Hydraglide top out

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nifty
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Hydraglide top out

#1

Post by nifty »

This post originated from Shovel section and a question by Roodog
Top out, my 2c
hydraglide damper tube.jpg
hydraglide damper tube.jpg (143.52 KiB) Viewed 297 times
hydraglide valve stack.jpg
hydraglide valve stack.jpg (154.37 KiB) Viewed 297 times
When Hydraglide forks rebound (extend):
The fork spring acts on the upper end of damper tube, pushing it down through the valve stack and extending the leg/slider, oil between head/flange of damper tube and top of valve stack increases in pressure, which pushes on the shuttle, which moves downwards approx ¼” (within the stack, shuttle compressing the lower shuttle spring) the same shuttle movement simultaneously all-but-closes-off the 5 oil pathways from below the stack (between each leg of shuttle), whereupon the oil can only take the restricted path via the small clearances of shuttle and even smaller clearances between outside of shuttle ring and inside of fork recess at12 slots and the oil flows upwards into the 14 slots of lower shuttle ring, then through the slots of upper shuttle ring and finally enters the newly created cavity below the stack (in fork leg/slider).
The annulus between OD of upper damper head/flange and ID of fork tube creates controlled oil leakage and limits damping pressure and flow, hence damping is dependent upon oil viscosity.

Hydraglide “topping-out” (aka “slamming” when fork fully extended)
Too much spring preload exacerbates Hydraglide top out, because it reduces static sag/droop, and thus reduces qty of oil between head of damper tube and top of valve stack. Hydraglide lacks rebound springs and thus relies upon sufficient oil between head of damper tube and top of valve stack to provide the oil controlled cushion in lieu of rebound spring.

Topping out is controlled by both oil flow through the shuttle and also the annulus between OD of upper damper flange and ID of fork tube. As the fork extends, the shuttle is closed and maximum damping is occurring, thus full extension is designed as an oil controlled event.
If spring pre-load correct, all clearances correct, all parts correctly made and installed, along with correct type and amount of oil, 49-77 Hydraglide will not have noisy top-out.

What goes wrong with Hydraglide fork?:
1. Owners neglect fork oil changes
2. Water enters via breathers and or seals causing internal rust damage (do not pressure wash)
3. Breather baffles rust & disintegrate, shrapnel circulates in oil jams damper valve & destroys fork
4. Shuttle springs break and jam shuttle = zero damping (spring breakage usually due to rust after water ingress via breathers or seals)
5. Wear/excessive clearance in slider bushes, results in wear/excessive clearance inside fork tube and wear at top end of damper valve. (leg cocks, rigidly attached head/flange of damper tube wears away the inside of fork tube)
6. Poorly made repo fork tubes with:
A. Excessive internal clearance to flange of damper tube and or poor machined finish. (little or no damping)
B. Nasty weld seam on inside of fork tube. (in use the fork spring rubs on seam, wears notch in spring which then breaks, spring wears seam away, shrapnel contaminates oil, destroys fork)
C. Oversize recess for valve stack (loose, oil bypasses around outside instead of through damper valve; little or no damping)
D. Mill scale on upper inside of tube (in use the fork spring rubs scale off, contaminates oil, destroys fork)
E. Out of spec OD tubes, usually “show chromed”, leg bushes must be enlarged to fit, but tube OD not being round or consistent is real problem, sometimes oversize OD tubes can be spun in a lathe and reduced with wet/dry.
Generally best to avoid crappy repo tubes (avoid all crappy parts)
7. Poorly made repo dampers (eccentric components, excessive clearances, springs without closed ends = little or no damping)
8. Rusty main fork springs and poorly made repo main springs with scale left on (rust & scale flakes off, contaminates oil & destroys fork (original fork springs and tubes were Parkerised)

What helps Hydraglide live longer & work better?:
Magnetic drain plugs keep ferrous shrapnel out of circulation, think of them as oil filter.
Change fork oil regularly (removes contaminants, prevents sludging) 192.2ml wet change & 207ml dry fill (if breathers deleted more oil can be used)
Ditch the stock felt wiper rings above seals, fit an extra real seal instead (felts become saturated with dust & water) lube the seals with light grease.
With stock cowbells also fit small boots to legs, grease inside boots for lubrication (prevents water & dirt sitting on top of seal)
Ditch the stock “breather”/ baffle set-up, Seal up vent drillings in top bolts.
drill out upper plugs 5/16” ID right through (makes refilling fork oil a lot simpler, use a squirt bottle)
Head of damper tube OD can be reduced, built up with bronze, re-machined to minimal clearance inside good ID of fork tube

Nifty
Last edited by nifty on Fri Sep 23, 2022 9:42 pm, edited 4 times in total.
RooDog
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Re: Hydraglide top out

#2

Post by RooDog »

I made up, and used, these extended damper tubes with rebound springs. Subsequently sold off on eBay....
DSC02523.JPG
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nifty
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Re: Hydraglide top out

#3

Post by nifty »

And they still topped out?

Nifty
RooDog
Senior Member
Posts: 5327
Joined: Tue Oct 31, 2017 1:00 pm
Bikes: 1950 Panhead, Resto-Mod
1968 90", 5 Speed Shovelhead,
1984 Home Built Custom Evo 100" Bagger
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Re: Hydraglide top out

#4

Post by RooDog »

I don;t remember, that was in the 1980s...
No internet back then to glean information from. Just doin' the best I could.
Check out my "Before the Wreck" pic....
....RooDog....
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