Disk Brake Pressure

Hey guy's,

My MKIII is close to getting on the road and I am sorting the brakes
wondering what kind of lever/pedal travel I can expect as normal?

I understand standard lockheed brakes are definately not this bikes strong
point but below is what I have done or had done

- Both Master Cylinders rebuilt and had the front modified with
the smaller diameter piston for more pressure
-disks blanchard ground
-rebuilt calipers
-replaced lines with new braided
-new pads
-Bled both front and back systems running probably 3 times worth of fluid
through each system only cracking the nipple very slightly and bleeding slowly,
I am confident I have no air in the lines and fluid comes out with no bubbles

The front is usable but I would think should be better?
but the back has me a little worried? would anyone be able to measure how
far the lever comes back on their mk3 to the grip and let me know? bit
harder with the rear I guess but I don't think mine is right on the rear
atleast it has about 2mm between the start of the master and the dust
seal grip

Front lever pressure


Rear pedal pressure

IMO you probably have air in the front....... My standard lockhead has "full on" pressure at ~50-60% of lever movement..

By the look of your 1 finger pressure are you may be able to "bottom out" the lever with a fist full of pressure??????? CAN YOU.... If that the case i would think that the "rubber" parts of the brake line may/could be expanding..

I wouldnt be tooooooo worried and reassess once you have had some onroad running in.......

Also, sometimes when i've let hydraulics sit overnight they can "self bleed" and have a very different feel the follling day. Sometimes good and others crap. That what i think!

The front definitely looks as if there is still some air in the system, and I'd say the same as olChris, I get about 50%-60% lever travel when 'full-on'.

The rear, it's difficult to say, if the braided line is a bit over length then air can be trapped in the upper 'loop' of the line as it can be higher than the caliper connection, so you could try re-bleeding it with the braided line tied down below the level of the caliper?

With the rear brake fully off, the distance between the nut and the master cylinder casting should measure 0.35" - 0.37" (8.9 - 9.4mm).

Charger
My MkIII with S/S MC sleeve and braided S/S brake line has very much the same lever pull as yours. It's hard to know what you are comparing its performance to but mine is the best of three I've had. In my experience, much less brake lever than this results in poor feel. I have a second MkIII with no MC sleeve. It's lever movement is somewhat less, has a dead feel and less braking power.

Phil

I have modified my 74 850 master cyl [ front in your case ] and although I can pull the lever back to the handgrip, I did manage to lock up the Front wheel that ran a metzler ribbed tyre on it. I did file the return stop on the lever to let the lever move away from the grip further. My modification allowed shims to be fitted under a cap on the end of the piston so that with only a short movement of the lever, the relief hole was covered. You can check tis out by looking at the master cyl fluid as you pull the lever back. You should see a squirt of fluid come out of the hole momentarily while the lever is pulled back. If the squirt persists for a lot more travel, then you have a problem. you will need to make a spacer cap like I did to take out the extra end float. Be careful that you don't block off the bleed whole completely or you may run out of brakes. The fluid is supposed to refill the master cylinder bore as the pads wear.

If you are having trouble bleeding the brakes, then what I suggest is that you find some way of pushing the caliper pistons back into the calipers. This should expel all fluid and air back into the mastercylinder reservoir. Then carefully pump out the cylinders, making sure your reservoir doesn't empty. I don't have the later disc brake on the rear of mine so I wont comment. My experience come from working on cars for 35 years or so.
Regards Dereck

L.A.B. said:

The front definitely looks as if there is still some air in the system, and I'd say the same as olChris, I get about 50%-60% lever travel when 'full-on'.

The rear, it's difficult to say, if the braided line is a bit over length then air can be trapped in the upper 'loop' of the line as it can be higher than the caliper connection, so you could try re-bleeding it with the braided line tied down below the level of the caliper?

With the rear brake fully off, the distance between the nut and the master cylinder casting should measure 0.35" - 0.37" (8.9 - 9.4mm).

Click to expand...

Upper loop scenario sounds very plausible in my case thanks for that tip! Makes sense I will definately look at that.

I have definately run so much fluid through both front and rear that I believe I have run the volume of the lines and calipers through probably 3 times now without letting the master go dry or getting any air leaks, only other thing I can think of is maybe air seeping in through the nipple threads but I have been real careful just to crack it open the tiniest bit.

CHARGER said:

L.A.B. said:

The front definitely looks as if there is still some air in the system, and I'd say the same as olChris, I get about 50%-60% lever travel when 'full-on'.

The rear, it's difficult to say, if the braided line is a bit over length then air can be trapped in the upper 'loop' of the line as it can be higher than the caliper connection, so you could try re-bleeding it with the braided line tied down below the level of the caliper?

With the rear brake fully off, the distance between the nut and the master cylinder casting should measure 0.35" - 0.37" (8.9 - 9.4mm).

Click to expand...

Upper loop scenario sounds very plausible in my case thanks for that tip! Makes sense I will definately look at that.

I have definately run so much fluid through both front and rear that I believe I have run the volume of the lines and calipers through probably 3 times now without letting the master go dry or getting any air leaks, only other thing I can think of is maybe air seeping in through the nipple threads but I have been real careful just to crack it open the tiniest bit.

Click to expand...

Modern brakes don't run out of lever pull at 50%. They come back to where yours is. What are you wanting to achieve? Have you tried it on the road yet? You might be happy with it though it will not stop like a modern brake.

Phil

I was having the same problem until recently; I could fettle with the lever position to get reasonable grip but when the system got warm, the front brake would seize. After easing the hydraulics, I could squeeze the lever right to the handle but the system still seemed soft. No amount of shimming/trimming would result in good braking. This was after I installed Madass's smaller diameter insert.

