Changing Gear Ratio

[centralman]

Hello fellow forum members may I ask what is the optimal gear ratio for my 1987 Toyota Dolpin RV (22-RE Engine)? It seems that the stock ratio may not be the best (4.10?)

And any tutorial on how to do a DIY on this project please? Thanks for all the help!

EDIT/Additional Info: I mostly travel on I-5 and would like to keep a constant speed on average in the range of 60mph. At that speed I noticed even in OD the engine is running at around 2700 rpm. Isn't that a bit high?

[zero]

Hello fellow forum members may I ask what is the optimal gear ratio for my 1987 Toyota Dolpin RV (22-RE Engine)? It seems that the stock ratio may not be the best (4.10?)

And any tutorial on how to do a DIY on this project please? Thanks for all the help!

EDIT/Additional Info: I mostly travel on I-5 and would like to keep a constant speed on average in the range of 60mph. At that speed I noticed even in OD the engine is running at around 2700 rpm. Isn't that a bit high?

I find 2700 RPM to be a little low since the 2.4 liter engine can barely make enough power to drive at 60 MPH in OD at that RPM. If you are saying that your rig easily runs along at 60 MPH in OD - I'm wondering what the heck is going on with your rig that makes it so much more powerful then any 20-21 foot Toyota with a 22RE that I've been in. From what I've experienced - 4.56 to 1 rear-axle ratio is the idea for a 4500-5500 high-roof Toyota RV with a 22RE if OD is going to be used as a cruising gear.

Too much to detail to describe how a gear change is done, start to finish. The Toyota uses a Hotchkiss-style rear-axle. Than means the entire differential with ring and pinion intact comes out as a unit. So, one option is to replace the entire unit IF you can find a good used one, with the gears you want, ready to install. If so - you pull the two axles out. Then remove the driveshaft. Then unbolt the diff-carrier and remove. Then stick in the new one and put all back together. If you plan to put new gears in your unit - it is MUCH more involved. I can post step by step photos if you want but it is NOT something to try unless you are a pretty good mechanic AND have a shop-press. Either way, the speedometer will be off when done. You can install a gear-speedo-drive-adapter-gearbox to correct the error. That costs $80.

With manual transmission (no converter slippage)

4.10 – 25.5” tires – with OD – 2400 RPM at 55 MPH

4.10 – 25.5” tires – with OD – 2750 RPM at 65 MPH

4.30 – 25.5” tires – with OD – 2500 RPM at 55 MPH

4.30 – 25.5” tires – with OD – 2950 RPM at 65 MPH

4.37 - 25.5” tires – with OD – 2950 RPM at 65 MPH

4.56 - 25.5” tires – with OD – 3150 RPM at 65 MPH

4.56 - 25.5” tires – with OD – 2650 RPM at 55 MPH

4.88 - 25.5” tires – with OD – 3300 RPM at 65 MPH

Automatic with torque-converter slippage factored in:

4.10 – 25.5” tires – with OD – 2640 RPM at 55 MPH

4.10 – 25.5” tires – with OD – 3000 RPM at 65 MPH

4.30 – 25.5” tires – with OD – 2750 RPM at 55 MPH

4.30 – 25.5” tires – with OD – 3245 RPM at 65 MPH

4.37 - 25.5” tires – with OD – 3200 RPM at 65 MPH

4.56 - 25.5” tires – with OD – 2900 RPM at 55 MPH

4.56 - 25.5” tires – with OD – 3450 RPM at 65 MPH

4.88 - 25.5” tires – with OD – 3600 RPM at 65 MPH

[WME]

Most of the owners here do not us O/D ever, well maybe going down hill. So at 65, again most don't drive that fast, your turning around 3850 in 3rd.

If you went to a 4.56 or 4.88 you would be turning less rpm in a now really usable O/D. You would also do much better in the hills.

If that rpm worries you remember that there are a zillion Toyota P/U with basic 4 speed manual transmission and they have been zoom up and down I-5 at for years at 4000 rpm.

[centralman]

Thank you @jdemaris for your reply. I have an external tachometer installed so I can only read from there, without knowing how accurate that is.

Yes, when I am traveling on a flat road at speed slightly above 60mph the tachometer states it's at around 2700-2800 with OD. When it is without OD it's at around 3600rpm.

