TLS Brake Drum Question - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 15 (permalink) Old 07-17-2019, 09:49 AM Thread Starter
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TLS Brake Drum Question

I'm putting new tires on my 70 Bonnie, and while apart want to work on the front brake. It judders a fair bit under heavy braking. I've had this bike since nearly new, along with a 69 BSA with the same tls front brake, and know that this can be a very smooth brake when working properly. The drum needs cleaning up, and "back in the day" it was routine to turn the brake drums when they started to do this. However, other than sending it out to some shop in Ca with a 6 month waiting list, I can't find anyone locally who has the equipment, much less the experience to clean up the drum.

I had an idea that perhaps I could take some old shoes and glue sharp sandpaper to them, and perhaps clean up the drum a bit by forcing some pressure and rotating the wheel manually while in a vise. Or something like that. The idea would be the large arc of the shoes would let the paper take down some of the rough spots of the drum, which are probably only a few thou out of round.

If not, does anyone have any other suggestions on how to clean up the drum and smooth out the braking, short of finding a competent machist? I'm in central NY, so perhaps there is someone in the area? It is not the shoes - I've tried several different new ones, but actually found the original ones (complete with asbestos) to work the best. But the drum needs turning, or smoothing out. Also, I noticed that tls backing plates are available, but I haven't found new drums advertised anywhere. In a pinch, are new drums available at all?

Thanks in advance your any advice.
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post #2 of 15 (permalink) Old 07-17-2019, 10:34 AM
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Hi,
Often spoke tension can distort the drum, a couple of overtightened spokes can give you real problems.
The first thing would be to true the wheel and make sure spoke tension is even, if you make adjustments to the spokes after the drum has been machined, there is a chance the brake drum will distort again.

Sometimes (rarely) a spoke retention can iron out judder, if the distortion is small (smaller than the metals elastic limit).

It is probably wise to have new wheel bearings as well at this point, the axle shaft is going to be the reference point for the skim so it is important that there is no play or judder.

Someone with experience and a special drum skimming machine is the ideal solution, but these can be very few and far between.
(Hopefully someone will upload a ‘give this guy call’ post, for someone in your area.)

If this is not an option:
A good engineer with a large gap bed lathe should be able to skim the drum concentric to the shaft, the ‘gap’ in the gap bed lathe must be able to accommodate the wheel rim.
At a push the drum also be trued on a mill, with the axle held firm and a method of spinning the wheel at even speed is rigged up.

After the drum is true, there is another process known as ‘brake arcing’ where the brake shoes are machined to match the curve of the brake drum.

Remember not to breath the brake dust, Mesothelioma is a very naughty disease.

Regards
Peg.

Quick fixes are named after how long they stay fixed, not how long it takes to make them.

Last edited by Rancidpegwoman; 07-17-2019 at 11:06 AM.
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post #3 of 15 (permalink) Old 07-17-2019, 12:18 PM
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Hi,

Quote:
Originally Posted by upstateTrophy View Post
70 Bonnie,
69 BSA with the same tls front brake,
It judders a fair bit under heavy braking.
"back in the day" it was routine to turn the brake drums when they started to do this. However, other than sending it out to some shop in Ca with a 6 month waiting list, I can't find anyone locally who has the equipment, much less the experience to clean up the drum.
From your linking your Bonnie's brake with one on your '69 BSA, I'm assuming no confusion on your part about your Bonnie's 'model year' and we aren't talking about a '71 'model year' conical-hub front brake. Therefore, I'm what "some shop in Ca", (special?) "equipment" and "experience" has to do with fixing the problem? If it isn't a conical hub, the drum's braking surface is parallel with the spindle and any competent machinist should be able to check the drum's braking surface for ovality and cure it if present?

The only possible caveat is the machinist's lathe spindle should be high enough from the lathe bed to take the complete wheel - although some drum brakes can be pulled out-of-round by irregular spoke tightening, Triumph drums were/are substantial; "back in the day", Meriden didn't use specialist wheel-builders but afaik skimming drums after wheel-building wasn't normal practice; however, if you can find a machinist with a deep enough lathe bed, no sense in dismantling the wheel for the sake of it. Fwiw, last time I needed to have drum-skimming done, a local agricultural engineer had the necessary deep lathe bed and knew exactly what was required.

