Instability under braking
Discussion
My recently acquired early ('93) Grif 500 seems to be slightly unstable when braking. When I come on to the brakes at higher speeds, the front end weaves slightly to one side or another.
I've checked the obvious things: geo has been checked by a TVR specialist, bushes and a worn ball joint replaced, tyre pressures checked etc.
A few questions for members:
1) Any other obvious culprits that anyone knows about?
2) I've heard the Griffith being criticised in road tests etc. for tramlining. Is it just a trait of the car - are they all a little unstable?
3) I want to strip and replace the sliders pivots on the front brake calipers, to make sure that the weave isn't caused by sticky calipers 'grabbing'. Anyone know which model of Ford (?) I will need the components from?
Thanks
Martin
I've checked the obvious things: geo has been checked by a TVR specialist, bushes and a worn ball joint replaced, tyre pressures checked etc.
A few questions for members:
1) Any other obvious culprits that anyone knows about?
2) I've heard the Griffith being criticised in road tests etc. for tramlining. Is it just a trait of the car - are they all a little unstable?
3) I want to strip and replace the sliders pivots on the front brake calipers, to make sure that the weave isn't caused by sticky calipers 'grabbing'. Anyone know which model of Ford (?) I will need the components from?
Thanks
Martin
Someone better qualified may post in a mimute but in the meantime, hope this helps...
1. Could be worn/uneven shocks? Does sound more like geometry but as you've had that checked, not sure. Do you have the same compound brake pads front and rear?
2. They will tramline a bit due to wide tyres and light weight. Shouldn't be a major problem though unless your geometry is out.
3. Not sure - could be escort cosworth/sierra I think.
This could be Grandma and Eggs but when you're braking are you pressing the clutch? If you leave the engine engaged until the very last moment the car brakes very much more smoothly.
1. Could be worn/uneven shocks? Does sound more like geometry but as you've had that checked, not sure. Do you have the same compound brake pads front and rear?
2. They will tramline a bit due to wide tyres and light weight. Shouldn't be a major problem though unless your geometry is out.
3. Not sure - could be escort cosworth/sierra I think.
This could be Grandma and Eggs but when you're braking are you pressing the clutch? If you leave the engine engaged until the very last moment the car brakes very much more smoothly.
Here's a bit of advise I posted on a different thread, weather you take it or not is up to you ,, ready? DO NOT PUT BLOODY FORD PARTS ON A TVR.
not difficult really is it?
guess what parts you should put on a very high performance TVR
any takers ??
well then I'll tell you get TVR parts especially on the brakes suspension side of things, you are trying to stop one of the quickest cars on the road , and you are looking for ford Anglia brake bits to save a few quid, if you cant afford to run a car like that properly then sell the dam thing. shhhhhheeeesh
simon
not difficult really is it?
guess what parts you should put on a very high performance TVR
any takers ??
well then I'll tell you get TVR parts especially on the brakes suspension side of things, you are trying to stop one of the quickest cars on the road , and you are looking for ford Anglia brake bits to save a few quid, if you cant afford to run a car like that properly then sell the dam thing. shhhhhheeeesh
simon
siwes said:
Here's a bit of advise I posted on a different thread, weather you take it or not is up to you ,, ready? DO NOT PUT BLOODY FORD PARTS ON A TVR.
not difficult really is it?
guess what parts you should put on a very high performance TVR
any takers ??
well then I'll tell you get TVR parts especially on the brakes suspension side of things, you are trying to stop one of the quickest cars on the road , and you are looking for ford Anglia brake bits to save a few quid, if you cant afford to run a car like that properly then sell the dam thing. shhhhhheeeesh
simon
But TVR fit ford parts, there's the label *FORD*
In my experience TVR consistently bias the brakes too far to the rear and it may be this is what you're picking up. But instability under braking is also a classic sign of suspension geometry problems, either from a poor setup or knackered bushes/ball joints/steering. It is also possible that the brakes aren't working correctly so you're right to consider an overhaul, but don't rule out the other checks first.
