Fork Baffle & Pounding

Information on forks/springers/shocks
Post Reply
VintageTwin
Panhead Register Member
Posts: 753
Joined: Mon Aug 16, 2010 7:18 pm
Bikes: '46 Knuck. '57 Panhead, '59 Panhead
Location: Repop Hell

Fork Baffle & Pounding

#1

Post by VintageTwin » Thu Dec 07, 2006 4:18 am

In Search of The Source of Rebound Slamming
A safe way to remove the fork tube plug is to remove the bracket (hex) bolt, and loosen the bottom-tree pinch bolt. Slide the fork tube down far enough to get a wrench on the plug flats, then tighten the pinch bolt, and loosen the fork tube plug.
damper11rg6.jpg
Then loosen the pinch bolt and raise the fork tube until the top of the plug is about a 1/2" away from the bottom edge of the top tree. Tighten the pinch bolt again. Then (wearing safety glasses) turn the fork tube plug out with a thin jawed wrench. The tube plug will snap upwards and into the top tree. Don't get your finders in the way of the tube plug. You will lose skin! (You can see between the spring coils - no baffle assembly.)
damper10bb2.jpg
Then, I checked the ride of a pair of OEM forks that have baffles, none of the OEM shims, none of the OEM spacers, 7 oz. of fork oil:
I rolled a rigid frame w/ rebuilt OEM forks down the street and compressed the forks pretty good coming up the driveway. They don't pound with the normal compression they'd normally get while riding or when you pull on the front brake lever to stop.

I think because my VT forks don't have the baffle stacks, that it could be why the VT forks pound more than the OEM set.

Look at the baffle assembly and you'll see how the bottom baffle disc has a 1/2 radius slot cut out for it. The other discs have the same cut out, but the cut outs are assembled at 180 degrees to each other.
baffle02qp3.jpg
The bottom baffle is backed up by a spring to rebound when the (solid) bottom disc gets hit by the slug of fluid (the top of the damper rod is solid) on compression (and water and fluid do not compress... but they are fluid).

So, the fluid is looking for a place to escape and the labyrinth of off-set baffle discs lets the fluid meander through the discs.... and the spring on the rod will move backwards as the fluid pressure increases and "dampens" the hit of the tube when it travel-stops. The shock is when the damper assembly shock-waves against the (0.004") free play at the slider tube snap ring (46172-48). [Assuming your slider busings are not worn, which cause other problems.]
This information is found on page 2F-10 of the '59-69 Service Manual, to wit:
Check clearance between snap ring and lower bushing. If clearance exceeds .004 in.,remove snap ring, gasket and lower bushing and insert additional shims to bring to a maximum of .004 in. clearance.
So, the shims were used to adjust free play between the snap ring and lower bushing. The spacer first showed up in the 1949-57 Spare Parts Catalog as (46045-49) and was used from '50-53 and was then removed from future service. Then the spacer showed up again, albeit briefly, as (12A) for '65-66, in the 1959-69 Service Manual on pg. 2F-3, but with no part number given and it never made it into the 1958-68 Parts Catalog.
The engineers at Tedd Cycle, Inc. improved, and made affordable (by eliminating the drain plug which would have required more hand work to produce) the Glide forks. Those rascals didn't include the (tube plug) baffle assembly, so what's new?, but there it is and the forks will function as well as OEM, if in fact the slamming problem is eliminated by baffles.
You do not have the required permissions to view the files attached to this post.
Last edited by Anonymous on Fri Dec 08, 2006 2:09 am, edited 1 time in total.



VintageTwin
Panhead Register Member
Posts: 753
Joined: Mon Aug 16, 2010 7:18 pm
Bikes: '46 Knuck. '57 Panhead, '59 Panhead
Location: Repop Hell

