I am investigating getting the brake shoes on my 1939 Rover P2 relined with Kevlar compound in order to improve stopping/reduce brake fade. The Kevlar reportedly has maybe 50% or more improved friction and resistance to fade. I wonder if any other owners have gone down this route and could offer advice? Or indeed others who might advise against it?
It is proving tricky to source the Kevlar linings - I have sent messages to various companies who reline shoes but havent found anything specific as yet.
Secondly what is the advice on whether to rivet the linings or to bond them in place?
Any help would be appreciated
Rob
Kevlar brake shoes
Re: Kevlar brake shoes
I can only write from my own experience, which is 6 separate Rover cars from 1938 to 1947 in the past 25 years, those being the closest to your 1939 car, . The brakes on all of them have proved highly efficient lined with either original Ferodo , Don or Mintex linings, or a modern substitute. All have proved capable of stopping the vehicle from an indicated 60+ mph in an acceptable distance , 70+ downhill with the freewheel on the 6 cylinder models. I have yet to feel any insecurity with the system well adjusted and set up on a car of this period, more than can be said for 1946 on cars of other makes with hydro-mechanical Girling brakes. What they all won't do is drive like a modern car.
I say the above with a particular instance in mind. Over 20 years ago, I had a 1939 14 and a 1947 14, both in really nice order. I left the 47 with my father to use as he'd had a lot of Rovers in his younger days and thought very highly of them. When I visited him to see how he was getting on with the car, he had a complaint every time. The steering was poor, the brakes were poor - a constant litany of woes. I'd try the car and compare it to the 39 14 and other makes I had at the time and the 47 14 was, genuinely, perfection. It took me a long time to accept that the fault lay not in the car but with my father who had become a little too used to his automatic Ford Fiesta and his memory of driving a Rover in his 20s was now rather rose tinted by his 70s.
I still rivet my own linings on with a floor mounted punch and find them to be satisfactory but it is a devil to remove all the material from bonded linings to fit riveted ones. I wouldn't now willingly buy an older car without Girling fully mechanical brakes as they are the most reliable and least troublesome braking system to be found on this age of vehicle suffering no ill effects from little use unlike hydraulics.
A common issue that I have found with linings supplied new now is the degree to which ,fitted as supplied, they contact with the drum when applied. When the cars were new or newer, the linings were accurately finished but now they just seem to be cut from a roll and this produces two potential issues. The first is that they can be slightly too wide and may need filing and chamfering at their edges. Secondly, they may need filing down to remove high spots making the lining have the maximum contact it should have with the drum. If only a small part of the lining surface is contacting the drum, this will heat up the lining locally at that spot and it will also provide a minimum of stopping power compared to what was intended. Over the four drums, this could lead to a significant loss in real braking power although externally the indication would be that all was well as the brake would be going on and off ok and holding the wheel when firmly applied. The "turn the adjuster until it locks then back until free" method assumes that the linings make maximum contact with the drum but this needs to be checked. Of course, through time with use the high spots would wear down but as they did, the clearance will also increase and so newly fitted linings would need re-adjusting after a relatively short time to avoid increasing pedal travel.
I've had three older cars in recent years which have all arrived with recently fitted bonded linings, all of which must have been fitted to the car as supplied by a brake relining firm, presumably as a last gasp attempt by the previous owner to "fix" poor brakes. Each had an over-large amount of lining material and this, I think, was intended to have been shaped to suit the brake drum and backplate and not just stuck on the car as supplied. A look at how the shoe is moved by the expander unit in relation to the adjuster will show how it needs an element of shaping to provide more contact rather than less.
