling side by side down the freeway so I assume it's got the same diff ratio as that MA70 89 Turbo and I know from 89+ MA70 Turbos ive owned before that just under 3k rpm's with that ratio in top gear on stock tire size is 80mph which his 89's speedo also agrees with.
Also, I watched the trip odometer on a 40 mile drive tonight and it rolled consistent at each mile marker while the speedo read >10mph high at freeway speeds the whole time, which is really annoying as I can't ever get the TEMS into soft mode on the freeway as a result in addition to guessing my actual speed.

I'm thinking of swapping the cluster from my low mileage bhg 92 Turbo Auto into this car for a day just to see what it says as a comparison since the odometer in this car seems to still track correctly while the speedo's reading wrong.

 

[te72]

I'm thinking of swapping the cluster from my low mileage bhg 92 Turbo Auto into this car for a day just to see what it says as a comparison since the odometer in this car seems to still track correctly while the speedo's reading wrong.

This part really doesn't make much sense... your speedometer and odometer are driven by the same cable, which is turned by the same gear in the transmission. One should follow the other. If one is reading off, so then should the other.

Maybe Jeff can make some sense of all this for ya, I'm running out of ideas here.

 

[Jeff Lange]

If the odometer reads correctly, and the speedometer doesn't, you need to change the calibration of the speedometer, of if you cannot get it to read correctly doing that, replace the speedometer.

Jeff

 

[te72]

I was unaware you could calibrate a mechanical speedometer, other than changing the gears that spin the cable itself... Quite honestly, my speedo cable broke after about 2000 miles, I'm about ready to just say screw it and get a gps of some sort for speed monitoring reasons. Yeah, the odometer is going to be off (it's rather off anyway) but I don't plan on selling my car, so...

 

[myothersupra]

I know there are companies that do certified calibration and they've been around since before the days of electronic speedo's but I don't know what exactly they do to a mechanical speedo to calibrate it.

Typically when a speedo quits operating on the auto tranny it's the 90 degree elbow (which the 5-speeds don't have) that connects the second cable section to the tranny, or the nylon drive gear in the speedo sleeve on the transmission strips. There are of course exceptions where the section of cable from the speedo or the section at the tranny end snaps but that's far less common. The elbow or nylon gear at the tranny are the most common culprets of auto speedo failure and both are easily replaceable from under the car without removing the transmission.

At this point I still think my speedo's needle was removed and put back on improperly which is the only sensible conclusion I can reach based on my understanding of this stuff since the odometer reads correctly but the speedo gets further off on the high side of actual as I go faster...
I'll have a better idea of the validity of that theory if I get around to trying the cluster out of my 92 Turbo Auto Supra in this car over the next few daysand see what happens...

 

[Jeff Lange]

Toyota mechanical speedometers offer about +/- 10% calibration. There is a lever on the rear of the speedometer that adjusts spring tension on the speedo. Provided your odometer is correct, this is the only way to calibrate the speedometer. If your needle sits at zero and your odometer is reading correctly, adjust the calibration lever. If you cannot fix it doing this, you're going to need to replace the speedometer.

Jeff

 

[myothersupra]

Apparently 2 owners ago white gauge faces were installed and later removed by that owner, and the speedometer needle wasn't lined up correctly when it was put back on last time.