Displaying items by tag: Brakes

For many years I drove on drum brakes particularly in MK7s and I did not have any major problems in pulling up. I am of the opinion that a well maintained set of drum brakes is nearly as good as disc brakes however they do have a problem with fade when hot and are darn near useless after being immersed in water while crossing a flooded causeway.

I was happily driving the metallic grey MK 1 which is equipped with drum brakes and knocking up a few Ks when I noticed an appreciable decay in braking effect and the pedal was getting closer to the floor. I almost ignored it as I am getting close to completion of the MK2 disc brake front end which is going to be fitted in the near future. However it is not in my nature to leave a vehicle in a "suspect" state and I also heard a couple of clacks from the front end while pulling up in the shed.

Getting my dearly beloved Honor to actuate the brake pedal while I roamed around outside revealed that there was obviously a fair bit of movement going on in the brake system in the front end. Jacking up the car, removing the front wheels and brake drums revealed brake shoes that were in very good order and brake drums that were smooth and shiny without any scoring. The previous owner had advised me that he had the brakes "done up" only a short time before I acquired the vehicle. When I was preparing it for a "roadworthy" (safety certificate) I had checked the brakes and the shoes and drums were in apparently first class order and they were also checked and passed by the person carrying out the safety certificate inspection.

On close inspection I noted that the automatic adjuster bar was at the limit of its travel. Hold on – what is going on here thought I!. I checked the lining thickness which was the correct ¼ inch and also noted that the trailing shoe on the right hand front brake did not show any sign of contact with the drum. In fact with the brake drums removed you could put your foot on the pedal and get brake pressure even though there was theoretically nothing to push against or to stop the slave cylinder pistons flying out of the slave cylinder.. It turned out that the brake slave cylinders were at the extremity of movement and locked up against the travel limit of the automatic adjuster bar.

The correct internal diameter of a MK 1 Brake drum is 11 1/8 inches. I checked the internal diameter of the drums on this car and found out that one was 11 5/16 inches and the other was very close to 11 3/8 inches. I.e. one was oversize by 3/16 inch and the other was nearly ¼ inch.

The person responsible for turning out these drums to such an amount and refitting them is guilty of criminal negligence. While I have been unable to find out any recommended limits by Jaguar, general automotive industry consensus is that on a drum of this size around 1/8 inch or about 125 thousandths of an inch (.125 inch) oversize would be the limit and after that the drum should be discarded. The problem is that a very hot thin drum under severe braking has the potential to separate the drum brake contact area from the brake drum face assembly leading to a total loss of brakes. What made matters worse is that they had not bothered to consider putting in thicker linings which are readily available by specific order.

I have all sort of good Jaguar things hidden away in the shed at the end of the stables which I have christened "Possum Palace" as a family of possums lives there as well. They have claimed their own paw paw tree which is regularly raided and I can't use the top shelf of the Dexion shelving as they use it for their daytime sleeping site. Anything stowed on the top shelf is promptly kicked off to the detriment of the car parked in the shed! Anyway back on to the brake problem. I found that I had four MK 1 drums which varied from .040 to ,080 inches. oversize and I selected the best two which got a quick hit from the angle grinder cup brush to clean up the light surface rust in the drum contact surface areas followed by a clean up with some 280 grit wet and dry paper.

Resetting the brake shoes and wheel cylinder pistons to the inboard limits of the automatic adjusters and fitting these "new" drums resulted in only a small movement outward in the automatic adjuster bar and the brake pedal returned to a maximum height. The differences in a road test were quite dramatic as I was able to lock up the front wheels on bitumen in a panic stop from 60ks/hr.

My advice to anyone overhauling early model drum brakes [which ceased in Jaguar production in 1959] is to speak to a brake specialist and ensure the drums are properly measured and reasonably legal and that appropriate thickness lining are used to re-line the brake shoes to account for any oversize drums. By the way the correct composition linings for a MK 1 drum brake system are quite soft and the experts at Action Brakes in Nudgee Road, Hendra suggest a maximum life of only 20,000 miles in normal use.

