Allan Westbury Posted August 26, 2014 Report Share Posted August 26, 2014 I have a 4a that I have fitted with an aftermarket servo but kept the standard pads. This has served me well for a number of years other than a tendency to lock up all 4 wheels under heavy braking. I am now looking to change the pads in an effort to get more gradual braking and would welcome suggestions from anyone who has solved this particular issue. Thanks, Ollie Quote Link to post Share on other sites
RogerH Posted August 26, 2014 Report Share Posted August 26, 2014 Hi Ollie, the standard car with standard pads can lock the wheels. Putting a servo on it makes it easier. ABS was invented because of this problem. Greenstuff pads may give the effect of softening the brakes but I wouldnt count on it. However it may be possible to reduce the effect the servo has. Sadly that is out of my area. Roger Quote Link to post Share on other sites
BrianC Posted August 26, 2014 Report Share Posted August 26, 2014 Dump the servo Quote Link to post Share on other sites
jerrytr5 Posted August 28, 2014 Report Share Posted August 28, 2014 Hi Ollie, Do you mean that you cannot apply even pressure to the brakes, and that they suddenly lock on? How heavy is 'heavy'? Locking up in an emergency stop is not unusual - learn to cadence brake. Disconnect the servo vacuum pipe so there is no servo assistance to see what difference it makes - you will have to brake harder, obviously. There are different servo ratios available, maybe yours is incompatible. Jerry . Quote Link to post Share on other sites
peejay4A Posted August 28, 2014 Report Share Posted August 28, 2014 Try Hawk road pads. I have a similar setup to you and I find these to be nicely progressive and they won't fade either. Quote Link to post Share on other sites
Alec Pringle Posted August 28, 2014 Report Share Posted August 28, 2014 If the servo is too high a ratio it can produce the symptom you describe . . . . Cheers Alec Quote Link to post Share on other sites
peejay4A Posted August 28, 2014 Report Share Posted August 28, 2014 I think they are available in 1.9 and 2.3 ratio from memory. How you tell them apart I don't know, presumably the higher ratio one has a larger diaphragm. Quote Link to post Share on other sites
Motorsport Mickey Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) As Roger says the standard system can lock the wheels without the servo, and as others have said the different servo ratios available may mean you have fitted a model with too high a ratio especially if you can lock all 4 wheels. That is not a symptom you want on a car, under all circumstances the front wheels should lock first. You could change the rear cylinders to reduce the braking effect at the rear which will make it less of a "widowmaker" but unless you can develop a more cultured braking foot removing the servo is the way to go. Mick Richards PS; Changing the pad material to something less effective just means the capability of the system is reduced, I think you are better off changing the mechanical application to make it a nicer brake. Edited August 28, 2014 by Motorsport Mickey Quote Link to post Share on other sites
peejay4A Posted August 28, 2014 Report Share Posted August 28, 2014 (edited) I don't think Hawk pads are less effective than standard, the opposite or at least the same I hope and I apologise if I gave that impression. They do brake differently though with no tendency to grab and the fade resistance is better. Edited August 28, 2014 by peejay4A Quote Link to post Share on other sites
stuart Posted August 28, 2014 Report Share Posted August 28, 2014 Servo`s are indeed available in all sorts of ratios from about 1.8 to about 3.5 or more so if you have a higher ratio then it would be very easy to lock the wheels up. Came across this years ago with a Citroen DS 19 that had a switch on the floor instead of a brake pedal, you only had to touch it and you were peeling your nose off the steering wheel. Stuart. Quote Link to post Share on other sites
Allan Westbury Posted August 28, 2014 Author Report Share Posted August 28, 2014 Thanks guys, From memory I bought the servo from TRBG so it should hopefully be reasonably matched to the car. I am loath to ditch the servo as I have uprated the engine modestly and had it showing 140 HP on the rolling road at Wiltshire Garages. Another well known supplier specialising in road/rally cars thought this was highly optimistic, but who am I to quibble! I remember reading somewhere that the first job when upgrading an engine is to improve the brakes so will probably follow peejay's advice and try the Hawk pads. Cheers, Ollie Quote Link to post Share on other sites
Alec Pringle Posted August 28, 2014 Report Share Posted August 28, 2014 Lockheed and Girling servos varied between 1.4 and 5 to 1 ratios - 1.4, 1.7, 1.9, 2.3, 2.4, 2.7, 3.0, 3.5, 4.5 and 5.0 are amongst the numbers I've seen. From past experience I wouldn't use anything higher than 1.9 even on a drum braked TR, and preferably 1.4 or 1.7 at most on a disc equipped car - except Wedges, for which higher servo gearing can be justified. I've seen TR specialists cheerfully offering servo units of between 2.3 and 3.5 in years gone by, absolutely bloody barmy in my view. Cheers, Alec Quote Link to post Share on other sites
ctc77965o Posted August 29, 2014 Report Share Posted August 29, 2014 I have a 4a that I have fitted with an aftermarket servo but kept the standard pads. This has served me well for a number of years other than a tendency to lock up all 4 wheels under heavy braking. Are your tyres any good? how old are they? What size are they? Quote Link to post Share on other sites
