New Rear Master Cylinder not performing well

Status
Not open for further replies.
p400

p400

VIP MEMBER
Joined
Jul 14, 2014
Messages
1,296
Country flag
I purchased a new stainless rear master barrel assembly from Bonnevilleshop and have installed it , tried to bleed the rear caliper, but this master did not seem to be pumping.

Removed new rear master, filled with fluid, attemping to pump, but it only pushes a inch or so of fluid when compressed, but sucks it back in when released.....when hooked up as shown.

There is about .005 - .010 clearance from this new stainless barrel and the pushrod.

Is a preload needed to achieve correct pumping?

New Rear Master Cylinder not performing well
 
Last edited:
So reading further - I have screwed the new barrel in one turn to preload and seem to get the same result of pump small amount out but suck it all back in .

I cannot get another barrel turn to achieve more preload.
 
p400 said:
So reading further - I have screwed the new barrel in one turn to preload and seem to get the same result of pump small amount out but suck it all back in .
Click to expand...

Have you tried restricting the return flow?


p400 said:
I cannot get another barrel turn to achieve more preload.
Click to expand...

Correct procedure is to screw the barrel assembly inwards until all pushrod play has just been removed.
The barrel should then be given one full turn plus whatever part of a turn it takes to bring the reservoir stud back to the vertical position at which point it should be possible to blow air back through the unit from the outlet to the reservior vent hole.

http://www.classicbike.biz/Triumph/.../Lockheed_Hydraulic_Brakes_Triumph_Norton.pdf
 
This Mk3 rear assembly, and I am sure any other mk3 would be same, has the push rod making contact and allowing 3/4 turn to complete the reservoir back to upright and no more turns allowed due to mechanical lock up of the push rod within the black cast housing.

Is the only test to confirm that fluid and air will return to the reservoir when at rest ?

New Rear Master Cylinder not performing well
 
p400 said:
This Mk3 rear assembly, and I am sure any other mk3 would be same, has the push rod making contact and allowing 3/4 turn to complete the reservoir back to upright and no more turns allowed due to mechanical lock up of the push rod within the black cast housing.
Click to expand...

The pushrod shouldn't completely lock up and prevent the barrel assembly from being screwed further in, if that's what you meant, or the pushrod wouldn't activate the piston.
If you mean the pushrod then starts to press against the piston as you screw the barrel assembly into the casting then that sounds normal.

p400 said:
Is the only test to confirm that fluid and air will return to the reservoir when at rest ?
Click to expand...

It's a check that can be done before reinstalling the master cylinder. It doesn't actually need a pump but it's probably healthier than physically blowing through the unit once it is contaminated with brake fluid and it doesn't need to have fluid in the reservior.

An alternative would be to check if the caliper pistons push back into the caliper relatively easily but the system needs to be connected and bled for that.
 
Last edited:
I was able to bleed the system with this additional 3/4 preload turn.
1/4 turn until no push rod clearance and then 3/4 to complete a full turn,
brake works okay , but too much rear brake pedal stroke required.

i believe that i cant get another barrel turn because of running out of clean threads.
So i can think of three options-
1. take apart and clean threads in the cast housing to allow another turn.
2. grind the first thread off the new barrel.
3. add a spacer to the push rod.
 
I have been riding this Mk3 for a year or more and have grown tired of the rear master pedal travel.
The rear Mk3 master requires 0.400" of pushrod travel to reach braking.
At the Mk3 pedal, this equates to 2.0"+ of travel.

I have bleed the system a number of times never finding any air or resolving this long travel issue.

20200817_Mk3RearMaster2.jpg
20200817_Mk3RearMaster3.jpg
 
One issue that concerns me is the "rest" or stop position of the pushrod.
It seems to me the pushrod is traveling too far out of the master cyl black alloy casting.

20200817_Mk3RearMaster4.jpg
 
p400 said:
It seems to me the pushrod is traveling too far out of the master cyl black alloy casting.
Click to expand...

The nuts don't look too far out (although the boot should be in the nut groove).
New Rear Master Cylinder not performing well


The shoulder on the pushrod inside the casting is the return stop and which is non-adjustable.

Norton Spare Parts - Genuine Norton Parts - Norton Motor - Norton Motorcycle - Norton Commando

Norton Spare Parts: We manufacture parts in our own workshops. We measure, test and inspect a selection of components from all inward deliveries.
andover-norton.co.uk

It's the setting of the master cylinder assembly in the casting that advances or retards the master cylinder piston so one extra turn of the master cylinder will probably reduce initial pedal travel, however, it's extremely important that screwing the master cylinder further into the casting doesn't result in the piston (seal) blanking off the vent port when the brake is released.