Whilst I had the MK 1 radiator out I was having a serious look around for rust and any other problems prior to painting the general area surrounding the radiator. I had a close look at the steel brake line that feeds the left front wheel brakes from the hydraulic distribution block just after the power booster. Overall it looked pretty good however there was one spot where there was some rust for about 10-mm. When I touched this the line started leaking hydraulic fluid. This spot is actually hidden from normal view as a U shaped bracket below the radiator supports the brake line in this area.

I went to make a new line but found that parts of the flaring tool were missing and suspect they were in eldest sons toolbox as he was the last to use it. I was also very busy with work and decided to outsource the manufacture of a new line to Stopmasters in Brendale. They made a new line complete with new fittings for the grand sum of $18 and at that price I have decided that I shall no longer persist in these sort of minor repairs with all the running around to get line, fittings and a working flaring tool all together at the same time.

I also enquired about the possibility of using copper line rather than steel but they informed me that Queensland Transport has ruled copper line as illegal because of problems of work hardening and cracking around the end fittings. That is a little strange as all of the Pommy restoration magazines seem to recommend copper brake line as a solution to their never ending corrosion problems.

Club member and friend Ben Stafford had just returned from Papua New Guinea and dropped in for a beer. I told him of this brake line problem and he said that he had had precisely the same problem in the same line in his 420. i.e. under the radiator. It appears that this "sleeper" corrosion problem may exist in MK1&2, S type and 420 cars, which share fairly similar engineering in their front ends. I'd suggest that next time you have the radiator out of one of these cars a close inspection of the brake line would be in order. It is relatively easy to replace the line with the grille and radiator removed.

I can hear regular readers groaning “he’s not on that brake hose subject again” however a bit of thought about this one is definitely worthwhile if you are restoring a car or doing a major overhaul of a brake system.

A company called BrakeQuip has gained Department of Transport and Regional Services approval for a Component Registration Number #30886 to manufacture stainless steel braid covered Teflon brake hoses. What attracts me is that teflon hoses have an infinite life in aeroplanes and are miles superior to the old cloth/rubber hoses, which only have a life of 6 years in an aeroplane engine bay.

There are also a number of other claims including less elasticity in the brake system giving firmer pedal pressure without sponginess and therefore increased efficiency particularly under heavy braking. They are slightly more expensive than rubber hoses typically costing around $65 each

They appear to have set up a number of outlets and franchised agents to make these hoses on the spot. . I found two in Pine Rivers, one at Brendale and one at Lawnton.

They make them on the spot to your specific requirements by copying your old hoses. They have a website which is www.braidedhoses.com.au.

A JDCQ member had a problem with his Jag 420 series brakes. The power boost system appeared to have failed and it required incredible pressure to stop the car. We got involved in a diagnosis one morning with the car upon his hoist and to be very honest it took a fair bit of effort to sort out the problem.

What appears to be a dual brake system is not quite what it seems. The master cylinder is in fact a single primary system that then feeds pressure and air information to the remote power booster system where the system becomes dual. Each primary and secondary system has its own hydraulic reservoir.

The power booster system uses vacuum on both sides of the air piston. A remote air valve mounted on the primary master cylinder supplies vacuum on the drive side of the piston but when the master cylinder is depressed introduces ambient air pressure to the drive side of the piston hence assisting the hydraulic brake action. Heath Robinson would have been proud of this arrangement.

The final diagnosis was that the air piston/diaphragm in the booster unit was leaking badly. By serendipity another acquaintance was "parting out" a 420 with a good booster and this was acquired to get the car back on the road while a more extensive overhaul takes place on the original booster.

It should be noted that we discovered that a number of E types from roughly 1965 on share the same braking system.

