No brake pedal pressure

[Aztec Rover]

Hi there, I am in need of some expert help.

I have a problem with the brakes in my Series lll. When I push the brakes it goes right to the floor. After 3 pumps I have a reasonable pedal although not great. There are no leaks and the pedal stays form until released. The rubber hoses show no signs of ballooning or over expansion.
I have re-sealed the rear cylinders, replaced the master cylinder and the front brakes are new by the way of a Rotor conversion kit. There is no air in the system as it has been bled several times both manually (pumping pedal) and by a power bleeder. My system has no servo.

Any suggestions? I am all out of ideas.

Thanks, Bob

[Les Parker]

Have you tried clamping off the 3 jump hoses to see if you have a firm brake pedal?
Then realease the clamps, rear first, until you find out which area is letting the pressure go.
Pse advise.

[Leslie]

Whoa.... I thought all SIII had a servo..... mine has a servo.

Anyway, I thought you needed a servo w/ the disc-brake conversion..... ?????

[Aztec Rover]

I was told that the conversion was good with all series vehicles. Definatly no servo on this rover. Its a 1973 RHD. The brakes were the same before the conversion which was part of the reason I re sealed and replaced everything. I even screwed the rear adjusters tight to make sure there was no travel on the shoes to see if that would make a difference.

[greenmeanie]

With disc conversions you have to be slightly careful as calipers respond differently from drums.

You'll need to check the details to make sure I've got it the right way round but IIRC drums require a small amount of residual pressure to hold the shoes out close to the drum surface. Disc calipers are self adjusting and keep themselves out close to the disc. You are having to pump your brakes to move the shoes back out to the drum. If you don't want to do a servo conversion you can look at Jegs/Summit who sell a pressure regulator that you plumb into the line to the rear brakes.

Copied from TeriAnn's webpage citing information from the supplier:
Which master brake cylinder:
Question: The calipers are 2 pot and the 88 master cylinder is designed to push fluid into a single cylinder at each front brake.
Does an 88 master brake cylinder pump enough volume for the disc brakes & get good pedal height on the first try or do you recommend switching to 109 master cylinder?
Reply: During application, the pads in a disc brake system are displaced much less than the shoes on a drum brake system so a smaller volume of brake fluid must be moved by the master cylinder. This is offset to some extent buy the larger cross sectional area of the disc brake caliper pistons as compared to the drum brake cylinders but a disc brake system in good condition will have less pedal travel and the pedal will "feel" firmer than in a drum brake system. Note that "pressure" is as important a design consideration as "volume" in choosing a master cylinder. I recommend upgrading any Land Rover to a dual braking system for the significant additional safety margin the dual system provides. Power boost is helpful (and commonly used) in disc brake systems which do not have the same "positive feedback" characteristics as drum brake systems.
Mel

For reference:
http://www.expeditionlandrover.info/discBrake_Torrel.htm#info

[Aztec Rover]

OK, I clamped off the two front brakes and the pedal was much better. It looks like I have a volume problem with the new front caliper pistons.

Would the best option be to bite the bullet and buy a servo, brake pedal and dual master cylender or is there an easier way around it?

[I Leak Oil]

You didn't say if it is an 88" or 109" but when I converted to discs on my 88" I upgraded to the 109" master cylider which has a larger bore for the front brake circuit. I also went with stainless braided lines and the two upgrades give a very firm pedal. Adding a servo will do nothing for the volume of fluid you need to push. Servo's simply reduce to amount of leg you need to stop the truck through force multiplication. I think you would welcome the addition of the servo with a disc setup.

With all of that said if you had the same problem before the disc swap then you might have a bad flex hose or a leak that is sucking air back in. Did you try unclamping just one front brake hose at a time?
Jason T.

[Aztec Rover]

My Rover is a 1973 88 with no servo and a CV master cylinder.
I assume I will need a different pedal and mounting box to fit a 109 master cylinder and servo?

[Jim-ME]

You would not need a new pedal or mounting box to swap to a CV style 109 MC only if you switch to a dual MC and servo.
Jim

[rbradley]

Hi Aztec Rover

Please let us know what you find. My Dad and I have the same problem
in our SeriesII. We have replaced all wheel cylinders,master and hoses.
We have bled the system from the pedal and with pressure bleeder. We
have even raised the car as per the workshop manual. Always the same
story pedal goes to the floor and only builds after a couple of pumps.
We have worked on British cars for many years but never had a problem
like this.

[graniterover]

Check the rear shoes. They can be installed incorrectly and the spring takes them too far from the drum, so you need to pump to get the shoe to go all the way to the drum. Also, they could just be out of adjustment pretty far. Check the manual for correct installation of the shoes in the rear.


Hi Aztec Rover

Please let us know what you find. My Dad and I have the same problem
in our SeriesII. We have replaced all wheel cylinders,master and hoses.
We have bled the system from the pedal and with pressure bleeder. We
have even raised the car as per the workshop manual. Always the same
story pedal goes to the floor and only builds after a couple of pumps.
We have worked on British cars for many years but never had a problem
like this.

[Les Parker]

There seems to be 2 questions here:-

1. Excessive pedal travel on original master cylinder

2. Benefits and requirements for upgrade to dual circuit brakes with servo assist.

I believe the original question relates to # 1

If the pedal is good with the 2 front brakes isolated, try releasing a front one and the rear jump hose to se if the pedal goes down at all.
Also, what happens when all 3 hoses are clamped off? You should have a rock hard pedal and no travel.
Lets deal with this before addressing # 2

[Aztec Rover]

Check the rear shoes. They can be installed incorrectly and the spring takes them too far from the drum, so you need to pump to get the shoe to go all the way to the drum.

Can you please elaborate on how they can be installed wrong?
I assume you are meaning the pin on the back of the shoe where the adjusting cam touches and pushes the shoe out?

[Jeff Aronson]

What can happen with the installation is confusing the leading and trailing shoe; it's possible to also get the springs hooked up incorrectly. I know because I have done it. Both will affect the braking power and result in a soft pedal, one that requires some pumps to get the pedal nice and firm.

I found myself with the need to pump my brakes to get a firm pedal after replacing all four sets of shoes. I was stumped, also. Mark Letorney got into my Rover, pumped the brakes, and told me to redo all the adjustments. I did just that, and sure enough, the pedal became firm again. It's easy to ignore the rear brake adjustment because of the front-weight bias of the Series Rover.

Lastly, I've also found that on occasion I cannot get the adjustment correct despite new shoes because I had worn out the rear brake drum. The Series 88" drum does not allow much room for turning and/or wear. When the drum is too big, then the shoe can't be pushed out against the drum with just one pump - thus, the need for the extra pump[s] on the pedal.

Les' brake line tricks do help with the diagnosis of the problem. Try it on your Series II to help you find the source of the problem.

Jeff

[Aztec Rover]

Hi guys,
Yeah I am still working on my brake issues. I fitted the 109 master cylinder to my 88 to compliment the disc conversion and to my disgust i found that the pipe to the brakes has a smaller fitting than the 109 cylinder takes. The brake pipes on my rover are 3/16 and the 109 takes the fitting that is usually on the 1/4 brake pipes. (same as the one from the reservoir)
What’s my options? Can I get the larger sized fitting that is suitable for the 3/16 pipes? :confused: