Outbraked by a Ford Focus...
Discussion
We spent some of today in the Tamora at CAT driver training at Millbrook. We had rearranged our performance driving day from earlier this month when snow stopped play, and today we had perfect dry weather.
Millbrook is a great place with an impressive variety of facilities. The driver training day uses the mile straight for braking and brake / swerve, the high-speed bowl, the handling circuit, the Alpine route, and a big skid-pan with lots of coloured circles of different diameters to follow.
It might use other parts too, but our day ended sooner than we would have liked.
As the TVR doesn't have ABS, we used a Ford Focus to practice some ABS braking / brake & swerve techniques before doing some threshold braking. We then swapped to the TVR which, until now, I have always driven fairly steadily and have not locked up the brakes.
The first stop resulted in a big cloud of tyre smoke as the rear brakes locked up, and the fronts did not. Same tyres front and back, running the same pressure. Further stops over 3 passes down the straight produced exactly the same problem and I was having to limit the braking force to avoid having the rears lock up. The deceleration the TVR could manage without the rears locking was less than the Ford Focus
This is not a stable car setup, and the brake test is a good thing to get done early in the day to check that aspect of the cars handling.
Colin discussed whether we wanted to continue with a car that was not handling properly, or postpone the day until we have the car fixed and then carry on from where we left off. This is very good of him, since it effectively writes-off 2 days of his time for our one day of training.
Before finishing, we went onto the 40m circle, and in both directions increased speed until the car started to lose traction. In this respect the TVR is set-up very well (thanks TrackVRoad) - it goes into very mild understeer when pushed, that can turn into slight lift-off oversteer, or can be balanced out with a bit more throttle.
On our way back we popped into TVR Power and had a chat with Jason. He noted that the rear pads were EBC Greenstuff, and it wasn't clear what the fronts were since the back of the pads is not visible. A mismatched set of pads seems the most likely reason for the brake issues, given the calipers all look in good condition, as do the disks and tyres.
We also discussed the coolant dripping problem and, given its location and a quick examination, he was fairly sure it was the plastic ends to the radiator...
I now have a to-do list of new pads, new tyres, and new radiator before I return to complete my driver training. Based on what we have done so far, I am really looking forward to returning to Millbrook, and am grateful to CAT for being so helpful.
There were lots of interesting development vehicles going round Millbrook. My photo from the day is here.
Millbrook is a great place with an impressive variety of facilities. The driver training day uses the mile straight for braking and brake / swerve, the high-speed bowl, the handling circuit, the Alpine route, and a big skid-pan with lots of coloured circles of different diameters to follow.
It might use other parts too, but our day ended sooner than we would have liked.
As the TVR doesn't have ABS, we used a Ford Focus to practice some ABS braking / brake & swerve techniques before doing some threshold braking. We then swapped to the TVR which, until now, I have always driven fairly steadily and have not locked up the brakes.
The first stop resulted in a big cloud of tyre smoke as the rear brakes locked up, and the fronts did not. Same tyres front and back, running the same pressure. Further stops over 3 passes down the straight produced exactly the same problem and I was having to limit the braking force to avoid having the rears lock up. The deceleration the TVR could manage without the rears locking was less than the Ford Focus
This is not a stable car setup, and the brake test is a good thing to get done early in the day to check that aspect of the cars handling.
Colin discussed whether we wanted to continue with a car that was not handling properly, or postpone the day until we have the car fixed and then carry on from where we left off. This is very good of him, since it effectively writes-off 2 days of his time for our one day of training.
Before finishing, we went onto the 40m circle, and in both directions increased speed until the car started to lose traction. In this respect the TVR is set-up very well (thanks TrackVRoad) - it goes into very mild understeer when pushed, that can turn into slight lift-off oversteer, or can be balanced out with a bit more throttle.
On our way back we popped into TVR Power and had a chat with Jason. He noted that the rear pads were EBC Greenstuff, and it wasn't clear what the fronts were since the back of the pads is not visible. A mismatched set of pads seems the most likely reason for the brake issues, given the calipers all look in good condition, as do the disks and tyres.
We also discussed the coolant dripping problem and, given its location and a quick examination, he was fairly sure it was the plastic ends to the radiator...
I now have a to-do list of new pads, new tyres, and new radiator before I return to complete my driver training. Based on what we have done so far, I am really looking forward to returning to Millbrook, and am grateful to CAT for being so helpful.
There were lots of interesting development vehicles going round Millbrook. My photo from the day is here.
BCA said:
Something sounds amiss?? Our T350 locks the fronts waaay before the rears, there is if anything, too much front bias... the Cerb used to brake better, but it could also lock all four wheels pretty easily if it was slippy. 
