Speedo Gear Change For Rear Axle Gear Change

[zero]

I'm thinking about changing the rear-axle gear ratio in my 1988 Mini-Cruiser. Has a 4.10 right now with the A43D auto trans. As it is - 4th OD is too high to be used most of the time. 3rd (1 to 1) ratio is a bit too low (high revs) for the best MPGs. I'm thinking a 4.56 rear would be much better. This way I could drive with OD on most of time and make use of the 4th gear. 4.56 gears would have the effect of driving with a gear in between 3rd and 4th/OD (as it is now with the 4.10 rear). That seems like the perfect spot to me.

I'm wondering if anyone here knows what speedometer gears the trans has in it now. The speedometer works perfect and I want to keep it that way after changing the rear-end ratio. I'm trying to calculate the new speedo driven gear I'll need and if it's available to buy. I want to avoid using some convoluted adapter gearbox to make the speedo work correctly.

I figure IF my trans has a 10 tooth drive gear - the driven gear will be 34 teeth. Once I put in a 4.56 rear - I'll need a 37 tooth driven gear for the speedometer to read correctly.

I'm hoping someone else has already done the research.

Right now:

4.10 ratio – 25.5” tires – 3rd gear – 3100 RPM at 55 MPH
4.10 ratio – 25.5” tires – 4th/OD – 2500 RPM at 55 MPH

With a ring and pinion change:

4.56 ratio – 25.5” tires – 3rd gear – 3400 RPM at 55 MPH
4.56 ratio – 25.5” tires – 4th/ OD – 2800 RPM at 55 MPH

[Vanman]

Go to page 2 of this thread post called"4.56:1 ring and pinon gear" , here's the link. But that's an adaptor only.

http://toyotamotorhome.org/forums/index.php?showtopic=7045&page=2 ...

john

[zero]

Go to page 2 of this thread post called"4.56:1 ring and pinon gear" , here's the link. But that's an adaptor only.

http://toyotamotorhome.org/forums/index.php?showtopic=7045&page=2 ...

john

Thanks. If I have to go that route I will, but I do not like the adapter gear boxes. My Dodge diesel truck came new with one OEM. I've had to put three new boxes on it so far. They don't last very long. The factory gears that ride in oil often last forever. I just don't know if Toyota or Aisin makes a correct gear set for 4.56 gears, 25.5" tires - against an A43D trans. And if they ever did - next question is - are they still available?

[zero]

I might be wrong . . but it looks like Toyota does not make a proper speedometer gear for an A43D auto trans, 185R-14C tires and a 4.56 rear. Trans seems to have a 6 tooth drive gear. Only driven gears that Toyota offers are - 19 tooth for a 4.10 rear and a 20 tooth for a 4.30 rear. A 4.56 would need a 21 tooth driven gear. No such thing in any Toyota master speedo gear listings that I've found. I hope I'm wrong. For now - seems the adaptor gearbox is the only way to do it.

[Derek up North]

Out of curiosity, how accurate is the existing speedometer? Have you you checked it against a GPS or mileage posts? They aren't exactly precision calibrated instruments like you'd find in a 'Police Package'!

[Maineah]

It's been a long time but I don't remember them having much in the way of choices of spedo gears they did use the little spedo gear boxes on some applications. The Trans was used in several different cars/trucks (Jeep, Volvo etc.) so maybe that might be an option.

[zero]

Out of curiosity, how accurate is the existing speedometer? Have you you checked it against a GPS or mileage posts? They aren't exactly precision calibrated instruments like you'd find in a 'Police Package'!

Checked my 88 Mini-Cruiser yesterday - against mile markers and also with a GPS. A43D trans and 4.10 rear. 100% dead-on perfect. I just put brand new tires on it - and obviously the 185R-14C tires match the speedo gears perfectly. Took it on a 140 mile "test" trip before we head across country in a few days.

Got 14.6 MPG doing 50-55 MPH. 600 foot altitude.

Funny thing is with my 1992 Dodge 4WD diesel pickup. It came from the factory with a adapter gearbox on the transfercase to run the speedometer. I found out when the first one went bad - that it was off and the wrong ratio. Nice thing is - it gave me 21 MPG many times. Once I fixed it with the correct box - mileage went down to 19 MPG (as calculated with miles on the odometer).

[fred heath]

I'm lazy. I just use my gps for speed.

On my unit, I touch the speed reading in the lower right hand corner when operating in gps mode. It turns the entire screen into a large digital speedometer with odometer. Another push and back to gps mode.

[zero]

Thanks to anybody who gave info on the place in California with the speedometer adapters. I searched around and I'm pretty sure nobody makes the correct speedometer driven gear for a 4.56 rear when used with the 185R-14C tires and A43D trans. Maybe because Toyota never built anything with that combo?

I checked around with several speedometer places and several gave me prices of over $200. I called the California place at 916-371-5873 and talking to the guy there was a pleasure. He is sending the adapter right out and only wants $80. I consider that a bargain for a specialty item in today's world.

Toyota RV with the normal 4.10 rear and A43D trans uses a 6 tooth drive gear and a 19 tooth driven gear for the speedo. The biggest driven gear offered that I can find is a 20 tooth gear for a 4.30 rear. A 4.56 would need a 21 tooth driven gear.

The only 21 tooth speedo gears that were ever used by Toyota that I know of were in a 2001-2006 Solara in Japan only, a 1989-92 Supra with a 3000 cc engine and 4 speed auto trans, a 1989 2.2 litre van with a 4 speed auto, or a 82-88 Tercel in the USA. Doesn't look like any of those gears will fit though (but have not thoroughly checked it out). . .