906UP
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First off, if you're not comfortable with tearing into the engine internals STOP right here & hit the back button. This isn't what most would consider an easy modification.
If you're still reading.....
Like many others I thought the P5 was geared extremely low from the factory, at the rev limit in 5th gear, I was able to squeak out 40mph on GPS with 27" tires. It really felt like there should be another gear. The intent was not to make the P5 into something it's not....sport SxS racer, I just wanted to bring the engine RPMs down at trail speeds, we ride a lot of forest roads, gravel roads, etc to get from one section to another UP here.
Parts needed
Here's what we will be changing, #2 & #3
Start by draining the oil.
Although I did it without loosening the front diff I'd recommend doing this. I may have damaged the front seal. This will take the preload off the final shaft from the front driveshaft otherwise it will want to push the final shaft backwards. Removing the top diff case bolt and the two bolts on the front of the diff to frame. Pulling the diff forwards will remove the preload.
Getting to the back of the engine is a bit of a chore, you need to pull the rear engine cover so start by removing the rear rack, 4 bolts on each side and one electrical connector on the passenger side for the taillights. This is a good time to disconnect and pull the battery.
Remove the air box, exhaust shield, throttle body. Disconnect the speed sensor, angle sensor, stator & pick up wiring. Unbolt the battery box and lay all wiring out of the way. This gives you access from the passenger side. Remove the speed sensor, 10mm socket and the angle sensor, 2 4mm allen wrench. Remove the reverse lockout cable & lever on the bottom of the engine, 10mm socket.
Pull the rear brake caliper & unbolt the rotor from the driveshaft hub, 6mm allen wrench. Rotor must be unbolted to provide enough room to get the clear the frame. Pull the 3 bolts that hold the rear diff so it can be moved back far enough to get the rear driveshaft off the final shaft at the back of the engine.
After pulling the throttle body out place a clean rag or paper towel in the intake, you really don't want to drop something in there!!!! (Green arrow)
Disconnect & pull the starter motor out, 10mm socket (Red arrows). Now you can start pulling the bolts out of the rear cover. (Yellow arrows, these go all the way around the cover, not just on top!)
The 2 gears being changed are on the left, the top is the counter shaft from the transmission, the bottom is for the final shaft, this shaft runs through the engine and connects to both F&R driveshafts.
Once the cover is removed the 2 gears will slide off their shafts, watch for the thrust washer on the counter shaft gear, you will need to reuse it.
Top gears are the old ones, 2016 & older are 16T/30T for a ratio of 1.875
(The OEM gears for the 2017 & newer are 22T/40T for a ratio of 1.818....more on this below)
Bottom gears are the new ones, 25T/37T for a ratio of 1.48
There is some minor interference with the new 25T gear and the case, you could grind the case a little but I chose to "clearance" gear a little bit on one side. The area that I ground is above the pitchline of the gear so I have no concerns about a decrease in strength.
Once everything is fit you can start reassembly.
Clean the edges of the cases, I recommend brake clean to get the oil & old sealant off, apply moto seal and reverse procedure. Keep in mind that there are 2 longer & 1 shorter bolts in the cover. The rest are the same length. Take care to make sure the shift sensor is lined up correctly, this will be a shaft about 1/4" with a small pin thru it. You may need to shim the speed sensor, I ended up putting a 6mm HD flat washer under the mounting tab to get the correct spacing to the new counter shaft gear. I added a little Motoseal around the sensor to prevent leaks.
OK.... so it's back together and full of oil but now we have to trick the ECU, otherwise you will get the dreaded "--" on the dash. This is where the SpeedoDRD comes into play. One end plugs into the speed sensor & the other into the P5 harness. It is easily programmed following their instructions on the website. Depending on the year of your P5 the settings will be in the -36% range for 2016 & older(16T gear) or -12% range for 2017 & newer(22T gear). The trick is to get the signal to the ECU to match the previous gearing.... on mine the old gear had 16T, the new has 25T. Keep in mind the speedometer/odometer will no longer be accurate, mine shows a speed of 40mph while the GPS shows 48mph.