FWIW on the TVR/Ford thing, TVR were definitely working to a budget when they fitted those Ford brakes. The mechnical components are standard Ford parts, but make sure you use decent quality fast road pads and DOT 5.1 fluid or better, and don't cut corners on cheap discs.
FWIW on the TVR/Ford thing, TVR were definitely working to a budget when they fitted those Ford brakes. The mechnical components are standard Ford parts, but make sure you use decent quality fast road pads and DOT 5.1 fluid or better, and don't cut corners on cheap discs.
joospeed said:
siwes said:
Here's a bit of advise I posted on a different thread, weather you take it or not is up to you ,, ready? DO NOT PUT BLOODY FORD PARTS ON A TVR.
not difficult really is it?
guess what parts you should put on a very high performance TVR
any takers ??
well then I'll tell you get TVR parts especially on the brakes suspension side of things, you are trying to stop one of the quickest cars on the road , and you are looking for ford Anglia brake bits to save a few quid, if you cant afford to run a car like that properly then sell the dam thing. shhhhhheeeesh
simon
But TVR fit ford parts, there's the label *FORD*
Joolz. Couldn't you offer this chap a couple of days work inspecting Ford brake components on TVR's (under supervision of course).
I'm sure he would offer his services for free when he realises the benefit he will gain from it.
>> Edited by ian8542 on Friday 27th August 08:18
siwes said:
Here's a bit of advise I posted on a different thread, weather you take it or not is up to you ,, ready? DO NOT PUT BLOODY FORD PARTS ON A TVR.
not difficult really is it?
guess what parts you should put on a very high performance TVR
any takers ??
well then I'll tell you get TVR parts especially on the brakes suspension side of things, you are trying to stop one of the quickest cars on the road , and you are looking for ford Anglia brake bits to save a few quid, if you cant afford to run a car like that properly then sell the dam thing. shhhhhheeeesh
simon
I'm well aware of the TIV's performance, Simon, but as others have indicated, we are talking about a component manufactured for Ford, whether you buy it from TVR or Ford.
ITS A BLOODY SLIDER PIVOT FFS..not difficult, really, is it?!
If you really believe that a TVR either manufacture their own brake slider pivots, or have the OE Ford part modified to a higher standard just for their cars, then I'm afraid you have a seriously distorted view of reality.
Anyone who knows anything about the motor industry will realise that even Ford doesn't manufacture this type of component themselves. I guess I shouldn't buy fuses or ty-raps from anyone but a TVR main dealer, either, for fear of buying a component that isn't capable of coping with the Griffith's performance?
I have spent 20 years tinkering with high performance road and racing cars & boats for both fun and profit, including machinery which makes the Griffith look both low tech and underpowered. Credit me with enough common sense to know when and where to fit generic parts and when not to! shhhhhheeeesh!
Martin
>> Edited by Martin_S on Friday 27th August 18:29
Garry,
Thanks for that. No, I'm not depressing the clutch. And I don't think it is the shocks. Difficult to tell worn shocks, of course, but no obvious leaks or symptoms of poor damping and the car is very stable most of the time, except when coming on to the brakes. That's why the brakes are the main suspect now that the bushes have been ruled out, 'cos I've never experienced a similar symptom that didn't show up under other aspects of the car's handling. It feels almost like bump steer, but then bump steer would be noticeable ato other times, not just when braking?
Starmist,
Could be tyres, certainly. The car came fitted with a set of Pirellis - not a tyre manufacturer I have any faith in whatsoever and probably completely unsuitable for the car. They are the correct size and are ZR rated, but other than that their characteristics are probably much better matched to a large uber-saloon than something like the Griff. Trouble is, they appear to be almost unworn and at risk of being told again by Siwes that I can't afford to run a car like a Griffith, I'm reluctant to throw away several hundred quid's worth of new tyres without ruling out the other possibilities first! Will definitely be looking at a set of Bridgestones or Toyos next time round, though!
