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Discussion Starter #1
I thought I'd share what I'm up to. I did a ton of research on bearing sizes, checking input shaft dimensions, spline counts on the diff, mounting locations, shifter compatibility on various transmissions and found that the manual trans in the 1G Insight, 1HCH and the GD3 Fit share so much that it parts should be interchangeable. I pulled a 1HCH 5spd from a junk yard and then swapped in the gears from an 07 Honda Fit. Only thing I have left to do is wait for the last shim that I need and then I can button it up and get it installed.

Yes, I know that means less MPG, but where I live and how I drive the shorter gearing is going to be so much more enjoyable.

Side note if I'm happy with the way things turn out I'll put up for sale the 1HCH guts. A person should be able to swap over the gears with Insight's 5spd. The only thing you can't use from the 1HCH is the differential, but the ring gear is the same dimensions and same bolt pattern, so can swap over as well if so desired.

The only really annoying thing is Honda hiked up the price on the tool for checking main shaft clearance. It delayed my progress for a month because when I ordered the part it was "back ordered" and they kept saying to check back in next week. I finally gave up on them and decided to look elsewhere and to my surprise everyone now had the tool listed for $200. So I ended up making my own for about $140. If someone has a good band saw and drill press they could make one for much much less. I can provide my cad drawings for those who want to make their own since it's still relevant for stock Insight trans.



Going through this whole process it really looks like Honda developed the 1HCH/Fit transmission and then shaved weight on anything they could for the 1G Insight. Pretty impressive with how much weight they took out of the transmission. And they even went pretty extreme with drilling holes in the rear drive gear and synchro hubs.
 

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Interesting stuff, how do the synchro designs compare? would this also solve the 2nd gear crunch issue more permanently (while retaining the double cone setup). Personally my commute I get better MPG running mostly in 4th rather than 5th so a lower ratio box is of interest from this side of the pond too!
 

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So to clarify, the 07-08 fit gears do or SHOULD fit in the Insight trans case?

If yes, this is beyond exciting news to me! I've been wanting to swap gearing for so long now but haven't had the spare money to spend on a hunch that the Fit gears were compatible.
 

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So to clarify, the 07-08 fit gears do or SHOULD fit in the Insight trans case?

If yes, this is beyond exciting news to me! I've been wanting to swap gearing for so long now but haven't had the spare money to spend on a hunch that the Fit gears were compatible.
More important to me, my partner has an 07 Fit and I can swap Insight gears into it? :D
 

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Discussion Starter #5
how do the synchro designs compare? would this also solve the 2nd gear crunch issue more permanently (while retaining the double cone setup).
The GD3 fit does have double cones, slightly different in design. From what I've seen people seem to have the 2nd gear grind pretty far down the line. But either way best to change it out if the trans is all open up.

Comaparison
1G Insight
48parts.com: Honda parts reference
GD3 Fit
48parts.com: Honda parts reference

Personally my commute I get better MPG running mostly in 4th rather than 5th so a lower ratio box is of interest from this side of the pond too!
Yea I barely can get into 5th, only going down hill. Also a ton of stop and go traffic which makes the 1~2 really bad when trying to keep up with traffic.


So to clarify, the 07-08 fit gears do or SHOULD fit in the Insight trans case?
Everything I checked out shows that the gears can be swapped, I only have a spare bellhousing to make sure the inputshaft length was indeed correct. The only part that I forgot to 100% double check is the ring gear size on the differential. But they have the same bolt pattern, same size housing, same spline count so it leads me to beleive that the ring gear should be the same size. If someone has the Insight's ring gear out to measure I can compare to the ring gear on the Fit's.

More important to me, my partner has an 07 Fit and I can swap Insight gears into it? :D
I don't see why not, but that seems cruel on the Fit XD I guess with the Fit's higher redline it would make it a little more bareable.
 

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I don't see why not, but that seems cruel on the Fit XD I guess with the Fit's higher redline it would make it a little more bareable.
Five is plenty of gears! If I want a higher ratio I can always downshift, but if I want to slow the engine down (increase engine lifespan, increase fuel economy, decrease noise) I can't do that without a different top gear. The Fit's 5th is just too short.
 

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Ah I see. I thought you wanted to swap all the gears over into the Fit.
I might just, but the Insight's 5th is just a little taller than the Fit's. The final drive is where the big difference is, which causes the Fit to have a really granny 1st - the Fit has a 50% larger engine and the same first gear, but a final drive that's 25% shorter (33% higher revs).
 

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Discussion Starter #10 (Edited)
Finally got the new transmission in. HCH1 5speed case with 07 Honda Fit gears, so nice to be able to start from a stand still without having to make the clutch slip so much :D



In the final installation I did run into one thing that needs to be modified whether it is a stock HCH1 5speed or if you use fit gears (same part number for the main shaft) you have to trim a little bit a of metal from the input shaft. It's a very small amount, any lathe should be able to take care of it easily. Oh and I needed to extend some of the slack for the reverse switch because it's located a little further on the HCH1 transmission case.



On the Insight main shaft with the shaft goes into the pilot bearing it's the same size all the way to spline. If you don't remove this stepped portion then it will cause just enough pressure to bind everything up from pressing against the pilot bearing.


Side note, found my clutch chatter. The springs in the stock clutch totally went super loose so much so it was coming into contact with something, yet I couldn't see what since I didn't see any wear marks other than on the springs themselves. Regardless I was surprised comparing the Exedy clutch next to the Honda branded clutch since I thought Exedy was making the clutches for Honda. You can see they are quite different with the Honda using smaller dual springs and the Exedy using a single larger spring. Also not in the picture is that I noticed the spring weights on the Exedy is larger. The clutch material construction looks a little different too with the exedy having the metal mesh running in different directions while the Honda is running radially. Additionally the groove pattern between the two clutches are different.