Quote:
Originally Posted by upstateTrophy View Post
I had an idea that perhaps I could take some old shoes and glue sharp sandpaper to them, and perhaps clean up the drum a bit by forcing some pressure and rotating the wheel manually
Even if this was practicable, if the drum is oval, by definition, the sandpaper has to be a constant distance from the spindle, not the drum - you want the drum surface to end up concentric with the spindle; so the pressure necessary on the brake linkage, shoes and sandpaper would vary depending on how far a given point on the drum was from the spindle.

Quote:
Originally Posted by upstateTrophy View Post
It is not the shoes - I've tried several different new ones, but actually found the original ones (complete with asbestos) to work the best.
Did you 'arc' any of the new shoes to the drum before testing? If not, you're assuming new shoes' braking surface will be concentric with a half-century-old drum; given the problems we have with new parts, is that a wise assumption? While finding "the original ones ... to work the best" wouldn't cause me to eliminate the possibility of the drum being oval, I'd bear in mind "the original ones" are the shoes most-likely to have worn most-concentric with the drum so should "work the best"?

Unless finding a machinist with a deep-enough lathe bed to take the complete wheel is easy, imho first locate some vernier calipers capable of measuring at least 8" ID, remove the wheel from the bike and measure the drum ID in at least three places 60 degrees apart; only have the drum skimmed if those measurements show the drum to be wildly-oval.

Once you know the drum braking surface is (pretty-much) round, use the aforementioned sandpaper to 'arc' a pair of shoes - sandpaper glued to the drum braking surface so it rubs on the shoes' braking surface - colour the shoes' braking surface with something so you can see when it's all been removed and the shoes' braking surface is concentric with the drum. However, one thing is important - each time you tighten the spindle brake plate nut, the cable must be connected and you must be squeezing the handlebar lever; reason is the shoes 'float' between pivot and cam and you want the 'arced' surface of each shoe to be concentric with the drum when the brake's applied. Fwiw, I've found it 'easiest' to clamp the drive-side end of the spindle in the timing-side slider, attach the brake cable, apply the brake, tighten the brake plate nut; yes, it's a faff but, when the brake's on a triple, it's being asked to pull up 70 lb.(?) more than a 650 twin ...

Hth.

Regards,

Stuart
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post #4 of 15 (permalink) Old 07-17-2019, 01:03 PM Thread Starter
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Thanks to both for the replies. Yes, this is the 70 tls, not a conical hub. I mentioned the 69 BSA because I bought one shortly after selling the Bonnie back around '72 or so, and it had the same front brake. I missed the Bonnie so much that I found it and bought it back a few years later, but that is another story. Anyway, as you all well know, this can be an excellent and smooth front brake when properly set up. Mine however is not smooth, although I don't feel it is dangerous.

I will try to measure the concentricity of the drum, although I'll need to find bigger calipers. Along with double checking the spoke tightness, that might help pull the drums into better roundness.

Maybe I am chasing the wrong cat here, and the juddering is coming from the shoes. I am aware of the desirability to properly arc the shoes, but without a machinist I have no way to do that, nor to skim the drum. Stuart's suggestion might be doable, if I glue some sandpaper to the drum with a removable glue and try to arc the shoes a bit. As for the asbestos dust, working in a garage summers during high school and college, it was common to blow the dust out of the drums with air, creating a huge cloud of asbestos dust, working in our T shirts with no protection of course. In '69, nobody ever thought much about it.

The brake shop I mentioned is "Vintage Brake" in Ca, and last time I checked there was a long waiting list. If so, I would put this off until winter then send them out. I'm sure there must be someone on the East Coast, but so far I haven't found anyone.

