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Discussion Starter · #1 · (Edited)
I am in the process of resurrecting a 1980 cm400T that sat in the PO's driveway (or garage) for 7 years after he bought it and rode for a few months. The master cylinder was trashed, so that's going to be a replacement. I got the caliper assembly off the front wheel (pic) but my impact driver is not making
Wheel Tire Crankset Bicycle tire Automotive tire

ANY headway on the 2 bolts holding the caliper assembly together, so I can’t try to refurbish or repair. (Yes, I've applied penetrating oil) So any recommendations for a replacement caliper set? Looks like 65mm between the bolt centers (pic)
 

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Hi al, engine a runner and charging system working ?

If caliper is refitted and suitable tools selected, the support of the bike is an advantage.

Try refitting caliper and have an other go at undoing the two bolts. See CMSNL exploded view for clarity and what other models the caliper etc. fit.

You see the two conical flat topped areas on the caliper outside by the two pad pins, those bolts screw into that area.

Pins free ?

Piston free ?

Can't see the bleed nipple so that's out ok or sheared clean off ?

Dd23🎅
 

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Correction, there's the bleed nipple as large as life.

Do not shear that nipple off.

Remember I mentioned hot water ?

Does the engine run and does the charging system work ?

Then clutch and gears.....

But it's your bike so any order that suits you.....

See the 500t thread, Vito is having real problems.....see last comment by bill.......
 

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Also, impact drivers/ cordless guns/pneumatic impact drivers...

Yes they have uses like undoing truck wheel nuts and subern screws etc., but I have never needed one to undo the caliper clamping/slide bolts or much else on these bikes really....

A hex socket is a must if using an impact driver else rounded of flats result using a twelve point socket.

That Speedo cable screw can be done on the bench when it's time comes, just don't break the Speedo drive unit...

You may not know of centre punch and small hammer yet.

Take your time, apply what you know, don't rush things......

Hare and tortoiuse...

and never be afraid to ask stuff. If your not sure, your not sure, and if you don't know, you don't know.
You have CMSNL and the wealth of knowledge and experience on here.....we will know what you are facing.....but pictures always help.

Dd23🎅
 

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Discussion Starter · #5 · (Edited)
Thank you, DD23. It’s comforting to know I can come on here and ask questions! I’ll refit it as you suggest and try again. That will give me some leverage.
i took the bleed nipple out and flushed it with cleaner and compressed air. I’m doing what I’m able to access - itchy fingers!
 

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Note, most ( not all ) brake fluids are brilliant paint strippers, brake fluid is hygroscopic, you will have to look that one up as "homework" , and is effectively killed with water.

Yes, remount the caliper to the fork, to keep it steady. Long extensions are good as they position your hands away from sharp stuff, they also "wind up" so torque can be sustained. You should support an extension so that the socket remains completely onto the bolts hex head, reducing tendancy to ride/slip off, and all the torque, the turning effect, goes into the bolt you are undoing. Rachel's are for quick turn action, not load. Breaker bars are for load. They are long so force X radius equals torque. Same force, longer radius means more torque, the turning effect or "moment".

Sneaky physics and maths and you didn't realise 😎.

Support the extension close to the breaker bar so socket does not ride off, extension stays in line with bolt, and all torque goes into bolt.

Always get Newton to help if you can. Steady torque rather than "jerking". A few please God's also helps.

You know what happens to metals ( usually, metal dependent ) when they are heated ?

Do different metals "change" at the same rate ?

Just look up alluminium and steel for now.

Why have I mentioned hot water ?

Glad that nipple came out all ok.

So, suitably equipped those two 14mm bolts will undo in say 10 seconds each, being generous.

The two pad pins, stainless steel ?

Will they rotate slightly ? Yes ? Good.

I can't quite see in your picture of the caliper if the brake pad cover is off ? Another possible shear off/ chewed screw possibility.

So, the two clamp bolts loose, bleed nipple out. Pads cover, wire clip, pins and both pads ( one has a "shim" ) out, brake hose removed ( mistake ! ), Remove the caliper unit from the forks and strip down. See CMSNL exploded view.

You will be left with a "haudraulic unit" with its piston still in place.

Look on CMSNL to see what is involved with that.

"How do I get the piston out ? " I hear you say.....

Itchy fingers, hare and tortoiuse....you jumped the gun a little but never mind, no damage done.

Come back when caliper unit is stripped down, leaving the caliper piston in for now.