Now I get 48mph on GPS and haven't hit the rev limit, I may try the OEM tires/wheels just to see.... How does it feel on the trails? It feels like I've dropped L gear and added 6th, I'm running the trails in a gear lower than previously while also going faster.
Here's a couple Youtube videos from @dpnorth during his install....
*Update #1* 7/23/18
During doing this mod I found the final shaft wanted to push out....towards the back, I wasn't really sure why at the time but I did the Torq Locker tonight and it dawned on me. The preload from the front driveshaft was pushing the final shaft out. In doing so it may have damaged the front seal. I will update the procedure above accordingly.
*Update #2* 7/25/18
I've put about 100 miles on it since the mod, I couldn't be more pleased. L gear is still incredibly low but it's usable now, before I would just skip over it. No lack of power going up hills, still climbing the same big hill across the road from my house in 3rd. Now I can run down the edge of the road at 40-42mph without it sounding like it's coming apart. I do have to change the front seal on the final shaft, it's leaking, hoping the Honda dealer has one in stock.
*Update #3 7/26/18
I replaced the damaged front output shaft seal, fairly simple job, took a couple hours.
*Update #4* 7/28/18
I swapped the original 24" tires on for a test, 46mph GPS / 42mph on dash, still haven't hit the limiter.
*Update #5* 7/31/18
I've put about 200 miles on since the swap, no issues. We did an evening ride last night, used the stock 24" tires, it did much better in the sand/mud than with the 27's. The Terrabites are heavy and robbing too much power when it gets bogged down w this gearing. Might look for a set of lightweight 25"or 26" rubber, I think that may be the optimal size for this set up. Found the rev limit in 5th for the 1st time, 43-44mph on the dash / 47-48mph on GPS.
*Update #6* 10/30/18
Another member @Duckhunt did this mod and had an issue getting the speed sensor spacing correct, after a few messages and some measuring we found that the "spacer" under the speed sensor it sorta critical.
From @Duckhunt
"I just wanted to put in a follow-up note in here in case people are considering this or following. The gears work awesome, Low is unnoticeable change (to me) and now in 5th upper 30's mph to low 40's mph is a pleasant cruise. But I had speedo calibration/ speed sensor reading issues causing an irratic speedometer, with and without the SpeedoDRD, and electronic-delayed shifting. On upshifts it would wait a good half second after the shift before firing the injector again. First, I thank @906UP for very much appreciated help. The new drive gear is APPROXIMATELY 5mm or .2" larger OD, or 2.5mm/.1" radius. This is an approximation by measuring the factory "old" gear and using pictures and CAD for calculating a size difference ratio of the two gears, neither of us ripped apart the case and measured the new larger gear. Now, @906UP is using a .1085" or 2.76mm spacer under the speed sensor, and I was using three .047" washers for .141" or 3.58mm total. I was .0325" or .82mm further spaced from the new driven gear. After installing a same sized spacer as @906UP I have corrected the speedo and shift-delay issues. The speed sensor spacing is that critical.
If you do this mod be sure the speed sensor has clearance, but also do not space too far. Unfortunately we do not know the exact tolerance of a spacer but .094" or 2.39mm (two of my washers) is interference, .1085"or 2.76mm works, and .141" or 3.58mm is too much. Again this is for the speed sensor spacing. Thanks again to @906UP for all the help."
*Update #7* 2/21/19
I have a few of the "special" washers I used as a spacer for the speed sensor. It is a heavy duty version of a 6mm flat washer that just happens to be the correct thickness. At the moment I only have a couple but can probably find more if needed. If anyone is planning to do this mod send me a PM with your address and I'll send you one for free if you make a small donation to the site.
If you're still reading.....
Like many others I thought the P5 was geared extremely low from the factory, at the rev limit in 5th gear, I was able to squeak out 40mph on GPS with 27" tires. It really felt like there should be another gear. The intent was not to make the P5 into something it's not....sport SxS racer, I just wanted to bring the engine RPMs down at trail speeds, we ride a lot of forest roads, gravel roads, etc to get from one section to another UP here.
