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low brake lever first pull

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hi all from an Ohio hick (ie. Kerry: "can I get me uh huntin' license here?"),

Just replaced pads two weeks ago, then rebuilt calipers and master cylinder last night on 1981 GS750E for reasons of preventative maintenance. (Brakes worked good before I started, and after I replaced pads. Since there was evidence of seeping under the caliper boots, I decided to rebuild calipers and master cylinder after a few weeks. Meanwhile, brakes worked perfectly.)

The job seemed very straight forward as I have rebuilt probably 100 calipers over the years as a professional mechanic. Cleaned and verified bore dia, then replaced pistons, seals, boots with genuine Suzuki parts. Cleaned and lubed caliper pins and bore, then reassembled. Bled brakes at bleeders and banjo bolts -- no more air. After doing this, the brake lever would go fairly low the first pull, then normal if pulled immediately again. Action nice and firm, not spongy. I then rebuilt the master cylinder (nothing wrong inside though). After prebleeding, installing, and bleeding again, the lever is still low first pull, then normal if pulling immediately again. The only unusual thing that I feel might be related is that the lower caliper "axle No.2" (SGP # 59306-45200) has an undercut, with a rubber tubular insert that has hardened with age so as not to provide fricton (especially after lubing with grease). It is my feeling that the rubber inserts provide friction to hold the caliper/pad in position so as to provide slight contact with rotor, therefore preventing excessive movement which would create low brake lever until tension taken up (by "pumping"). I ordered new pins, but alas, they do not have rubber insert (even though pictured). Has anyone else ran into this? (Any suggestions as to source of rubber tubing of correct ID/OD/durometer?) There is no air in the lines -- have bled them very well. Lever is not soft, just low on the first pull. Brake pad backing plate flat and in place (along with spring clip and pad rail shim). Rotors true with no runout. Slight clicking noise from lower caliper axles (the loose greased ones) when actuating lever indicating slight movement.

This reminds me of a car that has the rear drum brakes way out of adjustment (but no air in line): initial brake action low until pedal "pumped up". Adjusting brakes always takes care of low pedal in this circumstance.

Thanks for any help!

Brian
 
brakes

brakes

Disc brakes are self compensating as Iam sure you know already, if you are sure there is no air in the system including the hose Tee, then it could only be that a caliper is not retracting right, ( over retracting -ie whl. bearings) if you hold the leaver down with moderate pressure will it start to leak down as if it is by-passing? are you sure that you don't have a leak around any of the seal rings that are letting air in when you let up on the lever pressure, or a bad bleeder valve also when you apply the brake and release it do the calipers have a gap between the pads and rotors, Iam thinking you have an enternal leak some place or loose wheel bearings that is allowing over retractsion
 
Hi Gee-s-is,

Thanks for reply. Lever can be held firmly with no movement over time. All fittings dry. Wheel bearings tight (brake hydraulic action was perfect right before job). I am inclined to believe excess movement may be the culprit, but cannot observe pads pulling back from rotors. Movement is not visable though (only slightly audible, with slight click from greasy pin cocking slightly in bore due to loose rubber). Strange.
 
follow up: I put c-clamps on calipers holding pistons in, and obtained firm high lever. This shows problem is excessive mechanical movement, not hydraulic problem. Pads and backing plates clean and flat. Wheel bearings nice and tight, and rotor true. The loose rubber inserts still seem suspect. BikeBandit is reordering axle2 as rubber insert should be part of this assembly.
 
Problem fixed:

Still suspected master cylinder (even though seals replaced), so ordered complete rebuild kit with piston, cups, etc. Hummm -- new kit doesn't seem right -- maybe because previous owner put a GS1100 master cylinder on bike... Got a used cylinder off forum, rebuilt it, now brake lever high and firm!!!

BTW, caliper axle shaft rubber bushings found by Bike Bandit -- P/N 509991-001 (fits 1983 GS1100GKD and 1981 GS750EX). Installed them - still fit loose (normal). Moral of the story -- if it acts like a bad master cylinder it probably is a bad master cylinder...

Brian
 
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