Brake fade

[Storkfoot]

I have a reverse pull front drum. On the way back from the Euro, on one day, it was around 28 degrees in France. On that day specifically, I had bad front brake fade. The engine is a modestly tuned GT186. Probably on the cusp, or maybe over it, of where you should think about a better brake. I wasn’t riding like a maniac doing emergency stops but there was a lot of extra weight on the scooter. The reverse pull is in no way severe and really only provides a gentle pulling assistance.

The brake was okay the next day and since.

I have just pulled the drum apart. I am going to dress the shoes to get more surface area in contact with the hub but was just wondering whether anyone has a remedy for overcoming this hot weather brake fade.

I would add that I had another reverse pull drum brake on a different scooter going to Adria and back. That was over 30 degrees and I did suffer a bit with brake fade then.

[coaster]

That looks a little contaminated mate, could some grease have migrated from the speedo drive?

[Storkfoot]

No, mate. No grease. Any grease on that side is just because I had difficulty in separating the hub. Plenty of encrusted brake dust though.

The back plate is a new Uni, the hub itself is a NOS Innocenti that I bought many years ago but have never used.

[missing lynx]

Looks like the shoes are glazed through overheating which would need removing if you intend to re-use them. You can get them with diagonal cuts in the lining which is suppose to aid cooling

[Warkton Tornado No.1]

IMO, apart from the shoes were never in full contact - to be rectified as mentioned - therein lies the problem. With the valleys & troughs of the undressed shoes, the brake dust has built up in the low areas. That will have diminished the limited working area of the shoes even further. The consequences of the abrasive dust build up have also done the hub lining no good as well.

Thankfully, everything is correctable but I would advise that you assemble with just a trailing shoe with emery paper stuck on it to turn out the gouged portion of the lining to keep it cylindrical whilst ensuring the resultant dust is cleared as you do so. By that, I would keep the hub horizontal to allow the dust to drop out. Obviously, the converse of that - emery stuck to the lining - is a method by which to trim the shoes.

I believe that OEM drum brakes will perform extremely well if they are assembled correctly but that includes shoe trimming/bedding in. If you consider how large the drum is compared to wheel size, there is a mechanical advantage compared to motorcycles that used drum brakes.

[Storkfoot]

Looks like the shoes are glazed through overheating which would need removing if you intend to re-use them. You can get them with diagonal cuts in the lining which is suppose to aid cooling

The encrusted brake dust actually scraped off quite easily leaving a perfectly serviceable show surface. I have made my own grooves in other shoes I have fitted. Unsure why I didn’t on this occasion

[Storkfoot]

IMO, apart from the shoes were never in full contact - to be rectified as mentioned - therein lies the problem. With the valleys & troughs of the undressed shoes, the brake dust has built up in the low areas. That will have diminished the limited working area of the shoes even further. The consequences of the abrasive dust build up have also done the hub lining no good as well.

Thankfully, everything is correctable but I would advise that you assemble with just a trailing shoe with emery paper stuck on it to turn out the gouged portion of the lining to keep it cylindrical whilst ensuring the resultant dust is cleared as you do so. By that, I would keep the hub horizontal to allow the dust to drop out. Obviously, the converse of that - emery stuck to the lining - is a method by which to trim the shoes.

I believe that OEM drum brakes will perform extremely well if they are assembled correctly but that includes shoe trimming/bedding in. If you consider how large the drum is compared to wheel size, there is a mechanical advantage compared to motorcycles that used drum brakes.

Thanks for that. I’ll do as you suggest.

I know that you’ll invariably never get a brake shoe that is all in contact with the hub, but I was surprised that there were such large areas that weren’t in contact and allowed the build up of brake dust. That said, the shoes are pretty new.

I assume that the brake dust which encrusted the shoes has different properties when over a certain temperature. The following day, when the temperature had dropped, the brake was okay again.

[Warkton Tornado No.1]

IMO, apart from the shoes were never in full contact - to be rectified as mentioned - therein lies the problem. With the valleys & troughs of the undressed shoes, the brake dust has built up in the low areas. That will have diminished the limited working area of the shoes even further. The consequences of the abrasive dust build up have also done the hub lining no good as well.

Thankfully, everything is correctable but I would advise that you assemble with just a trailing shoe with emery paper stuck on it to turn out the gouged portion of the lining to keep it cylindrical whilst ensuring the resultant dust is cleared as you do so. By that, I would keep the hub horizontal to allow the dust to drop out. Obviously, the converse of that - emery stuck to the lining - is a method by which to trim the shoes.

I believe that OEM drum brakes will perform extremely well if they are assembled correctly but that includes shoe trimming/bedding in. If you consider how large the drum is compared to wheel size, there is a mechanical advantage compared to motorcycles that used drum brakes.

Thanks for that. I’ll do as you suggest.

I know that you’ll invariably never get a brake shoe that is all in contact with the hub, but I was surprised that there were such large areas that weren’t in contact and allowed the build up of brake dust. That said, the shoes are pretty new.

I assume that the brake dust which encrusted the shoes has different properties when over a certain temperature. The following day, when the temperature had dropped, the brake was okay again.

The dust created is due to the friction lining breaking away from the shoe as it does it's job, but the greater the contact of the shoes (100% is achievable) the less voids/pockets can exist for dust build-up.

