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Lowering External Spring Triumph Forks

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48K views 75 replies 21 participants last post by  bali-rod  
#1 ·
I've read through scraper's excellent tech posting on Lowering British forks. Judging from the assembly diagrams in my manual, I'm guessing this technique does not work on the '64-'70 external spring forks. Am I right? I'd rather not cut my forks if I don't have to.

Thanks.
 
#2 ·
conversion to internal springs is pretty easy. i have a 70 that has been done, but i was not in the shop that day. i have a 69 now that i am about to convert and then cut down...i may take apart my other set to peak at how it is done if i get stuck..

i will post picks on the board or the tech section......will be over the next couple of weeks after the DiCE party.
 
#5 ·
so, i think i have this external spring lowering thing sorted.

here is the stock set up on my '69 front end

Image


the bottom brass piece does not move, the black plastic one does and the top brass does, it seats in the oil seal....

i think i can have a new top brass machined only two inches longer therefore allowing the fork tube to ride two inches lower, then cut the springs about an inch and a half as per Scrapers instructions (link above) for the internal spring conversion. everything should function as it did before, only cooler. maybe even just a spacer would work. if the new machined piece is do-able i may have several done so if there is any interest i will post up and let you guys know about the availability and sell them for cost plus shipping.

here is another shot of the pieces "exploded"

.....any thoughts on this little trick move?

Image
 
#6 · (Edited)
To lower my forks, I just added an extra black plastic sleeve on top of the one that's already there, then trimmed and re-formed the end of each spring. The extra stock plastic spacer will drop the forks 2 1/8". I only took 1 1/2" off the springs to make them a little stiffer so they don't bottom out as easily. You can also swap out the black plastic sleeves for the long aluminum pre-unit fork sleeves, but they're pretty hard to find. Or machine something up- your choice. I think you get the idea.
 
#9 ·
I just put my forks together a few days ago, so no pics, sorry. Your 21" will only put your bike 1" higher than your stock 19" (radius= distance from axle). As far as the springs, don't measure down the length of the spring, then cut it, because when you finish the end, it will be even shorter. I figured out how much to cut, then squeezed the bottom two coils together in a vice to make a flat bottom, then quickly torched the opposite side of those coils to release the tension so they'll stay that way. Kinda hard to explain, but it's the same as dropping a car ghetto-style.
 
#13 ·
dropped off my stock bronze sleeve (the one on top with the shoulder) at the machine shop today. evidentally the metal stock is way expensive right now. regardless, they are going to dial it in, and make a prototype for me that is 2" longer. i should have them in hand sometime in the next week or two.

if anyone else is hip to dip PM me and i will let you know the final cost. i am sure the more i order the cheaper they get.

as far as the conversion to internal springs....

i took apart my '70 front end that has been converted, and although i am not done inspecting the set-up (waiting on that pesky special tool to remove fork bottoms, i bent mine) it looks to be super simple, just like i was told by the guy who did mine. i dont even have to cut springs because there is a spacer set on top of the springs that is about six inches long, all i am going to do is cut that down a bit......after i get it all apart i will take some pics and post all the details as i convert my second front end over.
 
#15 ·
If you can mock it up with pvc instead of springs, you can figure out the compressed ride height you will need. Just take a measurement of your current springs on the bike and then cut pvc 1" shorter, 2" shorter etc. Then keep swapping the sleeves in until you have the height you want. I cut the springs by measuring the point at which 2" shorter lands, and cut the spring above that. I heated, bent and reshaped it to sit flat on the spring stop like the originals. When I tear my bike down for paint and such, I am just going to send them out to frank's engineering and have them cut. Otherwise you risk bottoming out and a shitty ride.

My spring cutting method did not accomodate for the compressed height of the cut springs, so if your spacers are -2", you may actually want to measure at -1.5" and cut the coil above that.
 
#19 ·
If you add spacers inside the fork bottom, you increase your spring pre-load. Essentially it brings the tubes closer to the bottom of the fork slider which in turn increases the chances of bottoming out and also decreases the travel = worse ride. If you want to do it right, at least get the tubes cut down to lessen the chances of bottoming out. I'd still cut the springs because I want my forks to function and compressing your springs an additional 2" w/o cutting them is going to make an already stiff ride (hardtail?) even stiffer.
 
#20 ·
i dropped mine 2" .... cant feel a differnce in ride or handling. I would not go cutting tubes and spending a ton of time or money when adding the spacer is practically free and takes an hour or two. And i have not bottomed out. Did once before i lowered it, wasnt that scary.

my .02
 
#22 ·
I got another question. I have my dad making me some 3" spacers on his lathe out of aluminum. Should I emulate the plastic sleeves (skinny side, thick side) or is one inner diameter fine, as long as it slides on the forks. I was also thinking of drilling some holes in the side to help with oil circulation into the spacers.
 
#23 ·
i'm a little corn-fused. i read scraper's post on dropping 1970-on unit forks and then sat and gazed at my forks and wondered how the hell can i cut off a couple inches without actually cutting and re-threading the stanchions?

then i read this thread, and i'm even more cornfused. because as far as i can tell, the limiting factor for '63-70 forks is stanchion length. it seats in that cone at the bottom of the shuttle valve and goes all the way up to the fork nuts. so i'm still trying to see how the forks are becoming shorter without actually cutting and rethreading them?

Image
 
#25 ·
Hooker said:
i'm a little corn-fused. as far as i can tell, the limiting factor for '63-70 forks is stanchion length. it seats in that cone at the bottom of the shuttle valve and goes all the way up to the fork nuts. so i'm still trying to see how the forks are becoming shorter without actually cutting and rethreading them?

Image
Click to expand...
Hooker, you've got the C model (offroad type) dampers in your forks. They are great for reducing top out slam, as they dampen your rebound waaaaay better than the standard road forks do. I've got mine apart, setting up for a spacer drop. One set is the type you have, the other is a standard road set. I haven't decided which set I'll be running yet.

I've got a set of the Aluminum (3 1/4 inch) pre-unit style spacers, as well as the plastic (2 1/4 inch) ones. I'm thinking of simply combining the two to get 3 inches under which will get my machine to sit level with the 21 front hoop. I'll get you photos later tonight.
 
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