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New rear end gearing question 4:56 / 4.88 / or ?


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Most if not all cheap GPS units display MPH. Don't know if you have one.Ā 

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I thought about just taping the conversion numbers on the speedo but realized that they would not show up at night. I have a GPS but really don't want to take my eyes off the dash/road to look at either a phone or GPS. I am just to used to looking at the speedo at a glance. I don't really want to run calculations either. Afraid I would jump in one of the other (similar dash) Toyota pickups we have and go merrily down the road thinking 77 MPH is 65, although the noise might clue me in. I calledĀ  Commercial Speedometer 3 times before I got a hold of someone who could help me. But once I did I got a guy who would build it this afternoon and ship it tomorrow for 80$ plus postage. They have no website or email so just dial 916 371 5875

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  • 2 weeks later...

Chuck, the guy to talk to at Commercial Speedometer, was a little under the weather when he took my order, and forgot about me. I called him back when the part did not show up and he got it to me 2 days later shipped express mail. Original cost of 80$ was marked down to 75$ and free shipping, can't beat that. I got the speedo corrector put in today and took a nice test drive. I had 45 MPH headwinds while climbing hills that used to have me straining in 2nd or 3rd (hunting the right gear) without wind. Now I am doing them in third. 60 MPH is about 3150 RPM in third and 1900 RPM in 4th. 55 MPH is about 2750 RPM in 3rd. 45 MPH is about 3200 in 2cd, I now have a usable 4 speed automatic. I found that I was using less throttle foot pressure in every gear. I used to try to use 4th on the highway and found I was using way more throttle in 4th than in 3rd, and often would drop down to 50 in 4th, just could not pull it. Today I was using 4th and actually easing up on the throttle over 3rd under most conditions where I had a tailwind or a slight downhill section or even flat road.

I can back up my steep driveway without flooring it. I went by one of those flashing MPH speed signs a couple times and found that my indicated 60 MPH was 58. Before the speedo conversion and pumpkin swap it was similar 60=58. I think this is the second most effective driving improvement I have made. The best improvement was disengaging the rear brake proportioner, so I could improve braking and this pumpkin swap improves starting and lets you have a full 4 speed tranny so you can accelerate and climb hills faster with less engine strain. We will see if that also improves MPG, it feels like it should...

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Nice explanation Lee. Thanks!

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  • 5 weeks later...

An update on the 4:88 rear end conversion. I just got back from an 800 mile trip to the same location I went to a year ago (Brookings to Hood River and back). The trip has been taking me about 10.5 hours one way (400 miles). This time it took a hair over 8 hours...about 8.2 hours. The reason? I could hold 3rd gear much longer on a clime AND I could stay in 2cd gear on every hill that had me dropping into first gear previously. The engine and I were quite happy.Ā  I was using less gas petal while I was turning higher RPMs the whole trip.Ā  I spent way less time stressing about when best to shift down because the engine was holding each gear much better. I did not have to shift down "early" and listen to the engine screaming, I could wait and shift down when the gear I was in got down to 2400~2600 RPM when the next gear down would come in at around 3300~3500 and it would pull it. I spent most of the trip turning 2800 ~ 3300 RPM. These are my figures

Ā  SPEED Ā  GEARĀ Ā Ā Ā  RPM

Ā Ā Ā  44Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  2Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3200

Ā Ā Ā  50Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  2Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3600

Ā Ā Ā  50Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  2500

Ā Ā Ā  55Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  2800

Ā Ā Ā  60Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3000

Ā Ā Ā  65Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  3300

Ā Ā Ā  65Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  4Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  2200

I was keeping up with traffic for the very first time, no sweat going 65-70, much better acceleration both passing and away from stops. The last hill to my house I was doing 18 MPH straining at 1800 RPM with the 4:10, now I was doing 28 MPH in first and could have gone faster (I don't know the RPMs becauseI was giggling so much I forgot to look at the tach). I must note that I am pulling a trailer all the time, probably just under 600# with a 250# motorcycle. So I am smiling pretty good at this point. Now for the downside... I ran 7 tanks of gas on both trips, my 4:10 average MPG was 13.36 while my 4:88 MPG was 11.72, so about a 14% decrease in MPG. However my average speed with the 4:10 was 38.09 MPH while with the 4:88 it was 48.78 MPH which is a 28% increase in speed. Divide that into your 13% MPG loss and less strain on both the driver and the drivetrain & I think I can live with the result quite well. I still found little use of the overdrive, it is just too big of a jump, at 65 MPH it would be doing 2200 RPM and I suppose you could jamb your foot down and make it go, but I still went back into 3rd at 3300 RPM.

It is a ridiculous gear ratio on the A340F 4-speed automatic transmission . If it went from 1.00 to 1.00 to maybe 0.85 4th gear might be worth something, but the 30% jump is just too much even with the 4:88 rear end.

Gear

Ratio

1

2.80

2

1.52

3

1.00

4/OD

0.71

Maybe if I was not pulling a trailer, or had a REALLY good tailwind, or my whole trip was downhill...

Edited by Lee & Joan
add chart (AGAIN) by hand
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Maybe if I was not pulling a trailer, or had a REALLY good tailwind, or my whole trip was downhill...

Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā  OR ^_^

You slow down to 4.10 speeds and use even less throttle.

Ā 

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YEAH, I thought of that, and the extra 2 hours on the road and went NAAAHHHH

I will just buy the extra gas. But I will hold to the Toyota Motor Home secret hand shake (fingers crossed behind my back), so if anybody asks me I promise to say "Yeah... they get about 18 MPG"

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Excellent post Lee! I SO want to do that but not in the cards. I still have to disconnect the LS Ā thing and with your great description will be next on my list. Thanks!

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  • 5 years later...

Electric cooling fans are awesome for sure, but to match the stock fan clutch Ā in performance it would need to be variable and have a PWM controller.
Ā 

Turbocharging or supercharging a vehicle requires very deep pockets, tuning, custom fabrication, and a whole set of skills that even most professional shops donā€™t have. To get the job done right, can easily spin you well past $10k. And then you will end up with an unreliable ā€œspecial needsā€ vehicle.Ā 
Ā 

Doing a rear gear swap is actually in reach of many DIY driveway mechanics. And it is dead reliable. And cheap. Mine cost me total maybe $400. If you had to take the pumpkin somewhere and pay for it to be done, could still get on under a grand.Ā 

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