I guess I am curious how others with the same front brake find their braking action? I was hoping to improve mine with something I could do in the shop. However, it appears I may have to bite the bullet and send drums and shoes out to a competent specialist for proper skimming and arcing to get perfect brake action.

I'll try some of the suggestions to see if it helps, and let everyone know the results.
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post #5 of 15 (permalink) Old 07-17-2019, 03:01 PM
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Quote:
Originally Posted by upstateTrophy View Post
I guess I am curious how others with the same front brake find their braking action?
I have exactly the same issue on my '72 T100R and will be taking off the front wheel to have a look very soon. The brake itself is still very effective (far better than the disc on my previous W800) but the juddering is getting worse the more miles I do. I have a couple of local engineering firms with lathes big enough or milling machines if not or I can send the wheel to SRM in Wales where it'll be checked, trued and oversize shoes machined down to fit. I just hope it hasn't been done previously, there must be a limit to how much can be taken off the inside of the drum.
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post #6 of 15 (permalink) Old 07-17-2019, 05:03 PM
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Hi,

Quote:
Originally Posted by upstateTrophy View Post
I am aware of the desirability to properly arc the shoes,
I was hoping to improve mine with something I could do in the shop. However, it appears I may have to bite the bullet and send drums and shoes out to a competent specialist for proper skimming and arcing to get perfect brake action.
You aren't understanding my previous post:-

1. Ascertain if the drum is oval or round.

2. Only if it's oval do you need a machinist, to make it round.

3. Once you know the drum is round, arc a pair of shoes yourself. You don't need a machinist to arc shoes to a round drum. The method I posted I read in posts on BritBike so I'm not by any means the first to use it.

Quote:
Originally Posted by upstateTrophy View Post
the asbestos dust,
You just need some sort of spray to damp the dust. Here in GB, I could get aerosol "Brake cleaner" easily from Amazon or Fleabay if not in a local auto. parts store but tbh any number of aerosol or trigger sprays in the garage or house already are equally-effective. Wipe damped dust out of the drum and off shoes with paper towels you then discard.

Quote:
Originally Posted by upstateTrophy View Post
The brake shop I mentioned is "Vintage Brake"
Thought it probably was; I've heard of him before and I have it in mind he posts occasionally on BritBike. But, again tbh, as you're neither racing nor talking about a comical-hub, unless you find the drum is oval, I don't understand why you'd need any machinist, never mind Vintage Brake?

Quote:
Originally Posted by upstateTrophy View Post
I guess I am curious how others with the same front brake find their braking action?
While it's ok on a triple, it isn't by any means twin front discs. I've posted previously: several British circuits have a "Bottom Bend"; when doing classic track days on the T150, the brake seems to fade about two-thirds of the way through a given session; it might be my imagination but it seems to be always at "Bottom Bend" first, which tends to turn it into "Squeaky Bottom Bend" ... Years ago, when I had only the T160's, when touring with other triples, I perhaps should've paid more attention to why, given a long bendy downhill road, it was generally disc-braked triples that arrived at the bottom first (followed by pre-conicals, followed by comicals ... ).

Hth.

Regards,

Stuart
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post #7 of 15 (permalink) Old 07-18-2019, 02:42 AM
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Hi Upstate, I'm guessing your referring to Vintage Brake Sonora, California. About 100 miles from me.

Interesting fellow. He is mostly doing vintage aircraft brakes for big dollars & puts bike brakes to the back burner.

Fought this long & hard on the '69 Bonnie. Pulsating, but had good power. Over the next several thousand miles pulsating got worse & worse until it became what I'd call unsafe at any speed.

Attempted tensioning spokes & truing wheel etc. Attempted gluing sand paper to shoes to help surface drum. Tried Ferodo & Emgo shoes. Nothing helped. Vintage brake was back logged months. John drove up & spoke with Michael personally. Was very helpful & friendly, but overwhelmed with work.

He said the problem is simple.... Tension spokes/true wheel. Then turn drum. Fixes it every time. If drum is not round it will pulsate to a lessor or greater degree, not only depending on how out of round it is, but the shape of out of round as well.