Another club I am a member of , not Rover, has been investigating braking efficiency results between modern materials and original ones and while it is early days yet, difficulties seem to arise between friction material designed for holding a load (i.e. crane brake material purporting to be suitable for road use) and material designed for slowing and stopping a rapidly moving drum. Some modern asbestos free materials sold as being suitable for the latter purpose do not have the heat absorbing properties of the originals and so the suggestion is to seek data sheets for any new materials to verify their actual properties before fitting. Fortunately, the lining type fitted to the 1939 on models is common to quite a few vehicles and so the friction material is available in various forms. MZ41 was a material that was used originally and while obviously unavailable now, it was impregnated with zinc wire to conduct away local heat so a modern material that had similar characteristics to it would be a potentially good find. One modern material's data sheet , something called GGW, would appear to show that above 500 degrees F ( 260 C), it fails to have any stopping power and at that point I think my contribution stops but I hope it may help with some suggestions to think about further.
I say the above with a particular instance in mind. Over 20 years ago, I had a 1939 14 and a 1947 14, both in really nice order. I left the 47 with my father to use as he'd had a lot of Rovers in his younger days and thought very highly of them. When I visited him to see how he was getting on with the car, he had a complaint every time. The steering was poor, the brakes were poor - a constant litany of woes. I'd try the car and compare it to the 39 14 and other makes I had at the time and the 47 14 was, genuinely, perfection. It took me a long time to accept that the fault lay not in the car but with my father who had become a little too used to his automatic Ford Fiesta and his memory of driving a Rover in his 20s was now rather rose tinted by his 70s.
I still rivet my own linings on with a floor mounted punch and find them to be satisfactory but it is a devil to remove all the material from bonded linings to fit riveted ones. I wouldn't now willingly buy an older car without Girling fully mechanical brakes as they are the most reliable and least troublesome braking system to be found on this age of vehicle suffering no ill effects from little use unlike hydraulics.
A common issue that I have found with linings supplied new now is the degree to which ,fitted as supplied, they contact with the drum when applied. When the cars were new or newer, the linings were accurately finished but now they just seem to be cut from a roll and this produces two potential issues. The first is that they can be slightly too wide and may need filing and chamfering at their edges. Secondly, they may need filing down to remove high spots making the lining have the maximum contact it should have with the drum. If only a small part of the lining surface is contacting the drum, this will heat up the lining locally at that spot and it will also provide a minimum of stopping power compared to what was intended. Over the four drums, this could lead to a significant loss in real braking power although externally the indication would be that all was well as the brake would be going on and off ok and holding the wheel when firmly applied. The "turn the adjuster until it locks then back until free" method assumes that the linings make maximum contact with the drum but this needs to be checked. Of course, through time with use the high spots would wear down but as they did, the clearance will also increase and so newly fitted linings would need re-adjusting after a relatively short time to avoid increasing pedal travel.
I've had three older cars in recent years which have all arrived with recently fitted bonded linings, all of which must have been fitted to the car as supplied by a brake relining firm, presumably as a last gasp attempt by the previous owner to "fix" poor brakes. Each had an over-large amount of lining material and this, I think, was intended to have been shaped to suit the brake drum and backplate and not just stuck on the car as supplied. A look at how the shoe is moved by the expander unit in relation to the adjuster will show how it needs an element of shaping to provide more contact rather than less.
Another club I am a member of , not Rover, has been investigating braking efficiency results between modern materials and original ones and while it is early days yet, difficulties seem to arise between friction material designed for holding a load (i.e. crane brake material purporting to be suitable for road use) and material designed for slowing and stopping a rapidly moving drum. Some modern asbestos free materials sold as being suitable for the latter purpose do not have the heat absorbing properties of the originals and so the suggestion is to seek data sheets for any new materials to verify their actual properties before fitting. Fortunately, the lining type fitted to the 1939 on models is common to quite a few vehicles and so the friction material is available in various forms. MZ41 was a material that was used originally and while obviously unavailable now, it was impregnated with zinc wire to conduct away local heat so a modern material that had similar characteristics to it would be a potentially good find. One modern material's data sheet , something called GGW, would appear to show that above 500 degrees F ( 260 C), it fails to have any stopping power and at that point I think my contribution stops but I hope it may help with some suggestions to think about further.