So from your table, using 4.56 gear ratio will actually increase the RPM of the car when it's at OD than stock. But then I guess it wouldn't run to the point that will fell the power is not enough and need to downshift in order to keep the speed?

[centralman]

Most of the owners here do not us O/D ever, well maybe going down hill. So at 65, again most don't drive that fast, your turning around 3850 in 3rd.

If you went to a 4.56 or 4.88 you would be turning less rpm in a now really usable O/D. You would also do much better in the hills.

If that rpm worries you remember that there are a zillion Toyota P/U with basic 4 speed manual transmission and they have been zoom up and down I-5 at for years at 4000 rpm.

Thank you @WME for your post. I find the vehicle constantly forced to run in such a high RPM (Higher end of 3k RPM) quite worrying. Owned my Dolphin for about 6 and a half years now, and since my trips involved traveling the whole stretch of the I-5 (I go on annual trips from Vancouver Canada to Baja California) I would like my dolphin to run a bit less demanding of the engine and transmission, if anything I can do without a hefty price tag, I would do it.

[linda s]

Well this isn't a big V8 engine. These Toyota engines are made to run at higher RPM's. Stresses the engine more to run too low and lug the engine. If you are running stock 185r14 tires, your tach is off. With 4.10 gearing your RPM's at 60mph should be around 2350. I find it hard to believe you can even keep it at 60 in overdrive. Just the wind resistance is enough to slow you down. The constant back and forth from overdrive to 3rd also heats up the trannie and can destroy it.

Linda S

[centralman]

Well this isn't a big V8 engine. These Toyota engines are made to run at higher RPM's. Stresses the engine more to run too low and lug the engine. If you are running stock 185r14 tires, your tach is off. With 4.10 gearing your RPM's at 60mph should be around 2350. I find it hard to believe you can even keep it at 60 in overdrive. Just the wind resistance is enough to slow you down. The constant back and forth from overdrive to 3rd also heats up the trannie and can destroy it.

Linda S

Thank you for your post and advice. At long stretches of flat land, for example, driving from Albany to Roseburg in Oregon, my RV could stay at around 60mph in OD. But if I try to have it go at about 62/3mph, it starts cutting in and out of OD. One thing also concerns me is that when I tried cruising without OD at interstate speeds there things I noticed: (1) Coolant temperature rise (2) RPM high and engine noisy and (3) Significantly more fuel consumed.

I do have an external ATF Temp gauge installed also. I really didn't observe any ATF Temp change when the RV was shifting in and out of OD though.

[darrel]

Does anyone have RPM values for the 3 liter v/6 and automatic transmission with and without OD?

[zero]

One thing also concerns me is that when I tried cruising without OD at interstate speeds there things I noticed: (1) Coolant temperature rise (2) RPM high and engine noisy and (3) Significantly more fuel consumed.

I do have an external ATF Temp gauge installed also. I really didn't observe any ATF Temp change when the RV was shifting in and out of OD though.

Sounds to me like your RV is some sort of anomaly. I've seen road tests done of several and all showed worse fuel mileage in OD then when not. I assume because it makes the engine lug and work harder. I know my 20 foot 1988 Minicruiser got worse mileage in OD when I had the 4.10 to 1 rear. The trans also ran hotter in OD. Very noticeable whenever I was climbing even a slight incline. For most users with 22RE engines, 4.10 rear gears, and automatic transmissions - OD is pretty much not usable at high speeds so 3rd is the main travel gear. When I put the 4.56 gears in - OD became something I could use.

[centralman]

Sounds to me like your RV is some sort of anomaly. I've seen road tests done of several and all showed worse fuel mileage in OD then when not. I assume because it makes the engine lug and work harder. I know my 20 foot 1988 Minicruiser got worse mileage in OD when I had the 4.10 to 1 rear. The trans also ran hotter in OD. Very noticeable whenever I was climbing even a slight incline. For most users with 22RE engines, 4.10 rear gears, and automatic transmissions - OD is pretty much not usable at high speeds so 3rd is the main travel gear. When I put the 4.56 gears in - OD became something I could use.