You may realise"if I do this, and then that, it will come out ? ".....yes, think, no gorilla tackticts needed at all, just apply what you know to solve the problem. You will not have to touch the caliper piston at all......

So, come back after unit is stripped down apart from the piston, hygroscopic, wthdtm ! , Metals when hot..........?
Different metals have different....
.......... .

And your thoughts of how to get the piston out without damage or even touching it ?

You have everything needed to do that job in your workspace, or very close by, right under your nose probably......

Hare and tortoise, learn, increase/expand your skills but most of all Enjoy. Dirt washes off.

See you later...

Dd23🎅
 

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Discussion Starter · #8 ·
Refitting the unit to the bike and using a breaker bar made it all look so easy! just steady pressure on the long lever and the bolts eased up beautifully.Thanks for that suggestion.
So the caliper assembly is off and disassembled - pads and clip out, pins out (yes, they spun). piston not moving at all. Of course all I can do is push in… or? I suppose I could use the hydraulics to try pushing it out, but my master cylinder was trashed and needs replacing. There is a hint here that hot water is maybe part of the solution… if I heat the unit, would the bore expand? allowing the piston to move?

thanks for your help and cautions.
 

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Hi al,

Glad progress is happening for you drama free...

Someone said give me a long enough lever I can move the world...

So piston stuck as suspected.

Carefully peel back the pistons outer boot/dust seal. Brake fluid is a good lub for this. You may have noticed what penetrant does to brake rubbers, and other rubbers.

You have looked on CMSNL to suss out stuff with the caliper and know there is a rubber haudraulic seal in there.

Yes, I would have used the bikes own haudraulic to "excercise" the piston and eventually pump it out.

Ok, new to me farm find bike, bern outside in blazing sun, horizontal rain and buried in snow every year, caliper removed ( that was fun ) and partially stripped ( pad pins sawn in half as well and truelly rusted in ) leaving haudraulic part still connected to the master cylinder that after some coaxing actually seems to pump, thank you God !

No away caliper piston wants to move. Bucket of hot water, place haudraulic unit in hot water, count to ten and pump. Heat expands metals usually ( you did your homework ? ). Metals expand at different rates. Alloy expands more quickly than the steel piston, so helps free stuck piston.

Do not pump out piston all the way at the moment. Clean rust etc from chromed ( pitted to hell probably ) piston haudraulic sealing face, the sides of the piston really. Using protective wood, push piston back in a bit with a g clamp.

Then repeat process until piston frees off enough to make final extraction easy.

But hey, master cylinder disconnected and trashed anyway ???

What to do, what do I have to help me, what can mimic the "liquid lever" haudraulic ?

May I ask how did you clean the easily removed ( thank you God ) bleed nipple ?

Wrap haudraulic unit in rag.....apply what you know....use what you have.....piston may pop out with great speed hence rags.


Pictures of piston and the hole it came out of please.

I assume you have a small electric drill it a Dremel kit ? Small brass wire wheels are great, so are the small "plastic fibre" wire wheels which are more gentle to alloy.

Picture of master cylinder please.

Look at CMSNL to see what's involved inside.

Your dad will probably have a tap and die set as well as long nosed internal circlip pliers... ?

That master cylinder will be stripped down by your good self...

You have access to a vice ( with protective jaws, even wood or leather ), a hack saw and small scrap pile ?

Measure the handlebar diameter. Select suitable scrap steel tube same diameter. You need a length that will fit in the vice crossways, plus length to mount the master cylinder so it can be worked on and pumped. You may have to weld a suitable plate to the tube so the plate is clamped in the vice jaws, saves crushing the tube.

Give yourself a good pat on the back, you have just made your first "special tool" to make life easier for yoursekf. Loan it to NO ONE !!! Look after it as i suspect you may be using it a lot, probably into old age.


Wait for advice about the rusted in circlip, do not ( DO NOT ) break off one of the eyes !!!!!!!!!!!!!!!!!!!!!!!!

So pictures of brake stuff please.


Could you start an "engine" thread so that desperate subject can be seen, no clarification about that small but oh so important balance shaft dot.

Since bike was well maintained by the last owner, that nipple came out drama free is a good indication, this bike is Gunna be a good one, but care still needs to be taken and check list ticked off one by one. You need to prove engine fully viable early on else spend money on other stuff only to find the engine is junk.

As always, hare and tortoiuse...enjoy.

Feedback, pictures...

