Hello all.
I am seeking solutions to my front brakes on my MK V that is currently on the road to gain a better (compared to modern) brake peddle.
The issue are (1) bleeding air from the front brakes and (2) getting a better peddle response.
(1) Bleeding-:
I am seeking info from anyone who has left the front brakes as standard but reversed the entry point for the fluid to the lower piston and placed the bleed nipple on the upper piston, thus allowing the air to be easier expelled on bleeding.
This appears to have maintenance benefits to be and easy option with min changes.
(2) Peddle response
Has anyone replaced the existing master cylinder utilizing the existing mounting and peddle setup with a larger diameter cylinder thus delivering greater fluid for the same peddle movement or over bored the existing housing and used the existing piston with appropriate upgrade in seals?
Or is there a better way, say utilizing another master cylinder in the original mounting configuration?
I prefer not to change the mounting position of the master cylinder or add addition equipment such as boosters etc, but just want to improve the existing set up.
Don’t move the brake hose to the bottom cylinder position. Hoses are positioned high to be more protected from impact. It is not necessary to have the bleed nipple at the theoretical highest point, as the fluid is passing through small bore pipes and cylinders with small chambers, so the air bubbles can’t ‘pool’.
Don’t go to a larger master cylinder as you will need more effort on the pedal for the same braking performance. It reduces the pressure in the system and therefore the force pushing the shoes.
You seem to hint that you are having too much pedal movement. Check that you have enough lining thickness and that they are not unequally worn. Also the shoe manual adjustment should be set to the least running clearance. Two of the four adjusters on the front are behind the air scoop screens which you need to remove to be able to sight for adjusting.
You may have already gone through these items but I thought I’d note them anyway. My distant experience with a V reminds me that the brakes were quite adequate and had normal pedal travel after all the details were sorted out.
There were two types of brakes in the Mark V. Which do you have?
The early version was fixed pivot shoes with an anchor pin for the shoes.
The later version was sliding pivot shoes with a slot cap on the pistons for the shoes. This is what I have.
Agreeing with Peter, I think the brakes are fine as is. Maybe there is something else wrong with yours if you think they are not good enough for today’s traffic.
I always bleed mine with a clear tygon hose running into a jar with some fluid in it, so bubbles are expelled into the jar and only fluid is sucked back in.
Bearing in mind that a Mark V is not like modern cars with power discs all around, so go easy on the tailgating and cutting in and out.
Hello Jeffrey, brakes in the Mark V certainly are not great compared to modern. Over the years of usage with them in the original (later) design I am comfortable with them for the driving I do.
The bleeding of the brakes can be aided as Rob describes. I also put a smear of grease around the base of the threads of the loosened nipple during bleeding to remove the potential air path on pedal retraction. Bleeding my brakes was a bit frustrating before figuring out the smearing of the grease tactic.
It is important to have the brakes adjusted prior to bleeding since the pedal travel is substantial when properly adjusted and bled. Pedal movement over half the distance of pedal-to-firewall in normal braking is typical in several Mark Vs on which I have worked. The brakes can be adjusted so that pedal reaching firewall does not occur even in hard braking. Such a large pedal movement is not immediately indicative of bubbles in the lines, though large travel is present when bubbles are present.
Having said all these things, my biggest concern with the braking system (outside the several enhanced dangers of driving a very old car among moderns) is the single line master cylinder. Dual master cylinders give a confidence in failure that two of the brakes still will work if a flexible line bursts or leaks. The single line master cylinder goes to no brakes if any line is burst or leaks. Fortunately I have not had this experience in the Mark V (although I did have this problem on a mountain road in 1970 when using a 1964 Chevy Impala with automatic transmission, a ride not easily forgotten).
Thanks for the reply’s.
I do have the sliding pivot shoe (latter version) with the shoes adjusted as per the workshop manual on shoe to drum clearances all around. I had to readjust the vertical lay of the linings on the rear as they we not parallel to the drums (not done on assembly several years ago or partially done and not returned to complete??), this possibly eliminated some play in the pedal.
Yes agree with sentiments that compared to modern brakes they are very different. I do have a truck semi-trailer and bus license so totally agree re distance to other traffic, but you can never fully anticipate what other drivers will do, But was trying to maximize the effectiveness of the MK V brakes. Compared to my 1928 Dodge standard 6 with solid rods that I can lock all wheels if I try (different tyre size and pattern I know) , they seem less effective.
Thanks Roger for the suggestion of a smear of grease on the bleed nipples, as I was having air going back in on rear l/h on bleeding due to worn threads. this was rectified by re-taping and inserting an adapter to take the original bleed nipple size, all sourced from a local brake repair company in Geelong Victoria.
I agree that a larger bore in the master cylinder means greater pressure on the peddle for the same fluid out.
Back to hands and knees and re-bleed again to see if I can maximize the late 40’s state of the art system!
