Classic Audi Technical Mech/Tech Suspension & Brakes » Adjusting B4 rear calipers

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Old 26-02-17, 04:03 PM   #1
simonthemedic
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Default Adjusting B4 rear calipers

Hi, I am recommissioning my b4 2.0E it's been it's standing outside for over a year & having a problem with low efficiency of the handbrake. Anyone know when adjusting it do I need to use the pedal to set the disc pad clearance or pull on the handbrake a few times first then then press the brake pedal.

I have cleaned all the discs, slide pins and carrier brackets, wound the Pistons back in and reassembled everything but the handbrake won't hold it on my reasonably steep driveway yet it did so before
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Old 26-02-17, 04:35 PM   #2
V6Rob
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Question is does the hand break lever mover a long way or just a few clicks. If you have a long movement then the adjusters are probably not working properly. If it's a short movement then cables may be a fault, did you leave it with the handbrake on during storage as this would have stretched the cable.
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Old 26-02-17, 04:59 PM   #3
simonthemedic
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I have got 2 clicks on the ratchet, I have not touched the adjustment nut at the base of the lever yet so could possibly get more travel and yep it was parked up with the handbrake on, had not thought about cable stretching
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Old 26-02-17, 05:03 PM   #4
John.
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Whenever I've had cause to wind the piston in I've made sure I've given it a half turn back out before refitting, I think this seems to take out a bit of free play?
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Old 26-02-17, 05:23 PM   #5
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Don't go adjusting the cables before addressing the calipers.

I can't speak specifically about the B4 rear calipers, as I've never seen one. However, I have dealt with non-functioning calipers fitted to my cars, and rebuilt 4 of the type fitted to V8.

Firstly. When you pull on the handbrake, do the calipers move?

A failed piston/handbrake lever on one side will result in one Caliper doing all of the work.
A failed piston/lever on both sides will result in next to nil action.
While the handbrake may be moving the Pistons, it can only do so within the range of the cam movement on the handbrake lever. The internal adjuster of the Caliper is likely not moving.

Failed slider pins on one side will result in the Piston on that side moving outwards, but no reaction clamping effect, which is what had happened to one of my V8s. The pins had literally seized solid in the carrier.

Historically, moisture gets into the calipers, and corrosion sets in. The adjustment mechanism in the calipers requires free movement.

Having taken a few apart, now, I wonder if the following might not be effective, especially after a long period of inaction? I'm going to give this a go as and when I encounter it again.

First.
Disks and pads out. Check if the Pistons move when you pull on the handbrake lever either on the Caliper or inside the car.

Next.
Wind the pistons fully home, and try this again. Initially, you'll have to press the brake pedal to take up the slack. I'd use a block wood for the the calipers to press against, and aim for quite a lot of movement, at least equal to that of a fully worn set of pads and disks. This could also involve several applications of the handbrake lever, if the mechanism inside has been affected.

If that works ok, flush the brake circuit with new fluid. After a period of storage, it won't hurt. Brake fluid Should be changed every couple of years anyway.



To add, and so answering the original question.
The calipers would normally be fitted with the piston wound home, and handbrake off. The brake pedal moves the piston under hydraulic pressure. The internal mechanism allows the piston to move on the handbrake shaft/self adjuster. This is where the self adjustment comes as brake material wears down.
When the hand brake is applied, the cam on the lever pushes a solid shaft out, and so the piston moves out. When you release the lever, the piston relaxes a bit, but the rod should return to the start position, assisted by an internal spring in the adjustment mechanism.
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Last edited by Hanuman; 26-02-17 at 06:14 PM. Reason: I started writing this with more in mid...
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Old 26-02-17, 05:45 PM   #6
simonthemedic
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Thanks for the suggestions, I recall reading somewhere regards winding in and then back out half a turn, Hanuman, the calipers do move when I pull the handbrake lever and there is equal resistance on both left and right but I can still turn the wheel with moderate effort. I will follow your suggestions to ensure the Pistons are moving freely and hopefully that will sort my problem
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Old 26-02-17, 06:04 PM   #7
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From that, I would guess that the movement of the piston is limited by the handbrake rod, which is internal to the Caliper. The adjustment mechanism is likely not free, and so the clamping force is not there.

I would wind the Pistons fully in on both sides, bleed the brakes so that fresh clean fluid is in the brake circuit, and operate the brakes with the hand brake off. This should get you some adjustment function happening, and fresh fluid inside the Caliper.

In a worse case, I would consider actually taking the piston out, which can be done on the car, if you're careful, clean up inside the Caliper housing, and inside the piston. Reassemble, and do the same, set the piston fully in, bleed the brakes, operate the brake pedal.


I think that makes sense, but as I say- I'm basing this on all of the calipers fitted to my cars, so I may be at the wrong tree.

The internals of the V8/urS6/urq-RR caliper
Quote:
Originally Posted by Hanuman View Post



That's all of the internal components from a rear calliper, for the vented disc setup.
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Last edited by Hanuman; 26-02-17 at 06:11 PM.
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Old 26-02-17, 07:20 PM   #8
simonthemedic
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Thanks, very helpful. I will be back out working on the car next week weather permitting. Working through my list of jobs it's surprising what damage it can do to a car when it's left standing for a while.
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Old 26-02-17, 08:00 PM   #9
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Quote:
Originally Posted by simonthemedic View Post
Thanks for the suggestions, I recall reading somewhere regards winding in and then back out half a turn, Hanuman, the calipers do move when I pull the handbrake lever and there is equal resistance on both left and right but I can still turn the wheel with moderate effort. I will follow your suggestions to ensure the Pistons are moving freely and hopefully that will sort my problem
Can you turn the wheel when the brake pedal is pressed? If not, rusted solid sliders?
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Old 26-02-17, 08:15 PM   #10
simonthemedic
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With a wrench on the wheel nut I can just about turn it, there is only me here though so am wedging the pedal down against the front of the seat.

Think I may pull the rears apart as a rebuild kit is only around 30 from bigg red and then I have full peace of mind

Last edited by simonthemedic; 26-02-17 at 08:17 PM.
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