#2

Post by VintageTwin » Fri Dec 08, 2006 2:03 am

I installed baffles in the V-Twin forks. Without the baffles, there's an open 1/4 threaded hole, open directly to the fork tube, so if you don't have the baffle stem installed, fork oil will geyser up unimpeded, to the little breather valves that are within the top big hex bolts. So, you have to have the baffle assemblies installed in the tub plugs.
As far as slamming, once I installed the baffles, and rode tested it, I feel it slams less. If I hit a bump or apply the front brake lever hard, going downhill, I can't make the forks pound. But, it's a bare frame at present and it will handle differently fully dressed, and the forks won't rebound as much then as they can now.
I'm satisfied the baffle kits helped.
A 4x4, a 2x4 and a 1x2 drywall screwed together have a developed height of 5-3/4", which is a perfect height for working with fork change outs. Chock behind the rear wheel.
frk01nn9.jpg
The hunter tang of the top baffle disc registers into a hole in the plug.
frk03lg6.jpg
Hold the tube at all times or it can slip down into the slider and you'll get 7 oz. of oil coming out of the top. Don't try and support the bottom of the slider, you won't stop the tube from falling in. :lol:
The pinch bolt controls everything. You're tightening and loosening it a lot during the process.
frk05bp9.jpg
You do not have the required permissions to view the files attached to this post.

fourthgear
Posts: 1391
Joined: Mon Apr 11, 2005 1:12 pm
Location: north florida
Been thanked: 4 times

#3

Post by fourthgear » Wed Dec 13, 2006 4:46 pm

vintagetwin
I rebuilt my whole glide front end including new leg bushings and tubes and adding the proper amount of fluid (7 oz. for dry ) and I still got that hammering only on full extention, like when the bottom drop out going over a pot hole or some thing like it . I have the OEM baffles in there , after adding another 1.5 oz.( makes it 8.5 oz. total so far ) fluid , it seems much better and I am going to add 1/2 oz. more and stop there. I'm using Bellray syn. fork oil.

VintageTwin
Panhead Register Member
Posts: 753
Joined: Mon Aug 16, 2010 7:18 pm
Bikes: '46 Knuck. '57 Panhead, '59 Panhead
Location: Repop Hell

#4

Post by VintageTwin » Wed Dec 13, 2006 5:08 pm

I still got that hammering only on full extention
I have the OEM baffles in there , after adding another 1.5 oz.( makes it 8.5 oz. total so far ) fluid , it seems much better and I am going to add 1/2 oz. more and stop there.
Statements worth pondering.
JohnHD thinks the problem may be related to the damper assembly itself...being a loose fit within the fork tube. The pounding only at full extension may be a clue. He said overfilling his tubes with fork oil did help, but some fluid was forced out of the various seals.
I asked JW at Tedd for some insight. No reply. No reply means he doesn't know either, so we're on our own with this problem.

pomps_pans
Posts: 11
Joined: Mon Mar 25, 2013 3:54 am
Bikes: 1958 FL
1963 FLH
1975 FXE
1947 FL
Has thanked: 3 times

Re: Fork Baffle & Pounding

#5

Post by pomps_pans » Tue Mar 26, 2013 4:17 am

Hey guys, new here. I am trying to rebuild the front end of my '58, as it has been riding poorly. The bushings in the lower sliders have been replaced and fit well. I've gone through the damper valve assembly and all seems very well there. The problem I'm having is that the previous owner loved using silicone on everything. For the baffle assembly that screws into the top tube plug, he siliconed all of the baffles together. From the posts, I've realized that the fork tube plugs I have are not correct. They have no hole for the tang of the top baffle and they also have no hole to vent to the cap. I do have vented caps, but I have no breather valves (45757-49). The service manual and parts manuals don't show very good photos of the assembly, but it says that the breather valve is in the upper bracket bolt. My upper bracket bolts are made of solid hex stock with a small hole drilled in the center of the threaded portion and a hole from one of the flats to the center for venting. I can't see anywhere for a breather valve to reside, so I'm not sure what kind of upper bracket bolts that I have. I feel that I can modify my fork tube plugs to work with the baffle assembly, but I'm not sure what to do about the upper bracket bolt. Does anyone have a good photo of these? Are they available anymore? I will call a few HD dealerships tomorrow to see if there is a chance they might have one. Are there any available aftermarket??? Thanks for any help, and my '58 will thank you, also!



Also, the other thing I noticed is that there are two upper bracket bolt part numbers: 45754-49 (vented) and 45754-60. What was changed in '60?

Post Reply

Return to “Forks/Shocks”