I agree that something is seriously amiss. Very annoying to find my Tamora has dangerous on-limit brake performance during the first session of a driving day that we have gone to a lot of effort to attend.If the calipers are all in good condition, and the disks are all in good condition, hopefully new pads all round will correct the imbalance. The tyres are the same all round (Toyo T1-S), a little bit old, but I would rather change those after the brake pads to give me a good chance to test the brakes without smoking a new set of tyres.
Those stops where the rears locked up, despite quickly releasing some pressure and re-applying, made an impressive cloud of smoke
It will be interesting to know what pads are on the front as I don't associate the Greenstuffs on the back with massive performance, but maybe they are just working well on the back and the front pads are not good.
Zippee said:
I agree. I run DS2500's all round and have never managed to lock the rears, done the fronts a couple of times but the balance and stopping power is awesome.
OP - At least you found out about your problem in a controlled emergency situation rather than out on the road....
I agree. Much better now than in an on-road emergency situation. Or at the start of an expensive trackday. That said the driver training was way more £ than a trackday, but they were kind enough to allow us to postpone the training until it is fixed.OP - At least you found out about your problem in a controlled emergency situation rather than out on the road....
bobd said:
Get the car corner weighted and ride height sorted. I have seen this a lot on Tamoras and Tuscans light at the back end under heavy braking. Obviously check pads and lines, but usually a weight transfer issue due to poor suspension set up.
I would hope it isn't this. Thanks to the previous owner the car is on a 6 month old Gaz Gold Pro setup (yes, I know it isn't on Nitrons...). This was set up by TrackVRoad, and then the ride hights tweaked less than a month ago when I brought the car back to TrackVRoad at the end of its warranty.The handling in corners seems to be spot on, the ride heights are correct, and all the suspension components have been checked very recently. Unless there is a big fundamental failing of GGPs (yes, I know they aren't Nitrons), the weight transfer should not be the cause of the issue.
Further update...
Before I went on a 3000 mile road trip, TVR Power had a look at the brake set up, and changed the EBC Greenstuff on the rear for AP Racing pads which match the front.
They have had plenty of time to bed-in, and I avoided threshold braking on the road trip as that is best saved for track, just sticking to brisk driving.
I took the car out early this morning to find some quiet wide roads (M50...) to test the brakes.
Rears still lock up before fronts resulting in a little wiggle and a puff of smoke (I come back off the brakes as quickly as I can). Certainly the driver's side rear does as that was most obvious in the wing mirror. Not sure about passenger side rear. I assume if they both locked, the engine would be stalled and then bump-start when I came off the brakes. I don't think that happened.
Suspension set up should be ok. Gaz Gold Pros all round, damping still set to firm (12 from soft on front and back was selected for road trip with luggage).
The Tamora is going back to Track V Road in 2 weeks for its annual service and I really need to get this sorted since I have a driver training day finish when the brake balance is correct.
Track V Road say they often use good pads on the front (e.g. DS2500 which I like and have used on previous cars) and cheap pads on the back with less bite.
This sounds like a good option to me. More expensive options could be to use Red Rose front disks (£££) or do something with the suspension, but that should be fine, and since I only understand the basic of suspension, I am not sure what would be done to fix such a problem.
Any advice or experience welcome.
Before I went on a 3000 mile road trip, TVR Power had a look at the brake set up, and changed the EBC Greenstuff on the rear for AP Racing pads which match the front.
They have had plenty of time to bed-in, and I avoided threshold braking on the road trip as that is best saved for track, just sticking to brisk driving.
I took the car out early this morning to find some quiet wide roads (M50...) to test the brakes.
Rears still lock up before fronts resulting in a little wiggle and a puff of smoke (I come back off the brakes as quickly as I can). Certainly the driver's side rear does as that was most obvious in the wing mirror. Not sure about passenger side rear. I assume if they both locked, the engine would be stalled and then bump-start when I came off the brakes. I don't think that happened.
Suspension set up should be ok. Gaz Gold Pros all round, damping still set to firm (12 from soft on front and back was selected for road trip with luggage).
The Tamora is going back to Track V Road in 2 weeks for its annual service and I really need to get this sorted since I have a driver training day finish when the brake balance is correct.
Track V Road say they often use good pads on the front (e.g. DS2500 which I like and have used on previous cars) and cheap pads on the back with less bite.
This sounds like a good option to me. More expensive options could be to use Red Rose front disks (£££) or do something with the suspension, but that should be fine, and since I only understand the basic of suspension, I am not sure what would be done to fix such a problem.
