Unit Triumph Fork Rebuild
After successfully tackling the rear swing arm bushes I turned my attention to my second niggle since purchasing my 1967 Bonneville. Wear in the fork bushes was causing an annoying judder under brakes plus I had a split gaiter and poor handling but these were not the only problems as it turned out. Word of warning here, before going any further check carefully the actual parts fitted on your bike. My old Triumph is over 50 years old so it is highly likely not everything is standard and parts may not correspond to the parts book for the given year. I knew my Bonni had a twin leading shoe (TLS) front brake which is great but nonstandard for 1967. The cable also drops from the top so it’s not a 68 either. Just to confuse the issue further my top yoke is an original 67 because it doesn't have the ignition lock. By 1969 Triumph had moved the ignition lock to the left side headlight ear. This is the reason not to pre order parts for some jobs until you are sure of what you have. Triumph variations can sometimes be quite tiny and hard to spot so be careful.
Anyway it seems I have a mishmash (old English engineering term) of 67 & 69 parts on my forks so care had to be taken when ordering parts. I did my homework before stripping the forks and I also read on the CBS website a helpful hint on choosing the best fork bushes. CBS supply two types, solid brass bushes which are hard wearing and longer lasting or their standard sintered bronze bushes. After further reading I went with the sintered bronze bushes as they absorb oil and being softer should cause less wear to the fork legs but will probably need replacing sooner. The choice is yours and either is good.
Watching Youtube, although helpful, can also be a little off putting when they demonstrate by using a pair of badly rusted forks, welding torch, large hammer and a huge vice bolted to a massive work bench, none of which I have. I had a bag of spanners and a garage floor.
My first step was to remove the front wheel, mudguard (fender) and brackets. Unclip the gaiters and although a little fiddly they can be completely removed or if replacing simply cut them off. I did treat myself to the special tool available to loosen the dust covers which hold the fork seals. As I was fitting brand new covers with seals I didn’t want to risk marking them in anyway and this tool worked perfectly. Good idea at this stage to use a round ½ inch socket extension bar running between the fork legs where the axle fits. This allowed me to undo the dust covers without need for a vice as it prevents the lower fork legs from turning. The dust covers are normally stiff to turn initially but quickly loosen. Leave them fitted once you have them finger tight. See why later.
I used a very large adjustable spanner (wrench) to loosen by a half turn the chrome top nuts as the large smooth jaws caused zero damage and saved the cost of buying a special ring spanner. I then loosened the two bolts with nuts on the lower fork tree (yoke) that clamps the stanchions and gently tapped a screwdriver a little way into the slot to help with stanchion removal. Loosen the large chrome top nut by half a turn, protect with a block of soft wood and tap the stanchion down with a hammer. Keep turning the nut a little at a time and tap down until the stanchion nut no longer catches the thread. When this happens gently tap the lower leg fully down using the block of wood and hammer on the fender mounting (this is why I didn’t fully remove the dust cover and lower leg earlier).
Be ready to catch it as it will come loose suddenly together with the road spring and all the other bits. Unscrew the finger tight dust covers then holding the stanchion up vertically tap the lower leg down to remove it. Do this on both sides and if you are really lucky the legs will still contain oil rather than rusty water so be careful not to spill it. Why didn’t I drain the oil first? Couldn’t be bothered fiddling with the little drain plugs.
The left lower leg was much harder to remove from the stanchion and I noticed the lower bronze bush had odd looking damage. Further investigation revealed that a previous owner had used a slightly longer bolt (actually a rear sprocket bolt) than standard for the fender mount to the fork leg. In the words of Julia Roberts, “Big mistake, huge” as this had resulted in a sizeable dent inside the fork leg which was now rubbing badly on the bottom stanchion bush. How this went unseen I don’t know because even now the fork leg still jammed when it reached this point. I now understood the poor handling and rough ride. This was an easy mistake to make resulting in a major problem.
After much head scratching my solution was to tighten a large bolt with two nuts, one nut above and one below through the square hole of a normal socket that just fitted inside the fork leg. I left a few inches of bolt sticking up so I could pull (hammer) the socket back out. With plenty of grease I then hammered the socket using the bolt into the damaged area. I then used an open ended spanner on the bolt head to hammer the socket back out. Note that I held the fork leg in my hand whilst doing this so no nasty vice needed, but a friend to hold it would be easier. The result was that the socket pushed out the worst of the dent. I then used a length of round plastic tube (electrical conduit) and super glued a length of medium abrasive tape fully around one end. A piece of electrical tape on the tube served as a depth marker and kept me rubbing in the correct spot. Sixty minutes later with one aching arm and by carefully rubbing away at just the dimple of damage in the fork leg while constantly checking the fit using the undamaged right side stanchion with bush I eventually had the stanchion running smoothly inside the leg. Phew! A great result at no cost. New lower legs are still available but will cost around $200 each plus there are different types depending on the year. The wrong one can be dangerous but will still fit. This warning is actually mentioned in an original Triumph service bulletin regarding the fitting of the later TLS brake to earlier models. Yes, thankfully mine had the correct lower fork legs fitted.
