Do You Need New Brake Discs or Just Pads?
The decision between a £60-£150 pad job and a £150-£350 disc-and-pad job. How to tell which you need, and how to avoid paying for unnecessary disc replacement.
Pads Only
£60 - £150 per axle
Appropriate when:
- +Disc is above minimum thickness (check with micrometer)
- +Disc surface is smooth with only light marks
- +No visible cracking or heat discolouration
- +No vibration or pulsation when braking
- +No significant lip around the disc edge
- +Pads have worn evenly on both sides
Discs and Pads
£150 - £350 per axle
Required when:
- !Disc is at or below minimum thickness
- !Deep grooves or scoring on the disc face
- !Visible cracking in the disc surface
- !Blue or purple heat discolouration
- !Vibration or pulsation when braking (warped disc)
- !MOT tester has flagged the discs
The Measurement That Matters
Every brake disc has a minimum thickness specification stamped or engraved on it (usually on the hub or the outer edge). A mechanic should measure the actual thickness with a micrometer at the thinnest point of the disc.
The key question: how much material is left above the minimum? If the disc is less than 1mm above minimum, replace it now. New pads will not last their full life before the disc reaches minimum, so you would end up paying for another disc change when the pads are only half worn.
| Margin Above Minimum | Recommendation |
|---|---|
| 2mm+ above minimum | Pads only. Discs have plenty of life left. |
| 1-2mm above minimum | Borderline. Pads now, but disc replacement likely at next pad change. |
| Less than 1mm above | Replace discs and pads together. Not worth fitting new pads to nearly spent discs. |
| At or below minimum | Discs must be replaced. Driving is unsafe and illegal. |
Why Garages Recommend Discs When Pads Would Do
This section is deliberately honest. There are two reasons a garage recommends disc replacement when the discs still have life in them:
Legitimate reason
New pads on scored discs will be noisy for weeks as they bed in. The pads may never bed properly if the scoring is deep. Uneven disc surfaces cause vibration. Some mechanics prefer to fit new discs to guarantee a quiet, smooth result because comebacks cost them time and money.
Profit motive
A disc-and-pad job bills £150-£350. A pads-only job bills £60-£150. Some garages recommend discs because it doubles the invoice. This is especially common at national chains where technicians may have upselling targets. Ask to see the disc measurement and the minimum spec.
Both motivations exist. The way to tell the difference: ask the garage to show you the disc measurement and the minimum thickness (stamped on the disc). If the disc is 2mm+ above minimum with no deep scoring, pads only is the honest answer.
Always Replace in Pairs
Never replace one disc on an axle and leave the other. Both discs on the same axle must match in thickness and condition. Mismatched discs cause uneven braking: the thicker disc generates more friction, pulling the car to one side.
This applies to pads too. Always replace both pad sets on the same axle. You do not need to do both axles at the same time, though.
MOT note: Mismatched discs will cause a braking imbalance on the roller test, which is a major defect (failure). Even if the individual discs are above minimum thickness, the imbalance between a new and an old disc can exceed the 30% threshold.
New Pads on Old Discs: What to Expect
If you fit new pads to discs that have light scoring, expect some noise for the first 100-300 miles. The new flat pad surface needs to conform to the slightly uneven disc surface. This is called bedding in.
Light squeaking during bedding is normal. Persistent grinding, vibration, or squealing after 300 miles is not. If noise continues, the discs are too scored for the new pads and disc replacement is needed.
Deep scoring (grooves you can catch your fingernail in) means the pads will never bed in properly. In this case, fitting new pads without new discs is a false economy because you will be back within a few months.
Cost Comparison: Pads Only vs Discs and Pads
| Car Category | Pads Only | Discs + Pads | Saving |
|---|---|---|---|
| City car | £60 - £100 | £150 - £200 | ~£100 |
| Small hatchback | £70 - £120 | £160 - £240 | ~£110 |
| Family car | £80 - £140 | £180 - £280 | ~£120 |
| Executive | £90 - £170 | £250 - £380 | ~£170 |
| SUV / 4x4 | £90 - £170 | £280 - £420 | ~£200 |
Per axle at an independent garage. National chains add 10-15%.