[ais]

I couldn't find any thread or post on adjusting the rear drum brake shoes for optimal performance, so starting a new thread. This is important because it is a safety related aspect.

The information below will be applicable to cars with front disc and rear drum brakes.

I have a VW Polo 1L TSI MT, one of the last pieces from it's discontinuation 2 years ago. Several modifications and upgrades have been made for high performance- Bilstien B12 suspension, Whiteline rear sway bar and Wolf Stage 1 tune. The 1st upgrade made was of course EBC Yellow Stuff pads.

However, on a long highway drive, I kept feeling that the brake performance is inadequate, forcing me to plan braking well in advance and use engine braking as well.

I was contemplating switching to a larger brake caliper.

Then the car would also roll back if parked on uphill inclines with the hand brake fully engaged. Here I had to park in 1st gear as well to prevent the car from rolling back.

So on the next visit to the workshop, the mechanic adjusted the rear brake shoes to fix the handbrake issue. (Normally, this should be done from the handbrake cable). The outcome of the adjustment was that one of the shoe was touching the drum, and the other was spinning freely.

Subsequently, the braking performance leapt up. On my last visit to the workshop, I had the shoes adjusted evenly. This is roughly how the wheel rotation should be with the shoe just touching the drum-

https://youtu.be/8s9Pml6I09M?si=g9odtbdhdNCLwsDo

Now the performance is optimal.

When we apply the brakes, the rear brakes engage first, then the front brakes engage. The proportioning valve distributes the brake force as explained in this YouTube video-

https://youtu.be/tUEsxZGuMk4?si=VYQK-TDEmPTMpp7h

If there is a space between the shoes and the drum allowing the wheels to spin freely, there is a clear, perceptible and uncomfortable bias in brake force towards the front brake. On the other hand, if the rear wheels' shoes are in contact with the drums, all 4 brakes work equally, and that can be felt easily. The brake pedal feel, stopping power and control over the car is hugely enhanced.

I won't need the bigger front calipers now!

[Rehaan]

Originally Posted by ais

Then the car would also roll back if parked on uphill inclines with the hand brake fully engaged. Here I had to park in 1st gear as well to prevent the car from rolling back.

Please always park with the car left in 1st or reverse, regardless of if the handbrake is working perfectly or not.

The handbrake is simply not reliable or strong enough to hold a card in place on an incline with any safe level of universal repeatability.


Some related threads:
1 (Switch off / Park in first gear or neutral?)
2 (Best practice to use hand-brake while parking)
3 (What is the correct way to park on an incline?) (regarding steeringwheel rotation)

Originally Posted by ais

When we apply the brakes, the rear brakes engage first, then the front brakes engage. The proportioning valve distributes the brake force as explained in this YouTube video

I don't know the "correct" answer, but I don't think the above is the case.

I also don't agree with his "boat" analogy in the video. Whether the rear wheels are being braked or not has very little to do with their limit of lateral traction.

In fact, it could be quite the opposite -- too much braking at the rear could cause a break in traction, leading to the ass swinging around. This is also the reason you're recommended to put 2 new tyres on the rear axle... simply because lateral traction is more important at the rear (think understeer (safer) vs oversteer (more dangerous)).

[Bsilver]

Originally Posted by ais

When we apply the brakes, the rear brakes engage first, then the front brakes engage. The proportioning valve distributes the brake force as explained in this YouTube video-

https://Youtu.be/tUEsxZGuMk4?si=VYQK-TDEmPTMpp7h

Yes, the rear brakes will engage first in the vehicle, this has to do with rigid body dynamics. There is a term called pitch in a rigid body. The longitudinal axis i.e. the axis passing through the center of the vehicle, also know as roll center sometimes. Easy explanation is, imagine your vehicle in half front the front and this is the axis. Now assume this was not the case, and all the 4 brakes had equal forces, and the front brakes are engaging first, then the mass of the vehicle would be transferred from the back to the front causing a pitch angle of the rigid body (the vehicle). This would mean that there is less weight at the back, which means an equal braking force for all 4 wheels would end up locking the rear wheels and causing imbalance of motion. Hence the system is designed to first engage rear drums, which are not as powerful as the front discs, and then engage front discs in order to maintain the cars stability. Hope all of this explains!

Happy Motoring!

[ais]

Originally Posted by Rehaan

I don't know the "correct" answer, but I don't think the above is the case.

I also don't agree with his "boat" analogy in the video. Whether the rear wheels are being braked or not has very little to do with their limit of lateral traction.

The sequence of brakes appication is correct- rear shoes first, then the front discs. I've seen this in a couple of YouTube videos as well. More important than YouTube or Internet verification though, is how the car feels before and after adjustments. We can feel the bias of brake force shifting to the center, rather than the front doing more work than it should.

I'm got the rear shoes adjusted in my Baleno today at Panchkula. The outcome is the same. Though I've not yet driven at speeds above 60KMPH yet, there is a marked difference in stopping power. The bias has definitely improved. The front pads are Dixel, installed 5000kms ago. They were also cleaned.

The mechanic at Panchkula Auto (a really good service center) Anil Kumar remarked that while he makes this adjustment in every car, I was the first customer who knew about this. I remarked that he is the first mechanic I've met who knew about this!

[Cresterk]

Rear brake bias for weight transfer only matters in cases where we stop gradually. It is to make the car not pitch forward in mundane, every day driving.

In case of any kind of emergency stops or track driving where we jam on the brakes, 90% of the work is being done by the front. Upgrading just the rear brakes would do nothing to reduce your emergency stopping distance, because that was never limited by your rear brakes in the first place.