>> Edited by Martin_S on Friday 27th August 18:30
Thanks for that. No, I'm not depressing the clutch. And I don't think it is the shocks. Difficult to tell worn shocks, of course, but no obvious leaks or symptoms of poor damping and the car is very stable most of the time, except when coming on to the brakes. That's why the brakes are the main suspect now that the bushes have been ruled out, 'cos I've never experienced a similar symptom that didn't show up under other aspects of the car's handling. It feels almost like bump steer, but then bump steer would be noticeable ato other times, not just when braking?
Starmist,
Could be tyres, certainly. The car came fitted with a set of Pirellis - not a tyre manufacturer I have any faith in whatsoever and probably completely unsuitable for the car. They are the correct size and are ZR rated, but other than that their characteristics are probably much better matched to a large uber-saloon than something like the Griff. Trouble is, they appear to be almost unworn and at risk of being told again by Siwes that I can't afford to run a car like a Griffith, I'm reluctant to throw away several hundred quid's worth of new tyres without ruling out the other possibilities first! Will definitely be looking at a set of Bridgestones or Toyos next time round, though!
>> Edited by Martin_S on Friday 27th August 18:30
GreenV8S said:
In my experience TVR consistently bias the brakes too far to the rear and it may be this is what you're picking up. But instability under braking is also a classic sign of suspension geometry problems, either from a poor setup or knackered bushes/ball joints/steering. It is also possible that the brakes aren't working correctly so you're right to consider an overhaul, but don't rule out the other checks first.
Thanks - don't think it's the bias. The symptoms only occur when coming onto the brakes (ie. light, initial application) and are worst when 'check braking' the car to avoid getting too close up behind somewone on the motorway or similar. Nowhere close to lock-up, and when I've tried emergency stops, the fronts lock first and the car pulls up all-square every time.
All the front bushes and one of the front ball joints were replaced and the geometry checked, all work done by RT Racing in Sheffield who I assume to be competent in working on TVR's?
I would suspect the rear bushes, but for the fact that the instability only occurs under light brake applications and I would expect it to be even more noticeable under heavy forward weight transfer (ie. heavy braking) if the rear was at fault?
Curious problem, and I think you've covered all the bases here. Do you know if you have the same compound pads front and rear? Some of the fast road pads I've used have relatively little initial bite but work fine when you lean on them, whereas others feel as if they have constant Mu down to very low braking loads. Another possibility is friction in the front sliders causing one pad in each caliper to take all the load until the forces are high enough to overcome the friction. Um, clutching at straws, the master cylinder has a tandem piston arrangement with the two circuits mechnically connected by a spring of some description. Hypothetically, I guess that a failure here could cause backlash between the front and rear circuits so no load was applied to the front initially. You can probably guess I'm clutching at straws here!
Yeah, I'm clutching at straws myself!
'Stiction' in the front sliders is now my best guess, too (hence the request for equivalent Ford parts - not that I'm a cheapskate, just that Ford dealers are easier and quicker for me to reach than the nearest TVR dealer). I'll check the pads over the weekend, too.
Most of the race pads I've come across just plain don't work until they are up to temperature. I had a '60's Lotus Elan that basically needed all 15 stone of me standing on the pedal (with a servo, too!) to stop a 600kg car from 30mph for the junction at the end of my road on a morning! Worked fine once warmed up, though!
'Stiction' in the front sliders is now my best guess, too (hence the request for equivalent Ford parts - not that I'm a cheapskate, just that Ford dealers are easier and quicker for me to reach than the nearest TVR dealer). I'll check the pads over the weekend, too.
Most of the race pads I've come across just plain don't work until they are up to temperature. I had a '60's Lotus Elan that basically needed all 15 stone of me standing on the pedal (with a servo, too!) to stop a 600kg car from 30mph for the junction at the end of my road on a morning! Worked fine once warmed up, though!