Parts needed
- GEAR, FINAL DRIVE (25T) Honda # 23621-HP7-A00 from RMATV ,$33.19
- GEAR, FINAL DRIVEN (37T)) Honda #23631-HP7-A00 from RMATV ,$22.12
- SpeedoDRD, SpeedoDRD , $79.95
- A shim for the speed sensor, approx 2.76mm or .108" works well (HD 6mm flat washer)
- A tube of Permatex Motoseal or similiar. This is what Honda uses to seal engine/diff cases. Don't use regular silicone, it will leak.
- Oil & filter
- A set of 1/4" & 3/8" metric sockets, ratchets & various extensions
- A set of metric allen wrenches
- A set of metric combinations wrenches
- Can of brake clean & rags for clean up
- Bench grinder/right angle grinder to clearance the counter shaft gear if necessary
Here's what we will be changing, #2 & #3
Start by draining the oil.
Although I did it without loosening the front diff I'd recommend doing this. I may have damaged the front seal. This will take the preload off the final shaft from the front driveshaft otherwise it will want to push the final shaft backwards. Removing the top diff case bolt and the two bolts on the front of the diff to frame. Pulling the diff forwards will remove the preload.
Getting to the back of the engine is a bit of a chore, you need to pull the rear engine cover so start by removing the rear rack, 4 bolts on each side and one electrical connector on the passenger side for the taillights. This is a good time to disconnect and pull the battery.
Remove the air box, exhaust shield, throttle body. Disconnect the speed sensor, angle sensor, stator & pick up wiring. Unbolt the battery box and lay all wiring out of the way. This gives you access from the passenger side. Remove the speed sensor, 10mm socket and the angle sensor, 2 4mm allen wrench. Remove the reverse lockout cable & lever on the bottom of the engine, 10mm socket.
Pull the rear brake caliper & unbolt the rotor from the driveshaft hub, 6mm allen wrench. Rotor must be unbolted to provide enough room to get the clear the frame. Pull the 3 bolts that hold the rear diff so it can be moved back far enough to get the rear driveshaft off the final shaft at the back of the engine.
After pulling the throttle body out place a clean rag or paper towel in the intake, you really don't want to drop something in there!!!! (Green arrow)
Disconnect & pull the starter motor out, 10mm socket (Red arrows). Now you can start pulling the bolts out of the rear cover. (Yellow arrows, these go all the way around the cover, not just on top!)
The 2 gears being changed are on the left, the top is the counter shaft from the transmission, the bottom is for the final shaft, this shaft runs through the engine and connects to both F&R driveshafts.
Once the cover is removed the 2 gears will slide off their shafts, watch for the thrust washer on the counter shaft gear, you will need to reuse it.
Top gears are the old ones, 2016 & older are 16T/30T for a ratio of 1.875
(The OEM gears for the 2017 & newer are 22T/40T for a ratio of 1.818....more on this below)
Bottom gears are the new ones, 25T/37T for a ratio of 1.48
There is some minor interference with the new 25T gear and the case, you could grind the case a little but I chose to "clearance" gear a little bit on one side. The area that I ground is above the pitchline of the gear so I have no concerns about a decrease in strength.
Once everything is fit you can start reassembly.
Clean the edges of the cases, I recommend brake clean to get the oil & old sealant off, apply moto seal and reverse procedure. Keep in mind that there are 2 longer & 1 shorter bolts in the cover. The rest are the same length. Take care to make sure the shift sensor is lined up correctly, this will be a shaft about 1/4" with a small pin thru it. You may need to shim the speed sensor, I ended up putting a 6mm HD flat washer under the mounting tab to get the correct spacing to the new counter shaft gear. I added a little Motoseal around the sensor to prevent leaks.
