RD350LC 4L0 Brake Caliper Info
Feb 20, 2023 23:38:02 GMT 1
midlifecrisisrd, dougw, and 2 more like this
Post by ianlcsince89 on Feb 20, 2023 23:38:02 GMT 1
Info Article – Brake Calipers Yamaha RD350LC 4L0 1980-82
History
When Yamaha first introduced the RD350LC 4L0 model in the UK in June 1980, it had a pair of front brake calipers with narrow bodies and narrow mounts. They were adequate for the bike but prone to brake drag. Yamaha improved the design later in 1980 with a wider mount and wider body, a longer slide pin, longer pad pin and different brake pads. A few parts are interchangeable between the early and later type. The later calipers performed well but did need regular maintenance.
The RD250LC 4L1 used the same caliper, but right hand only with one brake disc.
Caliper Operation
When hydraulic pressure is generated behind the piston, the piston and outer pad are forced against the brake disc. Simultaneously the caliper body moves outward by sliding on the slide pin, forcing the inner fixed pad against the inside face of the disc with equal force.
The brake pads have ‘feet’ which bear on the two shim retainer plates and the anti-rattle sheet spring. Without these parts fitted, the pad feet will damage the soft alloy of the body and mount, creating wear issues.
Rubber boots are fitted to the mount, through which the slide pin fits. These are important parts because they ‘grip’ the slide pin and keep dirt out of the slide pin/mount interface.
The larger shim retainer is also very important because it provides a flat steel surface for the body to slide on smoothly, relative to the mount.
When hydraulic pressure drops, the piston fluid seal retracts the piston and the body moves slightly in the opposite direction, thus moving both pads away from the disc.
40+ Years Later - Inspecting a Used 4L0 Caliper
The main problem affecting these calipers is neglect. They need a regular strip, clean and rebuild to work correctly. With neglect the piston often seizes in the bore. This can be due to corrosion, the piston seals going hard or both. The slide pin can seize in the mount, due to corrosion or the rubber boots perishing or sticking to the slide pin. Bleed nipples can be seized also and are easily sheared at attempted removal.
Long term neglect results in general corrosion of the body and mount. If the corrosion is not in critical areas these parts may be useable. If the groove in the body cylinder bore for the fluid seal is badly corroded, then that body is probably scrap. Some owners responded to a seized caliper with hammer blows to the soft alloy, with predictable results.
Check all the female threads in the body and the mount are in good condition.
Excessive play between the mount and body can be adjusted to some degree by fitting a shim into the shim retainer.
Sourcing Spare Parts
Some of the parts for this caliper are easily found from aftermarket suppliers. Unfortunately some of the parts were not listed or identified by Yamaha, so are very difficult to source now. An example is the Anti-Rattle Sheet Brake Pad Spring (fits above both pads). This was originally supplied as part of a genuine Yamaha brake pad kit. Later pad kits contained a pair of pads only but no Sheet Spring. The shim retainer is not listed as a spare part either, so is almost impossible to source. The table below provides a list of all parts known to make up a complete 4L0 caliper. 22 parts in total.
It is important to note that some of the caliper parts are handed, that is specific to a left or right hand caliper. That makes sourcing the correct rare parts even more difficult.
The shim which fits between the piston and the outer pad is something of a mystery in terms of it’s function. It is probably not an essential part, but it may help to reduce brake pad drag.
Parts List Front Brake Caliper RD350LC 4L0 – Right Hand. Later Wide Type from 1981-82.
No. Part Description Item No. on Yamaha Drg D7 Qty Req Comments
1 Caliper Main Body/Piston Housing RH N/A Often damaged by corrosion and hammer blows
2 Mounting Bracket RH N/A Often damaged by corrosion and hammer blows
3 Large Steel sheet between body/bracket (shim retainer, RH) 9 Very hard to find. Stainless steel 0.5mm
4 Small Steel sheet between body/bracket on side leg N/A Very hard to find. Stainless steel 0.5mm
5 Anti-Rattle Sheet Brake Pad Spring (fits above both pads) RH N/A Very hard to find. Spring Steel plate. Search 4W1-W0045 or 4L3-W0045.
6 Mounting Bolt M10 x 1.25mm, 30mm long, flanged head. 22 2 Early type was 35mm long and used plain and spring washers.
7 Piston Dust Seal 6 Easy to find.
8 Piston Fluid Seal 6 Easy to find.
9 Piston diameter 38mm 36.5mm long 5 Easy to find.
10 Bleed Valve M8 x 1.25 thread. 90 degree incl angle male seat. 10 Easy to find.
11 Dust Cap for bleed Valve 10 Easy to find.
12 Rubber Boot for Slide Pin N/A 2 Easy to find.
13 Slide Pin 11 Easy to find.
14 Split Pin for Slide Pin 8 Easy to find, standard split pin.
15 Pad Retaining Pin N/A Easy to find.
16 Locking Pin for Pad Pin N/A Hard to find original type.
17 Brake Pad e.g. EBC FA70 7 2 Easy to find EBC or similar.
18 Shim which fits between piston and outer pad RH. N/A Very hard to find, but not a critical part.
19 Shim which fits inside shim retainer 12 Hard to find but not always required.
N/A = Not listed on Yamaha Drg. Note original brake pad kit included items 5, 15, 16 and 18 above with pads. Yamaha deleted this kit and superseded it with a pair of brake pads only. So items 5, 16 and 18 are without a known Yamaha part number and very hard to find anywhere.