Any advice or experience welcome.
MPoxon said:
May I ask which course you booked with CAT. I have always fancied taking the car to Millbrook.
We were on the performance driver day. It was recommended by Jo as a good all round course. Performance Driver Link
When the brakes are sorted and I have finished the course I will do a full write up. The part we did seemed very good.
ChrisPap said:
How's this problem going? Any update?
Thanks for asking. there are quite a few updates 
It isn't fixed though...
I started another thread on Pistonheads after I got an AP Racing adjustable brake bias valve fitted.
So that is the most recent thread.
There are also updates on my TVR blog, which make for very dull reading.
The adjustable valve may be able to fix the problem, but quite possibly only in the region of adjustability where it rattles.
In terms of what I am trying next:
I have been in communication with Ford to find out the specification of the standard brake proportioning valve which is fitted – Ford part 7117274. The initial response from Ford was not helpful but after some further communications it seemed that they would send me the specification. But they sent me some other useless information instead. I have now written a letter. If they can answer my not very hard question this would let me know where in the AP valve’s range of adjustability the standard valve sits.
Changing the front pads for new pads may help. I don’t know the history of the fronts. I have been told they are the correct model and that they have plenty of pad material left, but age is unknown and it is possible that they could be past their best. The knowledge I have of the brake pads is here.
The master cylinder could be faulty. I don’t imagine that would be easy to test so wold probably involve a straightforward swap of old for new at £120 for the cylinder and a fair bit for labour.
Car suspension setup is also an option. It has been looked at by good TVR garages, should be set-up correctly, and handles fine (to me), but maybe there is something that is missing. I am having some checks done by Centre Gravity who have a very good reputation.
I really want to get this sorted and get the car on a track - although that would require a quieter exhaust (currently JP sports exhaust).
Targarama said:
I still can't believe you haven't changed the front brake pads, they are still an unknown quantity and they could easily have been overheated. Stick some Carbon Lorraine pads in there and you'll not be worrying about the brakes any more.
Sorting this is a slow process - the car works fine for all bar the most extreme braking and I have had other things taking up my time (so I now know that a baby seat fits in the Tamora).I would most likely put in the pads that AP racing / TVR Power supply which are Ferodo DS2500s. These are pads I have used before on other cars and should suit the driving I do. Coefficient of friction I believe is 0.34, lower than the Carbon Lorraine's 0.4 from their RC5+ pad.
m4tti said:
More importantly you don't know what pressure is being applied to the front and rear. I personally wouldnt mess about with new valves etc we know the standard set up is pretty good. Everything you do is speculative until you've got some tangibles.
Is everything standard? Are you able to do any of this work your self?
Getting some tangibles is difficult. What can you suggest would be measured?Is everything standard? Are you able to do any of this work your self?
The idea behind the adjustable valve was that it would do everything the standard valve does plus have some extra adjustability. If I don't need it, I will happily swap to a standard valve and ebay the adjustable one.
The standard setup is indeed supposed to be good. Mine is standard (excluding new valve).
Regarding doing work myself, I would go as far as swapping pads / disks, but I wouldn't remove / refit valves etc.
Edited by Sevenman on Friday 2nd November 13:31
m4tti said:
I replaced all pads and disks on mine with the ap ferrodo set up including the sagaris upgrade and did a track day with an instructor pushing me. No lock ups and no fade doing 10 laps at a time.
Is the Sagaris update bigger disks? Given the weight of the car, DS2500s should be up to trackdays given how well they used to work on my heavy Saab Turbo that had smaller disks.
m4tti said:
I think on your other thread I linked to a brake pressure test kit so you could determine what pressure is reaching the front and rear calipers. I think till someone determines this you won't be able to clearly ascertain where the fault lies.
You did, and you had answered my question on the Sagaris upgrade.I am certainly considering the pressure testing, but I am hoping some of the other checks / research I am doing, the visit to a suspension specialist, and a change of the front pads will sort it. If not, it could be an option.
ChrisPap said:
I'm quite suprised that you haven't been able to get this sorted yet. It should have been relatively easy to troubleshoot.
My only suspicion is with your braking system. Tyres would have to be terribly out of whack, and likewise suspension would have to be rediculous before you start locking rears consistently. To the point where I'm sure you'd notice other problems.
I am surprised it hasn't been sorted as well. Tyres are all good (fitted in April) and I believe suspension is fine (fitted July 2011) but the tests later this month should confirm it.My only suspicion is with your braking system. Tyres would have to be terribly out of whack, and likewise suspension would have to be rediculous before you start locking rears consistently. To the point where I'm sure you'd notice other problems.