Thank you for your reply. I haven't been told by the previous owner (I think there were like 3 owners before me) that any modification have been done to the RV, it fact, when I bought the RV, the radiator was stock - so I don't think any modifications have been done to the gear ratio of it.

Much work have been done by me, full tune up, changing the timing chain/guides, tune up, water pump, fan clutch even fuel injectors. I have also put in a second Transmission fluid cooler, also a 3-row radiator.

I may try a full stretch of road with OD off in between gas fill ups to ascertain the MPG situation. I just worried that at about 60mph the RV is running at the high 3k RPM range constantly which could damage the engine. And, when I need to make the time and on the road I drive upwards of 600 miles per day (On a tight timetable as my time off from work are very limited).

[zero]

Thank you for your reply. I haven't been told by the previous owner (I think there were like 3 owners before me) that any modification have been done to the RV, it fact, when I bought the RV, the radiator was stock - so I don't think any modifications have been done to the gear ratio of it.

Much work have been done by me, full tune up, changing the timing chain/guides, tune up, water pump, fan clutch even fuel injectors. I have also put in a second Transmission fluid cooler, also a 3-row radiator.

I may try a full stretch of road with OD off in between gas fill ups to ascertain the MPG situation. I just worried that at about 60mph the RV is running at the high 3k RPM range constantly which could damage the engine. And, when I need to make the time and on the road I drive upwards of 600 miles per day (On a tight timetable as my time off from work are very limited).

Things like tune-ups, timing chains, fuel injectors, etc. gain nothing unless there was something wrong to start with. The nice thing about the Toyota engine is this. Any engine runs more efficiently when run near or at it's peak of the torque-curve. With many engines - that is around 1800-2200 RPM. The Toyota 22RE however makes peak torque at 2800 RPM. So running it in the higher RPM range is fine and fuel mileage does not sink drastically.

I know with mine - back when I had the 4.10 to 1 gear ratio, it went like this. In 3rd gear @ 60 MPH, RPMs were high but the engine was not working hard, nor was I pushing hard on the gas pedal. Trans temps stayed at whatever engine coolant temp was (around 190 degrees F). If I ran in OD @ 60 MPH - I found myself pushing on the gas pedal more to keep speed up, and trans temp went up to 200-210 degrees F. That due to more torque-converter slippage. I can't give a fair comparison of gas mileage because I was never able to run an entire tank full of gas in OD without fear of damaging something. From the official tests I've seen done on brand new 20-21 foot motorhomes - running in 3rd gear got an extra 2 MPG as compared to running in OD.

[linda s]

I agree with JD. I did many tests driving on highway 5 from San Jose to Sacramento Ca. All flat level road and I always got better mileage with the overdrive off. I never use it anymore at all

Linda S

[centralman]

Thank you JD & Linda for your posts.

My annual Mexico trip is coming up during Christmas-New Year holidays. I will try to run a full stretch of distance in between gas stations (I usually fill up at fixed points over the years) so I will be reporting back on the MPG without OD. As long as it's ok to run at those rather high RPM continuously, I am willing to give it a try.

My experience is on those flat roads on I-5, speed usually can be maintained at the 57-60mph range with OD on. Any higher will induce the kick-down on the transmission and I will then try to ease off the accelerator to let it go back to OD.

JD, does changing the gear ratio actually helps the engine overall on highway speeds?

[zero]

JD, does changing the gear ratio actually helps the engine overall on highway speeds?

I did it for two reasons. #1 to be able to use OD and have the RV running quieter at 55-60 MPH. #2 to get more pulling power in 1st gear. For those two reasons - what I did worked great. Running now in OD with the 4.56 rear puts the engine RPM in-between 3rd and OD 4th with the 4.10.

Best I can tell - there was no change in fuel mileage as compared to running in 3rd with the 4.10 rear, and then 4th OD with the 4.56 rear. Just nicer to drive. I now have a rear-life 4 speed instead of a 3 speed. A little bit less RPMs and ample power to stay in OD without pushing on the gas pedal much of the time. Before with the 4.10 rear - I drove in 3rd and at 55 MPH the engine spun at around 3200 RPM. Now with the 4.56 rear and driving in 4th/OD - the engine spins at around 2850 RPM which I consider perfect. Just at the torque peak.

