1978 T140 Stiff Suspension

[RobinV]

With a break in the rain yesterday it was an opportune time to get out the T140. I rode up the coast highway on a loop I usually reserve for my RE Bullet. The asphalt is in not so good condition and it is imperative to be aware of dips and potholes etc on the back road.
The big difference between the two bikes is the suspension stiffness. My Triumph ran perfectly, but the suspension is so stiff that there is no give. Like riding a hard tail.
I saw that a previous owner had placed two spacers on top if the springs, maybe an inch and a half in length. I can remove those and then try a rear shock adjustment. These shocks have springs at the bottom and adjust at the top. Gas shocks?
Anyone out there played with the suspension on their ride? Any tips I might use? Thanks, Robin

 

[speedrattle]

definitely take out the spacers if the shocks are OEM. or even if theyre not. see what happens.

if the PO was very heavy, those spacers might have worked for him.

 

[atomsplitter]

What is your measured static sag with the current settings? Sometimes the springs aren't the problem, it's the damping rates. To much damping and the ride can feel very harsh, too little and it feels like a pogo stick. To best find a solution, first what shock do you have installed? Second what adjustments are available (preload, rebound, compression)? To sort it out we'll need more info.

 

[Lordmac]

With a break in the rain yesterday it was an opportune time to get out the T140. I rode up the coast highway on a loop I usually reserve for my RE Bullet. The asphalt is in not so good condition and it is imperative to be aware of dips and potholes etc on the back road.
The big difference between the two bikes is the suspension stiffness. My Triumph ran perfectly, but the suspension is so stiff that there is no give. Like riding a hard tail.
I saw that a previous owner had placed two spacers on top if the springs, maybe an inch and a half in length. I can remove those and then try a rear shock adjustment. These shocks have springs at the bottom and adjust at the top. Gas shocks?
Anyone out there played with the suspension on their ride? Any tips I might use? Thanks, Robin

I loved riding those coast roads on my '78 T140V back in the eighties! And yes, the original Bonneville suspension is stiffer than a . . . a stiff thing. I have since replaced the forks with those fancy progressive springs and the rear with Hagon shocks. You cannot believe the difference. It still has good road handling but now it is much smoother and forgiving when encountering those smaller bumps which can take their toll on your aching back. The original suspension (I am guessing) is quite stiff so that you can ride corners at great and ridiculous speeds at sixty-degree angles and high g-forces without dragging parts on the pavement. I don't ride with quite as much verve these days so I cannot say if the new suspension I have meets that purpose.

 

[Rudie]

progressive springs

The original dampers were a poor design; before replacing standard fork springs, consider new dampers by "Made In England" sold by L.P. Williams in the UK. These dampers were originally designed, made and used by the late Richard Darby, he advised using standard linear fork springs.

Uncompressed original fork springs, both should be the same length and the tops should be about 1" above the tops of the stanchions; if not, both springs must be replaced. If this, check new springs are both the same length; unfortunately they are often not ime, in which case you might have to resort to progressive springs; in this case, I always use the ones specifically from Progressive Suspension, never no name.

Triumph
suspension is so stiff

Even if you consider those dampers too expensive:-

. Replace the standard 97-4003 O-ring seal between damper head and stanchion with 97-4003P, available in the US from https://www.bsaunitsingles.com/ The standard 97-4003 O rings cause much stiction, means the forks do not react easily to small bumps.

. Check the stanchions are polished inside, they should be but some both original and pattern have been found to lack the internal polishing, that will increase stiction.

 

[RobinV]

Thank you all for your replies. The weather is clearing this weekend and I will get sag measurements and devise a remedy. It is worth me doing a fork disassembly as I have a small seal leak with one fork. The po was a heavy guy, maybe 285lb or so, while I am 205. So he may have made personal adjustments. Thanks again, Robin.

 

[atomsplitter]

Thank you all for your replies. The weather is clearing this weekend and I will get sag measurements and devise a remedy. It is worth me doing a fork disassembly as I have a small seal leak with one fork. The po was a heavy guy, maybe 285lb or so, while I am 205. So he may have made personal adjustments. Thanks again, Robin.

If you have a seal leak, that needs to be remedied because your fork's damping is dependent on the oil volume and viscosity. Changing the fork oil (and possibly springs) could help a lot. The rear shocks can be more problematic since the OEM varietals are usually cheap and sprung for 2 up. If the rear shocks are only preload adjustable (damping rates fixed) and over sprung your only recourse may be to swap them out for better units.

 

[jwduke]

I would ask around at some sport bike shops for a highly recommended suspension tech. Pay him for a suspension adjustment to fit the bike to you. He will want to sell you a new suspension, which you might need, but tell him now you just need to get your bike setup.

 

[ManInTheJar]

Thank you all for your replies. The weather is clearing this weekend and I will get sag measurements and devise a remedy. It is worth me doing a fork disassembly as I have a small seal leak with one fork. The po was a heavy guy, maybe 285lb or so, while I am 205. So he may have made personal adjustments. Thanks again, Robin.

Rebuilding the front forks is fairly straightforward and should give improved operation.

As Rudie has said take the opportunity to replace the O'rings with phenolic seals (97-4003P). I have also fitted progressive springs, leak proof seals and gaiters to mine - the forks are so much better now. An impact gun is ideal for removing the Allen bolts which secure the damper rods to the fork sliders, re- assembly requires a tool to stop the damper rods rotating when re-tightening the Allen bolts, for example a long extension and suitable socket.

Take care fitting the dowty seal in the slider bottoms, this is really fiddly and it will leak if not fitted correctly. The fork tops can also leak if the threads at the top are malformed and the plugs not tightened/sealed correctly.

 

[Rudie]

I have also fitted
leak proof seals

78 should have Leak Proof seals as standard - what is actually fitted in the tops of the sliders should look like the parts book drawing and images online when you search the part number.

I have also fitted
gaiters

If you do, as you are in the US, I strongly advise only the ones from Classic British Spares with the 10 year guarantee.

Take care fitting the dowty seal in the slider bottoms, this is really fiddly and it will leak if not fitted correctly. The fork tops can also leak if the threads at the top are malformed and the plugs not tightened/sealed correctly.

Seal all threads with blue Hylomar, following the instructions precisely.