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Old 05-24-2018, 05:15 AM   #1 (permalink)
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Default My transmission swap

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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Old 05-24-2018, 06:22 AM   #2 (permalink)
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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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Old 05-24-2018, 06:45 AM   #3 (permalink)
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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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Old 05-24-2018, 07:54 AM   #4 (permalink)
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Originally Posted by Mattl92 View Post
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?
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Old 05-24-2018, 01:26 PM   #5 (permalink)
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Quote:
Originally Posted by Puggie View Post
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.

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Quote:
Originally Posted by Puggie View Post
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.


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Originally Posted by Mattl92 View Post
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.

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More important to me, my partner has an 07 Fit and I can swap Insight gears into it?
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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Old 05-24-2018, 01:35 PM   #6 (permalink)
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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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Old 05-24-2018, 01:41 PM   #7 (permalink)
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Ah I see. I thought you wanted to swap all the gears over into the Fit.
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Old 05-24-2018, 01:51 PM   #8 (permalink)
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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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Old 05-24-2018, 01:53 PM   #9 (permalink)
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Very true.
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Old 10-26-2018, 05:30 AM   #10 (permalink)
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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



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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Last edited by Sigma Projects; 10-26-2018 at 12:22 PM.
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