If you don't drive where there are very steep hills you may have never noticed, but . . When I had the 4.10 rear and stopped half-way up a very steep hill - and then tried to start again - it could barely get going. Now with the 4.56 it is never an issue. And note - this is not so uncommon. Many rigs are not designed to get started from a dead stop on steep hills. My 1987 Nissan Sentra with a four speed manual could not do it. Nor could my 1992 Subaru 4WD wagon and that had 4.33 axles! Also my 1986 Chevy full-size, V8 Chevy Blazer also could not do it in normal range. But - since it was a 4WD - all I had to do is stick the transfercase in low-range and it was fine. I lived on a dirt road in New York with a 35% grade for 40 years. Climbing the hill with the RV was never an issue as long as I kept rolling. If I ever had to stop half-way up - to get started again - I'd roll back a little where the grade was a little less and then get started. That rarely happened though. It was a one-lane width road - so if I met someone coming the other way - one of use would pull over and stop.

When I had the 4.10 rear - it was always quieter in OD but also working too hard if I went over 50 MPH. So I drove in 3rd.

I recently met a lady who had just bought a 21 foot Dolphin with the auto trans, 4.10 rear and 22RE engine. She told me she drives everywhere at 65-70 MPH. I asked her if she uses OD and she had no idea what I was talking about. I.e. she had no idea that there is a button to shut it off. She just pushes on the gas pedal and makes it go with no worry about fuel mileage or consequences. Maybe she is just too used to newer and more powerful stuff. And maybe ignorance is bliss? I suspect the RV did not last her very long. I know she was getting 11-12 MPG so I know it was working hard.

[centralman]

Thanks for the detail post again JD. Much appreciated.

For my Mexico trip, I drive all the way from Vancouver to Baja California and there are indeed steep hills, the two big ones being Siskiyou Summit (Oregon/California Border) and Tejon Pass (Just outside of Los Angeles). So yes I would like the engine to work not as hard so that it could last longer. I would also like to be able to maintain 65mph with OD on flat road if possible.

I bought my RV in 2009 and the first year I made a trip to Los Angeles/San Francisco and then I have made 5 trips to different places in Baja California. Some of the roads there are really steep as well.

You've mentioned there are two choices available: Could you tell me

(1) If I choose the Re & Re method, from what year/model Toyota can I get one that can "plug and play"?

(2) If I choose to redo my current diff, what parts should I order and what's the way to do it?

Thank you for your assistance.

[zero]

You can stick a complete differential section from most any four-cylinder Toyota truck or 4-Runner from 1977 to 1994 with a few exceptions.. Also some Tacomas that are even newer. Not many made though with 4.56 gears. A few 4-Runners that came new with 32" tires as I recall. A 90s 4-Runner with factory 32" tires, 8" "four cylinder rear" and the OEM 4.56 gears is what you'd want to find.

If buying new parts - you'd need a new ring & pinion, gasket, and an install kit. The kit comes with some gear-marking compound (Prussian Blue), some shims, new pinion seal, and a new crush-collar. Gear set is $150 and the install kit is $25. The bigger expense is the labor to get it installed. When setting up the gears - there is no "half right." It has to be setup pretty much perfect or the gears will make noise. Not every person in every shop will know how to do it. In fact, the majority of shops now-adays probably do not know how. At least not on my side of the country. It takes me half-a-day to set one up and that is with the differential out and on my bench. But I've done maybe ten in my entire life and am slow. For a shop that does many - it's a two hour job (just diff, when out of the truck).

The photos gives you some idea of what it all looks like. The last photo is the speedometer-correction gear-box. That adds another $80 to the job if you want the speedometer and odometer to rear right. Toyota never made any correct speedometer drive gears for a 4.56 rear and the 185R-14" tires.

[centralman]

Much appreciated for your write-up, JD.

I am more inclined to do the conversion as I know a trustworthy and experienced mechanic in town, also for the fact that I think even though I could find a diff with the desired gear ratio, that diff probably itself has a lot of mileage on already. Since my RV is just at around 123k miles at this time I think it still has plenty of useful life left in the original diff.

Could you kindly point me as to where I can buy (1) The gear set (2) Install kit and (3) Speedometer-correction gear-box? Please also provide me, if possible, the brand of the manufacturer of the parts mentioned and part number?

