I have a problem with the French bi-annual roadworthiness test tearing out the handbrake pads on my inboard axle on the rolling road handbrake test. It has happened as a delayed failure twice now: about a month after the test a pad drops off the backing.

On my Dana diff car, the only way I can see to change the pads is axle out. If anyone knows different from experience, please let me know.

I have an idea to reinforce the pad by countersinking a bolt into the disc-facing face of the pad by a couple of mm, that will go right through the pad and backing plate and then to the caliper. The pads effectively have zero wear, so I do not anticipate this being a problem. Any views on this, please, or any other ideas?


Greg

 

I think a bolt would work. An aluminum rivet from backing plate into pad material may do it as well.

Interestingly, when I had my rear cage out to refurbish stuff I noticed that two emergency brake pads were loose from backing plate. I attributed it the car's lack of maintenance and/or something weird. Guess not...

 

In addition, I would put a significant chamfer on the leading and trailing edges of
the pads so that they can engage more gently.

 

I wouldn't use an aluminium rivet as water will turn it into "salt" rather quickly... No matter if rain whilst driving or condensation.

How about trying a different glue to stick the pad to the carrier? There are loads of new agents to glue things together...

 

yes Gregg i will do the same with the countersinking next time I have the job to do,
I have tried to change the pads without removing the unit but finished up with no h/b for about 4 years before I finally removed the unit and sorted out the ratchet and adjuster, as I got a bit embarrassed at the mot year after year with the same adviser, the trouble is most of the stock of pads is old stock and the integrity of the bonding has diminished with age, so go for it and keep us informed,
ive also fitted a warning buzzer so I am less likely to drive off with it on, which used to happen a lot




you missed a good show at Warlingham last weekend rods and sods
mine was a sod

 

I'd go for a stainless bolt, as you say contact with the disc isn't an issue otherwise an old school copper rivet might work.

 

If you're able to thoroughly clean pad and carrier then an epoxy adhesive like araldite can give an extremely strong bond.

 

I'm sure, now........ where was that bolt?

 

RGP:
Thanks for the encouragement! Funnily enough I thought about a buzzer too. How and to what did you wire it, please?


Norri:
Stainless it is, though I am more worried about the bolt pulling through the pad material than I am about it rusting away.


Pads on order, will post pics etc sometime next week


Greg

 

Very clever



Cheers
DD

 

I had the friction material knock off a brand new pad just installing the handbrake calipers over the discs! Not terribly impressed with the manufacture.
Backing plates are supposed to have a textured surface for the pad to bond to, these were just flat steel.
If I were to consider mechanically fastening the material to the pad, I'd use a brass bolt or rivet as was done in the drum brake era. If brass contacts the rotor, it'll not do any damage and is a lot stronger than aluminium. Having said that though, it's not as if handbrake pads do much work, perhaps they could be machined out of solid brass? It would be good enough in friction for one emergency stop.
What REALLY annoys me is that modern testers consider a PARKING brake as an EMERGENCY brake on vehicles that were never designed to use the parking brake to stop the vehicle, and let's face it, if you lose all brakes on any modern vehicle with a dual circuit system, something really major has gone wrong.

 

I wired from the hand brake switch, it is an earth switch, I fitted a relay under the drivers seat that's ignition on live and the hand brake earths the relay, the buzzer is also under the seat, cant you glue a new pad to the old backing in situ to get the brake working again until you have a better reason to remove the cradle?

 

Thanks RGP. I'll put it on my list. I can only just see one of the two pads, and only feel the space where the one fell off. No chance of a bodge! Plus I have a theory about the XJS: fix things as soon as they go wrong or you end up with a rubbish car in no-time!


Today I prepared the cradle for demounting, exhaust off, brake line disconnected, handbrake disconnected. Now I await the pads. The reason the cradle is not removed yet is because I have the front hubs in bits. I have AT LAST nailed a 50 mph steering shimmy down to a failed top ball joint (12,000 km only on it). So I am awaiting the bits for that too. When will it end...


Greg

 

OK Guys, here's the story on the handbrake mods.


First, I have 12mm thickness solid discs on the back, thinner discs might, repeat might, give problems over disc grip by the calipers, as my mods in effect make the pas surfaces 4mm further apart.


There are three reasons why the handbrake pads fall off their backing when the handbrake is used with the wheels turning:
1) The glue fails for no very good reason other than it is rubbish glue (very common)
2) The glue is OK, but the machined indentation in the caliper into which the pad sits only supports the pad's metal backing against the torque load, and does not support the pad material. Thus the pad-to-backing glue has to withstand full braking torque
3) The WIDTH of the new pads that are sold - OEM or others - are actually UNDERSIZED by 2 to three mm compared with the original OEM fitted pads from the factory. I know this for a fact, because to do these mods I used the calipers from my spare axle, and this axle had never been touched since the factory. The handbrake pads on this axle are a significantly better fit in the caliper indentation.


