Heavy braking leads to pulling strongly to right? Any ideas?
Discussion
After discovering a cracked NSF brake disc after a check over from being at the Ring, and also discovering a partially failed OSF taper wheel bearing, I've now got new alcon 2 piece discs, new billet hubs (& associated uprated stub axles). Whilst fitting that lot, I decided to refurb my AP4 pots (CP3344) with new nipples/banjos all round and a new set of seals (and one new piston due to a tiny amount of scoring). PRF660 fluid all round. I have an AP racing m/c which is split into a seperate front and rear ciruit.
However, after a vacuum bleed and a further manual bleed, following a test drive on sat, the car pulled fairly violently towards the right under hard braking. I've had a *quick* look at the discs to make sure they're i) bedding in OK, ii) I have full pad contact (I'm using (very slightly) worn RS15s). Everything OK there.
As I see it I'm going to check the following tonight in an attempt to eliminate the problem:
1. Fluid leak from copper washer – tweak up all connections
2. Pad contact area – deglaze/sand pads
3. Contaminated disc - clean face
4. Damper settings out of balance L to R – wind in then back out equal amounts
5. Tyre pressures - equalise
6. Loose suspension component – check all bolts and torque settings
7. Air in LHF caliper – remove caliper to bleed!
8. Pistons stuck in LHF/RHF – monitor how far out pistons come and see how they go back in again (i.e. checked for partially seized/out of square piston alignment, or a twisted seal)
9. Swap pads L to R – easy try out
10. Check front wheel bearing preload – adjust as necessary
I don't think it's 1/2/3/5. It could possibly be 8, although having spoken to Mardi Gras (AP agent) this morning, they suggested if a piston was very out of alignment, it would be unlikely to retract far enough to fit a nearly new pad....
Although it appears that the OSF has far more power than the NSF, it could be one of the pistons here which is not retracting fully?
Any advice/suggestions welcome.
PS the car tracks in a straight line when not braking, so geo seems OK. Nothing else changed since last corner weighted. (plate) Diff preload is not likely to have magically changed since being unloaded off the trailer either!
PPS Anyone moved from a caterham to a radical?!
However, after a vacuum bleed and a further manual bleed, following a test drive on sat, the car pulled fairly violently towards the right under hard braking. I've had a *quick* look at the discs to make sure they're i) bedding in OK, ii) I have full pad contact (I'm using (very slightly) worn RS15s). Everything OK there.
As I see it I'm going to check the following tonight in an attempt to eliminate the problem:
1. Fluid leak from copper washer – tweak up all connections
2. Pad contact area – deglaze/sand pads
3. Contaminated disc - clean face
4. Damper settings out of balance L to R – wind in then back out equal amounts
5. Tyre pressures - equalise
6. Loose suspension component – check all bolts and torque settings
7. Air in LHF caliper – remove caliper to bleed!
8. Pistons stuck in LHF/RHF – monitor how far out pistons come and see how they go back in again (i.e. checked for partially seized/out of square piston alignment, or a twisted seal)
9. Swap pads L to R – easy try out
10. Check front wheel bearing preload – adjust as necessary
I don't think it's 1/2/3/5. It could possibly be 8, although having spoken to Mardi Gras (AP agent) this morning, they suggested if a piston was very out of alignment, it would be unlikely to retract far enough to fit a nearly new pad....
Although it appears that the OSF has far more power than the NSF, it could be one of the pistons here which is not retracting fully?
Any advice/suggestions welcome.
PS the car tracks in a straight line when not braking, so geo seems OK. Nothing else changed since last corner weighted. (plate) Diff preload is not likely to have magically changed since being unloaded off the trailer either!
PPS Anyone moved from a caterham to a radical?!
Red Seven said:
Old pads on new discs??
'sounds like a pad bedding issue to me.
OK, thks. Sanded down 'old' pads fully with P180 grit to remove any micro ridges or 'galazing' and will go down the checklist below sometime this week. How long would you expect for the 'old' pads to take to the new discs?!'sounds like a pad bedding issue to me.
I would check that the brakes are actually working on both sides (apply light pressure and check resistance when turning the wheel by hand), drive a hundred yards or so with the brakes held on moderately firmly and confirm both front discs equally hot to the touch.
If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
GreenV8S said:
I would check that the brakes are actually working on both sides (apply light pressure and check resistance when turning the wheel by hand), drive a hundred yards or so with the brakes held on moderately firmly and confirm both front discs equally hot to the touch.