Thank you so much for all the help given.

[DanAatTheCape]

these really are not "interstate" vehicles.

especially with the 4 cylinder.

2700 at 60 mph in 4th gear (OD) is not unreasonable to me.

wind her up!

[centralman]

What I don't understand is the reasoning for better fuel consumption with higher RPM, it is because I remember from my Toyota cars' owner manual they all say "shift up as soon as possible" "Maintain OD to have better fuel economy" ... etc. My reasoning for why they said it is because higher RPM = more fuel consumed over the same period of time.

[zero]

What I don't understand is the reasoning for better fuel consumption with higher RPM, it is because I remember from my Toyota cars' owner manual they all say "shift up as soon as possible" "Maintain OD to have better fuel economy" ... etc. My reasoning for why they said it is because higher RPM = more fuel consumed over the same period of time.

If is because the Toyota RV is underpowered and the engine becomes more inefficient at lower RPMs when trying to drive at highway speeds. In an ideal world - all gas and diesel engines are most efficient when run at the peak of their torque-curves at max load. That means the engine runs just one speed and load all the time. That is the way diesel-electric trains work. Not practical in an auto that sees various loads and speed constantly. When a Toyota does NOT have an extra 2000 lbs. of RV on it's back - it can get better MPGs in OD and running lower RPMs because of two factors. #1 the power-to-weight ratio has changed. #2 the wind-resistance has changed drastically and less horsepower is needed run down the highway.

[centralman]

Thanks JD for the info. I am leaving Vancouver this afternoon and will report on my progress. I really do want to get the gears changed after this trip, could you kindly provide me with the part numbers that I need in order to buy the necessary stuffs for the conversion?

I did some research on the internet, will this work?

[zero]

I'll get the part numbers later. I'm doing a gear change for someone right now and have all the new parts still in the box (from Yukon Gear).

A few facts to play with.

In 1978 - Toyota allowed a maximum of 38 square feet of frontal area for any motorhome put on their chassis.

By 1990 - Toyota allowed a maximum of 41 square feet if with single rear wheels and 55.8 square feet if with dual rear wheels.

A 1990 21 foot Toyota motorhome with dual rear wheels and weighing 6000 lbs. and auto trans uses power like this:

45 MPH - 33 HP, 50 MPH - 41 HP, 55 MPH - 51 HP, 60 MPH - 63 HP, 65 MPH - 76 HP

Now look at a 1978 Toyota Chinook motorhome with a pop-up roof, single rear tires, man. trans and 4000 lbs.

45 MPH - 15.4 HP, 50 MPH - 19.3 HP, 55 MPH - 23.8 HP, 60 MPH - 29 HP, 65 MPH - 35.3 HP

So a Chinook can go 65 MPH using near the same power as a 21 foot Toyota going only 45 MPH.

Back to a 21 foot Toyota motorhome. The 22RE engine makes peak torque at 2800 RPM. So the MH would make best fuel mileage at any chosen speed IF the RPMs were at 2800 AND the engine made the power needed AT that RPM and speed. In the case of a 21 foot Toyota - at 60 MPH - it needs 63 horsepower. The 22RE engine at 2800 RPM probably makes less then that so it lugs a bit. Drop the RPMs even lower and it lugs more and gets even more inefficient. I don't have the figures on that. The 22RE can make 105 horsepower at 4800 RPM. At 2800 RPM it is likely around 50 or 60 horse but cannot say for sure.

[WME]

This might help making up your mind

http://www.4crawler.com/4x4/Images/PowerCurve.gif

[zero]

If that chart is for a Toyota 20R or 22RE -there seems to be a mistake. Peak horsepower for a 22RE is 105 @ 4800 RPM. Peak HP for a 20R is 96 HP @ 4800 RPM. That chart is showing peak HP @ 3800 RPM.

[WME]

OOPs your right, it was the smoothest curve and all I looked at was the torque curve.

Just print it out and stretch out the HP curve

[centralman]

I would like to report back my findings on MPG in regards to having OD off full time.

I have a habit of fueling up as much as possible on every gas stop. I don't necessarily fuel only when the tank gets empty, but also when I need to make a stop shopping/eating etc.

My first fuel stop is at Marysville, Washington, Interstate 5 southbound exit 199. This is usually the first time the tank is completely full after refuel.

