Speedometer/Odometer issues

**RuralTowner** · 06-25-2011, 10:03 PM

I only put this in this section because the culprit is directly connected to the drivetrain...otherwise I ask it be moved to a more appropriate section.

Okay that 5sp is in and seems to be doing great so far. The engine even runs 20 degrees cooler now! thanks to that extra gear so the already worn engine doesn't have to work so hard anymore. (Rebuild is out of the question as long as it keeps ticking and giving up to 30mpgs). Now for my problem.

My speedometer is not the right one for the current transmission. When I still had the old 4sp, the original (85mph head) to the truck had went kaput so I used one from a parts 77 Corolla I had (110mph head). It worked but wasn't the most accurate range-wise due...the odo still worked but eventually stopped turning also. Finding out what speed was what was also a bit tricky. Found a proper replacement (another 85mph head) in the first week of this past May so THAT was nice for a change (1st time in 2 years I had a proper one!).

Now though I have the issue that 45mph indicated is actually about 60 real (figured this when doing a test run of the tranny with a lead vehicle and my keeping pace). The odo also reads way off now...its off by about 1/4 which throws a wrench into mpg checks. (Fortunately my commute has been done enough I can usually get the total to within a few miles...as long as not too many side runs are done). I will be going back to the Corolla head to see if it will work any better this time. BUT! By chance anyone know by chance if there are any aftermarket analog speedos out there that might work properly?

I took the drive gear (works perfectly) from the shot 4sp transmission with the notion of possibly putting it in the 5sp...but I can't remove that one w/o destroying the threads I'd attach the cable to. This wouldn't be so bad if the 4sp spare had this component as well...which it doesn't. This swap from 2 totally different transmissions (models and years) probably wouldn't work anyway. Any hits or help? I'm not totally comfortable with having to "guess" that I'm at the correct speed...particularly since my drive to work takes me through the one town in the US that has the highest cops-to-citizen ratio (not raw numbers) in the US (if it isn't...its real damn close between county sheriff, city cops, state dps, tribal cops, border patrol).

If it wasnt for the fact that my gas guage (the only other instrument in the cluster that works) I'd just as soon find a cluster (one of those where it comes as a unit...sadly) from a mid to late 80s truck.

**MuddyTacoma** · 07-05-2011, 04:36 PM

This is a long post, sorry, and a bit hard to follow. You can usually check your speed with a good GSP over a few miles, by the way.

What year truck is this for?

**Dadstruck** · 07-10-2011, 09:57 AM

did you get this figured out?

**RuralTowner** · 07-12-2011, 12:18 AM

Is for an 81....but that doesn't do me any good if the tranny is WAY newer. To check my speed using a GPS....pointless...I don't own one nor have any intention of buying one in the near future. I know my approximate speed...but the current 81' head doesnt have the proper speed range for the tranny (mid 80s I think went up to 100+) to be totally accurate. In another forum I brought this problem up....is there an aftermarket speedo (ANALOG! not the electric or whatever type that is bound to be a project itself just to make it register speed...not to mention get working right) that would work?

OR do you know if any mid 80s p/u that had a 100mph speedo (round head...not center placed that takes up half the cluster). In this case I could probably try looking locally...maybe.

**Dadstruck** · 07-14-2011, 09:06 PM

You might try looking at some local salvages that have a large selection. Ask the people working there if they know of any. There has to be something extremely similar that might work that they might know of, a lot of those older salvages will have people working there that would easily be able to help you out.

**MD_Weems** · 07-15-2011, 04:08 PM

Is this the same pickup that you just fixed the tranny on?

**RuralTowner** · 07-18-2011, 02:24 PM

Yes it is the same one. Its the very reason why the current speedo/odo reads off: the 1980 head replacement (identical to the one that originally came with the truck) is meant to work with a 4sp...or at the very least a 4sp of the very early 80s. A quick check locally has turned up squat...alot of stuff the only yard owner had went to the scrapper when scrap prices had gone up. So the hunt continues. Fortunately for the moment the current setup is consistent with the speed and miles traveled: speedo reads about 15mph slow making 40mph indicated about 50 and while my slightly oversized tired adds another 3ish (with the old 4sp this always meant I would drive say...50 to be near 55). The odo just makes me have to do some simple division and addition....every 5 miles traveled...add 2 more to get the approx real amount.

**GearHead** · 10-05-2011, 01:04 PM

Sounds like a tough time having to do math on the fly in order to calculate the speed and mileage for your pickup. I have often forgotten to factor in the few mph from the the oversized tires on my 2001 Tacoma as well. Seems like there should be a way to adjust or calibrate the existing speedo.

**RuralTowner** · 10-10-2011, 05:03 AM

Holy old thread (sorta).

Would be nice if it could be calibrated, but hardly worth the effort IMO. Coming up with the numbers hasn't been too difficult. I had to do it when using another temporary speedo...and to make adjustment to the odo (due to slightly oversize tires) when I still had the original 4sp in it (for every 20miles add 1 mile). The numbers I come up with for adjustment are typically about 5-15 miles different from the guesstimated miles traveled between fill ups which gives me a rough low//high mpg range.

The only other thing I see happening to fix the problem was if I was able to figure out exactly what year the tranny is from...and find a donor vehicle with the appropriate instrument panel. I THINK the tranny is from a mid 80s which more than likely means by then the speedo was an integral part of the instrument panel. As a result I'd have to hope the gas gauge in it would work with my sending unit (that is even if I was successful in finding the right wires to hook up).