Now undo the lower nut/damper unit that retains the bottom bush, a special spanner is helpful and fairly cheap but a C spanner will normally get the job done. If desperate and looking to save some dollars a screwdriver and hammer will also work but does cause a little damage. The lower bush then pulls off the stanchion together with everything else. It is now up to you how much you replace depending on the condition of your forks and the thickness of your wallet. For me it was all new chrome dust covers with seals, new sintered bronze bushes, new plastic damper tubes, new rubber gaiters, cork spacers and a pair of new stanchions. I probably could have got away with the original stanchions as they only had a small amount of localised scoring on both but what the heck, I’m here now.
Reverse the process to assemble. No need for instructions coz once you have got this far you already know what to do. Couple of tips, wrap a plastic bag around the bottom of the stanchion before sliding the dust cover on to protect the seal. Also, my new dust covers were not screwing all the way down without seizing so I spent a bit of time using fine valve paste on the thread of the dust cover and leg working it on and off to free up the extremely tight fit. Thoroughly wash off all traces of the paste when finished. Very glad I did this as it made assembly much easier and guaranteed I got the dust covers fully screwed into place without damage. I don’t think the original covers I removed were correctly fitted for this reason. Oh and please, just use proper fork oil in each leg and ignore the talk on Forums that discuss using engine oil, sewing machine oil, avocado oil or a mix of fish oils with a hint of wild Alaskan Salmon because it works so much better in an old Triumph! It won’t and it doesn’t.
I now have a fine pair of working comfortable forks. Don’t be alarmed, and I speak from experience, if your forks are stiff and don’t bounce back! A couple of miles had mine bouncing better than Pamela Andersen jogging down the beach in Baywatch.
So hopefully this (much longer than anticipated) guide to fork repairs has given you the confidence to tackle another common Triumph service issue. Unlike modern bikes old Triumphs will simply not be happy without constant love and attention, just like my wife really.
Best wishes and G’day from the DIY Mechanic Downunder.
After successfully tackling the rear swing arm bushes I turned my attention to my second niggle since purchasing my 1967 Bonneville. Wear in the fork bushes was causing an annoying judder under brakes plus I had a split gaiter and poor handling but these were not the only problems as it turned out. Word of warning here, before going any further check carefully the actual parts fitted on your bike. My old Triumph is over 50 years old so it is highly likely not everything is standard and parts may not correspond to the parts book for the given year. I knew my Bonni had a twin leading shoe (TLS) front brake which is great but nonstandard for 1967. The cable also drops from the top so it’s not a 68 either. Just to confuse the issue further my top yoke is an original 67 because it doesn't have the ignition lock. By 1969 Triumph had moved the ignition lock to the left side headlight ear. This is the reason not to pre order parts for some jobs until you are sure of what you have. Triumph variations can sometimes be quite tiny and hard to spot so be careful.
Anyway it seems I have a mishmash (old English engineering term) of 67 & 69 parts on my forks so care had to be taken when ordering parts. I did my homework before stripping the forks and I also read on the CBS website a helpful hint on choosing the best fork bushes. CBS supply two types, solid brass bushes which are hard wearing and longer lasting or their standard sintered bronze bushes. After further reading I went with the sintered bronze bushes as they absorb oil and being softer should cause less wear to the fork legs but will probably need replacing sooner. The choice is yours and either is good.
Watching Youtube, although helpful, can also be a little off putting when they demonstrate by using a pair of badly rusted forks, welding torch, large hammer and a huge vice bolted to a massive work bench, none of which I have. I had a bag of spanners and a garage floor.
My first step was to remove the front wheel, mudguard (fender) and brackets. Unclip the gaiters and although a little fiddly they can be completely removed or if replacing simply cut them off. I did treat myself to the special tool available to loosen the dust covers which hold the fork seals. As I was fitting brand new covers with seals I didn’t want to risk marking them in anyway and this tool worked perfectly. Good idea at this stage to use a round ½ inch socket extension bar running between the fork legs where the axle fits. This allowed me to undo the dust covers without need for a vice as it prevents the lower fork legs from turning. The dust covers are normally stiff to turn initially but quickly loosen. Leave them fitted once you have them finger tight. See why later.