Dd23🎅
 

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Discussion Starter · #10 ·
Yes you are right, no more rabbit holes after this one. I’ve been cleaning the carb and waiting for gasket set and will get back to that posthaste.

But a front brake update first. I have fresh master cylinder (I know I know, don’t spend more money until engine is tested) filled with fluid and mounted on a vise. Hooked up old brake line and tried to move fluid through - easy pumps turned to some resistance (exciting!) and a little bleeding through of old gunky stuff, but then it stops and no more pumping allowed. Does this mean the brake line is junked? (I thought I should see if the fluid flows through the line before I add the hydraulic unit with stuck piston, hot water, etc.)

Ingredient Metal Jewellery Fashion accessory Circle
 

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In a vice
I hope in a protected way...

New fluid in a new master cylinder...fill reservoir.

Hose fitted and dangling down into a bucket, to flush hose.

With reservoir lid off fluid should make its way down the hose by gravity, Syphon, leak down via that tiny hole, the one you may have seen a column of tiny bubbles

So, you saying fluid pumped through well initially then seemed to get blocked, so as not to give the lever any lever movement, it has the piston hung

Old bike old hoses, sunny clime, any cracks, bulges, worn chaffed sections, odd looking bits...

Probably wise to fit a new hose...

I thought you might use compressed air ?

Steady as you go, as always h and t, enjoy

Pictures pictures pictures...

Dd23🎅
 

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Note, compressed air down that brake hose will make it "whip" violently !

Compressed air to pop out the caliper piston is good but wrap the caliper in rags, piston could pop out with some speed.

Pictures, h and t, enjoy...

Dd23🎅
 

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Discussion Starter · #13 ·
Note, compressed air down that brake hose will make it "whip" violently !

Compressed air to pop out the caliper piston is good but wrap the caliper in rags, piston could pop out with some speed.

Pictures, h and t, enjoy...

Dd23🎅
In a vice
I hope in a protected way...

New fluid in a new master cylinder...fill reservoir.

Hose fitted and dangling down into a bucket, to flush hose.

With reservoir lid off fluid should make its way down the hose by gravity, Syphon, leak down via that tiny hole, the one you may have seen a column of tiny bubbles

So, you saying fluid pumped through well initially then seemed to get blocked, so as not to give the lever any lever movement, it has the piston hung

Old bike old hoses, sunny clime, any cracks, bulges, worn chaffed sections, odd looking bits...

Probably wise to fit a new hose...

I thought you might use compressed air ?

Steady as you go, as always h and t, enjoy

Pictures pictures pictures...

Dd23🎅
yeah, I’m afraid nothing is passing through that brake hose. Tried fluid out of reservoir and gravity; brake lever pumping; compressed air; Brake cleaner directed into threaded orifice just jets back out; and finally, a thin wire - it stops no more than 1.5 inch into the orifice - and Hose is 40” long! Outside of hose looks good, but I guess 7years of sitting turned whatever is In there into something else.
time to turn my attention back to putting the carb parts back together. I’ll put new brake hose on my Santa list ;)
 

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Discussion Starter · #14 ·
Note, compressed air down that brake hose will make it "whip" violently !

Compressed air to pop out the caliper piston is good but wrap the caliper in rags, piston could pop out with some speed.

Pictures, h and t, enjoy...

Dd23🎅
Thanks as always for your kind attention and good suggestions!
 

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Start a thread on the carbs as well.

Pictures pictures pictures, before and after...

I am still concerned over the balance shaft dot etc...

Xmas list, how is the caliper piston and it's bores upper face ?

Your list will grow...

Carb thread with pictures...

Take your time, do not "misplace stuff", handt, enjoy...

Dd23🎅
 

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Discussion Starter · #16 ·
Just an update: dipping the caliper assembly into hot water (briefly) allowed the piston to move out SLIGHTLY when using compressed air. (Too long in the water and the piston heats up, too, and I observe the movement outward ceases; try again next day; and so on.) Progress became miniscule to zero, this thing is really welded in there. Bought a grease gun and a nipple that matched the caliper threads, and this did the trick. Phew. Piston out.
 

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Cool 😎

I think I mentioned small electric drill mounted brass wire wheels/nylon strand wheels...

No need to go beyond the caliper piston seal groove...research red rubber grease...and silicon grease/oil

Everything Ultra clean and nicely lubed.

New master cylinder, flush brake hose if it passes very critically inspection. New braided hoses make a difference...
 
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