Have you tried adjusting the pedal slightly higher which obviously won't change the travel but could make the brake easier to use?
 
Last edited:
Mine has no where near as much pedal travel to engagement.
Keith Newton set it up sweet here in Ontario.
The boot doesn't last long though , I'm on my 3 rd. one , but no seal leaks yet.
 
In looking at this Mk3 rear master, I am concerned about the push rod engagement with the new hyd cylinder.
There seemed to be a lot of corrosion inside the original black body and and my concern is the push rod seating further into the body than acceptable......and this causing a need to require more pedal travel.

My B dimension is 0.440", and this needs to be to allow brake activation.
A dimension of 0.360" will stop and not allow brake.

New Rear Master Cylinder not performing well
 
p400 said:
There seemed to be a lot of corrosion inside the original black body and and my concern is the push rod seating further into the body than acceptable......and this causing a need to require more pedal travel.
Click to expand...

The master cylinder is adjusted according to the position of the pushrod.
If the pushrod had receded due to corrosion inside the casting then the master cylinder would compensate by screwing further into the casting.
 
Deets55 said:
Just my .02 cents but would that new M/C be the 13 mm one? If so I would expect it to have more travel than the old one.
Click to expand...

Good point! I went with the stock size for the rear and 13mm front just to avoid excessive rear travel.
 
Yes , mine is stock OEM. Less travel before engagement . Which tells me you need to play around with screwing in the new aftermarket unit more ?
BTW I have a MAP aftermarket one I purchased 20 years back still sitting in it's box , no instructions.
I do know that when they decide to rust up tight it's a chore to remove (heat) and clean up the threads and reassemble it all with new seals and getting the little fluid holes set up right.
 
I'm not sure if this has been said already,... If your disk is not flat that will drive the pads further backward, causing the distance they have to travel to be greater when you apply the brake again. That extra distance takes a greater volume of fluid to get the pad to the disc. That translates into longer pedal travel...

Also, the way the master unloads hydraulic pressure at the top of the pedal travel by exposing the secondary port keeps the master from sucking the slave piston backward excessively. If the secondary port wasn't there or was blocked (somehow) then when you released the brake lever, the master would suck all the fluid backward pulling the slave pistons back too, which would also cause excessive pedal travel to make the piston travel that further distance to again contact the disc...

As was said, a smaller diameter master will have a longer amount of pedal travel...
 
p400 said:
One issue that concerns me is the "rest" or stop position of the pushrod.
It seems to me the pushrod is traveling too far out of the master cyl black alloy casting.

View attachment 18251
Click to expand...

In the photo, the leg of the spring doesn't appear to be correctly located on what should be a shouldered nut?

Norton Spare Parts - Genuine Norton Parts - Norton Motor - Norton Motorcycle - Norton Commando

Norton Spare Parts: We manufacture parts in our own workshops. We measure, test and inspect a selection of components from all inward deliveries.
andover-norton.co.uk

Also, the head of the clevis pin (23) normally goes on the outside with the safety fastener (25) on the inside.

Norton Parts Drawings - Genuine Norton Factory Parts - Commando Parts -

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

New Rear Master Cylinder not performing well
 
Today i removed the rear master from Mk3 in question. I had forgotten the joy in servicing this master cyl.....lots of pieces need to come apart to get the cyl out, at least for me.

Anyway, back at the start of this new 13mm rear, i could not get the additional barrel turn because of the threads locking up and not permitting another turn. Today after removal, loosen tiny set screw, the barrel easily added another turn...WTF!
I pumped air back through the outlet end of this new 13mm cylinder and air travel thru to the reservoir first port.

I reinstalled master, bled as needed and now have 1.5" of pedal travel rather than the 2" i started with.,
Better , but not road tested yet.

New Rear Master Cylinder not performing well
 
Status
Not open for further replies.

Similar threads

A
Mk3 rear master cylinder rubber boot
Replies
14
Views
360
Torontonian
Torontonian
Leonc
Left Hand Rear Master Cylinder
Replies
7
Views
553
Ron L
Ron L
Chris
  • Locked
Rear master cylinder special
Replies
14
Views
2,276
SteveA
SteveA
possm
  • Locked
Rear Master-cylinder exploded view
Replies
2
Views
1,017
L.A.B.
L.A.B.
EstuaryBoy
  • Locked
Mk3 13mm Rear Master Cylinder
Replies
0
Views
848
EstuaryBoy
EstuaryBoy
Back
Top