I used a very large adjustable spanner (wrench) to loosen by a half turn the chrome top nuts as the large smooth jaws caused zero damage and saved the cost of buying a special ring spanner. I then loosened the two bolts with nuts on the lower fork tree (yoke) that clamps the stanchions and gently tapped a screwdriver a little way into the slot to help with stanchion removal. Loosen the large chrome top nut by half a turn, protect with a block of soft wood and tap the stanchion down with a hammer. Keep turning the nut a little at a time and tap down until the stanchion nut no longer catches the thread. When this happens gently tap the lower leg fully down using the block of wood and hammer on the fender mounting (this is why I didn’t fully remove the dust cover and lower leg earlier).
Be ready to catch it as it will come loose suddenly together with the road spring and all the other bits. Unscrew the finger tight dust covers then holding the stanchion up vertically tap the lower leg down to remove it. Do this on both sides and if you are really lucky the legs will still contain oil rather than rusty water so be careful not to spill it. Why didn’t I drain the oil first? Couldn’t be bothered fiddling with the little drain plugs.
The left lower leg was much harder to remove from the stanchion and I noticed the lower bronze bush had odd looking damage. Further investigation revealed that a previous owner had used a slightly longer bolt (actually a rear sprocket bolt) than standard for the fender mount to the fork leg. In the words of Julia Roberts, “Big mistake, huge” as this had resulted in a sizeable dent inside the fork leg which was now rubbing badly on the bottom stanchion bush. How this went unseen I don’t know because even now the fork leg still jammed when it reached this point. I now understood the poor handling and rough ride. This was an easy mistake to make resulting in a major problem.
After much head scratching my solution was to tighten a large bolt with two nuts, one nut above and one below through the square hole of a normal socket that just fitted inside the fork leg. I left a few inches of bolt sticking up so I could pull (hammer) the socket back out. With plenty of grease I then hammered the socket using the bolt into the damaged area. I then used an open ended spanner on the bolt head to hammer the socket back out. Note that I held the fork leg in my hand whilst doing this so no nasty vice needed, but a friend to hold it would be easier. The result was that the socket pushed out the worst of the dent. I then used a length of round plastic tube (electrical conduit) and super glued a length of medium abrasive tape fully around one end. A piece of electrical tape on the tube served as a depth marker and kept me rubbing in the correct spot. Sixty minutes later with one aching arm and by carefully rubbing away at just the dimple of damage in the fork leg while constantly checking the fit using the undamaged right side stanchion with bush I eventually had the stanchion running smoothly inside the leg. Phew! A great result at no cost. New lower legs are still available but will cost around $200 each plus there are different types depending on the year. The wrong one can be dangerous but will still fit. This warning is actually mentioned in an original Triumph service bulletin regarding the fitting of the later TLS brake to earlier models. Yes, thankfully mine had the correct lower fork legs fitted.
Now undo the lower nut/damper unit that retains the bottom bush, a special spanner is helpful and fairly cheap but a C spanner will normally get the job done. If desperate and looking to save some dollars a screwdriver and hammer will also work but does cause a little damage. The lower bush then pulls off the stanchion together with everything else. It is now up to you how much you replace depending on the condition of your forks and the thickness of your wallet. For me it was all new chrome dust covers with seals, new sintered bronze bushes, new plastic damper tubes, new rubber gaiters, cork spacers and a pair of new stanchions. I probably could have got away with the original stanchions as they only had a small amount of localised scoring on both but what the heck, I’m here now.
Reverse the process to assemble. No need for instructions coz once you have got this far you already know what to do. Couple of tips, wrap a plastic bag around the bottom of the stanchion before sliding the dust cover on to protect the seal. Also, my new dust covers were not screwing all the way down without seizing so I spent a bit of time using fine valve paste on the thread of the dust cover and leg working it on and off to free up the extremely tight fit. Thoroughly wash off all traces of the paste when finished. Very glad I did this as it made assembly much easier and guaranteed I got the dust covers fully screwed into place without damage. I don’t think the original covers I removed were correctly fitted for this reason. Oh and please, just use proper fork oil in each leg and ignore the talk on Forums that discuss using engine oil, sewing machine oil, avocado oil or a mix of fish oils with a hint of wild Alaskan Salmon because it works so much better in an old Triumph! It won’t and it doesn’t.
I now have a fine pair of working comfortable forks. Don’t be alarmed, and I speak from experience, if your forks are stiff and don’t bounce back! A couple of miles had mine bouncing better than Pamela Andersen jogging down the beach in Baywatch.
So hopefully this (much longer than anticipated) guide to fork repairs has given you the confidence to tackle another common Triumph service issue. Unlike modern bikes old Triumphs will simply not be happy without constant love and attention, just like my wife really.
Best wishes and G’day from the DIY Mechanic Downunder.
I agree 
