Brakes locking in reverse

[bodgerbedge]

I know - RD350LC's (4LO) are not designed to go backwards but... my front calipers / brake pads that have recently been rebuilt work perfectly with forward motion but when I pull the bike backwards, they seem to drag and try to lock-up the wheel. Pulling the brake lever on locks them OK and they retract very slightly to release the pads from the disc when the brake lever is let-go-of. They are reletively new pads and they seem to sit freely in the caliper.
The piston's are in 'square' so they apply even pressure all around. The master cylinder has been serviced and all ports are free so that they retract the pistons in the caliper albeit very slightly (not sure how much this should be?) but surely if this wasn't working correctly then I would have the same issue in forward motion? Brake pipes are clear and its new fluid.
I have recently realised that there are no brake shims / anti rattle plates but firstly I can seem to find who sells them and secondly, I cannot see how the lack of these will cause this problem.
This has been a problem since I've owned the bike hence the brake system rebuild. It's not a huge problem as I don't intend to go backwards very often but it does make it difficult to manoeuvre around! Am I missing something (other than shims)?

[shaunthe2nd]

The shims do help but I also found that the problem was with new pads.
New pads sit deeper into the caliper. If they are not gen Yam pads, they can twist slightly and catch the side of the caliper and lock slightly, causing it to rub against the disc.
I only had it in reverse on one bike, but in both directions on another.
To solve it I filed a small amount off the metal top corners of the pads and that no longer caught.

[elsiefan]

Mar 18, 2021 12:20:59 GMT 1 bodgerbedge said:

I know - RD350LC's (4LO) are not designed to go backwards but... my front calipers / brake pads that have recently been rebuilt work perfectly with forward motion but when I pull the bike backwards, they seem to drag and try to lock-up the wheel. Pulling the brake lever on locks them OK and they retract very slightly to release the pads from the disc when the brake lever is let-go-of. They are reletively new pads and they seem to sit freely in the caliper.
The piston's are in 'square' so they apply even pressure all around. The master cylinder has been serviced and all ports are free so that they retract the pistons in the caliper albeit very slightly (not sure how much this should be?) but surely if this wasn't working correctly then I would have the same issue in forward motion? Brake pipes are clear and its new fluid.
I have recently realised that there are no brake shims / anti rattle plates but firstly I can seem to find who sells them and secondly, I cannot see how the lack of these will cause this problem.
This has been a problem since I've owned the bike hence the brake system rebuild. It's not a huge problem as I don't intend to go backwards very often but it does make it difficult to manoeuvre around! Am I missing something (other than shims)?

Had the same thing with my 4L0, slight binding when rolling backwards.
I gently prised the pads away from the disc, ever so slightly and after a ride it all seemed to work ok.
I did think it might have been due to sitting around for a while, but it does have new pads in, so if it happens again I shall get the file out to the tops of the metal backing plates, as Shaun suggests.