My next fuel stop is at Kelso, Washington, Interstate 5 southbound exit 39.

The next stop is at Albany, Oregon, Interstate 5 southbound exit 234.

At this time, I have concluded that having OD off is consuming about 25% more fuel than having OD on. After the stop at Albany, I switched back to full OD mode.

I have also observed that with OD on at around 60mph on a flat road the engine revs at around 2800rpm. with OD off is at around 3700rpm.

[Smiley1n]

On 12/14/2015 at 2:19 AM, linda s said:

Well this isn't a big V8 engine. These Toyota engines are made to run at higher RPM's. Stresses the engine more to run too low and lug the engine. If you are running stock 185r14 tires, your tach is off. With 4.10 gearing your RPM's at 60mph should be around 2350. I find it hard to believe you can even keep it at 60 in overdrive. Just the wind resistance is enough to slow you down. The constant back and forth from overdrive to 3rd also heats up the trannie and can destroy it.

Linda S

Good morning I switched to a 488 and my Toyota mini motor home. It's a 1986 Grandville with a 4-speed manual. And I'm turning about 3,800 RPM at 60 MPH. Was wondering if this will hurt my engine you're driving for hours this way. In the meantime I'm trying to find me a 5-speed manual that will bow up to my four-speed bell housing without any modifications so I have a two questions here and I was wondering if anybody can answer both of these questions thank you

[extech]

3800 isn't excessive. 

  there are multiple 5 speeds that will bolt up, but not all will have the gear shifter fit in the same hole you have

[Smiley1n]

On 12/14/2015 at 9:52 PM, zero said:

You can stick a complete differential section from most any four-cylinder Toyota truck or 4-Runner from 1977 to 1994 with a few exceptions.. Also some Tacomas that are even newer. Not many made though with 4.56 gears. A few 4-Runners that came new with 32" tires as I recall. A 90s 4-Runner with factory 32" tires, 8" "four cylinder rear" and the OEM 4.56 gears is what you'd want to find.

If buying new parts - you'd need a new ring & pinion, gasket, and an install kit. The kit comes with some gear-marking compound (Prussian Blue), some shims, new pinion seal, and a new crush-collar. Gear set is $150 and the install kit is $25. The bigger expense is the labor to get it installed. When setting up the gears - there is no "half right." It has to be setup pretty much perfect or the gears will make noise. Not every person in every shop will know how to do it. In fact, the majority of shops now-adays probably do not know how. At least not on my side of the country. It takes me half-a-day to set one up and that is with the differential out and on my bench. But I've done maybe ten in my entire life and am slow. For a shop that does many - it's a two hour job (just diff, when out of the truck).

The photos gives you some idea of what it all looks like. The last photo is the speedometer-correction gear-box. That adds another $80 to the job if you want the speedometer and odometer to rear right. Toyota never made any correct speedometer drive gears for a 4.56 rear and the 185R-14" tires.

I put a Ford 88 gear and my Toyota re22 engine and I had a four-speed manual and I'm turning 3800 at 60 MPH so I was wanting to go to a five-speed manual but I need to know what five speed will boat up to my four-speed bellhousing without me having to do any modifications does anybody know which five speed in which vehicle I need to get it from. And I haven't done a gas mileage check yet I was getting about 20 miles to a gallon here in the flats of Michigan before I made the gear ratio change and I was only turning about 3,000 RPM to run 60 MPH now I'm turning 3800 RPM so I would think that I'd be consuming a lot more gas I just haven't done no few mileage check yet

[Smiley1n]

Just now, Smiley1n said:

I put a Ford 88 gear and my Toyota re22 engine and I had a four-speed manual and I'm turning 3800 at 60 MPH so I was wanting to go to a five-speed manual but I need to know what five speed will boat up to my four-speed bellhousing without me having to do any modifications does anybody know which five speed in which vehicle I need to get it from. And I haven't done a gas mileage check yet I was getting about 20 miles to a gallon here in the flats of Michigan before I made the gear ratio change and I was only turning about 3,000 RPM to run 60 MPH now I'm turning 3800 RPM so I would think that I'd be consuming a lot more gas I just haven't done no few mileage check yet

I meant to say a 488 gear