Allan Westbury Posted August 29, 2014 Author Report Share Posted August 29, 2014 Two questions: 1 Peejay where did you get your Hawk pads from & any idea of the correct part no? I see Cambridge Motorsports are stockists or Hawk sell direct online. 2 Alec any idea how you tell what ratio you have fitted? I will look up the receipt and see if it is mentioned but I cannot see any marks on the unit itself. Tyres are Firestone F590 185/65 R15 and I generally run at 26f 28r. They have plenty of tread and have a good 'feel'on the road. Thanks, Ollie Quote Link to post Share on other sites
peejay4A Posted August 29, 2014 Report Share Posted August 29, 2014 Hi Ollie, They were from Cambridge Motorsports, HB169 HPS fast road. Shown here : http://www.cambridgemotorsport.com/Hawk-Performance-HB169-Brake-Pads Quote Link to post Share on other sites
stuart Posted August 29, 2014 Report Share Posted August 29, 2014 Two questions: 1 Peejay where did you get your Hawk pads from & any idea of the correct part no? I see Cambridge Motorsports are stockists or Hawk sell direct online. 2 Alec any idea how you tell what ratio you have fitted? I will look up the receipt and see if it is mentioned but I cannot see any marks on the unit itself. Tyres are Firestone F590 185/65 R15 and I generally run at 26f 28r. They have plenty of tread and have a good 'feel'on the road. Thanks, Ollie What date is showing on the tyres? Stuart. Quote Link to post Share on other sites
peejay4A Posted August 29, 2014 Report Share Posted August 29, 2014 Hi Ollie, I just trawled my paperwork because my servo was from TRGB. It's a compact unit (7 inch I think) from Caparo-AP type HRK115. This is a 1.9 ratio servo so shouldn't be too fierce if it's the same as yours. Quote Link to post Share on other sites
Andy Moltu Posted August 29, 2014 Report Share Posted August 29, 2014 Before replacing brake parts check the tyres are not aged. Old tyres, irrespective of wear can loose grip dramatically and lock up with relative ease. Quote Link to post Share on other sites
littlejim Posted August 29, 2014 Report Share Posted August 29, 2014 (edited) ollieTR4A, on 27 Aug 2014 - 04:30 AM, said: This has served me well for a number of years other than a tendency to lock up all 4 wheels under heavy braking. Ollie Be tempted to find a skid pan, or some out of the way spot, and just tune my technique. Without ABS, would have thought that a white knuckle emergency stop would do that with many/most cars. (Other than my 4A when the brake pipe let go.) Edited August 29, 2014 by littlejim Quote Link to post Share on other sites
Allan Westbury Posted August 29, 2014 Author Report Share Posted August 29, 2014 Have only found one dot no. 0907 but presume others are on inside. Not too bad I wouldn't have thought. Interestingly I find I have Vredesteins on the rear and Firestone on the front. I obviously wore out the Firestone's on the back! Cheers, Ollie Quote Link to post Share on other sites
Ian Vincent Posted August 30, 2014 Report Share Posted August 30, 2014 I thought one of the benefits of a servo is that it allows you to fit harder brake pads that are less prone to fade under repeated heavy use. Rgds Ian Quote Link to post Share on other sites
Motorsport Mickey Posted August 30, 2014 Report Share Posted August 30, 2014 All braking ultimately depends upon the final arbiter and limitation, grip on the road. If you have a standard TR braking system in good order without a servo it will lock the wheels, even with the ultimate sticky tyres used in the TR Race championship and with Mintex 1144 pads that didn't fade and I could lock the wheels without a servo. The servo reduces the in car pedal pressure and does make the brake operation more like a modern car ie the wheels will lock even easier, if you have all 4 wheels locking you have the potential for a nasty situation. Mick Richards Quote Link to post Share on other sites
Lebro Posted August 30, 2014 Report Share Posted August 30, 2014 Ian. Agreed, When my '3 had drum brakes they used to fade dramaticaly under very heavy braking (I was younger then) My fix was to fit harder linings, & a servo (from a Cortina as I recall) worked well. I now have standard early TR3 discs, modern "standard" pads, & no servo, (& I am older & hopefully wiser !) so don't have any fading problems any more. On reason to fit a servo now would be to make pedal pressure more like a modern car. Bob. Quote Link to post Share on other sites
peejay4A Posted August 30, 2014 Report Share Posted August 30, 2014 (edited) Ian. On reason to fit a servo now would be to make pedal pressure more like a modern car. Bob. Precisely the reason why I fitted mine. My TR6 had one and I don't hear anyone advocating disconnecting the servo in that application. It's a personal choice at the end of the day. Edited August 30, 2014 by peejay4A Quote Link to post Share on other sites
ianc Posted August 30, 2014 Report Share Posted August 30, 2014 The TR6 was designed to have a servo and dual-circuit brakes, so I imagine that the sizing of master cylinder and servo is to obtain the best performance for that model. For that reason, disconnecting the servo on a TR6 would not be a good idea! On the other hand, the TR2/3/4 were designed without a servo in mind, and everything sized accordingly - a servo was an optional extra, but, in the opinion of a great many of us (even old and small fellows like me), quite unnecessary. Ian Cornish Quote Link to post Share on other sites
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