Rather than go to a TVR or Ford dealer and getting ripped off. Take your old calipers (leaving the bracket in situ) to a decent motor factors who will supply you with a pair of exchange remanufactured calipers from someone like AMK.
Tell them they are from a Sierra 4x4 non ABS or Granada circa 1988.They will probably be able to tell when they see your old ones.
Prices will be around £40 plus drat each.
On refitting clean the slider pins and use a little rubber grease. Threadlock on the threads.
(You will need a 7mm allen key for removing the slider pins.)
Contact me if you need any more info.
Tell them they are from a Sierra 4x4 non ABS or Granada circa 1988.They will probably be able to tell when they see your old ones.
Prices will be around £40 plus drat each.
On refitting clean the slider pins and use a little rubber grease. Threadlock on the threads.
(You will need a 7mm allen key for removing the slider pins.)
Contact me if you need any more info.
If it was calliper problems wouldn’t you get uneven breaking left to right (cant believe both sides are sticking by the same amount) and therefore feel a pull to one side, though £40 for a re-con and to rule it out may be worth it.
I know you’ve had it all checked once, but it does sound to me like some float in the suspension geometry which is taken up with forward weight transfer.
Good luck,
Simon.
I know you’ve had it all checked once, but it does sound to me like some float in the suspension geometry which is taken up with forward weight transfer.
Good luck,
Simon.
simon.b said:
If it was calliper problems wouldn’t you get uneven breaking left to right (cant believe both sides are sticking by the same amount) and therefore feel a pull to one side, though £40 for a re-con and to rule it out may be worth it.
I know you’ve had it all checked once, but it does sound to me like some float in the suspension geometry which is taken up with forward weight transfer.
Good luck,
Simon.
Until the calipers are removed and inspected you can only hazard a guess.
If it is caliper related, replace BOTH.
The pads may be the problem as standard TVR stuff has a tendency to break up if maintenance is neglected.
Allowing the pad material to wear down to the backing plate or even near is not to be recommended.
I would agree that it could also be suspension related, particularly with worn standard bushes or polybushes.
Have you compared it with any other similar cars to see how far off standard yours is? Instability under braking is one thing, and there are various possible causes. But the unusual factor in this case seems to be that it only happens under light braking. How pronounced is the difference between light/heavy braking? Can you definitely rule out external factors like the road camber and so on? If you have a favorite 'test track' this could affect the behaviour without you necessarily noticing it.
The symptoms seem to suggest that the brake balance is out, but I'm struggling to see how this would be severe enough to be so dramatic under gentle braking. Do you get a similar effect when you apply heavy engine braking (I mean lift off at high revs, not dumping thc clutch)?
Did you have the geometry checked before or after changing the bushes and ball joint? It wouldn't hurt to check again just in case something has changed in the meantime.
I wonder if the instability is associated with the transient weight transfer rather than the amount of braking? Presumably, by the time you've got the brakes on hard the car will have had time to settle into its nose-down attitude, but a quick gentle dab would produce a transient weight transfer. This means the dampers will get involved. I don't see why they would cause instability, but it wouldn't hurt to check the condition of the dampers anyway.
The symptoms seem to suggest that the brake balance is out, but I'm struggling to see how this would be severe enough to be so dramatic under gentle braking. Do you get a similar effect when you apply heavy engine braking (I mean lift off at high revs, not dumping thc clutch)?
Did you have the geometry checked before or after changing the bushes and ball joint? It wouldn't hurt to check again just in case something has changed in the meantime.
I wonder if the instability is associated with the transient weight transfer rather than the amount of braking? Presumably, by the time you've got the brakes on hard the car will have had time to settle into its nose-down attitude, but a quick gentle dab would produce a transient weight transfer. This means the dampers will get involved. I don't see why they would cause instability, but it wouldn't hurt to check the condition of the dampers anyway.
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