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Discussion Starter #1
I find my bikes rear wheel locks up far too easily. (81 T140) I don't dare use it on any bend as too dangerous, I can't really feel when it is near locking up. I have all new standard parts, new rear master cylinder, disc, pads and pistons and seals but I think the leverage by the brake pedal is just too much.
Are there any modifications to improve this?
Were the rear drum braked versions better?

Regards,

Alex
 

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IMHO much better because they don't brake so hard.
You can use them in turns and with passenger they help a lot, but don't have excessive braking of the disc with big leverage used for drum brake. Rear brake system is the same as front and rear needs to be much smaller in capacity and power.
This is why I like 73-74 bikes.
 

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Discussion Starter #3
yep, I would prefer a rear drum braked, spoke wheel bike.
Can't really customise my machine too much as it is fairly a limited edition but would like to improve the safety of the rear brake if possible.

Regards
 

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I would think the only area that is easily varyable would be the brake pads -- you could try different makes of pad , there may be some that are less effective -- bear in mind that some classic minis ( as in Austin Mini Cooper) used basically the same caliper and hence the same shape pads -- dont know if they are better or worse stoppers
 

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Hi Alex,
I think everyone with a Triumph rear disc has had that ‘why do I seem to be fishtailing all over the road’ moment.
The problem is not really the power of the brake, but the feedback (lack of it) to the rider.

If the ratio between the area of the face of caliper piston(s) is low compared to the area of the face of the master cylinder piston is too low, then the brakes will feel wooden and give no feedback. The 5/8" bore master cylinder coupled with the calipers twin 41mm pistons give a ratio of app:13:1, this is very low.
If you then couple this with a massive mechanical advantage lever from a very long brake pedal, that imparts a lot of force, but again with very little feedback, you have the perfect recipe for brake that works like an on/off switch.

The cheapest option is to lower the friction co-efficient of the brake pads, using ee (0.25-0.35 cof) ff (0.35 to 0.45)or gg (0.45-0.55) pads will help, do not use hh (>0.55) brake pads.
This will reduce the grip of pad on the disc, raising level where the wheel locks, but you still will get very bad feedback or feel to the brake, it will just be harder to lock the wheel, but the lock up point will still be unpredictable.

I have made several changes and after a lot of mucking about I have got a rear brake that is OK, not brilliant but 100 times better than the stock setup.

First to reduce the huge mechanical advantage by 50% to 70% I fit rear sets, T140 footpegs are too far forwards for my liking anyway.
The unfortunate consequence of this however reduce the rear braking power to pretty much useless.
The second stage is then to reduce the rear master bore diameter from 5/8" to 13mm, this increases the hydraulic advantage from 13:1 to app:20:1. This restores (some of) the brake power lost by the reduced mechanical advantage.
The change in in hydraulic advantage vastly improves the feel of the brake, and this is fed back to your foot much better through the shorter pedal.

You end up with a brake slightly less powerful than the standard setup, but you can brake progressively right up to the wheel lock point.
I have used a new alloy 13mm brake master cylinder from the USA (now available everywhere) and cylinder sleeve kits from RGM (Norton).
DO NOT put a reduced diameter master cylinder on the REAR brake without reducing the mechanical pedal advantage first, it will be lethal.

I am pretty happy with this setup, however I have it in mind a further reduction to 12mm or even 11mm master cylinder diameter might be better for feel and power. The problem with this is there is no ‘off the shelf’ solution and I will have to make my own master cylinder sleeve down kit.

Regards
Peg.
 

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Discussion Starter #6 (Edited)
Thanks all for the advice,
Stuart, I will keep the footrests where they are so would a larger diameter rear master cylinder help improve feel? I would like to have a bit more range in the pedal as not much between off and on with all new original kit.
This is one area of the bike I am happy to get away from standard so will consider all options. Will look at other bike makes of similar dimensions and weight and see if it is possible to replicate that setup on my old Triumph.
I am happy to weld (or clamp on) a new rear brake pivot if needed.
How about tyres? could a flatter profile tyre help? (at least when on the straight) I replaced the worn road runners with the Avon Roadrider equivalents, I hate the roadriders as they are considerably larger all round and make the bike taller, they don't even fit inside the front mudguard but the maybe profile does not give a larger contact area?
 

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I know and respect that many of you don't want to modify your bike...But I'm more interested in how it performs and not working around braking issues that may compromise my safety.....This solves two problems for me, rear brake feel and better foot peg position.. And weighs 5 pounds less with fewer monkey motion parts....No stock parts were butchered :wink2:

 

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Discussion Starter #8
Hey Truckedup,

Tell me about your setup, seems good.
I stopped riding my T140 last year because of the rear brake, been sitting in the garage since, I have only done about 100 miles since getting it on the road but would like to have confidence in the brakes.