If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
only hubs have changed (for billet items). Uprights are as before. Wishbones, etc were not removed, so geo should have remained the same unless the spanner fairies have been at work in the trailer If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
Can you explain contact patch offset? I presume you mean the tyre relative the line straight ahead? i.e. I may have introduced a 'dynamic slip angle' (if that makes sense) to the tyre?
The pickup points and the location of the stering arm as before so no ackerman effect, and the rack height hasn't moved, so b/steer shouldn't be a problem that I can foresee.
Both discs get warm, it's just that one side is significantly more effective than the other!!!
Thanks for the feedback. Keep the suggestions coming guys. Very helpful.
GreenV8S said:
I would check that the brakes are actually working on both sides (apply light pressure and check resistance when turning the wheel by hand), drive a hundred yards or so with the brakes held on moderately firmly and confirm both front discs equally hot to the touch.
If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
I've got a probe type pyrometer so can try this.If the above gives you any reason to think you have uneven braking them pursue the list you have above. Otherwise, bearing in mind that you have replaced the front uprights and hubs, it may be that the geometry is out. I don't mean just camber/caster/toe, but also the contact patch offset. Depending what's changed you could also have introduced bump steer.
Since you've kept the same uprights that eliminates some sources of geometry problems, but changing the hubs could have changed the position of the contact patch relative to the steering axis. If there is a big offset then this would make the vehicle very sensitive to any asymmetry between the two sides.
I've had another thought, which is that there may be slight pad taper from the 'old' pads on the old discs, which is resulting in an unbalanced frcition surface across the front 'axle'. Although I've sanded them, the backing plate may not be parallel to the friction surface, resulting in a poor contact patch... I think a vernier on both edges will tell me if there is a marked taper!
GV8S - can you explain contact patch in the context you've use it in plse?!
GV8S - can you explain contact patch in the context you've use it in plse?!
PS does anyone have/know anyone who would either allow me to pay to use or rent their c/w scales to check my car? The process is fairly simple once the car is on the scales and the scales are all level, etc. The ex touring car team whose scales I used to borrow have now moved to France, which is a long way to go to fiddle with my coilover platforms!
With the car on level ground and everything straight, turn the steering left and right through a small angle and look at the way the tyre scrubs on the ground. You'll see that the scrub marks are roughly circular. The center of the circle is where the steering axis intersects the ground. This will usually be close to the center of the contact patch, but not exactly on it. Increasing this distance increases the loads on the steering during braking and makes the steering more sensitive to any asymmetry in the rest of the car, or the road surface.
BertBert said:
Probably not right, but worth checking the lower spherical bushes. I had some very odd effects when one of mine got play in it. Including pulling to one side on braking. Long shot.
Cheers Bert. I took the circlip out and washed out the bearing, and fully regreased, so I know that there's no play and no stiction either!fergus said:
PPS Anyone moved from a caterham to a radical?!
Yep How do you find the Rad after the Caterham? I'm finding that I'm only using my car on track/Ring at the mo, as I think it's now too quick for the road. I may as well move to a Rad?! I can then go racing again! All the Caterham series require you to only have Caterham specified parts on your car, which mine unfortunately doesn't comply with...
Fat Arnie said:
Check you don't have a pad in with the metal back facing the disc, as popposed to the correct way round. I've seen this and it gives exactly the symptoms you describe. Easy mistake to make with some AP calipers.
I read what happened! I think the use of older pads on new discs is what's causing the problem. There is a 0.5mm run out on my current pads, which needs to be removed to make sure I have full pad contact. Trying to rub them down on a flat surface to achieve this is quite difficult, whilst still ensuring the backing plate is parallel to the friction surface.... I'll have a bash tomorrow night, then may have to stump up for another set of RS15s....PS whilst sat at work without the old pad in my hand, can anyone recollect which pad shape the CP3344 caliper takes? It could either be CP2340D43 or CP2340D51. The latter is 5mm deeper with a straight edge along the bottom edge of the pad? This translates to either Pagid pad E1749 or E1265 (the 1265s are what fluke et al sell, but the flat edge along the bottom of the pads seems incorrect from memory).
Incorrigible said:
Re braking:
Swap as much as you can from either side to elimiante the obvious (iffy pads discs etc)
Re corner scales:
You're welcome to use mine
BenSwap as much as you can from either side to elimiante the obvious (iffy pads discs etc)
Re corner scales:
You're welcome to use mine
You're a very generous man!
I've had a vernier caliper on the pads with a length of P80 sandpaper and have got them almost back to parallel (only about 0.1mm taper). If this doesn't work, I'll have to putr my hand in my wallet for some new pads!
PS new alcon 2 piece discs, new billet hubs/wheel bearings and new uprated stub axles!
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