History
When Yamaha first introduced the RD350LC 4L0 model in the UK in June 1980, it had a pair of front brake calipers with narrow bodies and narrow mounts. They were adequate for the bike but prone to brake drag. Yamaha improved the design later in 1980 with a wider mount and wider body, a longer slide pin, longer pad pin and different brake pads. A few parts are interchangeable between the early and later type. The later calipers performed well but did need regular maintenance.
The RD250LC 4L1 used the same caliper, but right hand only with one brake disc.
Caliper Operation
When hydraulic pressure is generated behind the piston, the piston and outer pad are forced against the brake disc. Simultaneously the caliper body moves outward by sliding on the slide pin, forcing the inner fixed pad against the inside face of the disc with equal force.
The brake pads have ‘feet’ which bear on the two shim retainer plates and the anti-rattle sheet spring. Without these parts fitted, the pad feet will damage the soft alloy of the body and mount, creating wear issues.
Rubber boots are fitted to the mount, through which the slide pin fits. These are important parts because they ‘grip’ the slide pin and keep dirt out of the slide pin/mount interface.
The larger shim retainer is also very important because it provides a flat steel surface for the body to slide on smoothly, relative to the mount.
When hydraulic pressure drops, the piston fluid seal retracts the piston and the body moves slightly in the opposite direction, thus moving both pads away from the disc.
40+ Years Later - Inspecting a Used 4L0 Caliper
The main problem affecting these calipers is neglect. They need a regular strip, clean and rebuild to work correctly. With neglect the piston often seizes in the bore. This can be due to corrosion, the piston seals going hard or both. The slide pin can seize in the mount, due to corrosion or the rubber boots perishing or sticking to the slide pin. Bleed nipples can be seized also and are easily sheared at attempted removal.
Long term neglect results in general corrosion of the body and mount. If the corrosion is not in critical areas these parts may be useable. If the groove in the body cylinder bore for the fluid seal is badly corroded, then that body is probably scrap. Some owners responded to a seized caliper with hammer blows to the soft alloy, with predictable results.
Check all the female threads in the body and the mount are in good condition.
Excessive play between the mount and body can be adjusted to some degree by fitting a shim into the shim retainer.
Sourcing Spare Parts
Some of the parts for this caliper are easily found from aftermarket suppliers. Unfortunately some of the parts were not listed or identified by Yamaha, so are very difficult to source now. An example is the Anti-Rattle Sheet Brake Pad Spring (fits above both pads). This was originally supplied as part of a genuine Yamaha brake pad kit. Later pad kits contained a pair of pads only but no Sheet Spring. The shim retainer is not listed as a spare part either, so is almost impossible to source. The table below provides a list of all parts known to make up a complete 4L0 caliper. 22 parts in total.
It is important to note that some of the caliper parts are handed, that is specific to a left or right hand caliper. That makes sourcing the correct rare parts even more difficult.
The shim which fits between the piston and the outer pad is something of a mystery in terms of it’s function. It is probably not an essential part, but it may help to reduce brake pad drag.
Parts List Front Brake Caliper RD350LC 4L0 – Right Hand. Later Wide Type from 1981-82.
No. Part Description Item No. on Yamaha Drg D7 Qty Req Comments
1 Caliper Main Body/Piston Housing RH N/A Often damaged by corrosion and hammer blows
2 Mounting Bracket RH N/A Often damaged by corrosion and hammer blows
3 Large Steel sheet between body/bracket (shim retainer, RH) 9 Very hard to find. Stainless steel 0.5mm
4 Small Steel sheet between body/bracket on side leg N/A Very hard to find. Stainless steel 0.5mm
5 Anti-Rattle Sheet Brake Pad Spring (fits above both pads) RH N/A Very hard to find. Spring Steel plate. Search 4W1-W0045 or 4L3-W0045.
6 Mounting Bolt M10 x 1.25mm, 30mm long, flanged head. 22 2 Early type was 35mm long and used plain and spring washers.
7 Piston Dust Seal 6 Easy to find.
8 Piston Fluid Seal 6 Easy to find.
9 Piston diameter 38mm 36.5mm long 5 Easy to find.
10 Bleed Valve M8 x 1.25 thread. 90 degree incl angle male seat. 10 Easy to find.
11 Dust Cap for bleed Valve 10 Easy to find.
12 Rubber Boot for Slide Pin N/A 2 Easy to find.
13 Slide Pin 11 Easy to find.
14 Split Pin for Slide Pin 8 Easy to find, standard split pin.
15 Pad Retaining Pin N/A Easy to find.
16 Locking Pin for Pad Pin N/A Hard to find original type.
17 Brake Pad e.g. EBC FA70 7 2 Easy to find EBC or similar.
18 Shim which fits between piston and outer pad RH. N/A Very hard to find, but not a critical part.
19 Shim which fits inside shim retainer 12 Hard to find but not always required.
N/A = Not listed on Yamaha Drg. Note original brake pad kit included items 5, 15, 16 and 18 above with pads. Yamaha deleted this kit and superseded it with a pair of brake pads only. So items 5, 16 and 18 are without a known Yamaha part number and very hard to find anywhere.
