Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties swapping tranny parts

swapping tranny parts

Post Sat Feb 23, 2013 5:08 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
If I were to have an older, U, EL, F/FL knuck/pan/side valve four speed tranny case, could I swap in the gears from 1964 or up tranny, as long as I used the short mainshaft?

Or, in other words, switch the guts from a later tranny into the old case, but again, using/ substituting the shorter mainshaft. ??

If it's possible, what would be the latest year tranny that I could steal the guts from?


krazy ken.

Post Sun Feb 24, 2013 7:22 am

Posts: 641
Location: Wisconsin, USA
You can use the gears from any of the later transmissions up to 76 or 77 when they changed from loose rollers to the torrington style bearings in the countershaft cluster and on the main drive gear. You will have to use the speedo drive ring gear from your trans on any 61 and later gearsets.

Post Sun Feb 24, 2013 12:34 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Hey thanks. That's good news.

Been pricing trannies lately, and noticed that you can find an older case for not too much, (might even have one that's repairable, but it's under the snow somewhere out back!) and later complete trannies for not too much, but prices on older transmissions seem to have gone through the roof. So...I think/believe that way to go is to pick up a case, short mainshaft, and then a later tranny and swap it into the older style case to save a couple of bucks...and freshen things up at the same time.

Thanks again.

krazy ken

Post Tue Feb 26, 2013 11:08 pm

Posts: 2688
Location: Los Angeles, CA
I put all new Andrews gears, shafts, ETC in my tranny case and it only cost $1475.00 wholesale. :mrgreen:

Post Thu Feb 28, 2013 7:18 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Ha ha, well right now I'm trying to avoid that thousand dollar plus zone, trying to get the old girl on the road and stay within a budget. Maybe further down the line I'll upgrade. Stock tranny in my knuck always served me well, and I think the flathead will be putting a little less power through this one. But I can appreciate a $1500.00 tranny.

Post Thu Feb 28, 2013 11:33 pm

Posts: 2688
Location: Los Angeles, CA
If yer near LA drop by. I have lots of good used BT gears that you can pick through.

Post Fri Mar 01, 2013 8:38 am

Posts: 497
Location: Six miles East of Cheney, Wa.
Grew up in the Valley, but haven't been down there in 25 years. If you have enough gears and shafts to put a tranny together we should talk. Shipping might be cheaper than driving down there and back from Eastern Washington state! And actually, if you have enough/all the gears, I can always find a main and counter shaft. Let me know.

Post Sat Mar 02, 2013 4:09 pm

Posts: 1676
Location: Interlaken, NY USA

The nice thing about Andrews gears is it fixes the Low first gear. Adding the Close third is nice, and I like it, but it's a matter of personal preference. If you do go first and third, all you need from a stock gear set is countershaft second.
I've even used Vtwin's close gear sets with good results. They only offer the later close third, but by using the later countershaft with the close third countershaft cluster, it works fine.

Post Thu Mar 14, 2013 3:00 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Well the happy ending is that I located a complete early tranny here on the forum for a very decent price.

On the closer gear ratios, for someone that never tries to keep up with the OHV's, or race their buddies or anyone else, are they of any value?

Post Sat Mar 16, 2013 2:47 pm

Posts: 1676
Location: Interlaken, NY USA

Probably not, but it is nice to have the approximate same rev drop between 1-2 and 2-3. I just came back riding to Daytona and back, and I'll admit that the close 3rd was a slight disadvantage on that ride. I had lowered final drive numerically, with a 25t countershaft and belt primary. The bike was the 65 pan, 84" S&S wheels, Andrews B. In traffic, I'd find 3rd a little low and 4th a little high sometimes. The bike was also carrying quite a load. With the usual 24T I run, it wouldn't have been a problem.
BUT, I was riding with an '05 Ultra, and an '85 FXRT, and we all cruised the Interstate at 70-75 all day no sweat. The old pan didn't mind a bit, it just gets on the cam and really pulls between 70 and 80!
We did about 3500 miles and all I did was clean my points once along the way. (forgot to do so when I prepped the bike)

Post Mon Mar 18, 2013 3:49 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
So, just theorhetically speaking, how would you gear (motor and trans sprocket) a light weight, solo-seated, '37 UL with stock tranny, about 7:1 compression, that will mostly run around the local area, rural and small city, mostly country roads and highways, and not spend a lot of time on the freeway, or when it does, cruise around 65-70 mph. ? And, no desire to keep up with OHV's or engage in contests of accelleration.

Post Mon Mar 18, 2013 5:16 pm
don User avatar

Posts: 575
Location: Spokane WA USA
Harley-Davidson Big Twin Gear Ratios

Post Mon Mar 18, 2013 7:05 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Hey thanks for posting that...but I do have that info. I was kind of looking for a more "seat of the pants" recommendation. I have lots of seat of the pants time on a Knucklehead, and I think that thing would have pulled just about any gearing, but I think I was running 24 motor and 23 trans, but I forget. On that bike, that seemed to be perfect. It was a lightweight bike, as will be this UL.

My last ride on a flathead was my 45, and I've never ridden a UL/ULH/VL/etc. Those (24/23) are the same sprockets I've got for this UL, and just wondering what others have found to work with their riding styles.

Or maybe I should be asking, what RPM do the UL's like to run at...where are they happy, and where do they begin to "stretch out"??

On the other hand, I suppose I can go up or down on the motor sprocket when she's up and running, as they are not that expensive or hard to change. !! Just curious.

Thanks agan.

Post Wed Mar 20, 2013 6:49 am

Posts: 1676
Location: Interlaken, NY USA

O.K., seat of the pants reckoning gear setups:
24 front sprocket, 24 tranny sprocket, nice overall cruising ratios,
24 front, 25 rear, good for over the road cruising that 65-70 speeds you asked about
23 front 24 rear, o.k. overall, little better acceleration.
Belt primary, 25 tranny ratio is between the 23 pri and 24 pri gearing. Good all around gearing, happy 60-65 cruising.
ratios for primary:
1.6:1. 23 front sprocket
1.58:1 belt primary
1.56:1 24 front sprocket

Important to have a good balance job on your engine to enjoy the high speed cruising. Been using 60% with good results.
Calculated engine speeds at 60 MPH:
23/24= 2783
belt pri/24=2736
belt pri/25=2626
My suggestion and what I use: Carefully balanced engine, and belt/25 tranny sprocket. I can cruise the interstates at 65, and still have good around town performance. This with a 84 or 88 stroker, which are what my 2 road flatties presently are. The stock motor is ok with this as well.

Post Wed Mar 20, 2013 9:43 am

Posts: 497
Location: Six miles East of Cheney, Wa.
That's what I'm talking about, seat of the pants "impressions"...hmmmm

For comfortable cruising I'll give up some accelleration. I also have a 25 tooth motor sprocket, for a 25/23, might put that on first just to see what happens, but most likely I'll start out with the 24 tooth.

Well I hope the engine is well balanced, but I don't know who rebuilt it. Looks like just a standard rebuild, so hopefully it won't be way off. I doubt that anyone actually balanced it.

Post Wed Mar 20, 2013 7:41 pm

Posts: 1676
Location: Interlaken, NY USA

All the balancing buys you is an engine that's relatively smooth an a certain rpm span. The 60% usually puts that around 2500-3000 range. It'll probably be smooth somewhere, so hopefully you'll get lucky.
Luckily, the BTSV's have plenty of low end torque, so all of these ratios are workable.
Have Fun.

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