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RobHomewood
- Posts: 320
- Joined: Tue Oct 22, 2013 8:04 pm
Re: Kevlar brake shoes
To be fair I was relatively impressed by the brakes on my 14 when I first got the car, this being the first time I had experienced using rod brakes. In normal circumstance they are fine but I have experienced life threatening brake fade ie the brakes faded away to nothing going down a long narrow hill with banks on either side so it was a choice of crashing into the bank to slow down or chancing exiting blind onto the main road totally uncontrolled. I chose the latter and got away with it that time, even with a 90 deg turn involved. I also have an issue with the hand brake not holding on steep hills (of which we have plenty locally) so the Kevlar route seemed plausible. I have not had brake fade since I removed the chauffeurs trims from the (wire) wheels but that could be coincidence. I keep adjusting the hand brake settings but its still not brilliant.
I would still like to find people who have had experience of using Kevlar (other than bikers or crane drivers perhaps) so may continue to hunt for feedback
Rob
I would still like to find people who have had experience of using Kevlar (other than bikers or crane drivers perhaps) so may continue to hunt for feedback
Rob
Re: Kevlar brake shoes
As I recall there has been a debate previously on the forum regarding Kevlar linings following the wheeler dealer program where Edd fitted some in lieu of a disk brake conversion but notably on a much younger classic car. Having watched a re run of the said episode I did some google research with a view to trying such a material when replacement is next required but I did conclude its by no means a universal offering by the classic car brake relining companies.
From my own experience on our 35 10, when restored in early 90's a long gone traditional brake specialist in stoke on trent used what he said was mintex woven asbestos lining which he riveted. He also said he could only obtain this material because it was still made at the time for pit head winding gear in the collieries. With these linings and a full rebuild the performance of the brakes was the best they have ever been.
Subsequently as replacements became necessary my Father had them relined in a bonded on modern material and the brakes were never as efficient and additionally squeal had to be overcome by wrapping some rubber and a jubilee clip around the drums. I also recall an article by Mike Evans offering a riveted on replacement relining service due to a risk that there is a risk of lining detachment resulting from relying on bonding alone to an aluminium shoe. The car has had very little use in the last 10 years but based on this knowledge I have it in mind to make some changes to the brake linings so I to am interested in the outcome.
From my own experience on our 35 10, when restored in early 90's a long gone traditional brake specialist in stoke on trent used what he said was mintex woven asbestos lining which he riveted. He also said he could only obtain this material because it was still made at the time for pit head winding gear in the collieries. With these linings and a full rebuild the performance of the brakes was the best they have ever been.
Subsequently as replacements became necessary my Father had them relined in a bonded on modern material and the brakes were never as efficient and additionally squeal had to be overcome by wrapping some rubber and a jubilee clip around the drums. I also recall an article by Mike Evans offering a riveted on replacement relining service due to a risk that there is a risk of lining detachment resulting from relying on bonding alone to an aluminium shoe. The car has had very little use in the last 10 years but based on this knowledge I have it in mind to make some changes to the brake linings so I to am interested in the outcome.
Re: Kevlar brake shoes
It is occasionally possible to find new old stock MR41 type linings at autojumbles.
Mike
Mike
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RobHomewood
- Posts: 320
- Joined: Tue Oct 22, 2013 8:04 pm
Re: Kevlar brake shoes
Since I last posted I have been engaged in refurbishing the compensators on my rod brake sytem to see how that improves the braking. Well today I have finally got the brakes back together with rebushed compensators with new yokes and in the short test drive around the block the difference is amazing. I can now skid to a halt with ordinary pressure and even bring the car to a skidding halt with the handbrake which previously wouldnt hold the car stationary on anything like a hill so I am really pleased. So I dont need Kevlar linings and I dont even need new brake linings at all. I just hadnt appreciated that I could get so much better performance from my brakes and I shudder to think about the hundreds of miles I did last year through France etc.