'Real' brake fade associated with non-hydraulic drums comes about due to the expansion of the drum when it get's really hot, though that was common with racing motorcycles despite adding air cooling scoops

[Storkfoot]

Thanks again.

The front brake was the one that caused me most concern in France but the back was far from great on the way back too. Just taken the rear hub off to find that the rear hub oil seal has gone and the shoes are covered in oil.

Perhaps that might be why It’s a good job I didn’t have to do an emergency stop!

[Fast n Furious]

Have a good checkover of your rear wheel bearing. If the cage has broken up it will lead to oil leaking past the seal.

[Storkfoot]

Have a good checkover of your rear wheel bearing. If the cage has broken up it will lead to oil leaking past the seal.

I was looking at this. I always fear the worst

It looks like the seal was leaking at the bottom but, yes, I have resigned myself to running it for a hundred miles, or so, and checking again. I don’t think the seal that was in there had been in too long but then it is easy to snag them when putting them in.

Thanks for the heads up I think it is an original hub bearing.

[Leotech]

Have a good checkover of your rear wheel bearing. If the cage has broken up it will lead to oil leaking past the seal.

I was looking at this. I always fear the worst

It looks like the seal was leaking at the bottom but, yes, I have resigned myself to running it for a hundred miles, or so, and checking again. I don’t think the seal that was in there had been in too long but then it is easy to snag them when putting them in.

Thanks for the heads up I think it is an original hub bearing.

Also if you swap the rear hub seal swap the O ring on the lay shaft too, I've started doing that as a matter of course now.

[Fast n Furious]

I automatically pull out the gearbox for a bearing inspection now if I see an oil seal failure, simply because these old bearings have a finite life and its too "squeeky bum" to be ignoring it.

[Storkfoot]

I’ll see what the outer seal/ rear hub looks like after a hundred miles and take it from there. Thanks again

[Storkfoot]

Well, 65 miles on, I took rear hub off and I do still have a leak. It appears to be coming from between the lip of the seal and the inner part of the bearing.

This seal was an MB one but I think the previous one was Rolfe.

Further investigation needed. The retaining plate is bowed so that will need replacing along with the studs. I suppose it makes sense to replace the rear hub bearing too.

[Warkton Tornado No.1]

Both the retaining thick plate & the spring plate are bowed intentionally, but you most probably mean yours are excessive.

IMHO Rolf seals are very good. Quite why Lambretta 'specialists' dabble in the production of components often best left & trusted with other, power transmission component manufacturers is a mystery to me. Take the example of remade rear hub bearings with plastic cages which are potential death traps. Frank will be spinning in his grave knowing that they came etched with the word INNOCENTI....

Stepping down from my soapbox did you ensure that the surface of the bearing where the seal lip runs was rough enough & lubricated? It should not be polished & a suitable finish can be achieved with a Scotchbrite pad. Without a texture to retain oil, the lip will burn out.

[Storkfoot]

Both the retaining thick plate & the spring plate are bowed intentionally, but you most probably mean yours are excessive.

IMHO Rolf seals are very good. Quite why Lambretta 'specialists' dabble in the production of components often best left & trusted with other, power transmission component manufacturers is a mystery to me. Take the example of remade rear hub bearings with plastic cages which are potential death traps. Frank will be spinning in his grave knowing that they came etched with the word INNOCENTI....

Stepping down from my soapbox did you ensure that the surface of the bearing where the seal lip runs was rough enough & lubricated? It should not be polished & a suitable finish can be achieved with a Scotchbrite pad. Without a texture to retain oil, the lip will burn out.

I bought this engine casing around 10 years ago. It’s an Italian GP125. I forget to be honest but it looks to me like I have used the rear hub bearing that was in there and possibly the retaining plate. The bow on the retaining plate is excessive and so I’ll definitely replace it. I usually use Rolfe seals too. I just lubricated the surface of the inner bearing before fitting the seal.

I use Rockoil Lite Gear Oil on non standard clutches and whilst this is very thin, I run it on my TS1 and have never had this issue. The TS1 rear hub bearing was new ( can’t remember where from) when I first built that engine in 2010.

Any thoughts on good new rear hub bearings?

[Warkton Tornado No.1]

I use Rockoil Lite Gear Oil on non standard clutches and whilst this is very thin, I run it on my TS1 and have never had this issue. The TS1 rear hub bearing was new ( can’t remember where from) when I first built that engine in 2010.

Any thoughts on good new rear hub bearings?

I'm sure that oil you use is good enough. Funnily enough, though, today I was with the chap that I built a TS (70 x 60, boost ported direct from crankcase/slotted spigot etc etc. Estimated BHP mid thirties) & asked him how the clutch was coping - a six plate CamLam in modified OEM Innocenti components - & he said it's great. The crankcase cover NEVER gets hot & you can put your hand on it after a hard thrash because of the heat shredding character..... Yet another convert to ATF!

I've just checked as to my thoughts on a rear hub bearing but they are out of stock. Scooter Restorations "REAR HUB BEARING (INNOCENTI) USED" OEM Innocenti & Eibar bearings rarely need replacing & TBH I am unaware of anything better....

[Fast n Furious]

I like the new AF double row bearing. Seems to do the job.

[Warkton Tornado No.1]

I like the new AF double row bearing. Seems to do the job.

My concern with the AF product is the wheel alignment.

As rear punctures were so likely in racing, we used the SIP tubeless rims for racing, but only in pairs, ensuring front to back remain in line.