4 speed review

[RooDog]

https://ebay.us/m/UAvVbh

Here's a kit on ebay..

That too is a V-Twin item, and in stock for your local indie dealer to get for you....
https://www2.vtwinmfg.com/45-wl-transmi ... r-kit.html

[WLA_Flattie]

https://ebay.us/m/UAvVbh

Here's a kit on ebay..

That too is a V-Twin item, and in stock for your local indie dealer to get for you....
https://www2.vtwinmfg.com/45-wl-transmi ... r-kit.html

spot on

[Buster]

I've done two of these conversions on my own 45's and will be doing a third. The conversion is no more difficult then rebuilding a stock three speed, just follow manual, first goes where reverse would be, and no reverse idler gear. My kits where VT and they shift smoothly. You do have to ream the gear bushings to fit the main shaft or you can have a machine shop ream them. Like any trans rebuild there is shimming required, however shim kits are available. Just follow the manual. First gear is 8 percent lower than a stock three speed first gear and 4th gear is 1 to 1. I run a 33 tooth motor sprocket on my WL and a 27 tooth motor sprocket on my Servicar. Starting out in first gear and going up grades is no problem; however cruising speed is higher with lower rpm.

[Inge]

I really want to understand it. 3 speed and 4 speed have 1 to 1 top gear. Why is the crusing speed higher with lower rpm?

[RooDog]

I really want to understand it. 3 speed and 4 speed have 1 to 1 top gear. Why is the crusing speed higher with lower rpm?

Overall sprocket gearing ratios may be upped for the highway, while the lower first gear allows one to maintain take off ability, the hole shot if you will.
That is why the 3.24 1st gear in the Big Twin 5-speeds work so well in Shovelheads....

[kitabel]

I really want to understand it. 3 speed and 4 speed have 1 to 1 top gear. Why is the crusing speed higher with lower rpm?

33 tooth engine sprocket

[70 servi]

Buster, is your SC stock gearbox or is it a 4 speed forward now?

[kitabel]

W/r/t above post describing "27 tooth motor sprocket on my Servicar": smaller 37 tooth rear sprocket vs. 41 tooth on the solo.

[kitabel]

The 4-speed discussed here is certainly preferable to the OEM 3-speed, but (as above) have chosen ratios (I suppose) due to the availability or price of the components they selected.
Generally, engines with high and narrow power bands favor smaller progression", recovering more RPM at each shift. This severely limits the torque multiplication of a relatively low (numerical) 1st gear., typically no larger than 2.40:1.
In the reverse case, engines with good torque but pulling heavy loads tend to favor wider progression to allow a higher 1st gear ratio such as 3.20:1.

You will on occasion read a remark praising "exactly even split between the gears" (same RPM recovered after every shift). I've never seen one, nor is it a good idea.

[kitabel]

Consider swapping to a British box. Yes, it's work (instead of money), but the ratio choices are wide, hand clutch.
The BSA A10 (A7, Gold Star) choices begin with a 3.17:1 or 2.87:1 1st gears, and many choices for 2nd & 3rd.
IMHO the std. BT box ratios (3.00, 1.82, 1.23, 1.00) are ideal, but $$$, more work, heavier, etc.

[Buster]

My servicar transmission has been converted with the 4 speed kit. No reverse now. My 45 solo has also been converted. I believe it is best upgrade for the cost you can do to a 45 flathead. Easy conversion and really improves performance and rideability.

[kitabel]

How I think of it:
It's something you always use (as opposed to speed equipment), and smaller engines need it most.