fork difference info through the years & tapered head bearing recommendations needed!

[Ilovemountains]

fork difference info through the years & tapered head bearing recommendations

I bought a clean pair of 1981 forks to tear down for their uppers as mine are pitted. Does anyone know if my 1977D springs are any different or if there is anything that needs changed inside of the dampers themselves or am I good to swap the 1981 uppers over to my 1977 lowers as Im going to be running dual disks up front? Just curious if the internals are the same!

Also Id like go with new tapered bearings in the head rather than the old rollers since everything is torn down and clean. Ive heard that some have had issues with the tapered kits not allowing the top nut to be tightened, I didn’t have this issue 8 years ago when I built my first XS400D, I cant remember what brand or where I got that kit! Can anyone recommend a good setup to me that will fit 100%?

Thanks! Matt

 

[Greasey Fingers]

Hi mate, as for the forks they should be interchangeable no problems but maybe someone else might clarify that. The tapered bearings don't fit perfectly, but if you omit the lower dust seal in the new kit they fit fine that's how I made mine fit and they work great. Hope this helps!

 

[eric123]

Don't know about the upper tubes, but the lowers are different for drum versus disk brakes...

 

[bcware]

I put '81 forks on my '78, but mine has a drum up front. The forks look identical as long as you're swapping out for some that use the same brakes.

If I recall correctly you'll need to find a lower fork from a different model if you want to use double discs in the front.

If you search a little you'll find it. Drewpy has spilled the details about how to do the conversion more than once.

I converted to All Balls taper bearings. One of the included dust seals (I think the lower) would not work. All I had to do was use the original dust seal with the new bearings and all went together fine.

 

[Ilovemountains]

I'm re-using my 77D lowers, I ordered a set of Japanese SSY125 tapered bearings, the same setup I used years ago on my first XS400D...

I also tracked down a clean XS750 left caliper and bracket so all that I need for the dual disk setup now is another rotor "my wheel is already tapped on the left and the 77 fork lowers both have the mount tabs", a larger master cylinder and a 2nd hose with a double banjo bolt.

I was more concerned about the spring rate of the 81 forks over my 77s, as far as swapping them over from one to the other. My uppers are pitted, not bad but bad enough that I wanted to swap them out considering the amount of work I'm pouring into rebuilding this thing the way I want it!!!

 

[drewpy]

Hi, Have you tried cx500 upper stantions?

they fit well I believe and hopefully you can find a set cheap and in good condition.

I uses Pyramid parts only because they were the cheapest and omitted the lower seal for them to fit.

 

[Ilovemountains]

Argh, I was pressing the lower race into the frame and snapped it in half.... Does anyone have a supplier for bearing races or did I just slip and cost myself another $70? The upper race is in, the lower bearing is pressed onto the stem but I bet I have to buy another kit.... damn.

 

[Greasey Fingers]

Why $70, pyramid parts ones are cheaper than that. How did you snap the lower race?

(You need to drive it in progressively with short even taps, alternating the position where you are driving it in from so it goes in straight)

 

[bcware]

I didn't have much trouble driving mine in and I didn't even stick the races in the freezer or anything. I used the old races as a driver because they are the perfect size. I think I also used a flat piece of wood to drive it in squarely first. Once it was in the neck I think I switched to the old race to drive it in all the way.

I think you're out of luck in terms of finding a replacement; you'll have to get a new kit. Last I checked they were only like $35 dollars give or take on ebay.

How exactly were you pressing the race in? It seems like a pretty beefy piece of steel to break.

 

[Greasey Fingers]

I used the old races as a driver because they are the perfect size. I think I also used a flat piece of wood to drive it in squarely first. .

Exactly what I used, lol! Worked a treat, I guess it wouldn't hurt to throw the new race in the freezer overnight if you got a tight neck I think I did freeze mine I cant remember.

 

[Ilovemountains]

I was using an old tree as a clamp to pull the races into the frame, the last setup I installed like this I tapped them in with the old race, I honestly was being lazy and didnt want to flip the frame over in my stand Lesson learned, the set thats on its way is from Pyramid, I bought them ala-carte from their ebay store for $12 each!

As far as the forks go, the 1981 fork tubes are 1 & 1/8" longer than the 1977D series inners. I wonder if the 1981 springs are the same, or if they would be better fit with more pre-load in a pair of 77 uppers?? Good question!

my stock 77 internals are on the left my "new" 81's are on the right...


http://xs400.com/forum/album.php?albumid=489&pictureid=3528

The actual lowers are the same length, the 1977 lowers both have caliper bracket mounts where the 1981 lowers that came with my new forks are drum only...

 

[Ilovemountains]

Finally got some free time to tear the inners apart. The 81 springs are longer and the valve / plunger does not have the tip on the spring end that helps keep the spring centered. I am going to use the longer springs from the 1981 forks and the plungers from my 1977. Take a look and let me know what you think. I bet the longer springs would be a good upgrade for stock 77 forks with a little added pre-load!

 

[Ollie]

Hi, I'm trying to source some loose head bearings but can't find what size they are. I don't suppose you would be able to measure them for me would you?

Thanks, Ollie.

 

[Ilovemountains]

Ollie, I can mail you my stock head bearings if you want them, you pay shipping! If not I can measure them for you, shoot me a PM and let me know, Matt

 

[Ilovemountains]

Stock 1977 400D fork bearing size:

With digital calipers the balls are 6.335mm or .249”

 

[salisride]

i used spare bearing i had from all balls i was gonna use for a fork swap never happened, but anyway i inded up using one set in my 650 and the other in the 400. you dont need rollers in the upper just the bottom, but any way the bearing size was 36mm x 48mm x 12mm thick thats what you need for the bottom.

to measure what thickness you need for the bearing you measure the thicknes of the stock balls and races sandwiched together