 

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Yesss! So glad this has finally been done! Thank you for going out and trying!

Out of curiosity, why is the HCH1 case needed though?
 

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Discussion Starter #12 (Edited)
It's not really needed, but I didn't have a spare Insight trans and I wanted to have a transmission ready to swap in instead of having my daily driver torn all apart only to find out something didn't work. But the only side benefit of the HCH1 trans is that it uses larger bearings for the ISB and differential and if I so choose I could get a LSD for the car, which you can't with the Insight because they made the differential just slight different.

Further update: bummed to feel that first gear synchro seems pretty beat even though when I looked at all the teeth they looked really good. 2nd is ok, 3/4/5 are buttery smooth. I'm also super happy I can finally back up in my steep drive way without having to slip the clutch so much. I need to get an alignment since I've changed the camber bolts as well as the control arms so I think I have bit too much toe out right now so straight line feel is probably not accurate, but it's nice to feel TQ in just about every gear.
 

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This is awesome! Thanks for leading the charge!


Can you give us the RPM you are running at maybe 70 mph in 5th?

Also, what differences you have in MPG? I'm guessing the MPG might not change much since the Insight is so happy running along in 3rd or 4th gear when the stock 5th is just unsable.....


I'm really tempted to do this to my car. That reverse gear is just bonkers on the staock trans.....
 

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Discussion Starter #14 (Edited)
Thanks :D when I get on the freeway I will let you know.

Also my synchros weren't really bad, my bleeder screw was leaking! I forgot that with speed bleeders you need to reapply thread sealer and since I replaced my slave the speed bleeder leaked on me, which was embarrassing. After fixing that it's all good. Also with these really short gears I think my motor mounts aren't happy, but the HCH trans case has a front mount, so I think I will make front brace system to bolt the mount too. It's something that I wanted to do since I was already unhappy with how much play there is in the stock mounts, but now seems necessary with the extra tq.

Also separate thought, for those interested in installing any of these type of gears using the HCH flywheel might alleviate the need to trim the mainshaft.

Edit: view from below
 

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Thank you for posting this. For comparison, can you post RPM vs MPH in each gear so we can compare with the stock transmission?

It sounds like this is a welcome change to make the gearing more sane. Sounds like having first geared lower is a really nice change. Is second then also much lower? If I want to get on the freeway in a hurry, I wind it up in first to redline, then I'm about 3000 RPM in second where I keep it until redline, then third. On each shift there's a drop in power until it gets back up to 4000 RPM. Does this change bring the shift points lower, so that we can keep the engine at higher RPMs when accelerating?

It feels like the current car has two personalities. Mr. Gutless, who at 1500-3000 really doesn't want to go anywhere, and Mr. Zippy, who emerges when you wind it up past 4000 RPM. When I invoke Mr. Zippy, a part of me feels like Mr. Zippy is going to punch a hole in the side of my engine someday.
 

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Discussion Starter #16 (Edited)
Sure, some time tomorrow I will try to get some specifics. Although I think most would prefer the HCH ratios since the final drive is not as short as the Fit. I am running a final drive of 4.29. The stock final drive is 3.208 and the HCH is 3.6. But first and second gear between the HCH and the GD3 Fit are the same. And once in third and beyond the Fit gearing gets even shorter than the HCH making it more of a close ratio gear set in comparison to the Insight and HCH. But the good thing about the HCH's gearing is that 5th is the same as the insight so in fifth the only difference is the final drive, so it might make 5th more useful for those in areas where previously felt pointless while trying to achieve decent MPG.

At the moment I don't know off the top of my head the difference in rpm/mph, but I did notice in second gear I was toping out around mid 40's.

Edit: sorry I noticed that I didn't answer your question completely. First gear is virtually the same between all three trans, the final drive is the difference. Second gear both HCH and GD3 fit gears are the same, which is shorter than Insight's second making it a little less of an rpm drop between the two. Third is shorter than the insight's with the GD3 being shorter than the HCH making it closer in ratio. Forth, the Fit is the shortest with HCH a little shorter than the Insight. 5th the Fit is a little shorter than the HCH and Insight which are the same.

I hope that makes it a little clearer.
 

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Discussion Starter #17
Some rough speed/rpm readings I was observing.
1st gear
25mph @ 5500rpm

2nd gear
45mph @ 5500rpm

5th gear
65mph @ 3100rpm
43mph @ 2100rpm

I forget what my speed to rpms were for 3rd and 4th. I will add those in later. I am also going to hook up my friend's Honda scanner to see if the speed readout is happy or not. But you should be able to search the net for whatever the Honda Fit (GD3) is doing as the wheel diameter between the Insight and the Fit are the same.
 

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Wow - thanks for this info! I am almost hoping for a reason to change out my tranny! (Well, maybe not yet :))
 

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Excellent Job

Impressive, thanks for sharing.
Nice to see some others blazing a trail in different areas.
 

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Does anyone have any ideas on why the lower gears in the Insight are set up the way they are? Would we be shooting ourselves in the foot from an MPG perspective to go for a setup like that described? I don't have enough experience driving mine to know what the amount of acceleration and shift points get the best mileage when you are coming up to speed from a stop. Wind it up to a high RPM and get to speed as fast as possible, then coast/lean burn? Stomp on it at a lower RPM and take a bit more time? Or get there with a light foot? How would this gearing affect that?
 
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