ChrisPap said:
My first suspicion would be Brake calipers themselves or pads. I'd check that all pistons were working without any siezed ones. This can be done just by taking the wheels off and having two people available. Then check pads to make sure that they're at least servicable. If all checks out I'd be looking at the brake maser cylinder. I'm not sure what system the TVR has, diagonal split, 2 front and one rear, or front and rear lines only. Whatever way, if the cylinder bore is scored it could easily affect brake performance. Proportioning valve would have been the last place I'd look because they almost never go wrong.
I'd also be looking mostly at the front end because it's far more likely that the front brakes are underperforming than the rear brakes are overperforming.
I'll happy have a look over it with you if the weather is not too moody next weekend and if you can get the car over to Buckingham MK18.
I suspect underperforming due to pads / bias valve, although the master cylinder is an option (£120 + fitting). I did have the adjustable bias valve in a position where the fronts locked first (but then struggled to repeat it), and it has been braking evenly, not pulling to either side.I'd also be looking mostly at the front end because it's far more likely that the front brakes are underperforming than the rear brakes are overperforming.
I'll happy have a look over it with you if the weather is not too moody next weekend and if you can get the car over to Buckingham MK18.
I believe the TVR has separate front / rear circuits rather than diagonals. I hope I / the TVR garage are not wrong, as if it is diagonal 2 bias valves are needed... I am pretty sure it is separate front / back
Should be easier to find out when it is up on a lift for suspension work.
Thanks for the offer of helping with a look-over of the car. I will see what happens after the suspension checks and front pad swap later this month and how much progress has been made.
Hopefully it will be 3rd time lucky and Ford will answer my question on the bias valve.
HarryW said:
Would a MOT type brake force testing rig be able to tell you something that may help here........
Not sure - never seen one in action.The brakes have passed an MOT in their current configuration. I thought they tended to measure across an axle to make sure they were balanced, rather than the front-back balance that would require 2 sets of rollers.
gruffalo said:
can not believe that OP has not changed the pads to same all round and not cheap EBC either, had far to many instances of brakes fading to nothing with those pads to ever return.
Working on it slowly... EBC Greenstuff have been removed from the rear to be replaced with Ferodo DS25HP. These are very similar to DS2500, AP Racing supply TVR Power with these for the rear and DS2500 for the front and I have had a few chats with AP about the brake compounds, coefficients of friection etc.
Front pads are, I believe, Ferodo DS2500 of unknown age / use and will be changed to fresh DS2500 next week.
In addition, to help even out the brake balance I intend to remove the Toyo T1-Sports from the front axle (had 4 new T1-Sports fitted in April) and replace them with 'Sunew Sport', keeping Toyos on the rear. The Sunew tyres are only £50 a corner, not the £160 I paid for the Toyos and this should help ensure the front brakes lock first, and also make the car understeer severely at the limit, which is of course a great handling characteristic.
Sunew tyre link here
Please don't believe that last bit about the tyre swap...
PascalBuyens said:
LOL... out of all those brands on that link, there isn't one I ever heard about...
I suspect they market those tyres to people who want some cheap low-profile tyres on cheap 18" wheels on cheap low-performance cars.If I had a spare set of wheels and wanted to learn to drift the car at relatively low speeds then I could see a place for those tyres.
Having been to an interesting meeting at Continental's UK tyre distribution centre last week and found out a bit more about the technology and quality control that goes into the tyres made by a premium company, and the performance in tests of some of the cheap Chinese tyres, I wouldn't touch them for road use.
Keri said:
Hang on a sec...
Your car is locking the rears first, so you're going to fit "less grippy" (TBC) tyres to the front?While that may stop the rear from locking first, it will only work by reducing how hard you can brake and grip is the ULTIMATE limiting factor! It's like having trouble with wheelspin reducing your acceleration, and "fixing" it by fitting a smaller engine.
I refer to the very bottom of the post to which you refer.Your car is locking the rears first, so you're going to fit "less grippy" (TBC) tyres to the front?While that may stop the rear from locking first, it will only work by reducing how hard you can brake and grip is the ULTIMATE limiting factor! It's like having trouble with wheelspin reducing your acceleration, and "fixing" it by fitting a smaller engine.
Sevenman said:
Please don't believe that last bit about the tyre swap...
But now that you mention it, I do sometimes get wheelspin.Maybe the TVR would be better off with a nice lightweight Rover K-series engine up-front
Keri said:
In any kind of testing you need keep as many things equal as possible to eliminate them, so start with all one type/age of tyre, and all one pad compound/age (confirmed). You may also find someone got oil or grease into the front pads for instance even if they are also DS2500.