OK.... so it's back together and full of oil but now we have to trick the ECU, otherwise you will get the dreaded "--" on the dash. This is where the SpeedoDRD comes into play. One end plugs into the speed sensor & the other into the P5 harness. It is easily programmed following their instructions on the website. Depending on the year of your P5 the settings will be in the -36% range for 2016 & older(16T gear) or -12% range for 2017 & newer(22T gear). The trick is to get the signal to the ECU to match the previous gearing.... on mine the old gear had 16T, the new has 25T. Keep in mind the speedometer/odometer will no longer be accurate, mine shows a speed of 40mph while the GPS shows 48mph.
Now I get 48mph on GPS and haven't hit the rev limit, I may try the OEM tires/wheels just to see.... How does it feel on the trails? It feels like I've dropped L gear and added 6th, I'm running the trails in a gear lower than previously while also going faster.
Here's a couple Youtube videos from @dpnorth during his install....
*Update #1* 7/23/18
During doing this mod I found the final shaft wanted to push out....towards the back, I wasn't really sure why at the time but I did the Torq Locker tonight and it dawned on me. The preload from the front driveshaft was pushing the final shaft out. In doing so it may have damaged the front seal. I will update the procedure above accordingly.
*Update #2* 7/25/18
I've put about 100 miles on it since the mod, I couldn't be more pleased. L gear is still incredibly low but it's usable now, before I would just skip over it. No lack of power going up hills, still climbing the same big hill across the road from my house in 3rd. Now I can run down the edge of the road at 40-42mph without it sounding like it's coming apart. I do have to change the front seal on the final shaft, it's leaking, hoping the Honda dealer has one in stock.
*Update #3 7/26/18
I replaced the damaged front output shaft seal, fairly simple job, took a couple hours.
*Update #4* 7/28/18
I swapped the original 24" tires on for a test, 46mph GPS / 42mph on dash, still haven't hit the limiter.
*Update #5* 7/31/18
I've put about 200 miles on since the swap, no issues. We did an evening ride last night, used the stock 24" tires, it did much better in the sand/mud than with the 27's. The Terrabites are heavy and robbing too much power when it gets bogged down w this gearing. Might look for a set of lightweight 25"or 26" rubber, I think that may be the optimal size for this set up. Found the rev limit in 5th for the 1st time, 43-44mph on the dash / 47-48mph on GPS.
*Update #6* 10/30/18
Another member @Duckhunt did this mod and had an issue getting the speed sensor spacing correct, after a few messages and some measuring we found that the "spacer" under the speed sensor it sorta critical.
From @Duckhunt
"I just wanted to put in a follow-up note in here in case people are considering this or following. The gears work awesome, Low is unnoticeable change (to me) and now in 5th upper 30's mph to low 40's mph is a pleasant cruise. But I had speedo calibration/ speed sensor reading issues causing an irratic speedometer, with and without the SpeedoDRD, and electronic-delayed shifting. On upshifts it would wait a good half second after the shift before firing the injector again. First, I thank @906UP for very much appreciated help. The new drive gear is APPROXIMATELY 5mm or .2" larger OD, or 2.5mm/.1" radius. This is an approximation by measuring the factory "old" gear and using pictures and CAD for calculating a size difference ratio of the two gears, neither of us ripped apart the case and measured the new larger gear. Now, @906UP is using a .1085" or 2.76mm spacer under the speed sensor, and I was using three .047" washers for .141" or 3.58mm total. I was .0325" or .82mm further spaced from the new driven gear. After installing a same sized spacer as @906UP I have corrected the speedo and shift-delay issues. The speed sensor spacing is that critical.
If you do this mod be sure the speed sensor has clearance, but also do not space too far. Unfortunately we do not know the exact tolerance of a spacer but .094" or 2.39mm (two of my washers) is interference, .1085"or 2.76mm works, and .141" or 3.58mm is too much. Again this is for the speed sensor spacing. Thanks again to @906UP for all the help."
*Update #7* 2/21/19
I have a few of the "special" washers I used as a spacer for the speed sensor. It is a heavy duty version of a 6mm flat washer that just happens to be the correct thickness. At the moment I only have a couple but can probably find more if needed. If anyone is planning to do this mod send me a PM with your address and I'll send you one for free if you make a small donation to the site.
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