The MK1 was inclined to pull itself into the middle of the road and make a Kamikaze attack on any oncoming traffic whenever I hit the brakes. It was definitely not the best way to drive and tended to worry oncoming drivers. After some serious analysis over a 6 pack I went after the possibility of failure of the left front calipers, however my mind said both left front calipers were rebuilt to new specification and a double failure/freeze up would be most unusual.

A simple check by cracking the brake bleed valves while my “dearly beloved” pressed the brake pedal showed little flow or pressure to the pair of LH front calipers. Further investigation revealed that the left front brake hose was blocked. When I put the brake system together a couple of years ago I had checked the hose was OK by passing a piece of wire through it. I had no knowledge of the history of the hose but it had looked and checked out OK. In fact due to age it was developing a severe case of a blocked artery over a short time period.

The offending hose was extremely difficult to remove especially at the body bracket end of the system. I resorted to the “hot spanner” i.e. oxygen/acetylene torch and after successfully setting the MK 1 on fire three times finally resorted to grinding through the retaining nut with an angle grinder. That got it off the car but my problems were not over. I then had to get a replacement hose.

Every retail source was checked and I kept getting the reply “not in stock”. Interestingly enough all the suppliers could quote me prices between $59.00 and $67.00. In desperation I contacted Graham Deahl who is the Victorian MK 1 register giru and explained my problem. He advised that they had similar problems with brake hoses and I had best contact a hose manufacturer.

Serendipity prevailed because a local parts supplier had suggested the same thing and had recommended a company called Brake Parts Australia [BPA] at 109 Links Avenue, Eagle Farm. For readers remote from Brisbane their address is Ph [07] 3268 2211. Fax [07] 3268 2533 and Email This email address is being protected from spambots. You need JavaScript enabled to view it. and they also have a web site at www.bpa.com.au

I approached BPA and put the problem to them. The reply was laconic. Gary their technical fitter said

“ They had never been stumped by a brake hose” After examining the remains of the MK 1 hose said it was no problem to make me a new one with all new fittings. He also said that they had never had a hose returned after failure as their equipment was checked regularly by [transport?] authorities.

I asked what was the price?

He answered ” $60.00 - that is the standard price for a one-off hose”.

Me: Does that include GST?

He: “yes”

Me; Are you approved to manufacture brake hoses?

He; “Yes” [and proceeded to show/tell me about the certification]

Me; How long for delivery? [Believing fittings would be a problem and may need to be ordered in]

He; “about 15 minutes or less if you are in a hurry”.

I said, “I am in a hurry but I’ll wait - make me two of them”

“OK” sez he

And that readers was what took place. About 10 minutes after the start of the conversation I had in my hand two brand new brake hoses to the exact and original specification for a MK1. I might add that I had spent almost two weeks trying to source a replacement brake hose.

I dropped in next day as I had a problem with the 5/8 inch 26 TPI nut at the body end. I had destroyed the original with the 4-inch grinder just to get the hose off the car without destroying the mounting bracket. Nobody could supply a nut however Gary sorted this out by re-cutting the inner hose retaining thread for a SAE national fine] NF] nut. I noticed about 150 new [after market] hoses he had just turned out for distribution into the retail market. He remarked that the hoses had been ordered the day before and he expected pickup at any time. In other words this company was seriously involved in after market supply.

Somehow I think we Jag owners believe that English magic is used to produce parts for our cars and it must be “original” to be any good. After market organisations like BPA turn out a product standard which is controlled by Australian government authorities and are more than willing and able to support our old car cause. The important thing for we restorers is that they can supply “one off” requests at short notice and within the normal retail price range.

I don’t apologise to our normal retail suppliers. Having copped the trauma of “unable to supply” or “not in stock” it is only fair that alternatives should be readily available to club members.

Brake Boosters Another issue came out of my visit to BPA. They are equipped to overhaul brake servo power boosters. This was qualified by remarks that parts are difficult to obtain on some types but the customer should liaise with them and they would make recommendations on the best course of action i.e. repair or replace with an Australian made product.