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Hey Truckedup,

Tell me about your setup, seems good.
I stopped riding my T140 last year because of the rear brake, been sitting in the garage since, I have only done about 100 miles since getting it on the road but would like to have confidence in the brakes.

Regards
It's a 14mm Brembo knockoff master cylinder and the rear set pegs and brake lever is fabricated from 70- 80's Honda 750 parts. The leverage ratio is the same as the stock Triumph..I did weld two bolts to the frame for mounting the master...It's has a more live feel and lock up is easy to modulate..Don't the last few years of T140 have the master cylinder mounted something like this ?
 

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Discussion Starter #10
Thanks for the info,
My bike is an 81 and has the rear master cylinder inside the frame right where all the grit and crap can seize it up as fast as possible. Happy to try out anything.
Maybe some T140 expert out there could make a go fund me to come up with an effective solution :) I would contribute.
 

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It's a 14mm Brembo knockoff master cylinder and the rear set pegs and brake lever is fabricated from 70- 80's Honda 750 parts. The leverage ratio is the same as the stock Triumph..I did weld two bolts to the frame for mounting the master...It's has a more live feel and lock up is easy to modulate..Don't the last few years of T140 have the master cylinder mounted something like this ?
Hi Truckedup
I think the TSX custom had a Brembo or grimeca external rear master cylinder bolted on, so they could squeeze the big fat custom cruiser tyre in.
Regards
Peg.
 

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Discussion Starter #12
Great bike, those side panels would be perfect on my bike.
I never realised that Triumph changed the rear brake setup so much.
Was it a big improvement in feel and effectiveness? It looks like an even more crazy contraption.
Going to a bike shop this weekend to see all the variations of how to make a rear disc work.
 

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Hi Alex,

I find my bikes rear wheel locks up far too easily. (81 T140) I don't dare use it on any bend as too dangerous,
With respect, the standard rear disc on a Meriden twin is not "dangerous". Meriden first fitted a rear disc for '76, the vast majority of bikes made 'til '83 had exactly the same lever, master cylinder and caliper. My T160's have exactly the same parts and, while I agree with Peg's assessment of the primary problem (crap lever pivot position for the standard footrests) and at least some of his solutions (rearsets :thumb but I'm still using the standard master cylinder and caliper), while it isn't great, it isn't "dangerous".

Imho, there are three questions not asked so far in this thread:-

. You posted, "I have all new standard parts, new rear master cylinder, disc, pads and pistons and seals"; have you done something wrong to make the rear brake on your bike "dangerous"?

. If you're certain not, why are you using the rear disc so hard you're locking it up in the dry? Your bike has pretty-much the same twin front discs as at least one of my T160's, mine are great even two-up carrying enough for a two-week Continental camping trip; you're talking one-up on a considerably-lighter bike. Remembering the brakes on your bike have been a saga since you bought it, have you sorted out your bike's front brakes properly?

. If you have, is your problem simply poor technique - using the back brake much more than the front?

rear drum brake
There might be a way of fitting your bike with a drum rear brake but it won't be easy:-

. Conical-hub rear drums fitted '71-'75 are on the drive-side.

. The TR65 Thunderbird and TR7T Tiger Trail were fitted with rear drum brakes, an educated guess says by making as few changes as possible to the rest of the basic twin. Essentially, the drum bolts in the same place as the disc; however, aiui the spoked wheel hub is narrower than the disc hub, possibly by leaving out the centre section? It'd be wise to confirm all this by physically comparing your bike's rear wheel and brake with a TR65's or TR7T's. However, then there weren't any ally-wheeled TR7T's; if ally-wheeled, drum-braked TR65's exist, they're rocking-horse poo; so either put up with mismatched wheels, or change your bike's front for spoked, or maybe a drum-brake rear Morris from a 1980's Kawasaki?

Hth.

Regards,
 

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Discussion Starter #14
Thanks for the good suggestions,
Part of the issue could be me not being used to the bike, all my other bikes brake and feel fine.
I like the idea of a Kawasaki Morris wheel, never knew they done that, will keep a look out.
Front brakes work fine but I know I would jump on the rear in any emergency.
Will try softer pads and use the rear brake more to develop some better feel for it.
These forums are a great help.

Regards
 

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Just out of interest, in the dry, on a straight road, how do you split your braking?
I always use about 75/25 in the dry and nearer 50/50 in the wet
 

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one thing I didn't catch, you said all new standard parts. did that include a new brake line also? after years brake hoses will swell almost shut inside and not allow the fluid to return & the pads to release from the disc. just sayn'
 
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