Greg's fixes:


a) The pad indentations in the caliper arms were machined deeper by 2mm. Thus in total the indentation in each caliper arm is now 5mm instead of 3mm. As you can see from the two pics below, the pad itself is significantly deeper in the arm, and once the gap each side of the pad is filled with JB weld the pad material will be supported by the side of the indentation as well as the backing plate. Note on factory pads at the time, the JB weld would not be required as they were wider.





b) I have drilled out a second hole in the pad and arm, and fitted a 5mm countersunk-head brass bolt though the pad material and the arm. This should prevent the pad falling off if the glue does fail and also reinforce the pad to backing plate joint. So even if the glue does fail (in spite of fix (a) above) the pad should still function properly. The brass bolt head is countersunk 5mm into the pad. The original pad fixing is used unchanged. pics here:









The arms needed quite a bit of machining to get suitable surfaces for the machine tool to mount them securely, and for the surfaces for the nuts on the new bolts. Also there are four to be done and the new pads have to be available to align the new holes properly. All in all nearly three hours for a skilled guy. Also, the arms, pads etc are all handed, so be very careful you know which side is which and which way is up, or it is all too easy to make holes in the wrong arm in the wrong places!

The JB weld to fill the side gaps in not yet in place in these photos, but it will be before fitting them. Anyone who wants my machinist friend to do theirs, pm me, but it would cost around 160 UKP. I will report in due course how it works!

Greg

 

I like that a lot! I need a machinist friend.

 

So of the mods I tried, the two bolts work fine, but machining a deeper shoulder to support the pad material against the disc torque did not. SO the problem of supporting the pad material I have solved as follows:


First I shimmed up the machined arms to their OE depth, this moving the pad nearer the disc. This is particularly Important at the fulcrum end of the caliper, as when the handbrake is applied this end move only about 1/3 the distance to the disc as the swinging end moves.


This left the problem unresolved of how to support the pad material and the pad to backing glued joint from the turning torque. I have fixed this (I hope) as follows. I have welded a shoulder to the arm at the downstream (fulcrum) end the of arm, the end against which the turning torque is pushing the pad, amazingly there is plenty of space, that supports the pad material. pics here:



and with the pad loaded





Finally, the handbrake's weakness is, as far as I can see, is only because the pad sheers off the backing plate - which has happened to me twice after the French MoT test on the rolling road. The rest of the mechanism is incredibly strong. However I now realise that the gap between the pad and the disc is absolutely crucial to setting the handbrake up. New discs are 13mm diameter, mine are worn to 12 (still within spec). The effect of this wear is to make the handbrake much less effective as only the tip of the swinging end of a NEW pad makes contact with the disc. While at rest, the fulcrum end of the pad can be over 1 mm away from the disc, and NEVER make proper contact even when the handbrake is applied.


I have corrected this by carefully shimming up the pad and trial fitting until the pad is parallel to the disc at rest and only about 10 thou away from the disc at the fulcrum end of the pad. Now the handbrake works far more effectively than it ever has and the entire pad makes proper contact when applied.


So to summarise the fix:
1) Weld a small shoulder on the fulcrum end of the caliper to support the pad material against the torque
2) Put a second bolt through the pad material and the caliper arm to reinforce the pad-to-backing plate join. This is easy to do and requires only a drill, no machining at all is needed to the caliper arms.
3) when refitting, take each arm in turn individually, and mount it on its fulcrum bolt. This is easy to do. See what size of gap is between the arm and the disc at the fulcrum end of the caliper when you swing in the arm against the disc. If it is more than 10 thou, remove the arm and shim the pad to remove this gap. This is somewhat of a royal pain to do as the sims need to be drilled as the two pad fixing bolts go through them. But you end up with a handbrake that really works well.


I just hope the shoulder and the extra bolt really fix the pad sheering off problem in the longer term!


Greg

 

I have completed my handbrake improvements, which in their final version to date differ in some important respects from what I have posted earlier in this thread.


The outcome of these changes is as follows after a couple of days of road testing:

• With the car left in drive at 20mph, foot off the throttle, the handbrake will stop the car.
• On a loose surface in neutral it will lock the back wheels at 15mph.
• It will hold the car stopped in drive with engine doing 1300 rpm.
• The pads did not tear out.
• There is no driveline "shunt" or slight movement when the handbrake is applied and the footbrake released, it locks the wheels very solidly.
• If the handbrake is on, it is impossible to pull away without noticing it is applied, as the car will hardly move. This is a very substantial improvement on the original.

After the first road test the cable needed some adjustment at the adjuster behind the lever under the carpet on the rear inside sill, maybe 15mm. I think this is a result of cable stretch as it has not had much use beforehand. It is also possible that the calliper mechanism and the pads/shims were bedding in further, in spite of the care taken to remove lost motion from the system.

Lever effort was noticeably higher than before (greater pad area, new discs?) and it needs to be applied with decent effort; however it is probable that as the discs and pads wear off their break-in surfaces, this will reduce, which seems to be happening already.

I have made quite a detailed illustrated write-up of what I did and how I did it. If anyone wants a copy, please PM me with an email address to send it to. Obviously I am making no recommendations and giving no advice about what you should do with your own vehicles.

Greg