I’ve always bled brakes with an assistant. I get them press the pedal slowly down and they tell me when it’s at the floor and I tighten the nipple. I shout release, they release the pedal then I open the nipple again and we continue until we get no bubbles. I know that you do get automatic bleeders that have a one way valve but the valve might as well be you because can monitor the bubbles and you need to be out of the car to regularly top up the master cylinder anyway.
I just open the bleeders a quarter turn, I guess fluid gets in the threads along with the grease and they don’t seem to leak air back there then.
You should be able to lock up the wheels, but the best braking is achieved when you almost lock them up. Then braking distance is as good as your tires. Radials would be an improvement.
A 1928 Dodge flathead 6 was the first antique car I ever worked on, a neighbor let me help him a bit.
Just an interesting note about the last V brakes I worked on.
The car had not been used for some time and on first driving, the brakes pulled to the left, dangerously so when pushed hard.
An inspection showed reasonably equal wear and adjustment all round and everything in excellent condition except that the linings were showing delamination from the shoes. A potential accident waiting to happen.
This did not explain the harsh pull to the left but I had the shoes relined to start from scratch. I then had a problem refitting the drum on the offending side. It was not possible to get a running clearance. Closer inspection revealed that the piston on one cylinder was projecting about 3mm more from the body than the other. Withdrawing all pistons confirmed that only that one was longer than the others. A replacement was found amongst the spares the owner had and the problem was overcome and they worked extremely well.
I do not know what application this alternative piston is relevant to but there is a risk of mixing the two types if one is not aware of differences. I only raise this for general information. Does anyone know of this anomaly?
Yes, this is part of the procedure on the sliding pivot brakes under discussion, although it doesn’t do anything with the earlier fixed pivot type.
I have another anomaly possibly related to that reported by Peter. My original wheel cylinders all had a steel skirt over the pistons with the slot pressed into the skirt, and the OD of the cylinder machined smooth.
I also have some nearly identical cylinders with a lip for a rubber boot as part of the casting, and the pistons have a slot machined in, which I believe were later replacements.
Possibly the piston from one type could have found it’s way into the other type?
I have MKVIII front drums at the moment but they are the same size as original MKV
We have annual MOT/TÜV inspections, but for historic cars it used to be biannual, for cars first registered before 1960 it’s every four years.
In the compulsory brake dyno I have always gotten 3.6+ kN per wheel.
That’s more than on any of the disc braked cars I have ever had, incl. the V12 E-type, Ser. 2 XJ6C and the Ferrari 456GT. The tyres are the limiting factor, so IMO no point improving the brakes as long as they work as designed. YMMV.
Also FWIW my original slave cylinders, Girling from July 1950, look just like that. AFAIK they were also used in some Ferraris and Alfa-Romeos of that era.
Another variable is lining compound. I worked in the brake industry for a while and we fine tuned lining and pad compounds based on the OEM and aftermarket desires. There are soft, high friction compounds that cause good pedal feel, powerful retardation and hardly any noise. But these compounds tend to make much dust and need replacing too often for the OEMs. My sources for these older brake linings are gone, but they are around in old stock. Asbestos was used because it worked well…. I did have an old set of soft, aggressive linings that I’ve used in my SS100 restoration.
The XK120 went through several changes in brake shoe material during it’s production run, presumably developmental improvements.
Shoe and lining design is getting to be a lost art. There is a center of pressure, and too much lining can be as bad as too little.
When I got new linings bonded on my 120 shoes they were a half inch too long and I trimmed them off with a saw. I arced my shoe linings by hand with a file to fit the drums.
When I got my Mark V in 1969 it had a broken rear wheel cylinder, and I got one from a local foreign car parts place. It fit and I drove it as my only car for 3 years. Decades later I discovered it had smaller diameter pistons and was for a Mark VII.
Thanks all for the great insight for the brake issue. There is a wealth of knowledge out there.
I do have the earlier type slave cylinders as per Rob’s info and are both the some on rear.
Will re-bleed ,as I feel I still have air somewhere in the system to be eliminated, with a 2nd assistant which has always been my preferred way but have used the single hand pump bleed with some success.
Old saying why change some thing that work, just because it is a new idea.
cheers Jeffery
Unlike the later, two-circuit, boosted and much more complicated systems found in E-types, Saloons and XJ’s (which may already have had also ABS) which require specific bleeding order and possibly the power and engine on, the MKV system is the simplest possible, the fluid flows down from the reservoir and the single main cylinder pumps the fluid to all six slave cylinders.
But in all hydraulic systems one weak spot is enough to ruin the whole system, any leak or any air anywhere would mean it does not wirk right.
I also agree that the way the linings sit and how they touch the drums is of course essential. The reason why no booster is neeed is that when correctly set the linings bite into the drums evenly and progressively, but ONLY moving forwards!
I have had a couple of cases of my heart jumping to my throat as I have very steep ramps in the city garages and if reversing down on a ramp it does feel as if there’s something wrong with the brakes! Yikes!
