Front brakes brake harder once every wheel revolution when brakes are warm

johnsimister

Active Member
I fitted new front discs and pads to my 2000 TC about 1000 miles ago. When the brakes are still cold the response is smooth and firm. Once the brakes have been used a few times and are warm, the front brakes seem to brake more firmly once every wheel revolution, leading to an annoying surging as the car comes to a stop. The pedal doesn't pulsate, as it might do with warped discs. I can't see anything wrong with the discs, and there appears to be no run-out. There is a very slight steering vibration at speed which wheel-rebalancing hasn't entirely eradicated. I replaced the old discs because they had patches of corrosion where they had been immobile against the pads for many years, leading to noise and snatch when coming to halt.

It's almost as if the new discs have a varying density of metal, so parts of them expand more than other parts when hot. That could also explain the slight steering vibration. Is it possible that the discs are badly cast and contain unseen air bubbles? Seems a weird idea but I'm at a loss.

I'll measure the thickness of the old discs and see if it might be possible to skim them, but that doesn't solve the problem of what is wrong with the new ones. Has anybody else experienced anything similar with the new discs currently available?
 
Considering I was at Classeparts a few years ago, and he was buying different discs, and then grinding them down to size.. I don't trust anything new, unless it's old stock.
 
sounds like your new discs were warped from the molding then machined straight....not all that uncommon, in fact it was one of the main reasons discs weren't OE till the 50s. Issue is the grain structure is uneven as it follows the bend in the casting. When cold they are straight but when they get hot the varying grain structure (cut through on an angle during the machining) tries to straighten out (following the old warp), bending the disk. Only solution is new discs.... Might be time to do a Fosseway upgrade...
 
Perhaps Quattro can give us an up to date review on the Fosseway product. As I understand the package does not give any huge performance uplift over the already excellent stock set up, but you do win on cooling from the ventilated disc and save on unsprung weight.
 
Considering I was at Classeparts a few years ago, and he was buying different discs, and then grinding them down to size.. I don't trust anything new, unless it's old stock.

Wasn’t he doing a vented brake upgrade, machining transit discs to fit?
 
Perhaps Quattro can give us an up to date review on the Fosseway product. As I understand the package does not give any huge performance uplift over the already excellent stock set up, but you do win on cooling from the ventilated disc and save on unsprung weight.

Sparky's winter/spring/summer/autumn work

I haven't replaced the cover plates yet as they don't fit and will need some modification. They also squeal a bit, possibly because of the missing back plates.

I don't know about the reduction in unsprung weight though as the calipers are much lighter but the discs are a lot heavier :hmm:
 
Sparky's winter/spring/summer/autumn work

I haven't replaced the cover plates yet as they don't fit and will need some modification. They also squeal a bit, possibly because of the missing back plates.

I don't know about the reduction in unsprung weight though as the calipers are much lighter but the discs are a lot heavier :hmm:
I thought after I typed that it would be handy to weigh a FW caliper and disc against stock caliper and disc.
Do the FW have anti squeal shims ?
 
I thought after I had fitted them, that I should have weighed both sets, but it was too late :(

No anti squeal shims on the FWs
 
Perhaps Quattro can give us an up to date review on the Fosseway product. As I understand the package does not give any huge performance uplift over the already excellent stock set up, but you do win on cooling from the ventilated disc and save on unsprung weight.

Fairly sure that Ranald is running fosseway on his 64 2000 car that he's done the Monte in a few times.
 
I fitted new front discs to my 3500S 2 years ago, from well know supplier in SE England. Vibration from new. Supplier mentioned they might have been 'bad batch' and offered to replace. I did not take he offer, hoping they would bed in with use. They didn't. Had to replace with another new pair from different supplier. Fitted and no trouble since. Garage that fitted first discs mentioned they 'looked to be Chinese.' as they had Chinese markings on them. I never saw the discs to verify this.
This may be more of a problem as new old stock is used up. I could not find NOS brake discs anywhere. Nor could I find anyone who was prepared to skim the first set of discs.
 
All very interesting, thank you. The supplier of my discs said he'd had no complaints about 2000/2200 discs like mine but there were problems with V8 discs a while ago. Could be the same supplier as Robin mentions above?

I'm going to investigate the possibility of having my original discs skimmed, I think. I'll dig them out of the shed and measure the thickness to see if there'll be enough metal left after the skim.

As The Rovering Member implies above, the poor quality of some replacement parts for classics is very disappointing, and very annoying when you end up doing the job twice.
 
As The Rovering Member implies above, the poor quality of some replacement parts for classics is very disappointing, and very annoying when you end up doing the job twice.
Had NOS parts fail too, including a clutch friction plate which was super annoying.
 
Original discs skimmed and now refitted. Problem has gone away. Now to convince the supplier of the replacement discs that they were faulty.
 
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