I think, and others will disagree, that the Lockhead cylinder in & relief ports (two small and smaller holes inside the reservoir) may not have be consistent throughout manufacture and as such, the new piston may not have be configured to the master cylinder on the bike.

That said, I then purchased this unit:

http://www.ebay.com/itm/201103609277?_t ... EBIDX%3AIT

Works like a charm.

Note that the new unit comes with the braided steel brake line. I'm wishing I had started with that.

BC

phil yates said:

Modern brakes don't run out of lever pull at 50%. They come back to where yours is.

Click to expand...

Indeed so, but of course it ain't a modern brake, but a modified old brake, and with the sleeved (presumably his is 13mm?) master cylinder and a braided line I wouldn't expect the lever to pull back quite as far as that, not with one finger.

L.A.B. said:

phil yates said:

Modern brakes don't run out of lever pull at 50%. They come back to where yours is.

Click to expand...

Indeed so, but of course it ain't a modern brake, but a modified old brake, and with the sleeved (presumably his is 13mm?) master cylinder and a braided line I wouldn't expect the lever to pull back quite as far as that, not with one finger.

Click to expand...

Maybe not with one finger Les, but again mine is similar easily with two. I am thinking yours probably has that hard dead feeling when you pull the lever in and it suddenly stops. Mine actually feels like a modern brake. So if mine needs bleeding (which it doesn't) I'd advise everybody to get some air into the brake line, it makes the brake feel good.

My second MkIII has that hard dead feel and so so (read poor) stopping. I'm guessing it has no MC sleeve but don't know. Nor any idea why or if a sleeve would change the feel. I'll think more about this.

Phil

phil yates said:

I am thinking yours probably has that hard dead feeling when you pull the lever in and it suddenly stops.

Click to expand...

Yes, well, there's no harm in you thinking that I suppose, even though it isn't, and it doesn't.

L.A.B. said:

phil yates said:

I am thinking yours probably has that hard dead feeling when you pull the lever in and it suddenly stops.

Click to expand...

Yes, well, there's no harm in you thinking that I suppose, even though it isn't, and it doesn't.

Click to expand...

If you can't "squeeze" it back to near the position in the photo, I think yours does Les. Not meaning to be smart but my brake takes effect somewhere before this position and progressively brakes to this position. It is just like a modern brake in feel except that the stopping power isn't there.

If your brakes "feels" like a modern brake then I can't say any more. Is your MC sleeved? When you think about it, you want the lever squeezing back. Trying to apply finger pressure at a 50% position is not good.

Phil

Bungee that lever back against the handlebar overnight. Should be substantially firmer in the morning - IF your problem is air in the system.

BrianK said:

Bungee that lever back against the handlebar overnight. Should be substantially firmer in the morning - IF your problem is air in the system.

Click to expand...

Not sure if you are referring to Charger's problem or are you thinking I have a problem? I don't. My brake feels good and consistently works well.

Phil

phil yates said:

If you can't "squeeze" it back to near the position in the photo, I think yours does Les.

Click to expand...

You can think that-but it doesn't make me want to alter anything I've said so far. :|

phil yates said:

If your brakes "feels" like a modern brake then I can't say any more.

Click to expand...

No, I didn't say it actually felt like a 'modern' brake, :? although it is noticeably less wooden than the original 5/8" cylinder.

phil yates said:

Is your MC sleeved?

Click to expand...

Yes, it is.

phil yates said:

When you think about it, you want the lever squeezing back. Trying to apply finger pressure at a 50% position is not good.

Click to expand...

Do I? If you say so.

Sorry - Charger's.

BrianK said:

Sorry - Charger's.

Click to expand...

Just that you didn't quote him, I wasn't sure. If you have air in the line, generally the brake will feel very spongy and with pressure applied will squeeze back to the handlebar or close. But even some modern brakes tend to feel like this. I'm talking stationary application of course. You'll only try it once at speed.

Anyway, it's almost instinct to know whether your brake feels right or not. All I can say is that my experience with Norton disc brakes is a non progressive dead feel and crap stopping. Others have reported differently. I have one MkIII with good feel and relatively good stopping power. The new arrival feels just like a typical Norton disc brake.

Phil

L.A.B. said:

phil yates said:

If you can't "squeeze" it back to near the position in the photo, I think yours does Les.

Click to expand...

You can think that-but it doesn't make me want to alter anything I've said so far. :|

phil yates said:

If your brakes "feels" like a modern brake then I can't say any more.

Click to expand...

No, I didn't say it actually felt like a 'modern' brake, :? although it is noticeably less wooden than the original 5/8" cylinder.

phil yates said:

Is your MC sleeved?

Click to expand...

Yes, it is.

phil yates said:

When you think about it, you want the lever squeezing back. Trying to apply finger pressure at a 50% position is not good.

Click to expand...

Do I? If you say so.

Click to expand...

Crossed wires here Les.
By "you" I mean a person, not you in particular.
You hadn't described your brake's feel so I was asking re modern brake feel.
MC sleeving question was for my benefit.

If your brake is progressive in feel but stops hard at 50% lever position, I assume braking effect starts almost on initial finger application. That's what I mean by not being good, less finger leverage available this far out.

But it's a waste of time trying to describe or compare in here. Send your bike over and I'll give you a full braking report. And return your brake lever only.

Phil

CHARGER said:

Upper loop scenario sounds very plausible in my case thanks for that tip! Makes sense I will definately look at that.

Click to expand...

I have the sleeved master and if I could get the lever to the position you show, the front wheel would be locked up solid. When originally fitted I had air "in the loop" and a spongy brake. After all else failed, (including vacuum bleeding) I cracked the brake hose very slightly at the master cylinder while holding down the lever and air came out. Fixed.