ATE calipers brake pads won't release

[Boertjie]

My friend and colleague have acquired a 78R100S (in a hundred pieces), with parts missing etc. but between the 2 of us we'll get a decent bike back to life again.
Sadly the PO lost his life on this bike, banged against the paving and flipped over. The front wheel is broken in half, and the handle bar switches is broken with the cables all ripped of and broken. But except that, no other broken bits. I did not know the PO nor when this happened, and maybe better this way!
IMHO I suspect the front brakes not working as they should in this particular incident.

Anyways, the brake lever is very spongy and if you release the brake, the brake pads won't budge and you have to release them with a screwdriver or tool. I suspect still lots of air in the system and advise my Friend to strap some cable ties on the closed lever position and leave it over night for the air bubbles to rise up. The pistons on the calipers are good. New braking fluid as well. Something else to look at maybe?

Thanks

[Garnet]

Did this bike have "Snowflake" mag wheels?

[Boertjie]

Did this bike have "Snowflake" mag wheels?

Yes

[Ken in Oklahoma]

My friend and colleague have acquired a 78R100S (in a hundred pieces), with parts missing etc. but between the 2 of us we'll get a decent bike back to life again.
Sadly the PO lost his life on this bike, banged against the paving and flipped over. The front wheel is broken in half, and the handle bar switches is broken with the cables all ripped of and broken. But except that, no other broken bits. I did not know the PO nor when this happened, and maybe better this way!
IMHO I suspect the front brakes not working as they should in this particular incident.

Anyways, the brake lever is very spongy and if you release the brake, the brake pads won't budge and you have to release them with a screwdriver or tool. I suspect still lots of air in the system and advise my Friend to strap some cable ties on the closed lever position and leave it over night for the air bubbles to rise up. The pistons on the calipers are good. New braking fluid as well. Something else to look at maybe?

Boertjie, is your description of the symptoms coming from you or your friend? When the brakes are released the pads don't retract per se. And indeed, to spin the wheel freely one would have to force the piston back onto place with something like a screwdriver. In practice the rotating brake disk will force the pads away from the disk such that there is only a light rubbing.

If, on the other hand, with the brake lever released, the pads are still gripping the disk hard, then there is indeed a problem. One cause could be a very dirty/corroded piston effectively stuck in the bore. For that the caliper will have to be taken apart, cleaned, and inspected.

Another, perhaps more likely scenario, is that a very small return hole in the under the tank master cylinder is plugged. What happens is that the master cylinder piston pressurizes the brake line, but because that little return hole is plugged, the pressure doesn't release when the brake lever is released. To find out if the brake line gets pressurized and doesn't release simply open up the bleeder screw. If some brake fluid squirts and the brake pads release, then that is the clue you are looking for. Aside from the brake fluid return hole being plugged there is a slight possibility that the brake line itself is in bad shape with a deteriorated inner lining stopping the fluid from returning to the master cylinder.

Whether I'm on track with the above, or not, since the brakes are suspect anyhow, I think a teardown, cleaning, and inspection of the brake system is in order. By that I mean the calipers would be taken apart, cleaned, inspected, and parts replaced as needed. The rubber brake lines, if suspect, would be replaced. The master cylinder would be taken apart, cleaned, and inspected, honed clean (with some fine wet or dry sandpaper in a slotted wooden dowel, turned by a drill). If there are pits (almost always near the mouth) some honing with the fine wet or dry sandpaper may get them out. If not you have a master cylinder problem that is going to be expensive. Finally, the brake cable from the hand lever to the lever on the under the tank master cylinder needs to be inspected for easy actuation.


Ken

[Boertjie]

Hi Ken, I was inspecting the bike this afternoon, brake fluid was poured from the top and it went down to the bleeders. The calipers are good, pistons are loose. The obvious thing now is to check the small hole in the master cylinder, but I think the mc but be stripped and inspected as advised. And the brake hoses as well. Thanks!

[Garnet]

I have no comment on the brakes, but I'm wundern if this bike had a Snowflake that should have been re-called.
http://robfrankham.co.uk/bike/dreaded_b ... recall.htm

I have seen a pic somehwere of one that broke in two. That may have caused the fatal crash of the PO. A very sad and proventable case, if in fact it is the case.

[Boertjie]

I have no comment on the brakes, but I'm wundern if this bike had a Snowflake that should have been re-called.
http://robfrankham.co.uk/bike/dreaded_b ... recall.htm

I have seen a pic somehwere of one that broke in two. That may have caused the fatal crash of the PO. A very sad and proventable case, if in fact it is the case.

Will go over there and have a look in the morning. I only saw a glimpse of the rim in the back of the garage. Will report back.

[Boertjie]

I have no comment on the brakes, but I'm wundern if this bike had a Snowflake that should have been re-called.
http://robfrankham.co.uk/bike/dreaded_b ... recall.htm

I have seen a pic somehwere of one that broke in two. That may have caused the fatal crash of the PO. A very sad and proventable case, if in fact it is the case.

Will go over there and have a look in the morning. I only saw a glimpse of the rim in the back of the garage. Will report back.

No, it was a replaced wheel with the web stiffeners.

[vanzen]

... But except that, no other broken bits ...

Given the description of the damage, and the implied force of impact to cause it ...

"no other broken bits" ???

I'd not bet my life on it !

[Boertjie]

... But except that, no other broken bits ...

Given the description of the damage, and the implied force of impact to cause it ...

"no other broken bits" ???

I'd not bet my life on it !

You see that's where the missing parts come in. The seat is missing and the tank is resprayed. If it is the original tank, I don't know. The bike comes from a Airhead restorer and I did not have a really good chat about all the parts etc. He recently had a major back operation and is scaling down his bike activities.