Hey everyone, I am compiling some new information from an older thread of mine to repose my question in a more comprehensive manner with the goal of getting some input from all you Toyota brainiacs out there!

So, I have a manual 1993 Toyota pickup 4x4 with 280 000 kms. Unfortunately, I am unable to contact the previous owner of the truck and this is why I am taking to the forums to hopefully have my question answered. When driving the truck, it seems to be at far higher RPMs than I would think is normal. in 4th gear at 60kmph (37mph) the engine is at 3000RPM, when in 5th gear at 100kmph (60mph) the engine is at 4000RPM.

The RPMs seem to be far higher than they should be for the speeds I'm going at. I then had wondered if my differential gearing had been changed, I found on the door sticker that I should have 4.56 gears and after doing the wheel spinning method I could confirm this.

With this in mind, I took to an online gear speed calculator and put in all the information I had. With 29" tires, 4.56 gears, and the gearing from a r150f (which I confirmed I have) I got the following results:

In 4th gear (1.0) at 3000RPM I should be going 90kmph (56mph)

In 5th gear (.838) at 4000RPM I should be going 144kmph (90mph)

I have confirmed this math both on paper and with different websites.

Now, how could could I be going so much slower than what the math says I should be at. I had double checked my speedometer with a GPS speedometer and it was fairly accurate. Is it possible my clutch slips at high RPM? Is it possible my tachometer reads incorrect at high RPM? (I find that unlikely because it seems to read accurately at idle and low RPM), Maybe the sensor that reads my RPMs has gone bad?

I would really appreciate any input as to what may be going on here. Because the math and the reality of the situation aren't matching and for the life of me I can't figure out why. I have to do a fair amount of highway driving and I feel bad for my poor old truck only being able to go around 100kmph if I don't want to push it above 4000RPM.

Thank y'all!

 

I dont think your clutch is slipping. You would smell it and it wouldn't last much longer.

...your not in low range are you? lol

 

I forgot to mention that, I am not in low haha, I almost wish I was though for a simple solution.

Thanks!

 

What is your idle RPM?
I'm spit balling here but after reading your other thread, if someone swapped in a 4cyl gauge cluster, the tach would be reading off. I know I had to adjust mine with the potentiometer in the gauge when I did the cluster swap out of a V6 but I can't remember if it was reading high or low RPMs.

 

Hook up a separate tach on the engine to see if it matches the dash

 

Oh the Canadian kph...Both times my clutch has worn out, it slipped going into gear and then ran at very high RPMs. You could smell the burnt asbestos or whatever mix they use for lining now. But you could feel it slip and it was terrible to go in and out of gears and like the above comment, it didn't last long until it was completely gone.
I would look at the instrument cluster, I've have two of them as I the speedometer died on the first cluster. The external tach would tell you if it's the cluster or the engine itself. Take out your cluster and look the number up online, find out if it matches your vehicle make and model. All the specifics are on the door jam of the driver door or close by usually. My second cluster is from a 1993 4 x 4 22RE and it reads some things a little off from the original set. This could be what is happening, there are a lot of models with different specifications and if the cluster is wrong, it will never read correctly.

 

Thanks for the input! Ya, I think my first step will be to hook up an external tach and see what exactly is going on. with any luck, it will just be that the previous owner had changed the cluster or something of the sort.

Thanks!

 

Idle rpm is around 1400, I know that is too high for the manual so either it is in fact idling too high or maybe like you said, the tach is off. I'm about to finish the semester at school so I'll be going home in a couple weeks to hole-up in the garage and find out wth is going on. I won't lead this thread die in the off chance anyone else has the same question and needs answers!

 

I had an instrument cluster go out on my Dodge once. Read normal tach at low speeds but as soon as I got up into 4th, 5th, 6th gear it jumped up into the red line range. Replaced the cluster and fixed the problem.

 

4.56 gears came with 31x10.50 tires if you have a V6. Check speeds on the calculator for 27" vs 31" and see what the difference is.

 

Ok, I installed an aftermarket tach and it is reading like it should, my RPMs are now what I calculated they should be. Maybe someone installed a cluster from a 22re or something, idk but atleast I have peace of mind now knowing I'm not doing 4k rpm while going 110kph in fifth lol