Impreza 5 speed swap problems
 

My 92 Ls-L has a 98 Impreza swap but my speedometer now reads like 10MPH under what I am going and I was wondering if anyone had any ideas why.

Re: Impreza 5 speed swap problems
 

did you remember to swap the svx speed sensor in the 5spd?

Re: Impreza 5 speed swap problems
 

The speedo gear in the Impreza (depending on the year and model of Impreza) is set up for as small as 13" tires, you are now turning 16" tires which are probably 10% bigger than the 13's it was set up for.....so your speedo is off....there are aftermarket fixes for this, but they do cost....

My little Daily Driver is a Impreza L FWD 5-Speed, which came with 13" wheels, and I have a set of 16" rims on it, and my Speedo is off 10%.....so 50 on the speedo is 55, 80 on the speedo is 88, and so on...you can just adjust your driving to match it, or open up the tranny and install a different speedometer gear set, or get an aftermarket electronic fix for it...

Re: Impreza 5 speed swap problems
 

Wheel size has nothing to do w/ the speedo being off. Usually when you got from 13" wheels to 16" wheels, you're also going from 70 series tires to 40 series tires, so the overall diameter is similar. If your speedo is off, it's because you're not running the right size tires on those 16" wheels to match the original expected tire diameter from the original tires.

Try this page to sort out what you should be running: http://www.wheelsmaster.com/rt_specs.jsp

As far as the OP's problem. It sounds like he's got the wrong speed sensor in the tranny. Since he's running the same tires before and after the tranny swap (I'm assuming) there shouldn't be a discrepency due to the 5MT.

Re: Impreza 5 speed swap problems
 

I believe sperry is right. Since the sensor measures the outgoing rpm of the transmission and factors in the differential ratio as well as the tire size.
As 5 speed do not have the SVX stock differential ratio to swap the SVX sensor to the 5speed would not help. So you need to match the tire size to Impreza value.

Please let us know about the outcome on this.

Thanks!

Marcus

Re: Impreza 5 speed swap problems
 

OK, Wheel size isn't exactly what I was saying, but thought that would get the point across...
The Circumference of the tires that the tranny came with will be the difference, because all trannys DO NOT turn the same output at the speed sensor location, as the Subaru Manual Trannys are still set up to drive a cable driven speedometer which they had up untill the mid 90's, and there is a gearset inside the tranny that is matched to the final drive ratio and the tire circumference Do yes, he's running the same tires before and after his swap, but the TRANNY is NOT running the same tires it was set up for, the Speed sensor just converts the rotational output of the transmission into a digital signal so no matter WHAT speed sensor you install it will not read correctly, there are aftermarket setups that adjust the digital signal between the speed sensor and the speedometer, but without that you either need to find lower profile tires to try to match the transmissions original tire size (and if it were a tranny set up for 13's you'd probably have to run just the 16" rim with a strip of rubber around it:rolleyes:) or you would have to open up the transmission and install a different speedometer gear drive set.

A bit of a plus is the SVX (as most cars) stock the speedometer is off to the slow side, saying you are going faster than you really are...so some tranny swaps actually work out to a more accurate reading, some make it worse,,,

Re: Impreza 5 speed swap problems
 

I don't know if the person who had the SVX did the sensor switch. As for the aftermarket thing how much does that usually run?

Re: Impreza 5 speed swap problems
 

Forget about the speedo, I think you should use a GPS and hook up an external aerial to use it.. there are several options available.. if you have an iphone you already have what you need.. use this app

http://www.i-hud.com/

Also.. Do you think a tranny swapped in from a 2.2l engine will be able to stand up to an eg33 ? seems like the svx engine will eat that transmission for breakfast...

edit.. better link
http://appulo.us/appdb/?page=viewapp&id=4423
or this one
http://appulo.us/appdb/?page=viewapp&id=3222

Re: Impreza 5 speed swap problems
 

I've run a 1.8 Impreza Tranny in a coupe different SVXs, with no problems (my RWD 5-Speed is out of a 1.8 Impreza) Subaru has been using the same basic transmission since the late 80's, so unless you get a WRX one, or an STi one they are all about the same, 1.8, 2.2, or 2.5.

Again, as for holding up, that completely depends on how you drive, if you flog it on a daily basis, yeah, it'll probably break (but so does the auto) and a STi one will break under those conditions too...might take a little longer, but drag launches will end up destroying ANY transmission over time.
But if you drive it in a sane manner (at least Most of the time) they hold up fine.....

Re: Impreza 5 speed swap problems
 

I was under the impression that the speed sensor on the tranny simply read the rpm of the half-shaft. That leaves the actual speed calculation up to the interface between gauge cluster of the car and the sensor. So, for example, the transmission and can be identical between a Legacy and an Outback, but the Outback's gauge expects the larger tires that come on the car, and therefore the speedo reads correctly on both cars with the mechanically same transmission.

I figured, the OP's problem was simply using the wrong speed sensor, which reports an incorrect rpm to the cluster, resulting in being off by 10 mph. If the issue were related to diff ratios and tire sizes, then the speedo wouldn't be off by 10 mph across the board, it'd be off by some percentage of the actual speed, like off by 2 mph @ 30 mph, 5 @ 60 , 10 @ 90, etc.

I was under the impression that when doing a 5MT swap, if you simply re-use the SVX's speed sensor in the 5-speed, your speedo is as accurate as it ever was before the swap. Having not done a 5MT swap myself, I can't really claim to know what I'm talking about, but I'd be surprised if there were mechanical differences between every transmission related to the size of the tire that was expected to be attached to that transmission. It would be so much simpler just to draw the lines on the gauge in different spots and/or use a different speed sensor.

Re: Impreza 5 speed swap problems
 

The largest variance in tire diameter from a stock Impreza size is 195-60-14. You would find a 10mph discrepancy only if you were traveling at 99mph. Any other stock Impreza size would be less. In nifty irony, the largest Outback tire also has a 10mph discrepancy at 99mph, albeit in the other direction.

There's some very basic math at play here.

EDIT: My mistake... The following is incorrect. The cluster is driven off of VSS2.
Your cluster doesn't care what size tires you have, nor what speed sensor you have. It does what the ECU tells it.

Your ECU only cares about two things: How many pulses it gets from the speed sensor in a given amount of time, and what size your tires (not wheels!) are.

If your transaxle is definitely from a 1998 Impreza, and if you're using a stock SVX diameter tire, then your 10mph discrepancy can be found at no less than 333mph if the speed sensor is functioning correctly and to blame. :lol:

Re: Impreza 5 speed swap problems
 

Sorry Rob, but the speed sensor feeds directly from the sensor to the TCU/ECU/Cluster. So the speedo runs off the signal provided by the sensor itself. Check the wiring diagrams, it forks into the 3 seperate leads.

Tom

Re: Impreza 5 speed swap problems
 

I stand corrected... A different diagram had some misleading information, but the main wiring diagram shows what you said as true.

Do you consider the rest of my post to be valid?

Re: Impreza 5 speed swap problems
 

yes I do. but just wanted to make the single thing clear so no one starts trying to reflash their ECU to get their speedo to work right;)

The problem is likely due to speedometer itself. I have done numerous 5mt and auto swaps with numerous different transmissions. None of them were more than 2-5mph off

Tom

Re: Impreza 5 speed swap problems
 

Ah, here it is... G__TESTS_WITH_CODES.pdf, figure 29, shows VSS2 wired to ground, battery, and ECU exclusively. :confused:

I'm starting to put less and less trust in these books! :lol: