Handbrake
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Application
Girling/Lucas calipers used on the following platforms:
- Audi 80, 90, Coupe, 4000 (B2, 1978–86)
- Audi 80 (B3, 1987–91)
- Audi 80 (B4, 1991–1995)
- Audi 100 and 200 (C2, 1976–1984)
- Audi 100, 200 & 5000 (C3, 1982–1991)
- Audi 100 and S4 (C4, 1991–1994)
- Audi A6 and S6 (C4, 1994-1997)
Common Problems
The handbrake (called emergency brake or e-brake in the US) is notorious for causing problems on older Audis. The three most likely reasons for this are:
1. Binding handbrake cables 2. Caliper sliding pins seized inside carriers (often accompanied with the pads frozen to the carrier) 3. Seized parking brake mechanism inside the caliper
Binding Handbrake Cables
Binding handbrake cables are easily solved by replacement. The inner cable should be free to slide in and out of the outer. After about 10 years, both inner and outer tend to rust. Initially this causes tight spots leading to restricted movement of the parking brake mechanism inside the caliper leading eventually to a seized caliper. It is false economy to try to salvage a cable in this state. Once the nylon coating of the cable inner is breached, the cable strands begin to rust very quickly. This causes more swelling and in a short while the strands rot away leading to a potential catastrophic failure of the handbrake. New cables are usually fairly cheap - typically about £20.
Seized Caliper Sliding Pins
Seized sliding pins is very common and is usually caused by a failure of their dust seals. If they haven't been seized for very long, they will probably work loose given sufficient penetrating oil and sympathetic use of a spanner. If they have been seized for some time, then heating up with a blow torch may be required. Clean the pins thoroughly and if necessary use something like metal polish. Grease the pins an the bores lightly and reassemble making sure that the all-important dust seal is fitted and in good condition. I believe replacement carriers are available if yours are in a state.
I have often found that the rear pads no longer slide in and out or even along the carriers due to excessive rust build up. I usually take a file to both the rusted edges of the pads and also the rusted edges of the carriers where they grip the pads. The job is made much easier if you remove the carrier as this gets the disk out of the way.
Seized Parking Brake Mechanism
A seized Parking Brake Mechanism (PBM) is not so straightforward. The Bentley manual makes no reference to the PBM. Most Haynes manuals follow the Bentley example, but one manual specifically say that the PBM is not user serviceable. However, I and many other like-minded stingy Audi enthusiasts have had a fair degree of success in stripping them down and repairing them. No specialist tools are required (except for a 12mm Allen key or piston retracting tool and a long-nose or circlips pliers).
Description of Parking Brake Mechanism (PBM)
I have come across two different types of Girling/Lucas rear caliper - both using a 36mm diameter piston. The older type has the parking brake mechanism (PBM) bolted on the end of the caliper using three bolts. The newer type has the PBM as part of the caliper casting and at first look doesn't appear to be capable of being dismantled (but it is).
Note: Be careful if obtaining new, reconditioned or used parts to get the correct diameter calipers. They exist in at leat two sizes (36mm and 38mm). Although they are bolt-on replacements, they will mess up the balance of your brakes. The number '36' or '38' will be clearly embossed somewhere on the caliper body.
Both types work by using the handbrake cable to pull on a lever attached to a 16mm diameter 50mm long shaft inserted into the back of the caliper. An oil seal (16mm x 24mm x 6mm according to some accounts, 16mm x 24mm x 7mm according to others) prevents water and dirt ingress (not very successfully!). The lever rotates and a cam cut-out in the centre of the shaft pushes a small rod (about 15mm long with rounded ends) against the back end of a long threaded shaft (coarse pitch) which is screwed into the back of the piston. This presses the pads against the disk. The self-adjusting part of the mechanism is achieved by the threaded shaft gradually unscrewing itself from the piston to compensate for pad wear. Hence the instruction to rotate the piston clockwise (screwing it back onto the threaded rod) when resetting it.
There is an extra component in the older mechanism - a cup which the small rod presses on and which in turn presses on the back of the threaded shaft. This cup is not needed in the case of the newer mechanism as it is built into the back end of the threaded shaft.
Before doing any dismantling, obtain repair kits containing all the rubber seals, o-rings etc. Then give the calliper a thorough clean. The less grit and dust that gets into the bores the better.
Older Mechanism (early 80s) - Bolted On
Taking the older mechanism first, dismantling is fairly straightforward, except for the fact that at least one of the three bolds holding the PBM onto the back of the caliper usually shears. It is usually possible to remove the remainder of the bolt with a vice grips. Obviously soaking the bolts overnight in penetrating oil will help matters. When reassembling this section, use an anti-seize compound like Copaslip or a water sealing substance like Loctite on the threads of these bolts.
Dismantling the PBM itself might be a little more difficult as it is usually rusted. The shaft with the lever on it will NOT come out until the internal components have been removed. If you are not prepared to go to the trouble of a complete strip down, then the shaft can be raised up 10mm or so to allow a small brass brush or strip of abrasive paper to be used to remove the rust band.
Complete dismantling proceeds as follows. Rotate the lever backwards and forwards as much as possible. That will push the cup out of the hole far enough that it can be removed. If you need to help it with a pliers, be careful not to mark it. Once the cup is out, then you can remove the small rod (with rounded ends). Once the rod is out, then the 12mm shaft with the lever attached can be removed. The shaft is often heavily rusted and needs to be worked back and forth a few times before coming free.
Clean up everything thoroughly - use fine grade (400 grit) wet and dry abrasive paper on the rusted components, removing as little metal as possible. Service the rest of the caliper as normal as detailed in the instructions in the repair kit.
Note: caliper kits often do not include any seals for the PBM - they might need to be obtained separately.
Newer Mechanism - Integral
In the case of the newer mechanism, the PBM cannot be unbolted from the caliper as it is integral. In this case it has to be dismantled internally for thorough cleaning. Once again, it is possible to do some limited cleaning of the PBM by removing the return spring and the 10mm retaining bolt. This will allow the 16mm shaft to be raised by about 10mm or so to allow a small brass brush or strip of abrasive paper to be used to remove the rust band.
For complete disassembly, start by removing the piston by unscrewing (anticlockwise). On the older types, you need a 12mm Allen key; on the newest versions they seem to have changed to a piston design with two opposing cut-outs - a pointed pliers might be able to engage with these, alternatively buy a universal tool made by Lisle and others - this is a cube that fits a 3/8" ratchet and has different pins on each of the 6 faces. It is also possible to manufacture a suitable tool by using an angle grinder to shape an old 1.25" socket or something similar.
Once the piston has been removed, then you need to remove the circlip holding a retaining plate (with a vaguely rectangular cut-out in it) in position at the bottom of the cylinder. A long needle-nosed pliers should do the job perfectly. The retaining plate is holding the large threaded shaft in position and probably won't want to come out. Lever the threaded shaft out and that will pull the retaining plate with it. Some people have had success by reattaching the heavy piston to the threaded shaft and then pounding the entire caliper onto a block of wood. The slide hammer effect of the piston might break the threaded shaft and the retaining plate free. Then again, it might not! In that case, screw a nut of the correct size onto the threaded shaft and lever the nut (and shaft and plate) upwards with a couple of crowbars taking great care not to mark the threaded shaft.
Eventually the plate will break free and you should be able to remove the shaft, plate and a rubber o-ring which seals the brake fluid part of the caliper from the PBM part. Has anyone got the dimensions of this o-ring? Some calipers have a spring in here, some don't You will now be able to remove the small 15mm rod that connects the mechanism actuating shaft to the large threaded shaft. If you find corrosion on the base of the threaded shaft that is shaped like a mini piston, this will need to be cleaned up (using fine grade - 400 grit - wet and dry paper on the rusted parts). As for the older PBM above, the actuating shaft can now be removed for thorough cleaning.
Once again, clean up everything thoroughly - use fine grade (400 grit) wet and dry abrasive paper on the rusted components, removing as little metal as possible. Service the rest of the caliper as normal as detailed in the instructions in the repair kit.
See the exploded diagram of the caliper on the 20v.org site.
Note: caliper kits often do not include any seals for the PBM - they might need to be obtained separately.
Reassembly
During reassembly, reinsert the well-greased (high-temperature brake grease) 16mm diameter actuating shaft, then insert the small 15mm rod, then the large threaded rod with the o-ring on it and then the plate. Check that the cut-out in the plate is orientated in the same direction as the rectangular cross section part of the threaded shaft and then push the plate down. Use a suitably sized socket to make sure it's driven all the way down and that that it's straight. Next, compress the circlip and fit it into position. It might need a prod with a screwdriver. Check that it has clipped into position all the way around with a screwdriver.
When reattaching the return spring, you might consider replacing it with a stronger one. Apparently there is a European Ford brake return spring that works: The Ford P/Ns are reputedly: 6141147 & 6141148.
If all goes well, you will now have a perfectly functioning parking brake.
Success rate seems to be about 80%. Failure mode usually manifests itself as brake fluid even at low pressure pouring out of the dust seal for the actuating lever - probably due to perishing of the o-ring.
Paul Heneghan 23:45, 13 September 2009 (BST)