He suggested a street use lining that stops good cold, but can fade. He said his racing linings don't fade, but not good cold. He relines your old shoes himself with whatever lining you choose. He said if wheels were dropped off wheel now, might be done in 3 months or so.

As luck would have it a retired coworker is a hobbyist machinist with a gap bed lathe. He made an arbor that mounted through the wheel bearings. Driving the hub was another issue. He made a device to drive hub also. Ground the drum with a tool post grinder. Did front & rear drums. Rear was done with drum on the wheel assembly.

He made a special face plate that held the shoes like the bike's backing plate. Then ground shoes to fit drums. A very precision arcing. That's what Vinatge Brake does also.

He refuses to do more, was way too time consuming. Too bad for us as the need is huge.

The results was perfect. No hint of pulsation. Ended up with a few sets of shoes. Ferodo, & Emgo. Emgo tended to stop better so that's what stayed. However the original Triumph shoes worked the best of all, way better. John didn't want the asbestos of originals so settled for the less stopping power of Emgo.

We searched high & low for a brake shop or machine shop to turn the drum. We have several machine shops in our area & brake shops also. No machine shop would take the job. Not a single brake shop had a lathe that would reach around the rim. Their smallest spindles were just a little too large to pass through hub.

Speaking of brake shoes, I still have my original rear. So far 100% of the guys that replace shoes find the new shoes have less effective friction. New old stock of genuine Triumph shoes are very hard to find. I don't know what I'm going to do when mine wear out.

This is the arcing machine we had in our shop. It worked great. Pretty much against the law to use these now. Now they require 100% dust containment.

https://www.ebay.com/itm/Ammco-2000-...AAAOSw0RddFpNO


Might give Baxter Cycles a call & see what they do or have someone to recommend.
Don
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post #8 of 15 (permalink) Old 07-18-2019, 08:03 AM Thread Starter
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TR7RVMan, thanks for the feedback. Wow, this is becoming interesting. For all the other parts of these bikes that we can readily get aftermarket, the drum brakes are a problem with no easy solution. Front disks and calipers are readily available, but for a bad front drum there doesn't seem to be an easy solution.

As you said, proper spoke tensioning then skimming is the proper fix. Even with a new drum, by the time the wheel was laced, the drum would be out of round and still need skimming. I would think arcing the shoes is less critical, since eventually anyway the shoes will wear to fit the drum, although until that happens their stopping power will be less. Like you, I found the original Triumph shoes worked the best. I didn't like the EMGO shoes very much. Luckily, I found an extra pair of NOS Triumph shoes, plus my old ones were still workable.

I'll still keep searching on the East Coast for someone with the proper lathe and the knowledge to work on drum brakes. This is not an uncommon problem, so I'm a little surprised there aren't more small specialty shops that could do the work.
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post #9 of 15 (permalink) Old 07-18-2019, 09:20 AM
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Apologies if I've missed it, calipers are of little use in checking drum concentric's relative to the spindle, better to clamp the spindle in a vice with the wheel horizontal and use a dial gauge on the inner drum. I find truing the drum via spokes from about a 'loose' 5Ibft all round usually gets the drum within a couple of thou, and that's probably as good as it gets until the shoes bed in. Though some drums are so far out as to require unreasonable tension to true up. This always happens on the open drum side that has less reinforcement, so it's best to check the drum at top and bottom. It's also easy to go wrong and not run shoes in, once glazed they tend not to conform to any deviation. Another symptom which is compounded by any drum run-out is the fork to hub retention; This will tend to oscillate causing chattering and pulsing, amplifying that characteristic lurch. As this happens under load, it can be tested on the machine by applying the rear brake before the front. If the drums out, the chattering will reduce using this test.
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post #10 of 15 (permalink) Old 07-18-2019, 04:37 PM Thread Starter
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Freakmaster,

Thanks for the tip. It makes perfect sense. I have a decent runout gauge and a big vise, so this weekend I'll pull the front wheel and see what the runout is at different points around the drum. That will also let me play with the spoke tensions a bit a see what effect they have.
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