Tyres done in April, brake pads soon to be done. Also getting some further insprections done on the car.The rear bias valve is a replacement, not an addition, but it does complicate matters by giving me an extra degree of freedom so may get changed back.
Next week should see some good progress with a day set aside and 2 places to visit with the car that should be able to help.
Keri said:
What about the master cylinder connections - that one thing (while unlikely) if wrong will cause all the symptoms you've described?
That area has been looked at in detail by a TVR Specialist, but I can get TVR Power to double-check when it is in next week.I don't think that design of master cylinder has outputs at 2 different pressures, hence why the cars came with a brake proportioning valve in the rear line.
Update - Front pads will be changed for fresh DS2500 next week.
Does anybody know the piston size in the front / rear calipers as used in the Tamora (and I assume T350 / Sagaris)?
The rears and single-piston, the fronts four-pot.
I am trying to work out what bias the valve needs to apply given different calipers and disk sizes.
Disk size front/rear is 304mm/282m and a simple calculation gives a ratio of 1.078 (there will be a more accurate way of calculating given the pad dimensions, but that would be tricky).
This means that, on disk size alone, the rear has 0.927 of the braking force of the frot.
If I know piston diameter (and hence piston area) then I can add that into the calculation and see what the bias is before a valve is fitted.
Does anybody know the piston size in the front / rear calipers as used in the Tamora (and I assume T350 / Sagaris)?
The rears and single-piston, the fronts four-pot.
I am trying to work out what bias the valve needs to apply given different calipers and disk sizes.
Disk size front/rear is 304mm/282m and a simple calculation gives a ratio of 1.078 (there will be a more accurate way of calculating given the pad dimensions, but that would be tricky).
This means that, on disk size alone, the rear has 0.927 of the braking force of the frot.
If I know piston diameter (and hence piston area) then I can add that into the calculation and see what the bias is before a valve is fitted.
swanny71 said:
That spec lists the 4-pot calier as having 2 x 38.1mm pistons and 2 x 41.3mm pistons.This gives a total piston area of 4959 mm^2
I understand the rear calipers to be Ford Sierra Cosworth front calipers?
If so, then this link gives some specifications.
http://www.brakepartssuperstore.org.uk/contents/en...
Piston diameter is listed as 39.97mm. But this does not look like single-piston to me.
If it was single-piston of 40mm, then the brake bias without a valve would be 81:19
If it has 2 pistons, then the brake bias without a valve would be 68:32
Maybe that is the wrong brake above?
But for either of those calculations, it does not look like the bias valve should need to do a lot to get the balance right. Given the valve is currently et more than 1/2 way through its range (so should drop 50% of the rear pressure), I would think that the brake bias would be just fine. Unless the front pads or something else is faulty.
Does anybody have better information on the rear calipers or thoughts on the above?
Keri said:
The link and the photo you've got above are both for the front of the 2WD Cossie, which is a 4-pot opposed piston design - very unlikely to be used on the rear of anything as it's very heavy and has no handbrake built in.
Here's what you need to work out the torque from each setup: http://www.stoptech.com/docs/media-center-document...
It's worth noting that with any sliding caliper you double the actual piston area to get the effective area (the sliding actual doubles the clamping force for a given pressure, and doubles the pedal travel as well).
That explains why it looks wrong. From Graham Varley's site it says that the rear caliper has been the same from Griffith onwards, and I think it means the Sierra Coswoth rear, which are shown hereHere's what you need to work out the torque from each setup: http://www.stoptech.com/docs/media-center-document...
It's worth noting that with any sliding caliper you double the actual piston area to get the effective area (the sliding actual doubles the clamping force for a given pressure, and doubles the pedal travel as well).
The BCA1346 is mentioned in other Pistonheads threads as the caliper used. As is BCA2060, but that has the same piston diameter as BCA1346 (42.81). My copy of Graham Varley's book is at home so I can check tonight.
42.81 on a sliding caliper, if that doubles the force, gives an effective area of 2879 mm^2 compared to 4959 on the front.
Given the factor of 0.93 from brake disk size gives a 65:35 split.
Looking at the StopTech calculation, my calculations above should be ok. They are working out the torque on each wheel. I am working out the ratio if torque given an equal system pressure and coeefficient of friction.
To get a 75:25 bias from the above setup, given lots of assumptions, the bias valve would need to pass 60% of the brake line pressure. It may be the case that under heavy braking on grippy tyres 25% is still too much rear force and more bias is needed (46% pressure passed to get 80:20).
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