Disbalanced parking brakes

Jochen,

I presume you will do this with the cage in place…
Raise the car quite high so you have some space. (be safe !!)
Once under this is what you will see

The mounting bolts in question are the two bolts behind the return spring.
Under them there is a plate with locking tabs. You have to bent them back and undo the bolts.
The forks are under the locking tabs plate, all supported by the two bolts.
Remove the bolts and fork and then you can retrieve the handbrake assembly.
Maneuvering it out of the cage is somewhat fiddly.
Once you have them out it will be very apparent of how the system works.

The handbrake caliper goes in between the slots of the brake caliper.

The fork and locking tabs plate go on top of the caliper.
The fork’s ends go in the smaller holes on the handbrake caliper.

Hope that helps,
Aristides

Thanks Aristides,

that was exactly what I needed: it pretty much closed the gaps that my imagination hadn’t been able to cross - I even printed your and Peter’s pics out to get a good start tomorrow morning!

Merci beaucoup! Je serais ravi de t’inviter à une bière ou deux - le rouge ici ne va pas t’impressionner, si tu es habitué à ceux du Midi;-)

Hope everything will go smoothly tomorrow - will report back!

Thanks to all

Jochen

75 XJ6L 4.2 auto (UK spec)

Avec plaisir Jochen!
Mieux le vin d’ici que l’eau de la !

Good evening, Gentlemen,

this is first and foremost to repeat my sincere thanks to everyone helping me out, then of course to report back how things went on and maybe to give others that bit of info they may need.

So starting with the simple story: it was a hell of a day, going in at 8.30 a.m. and finished only at approx. 3 p.m. with just a few minutes coffee break. Why? Well, not because I wasn’t prepared or because bolts were frozen or anything - just because it was a really hard job! Let me start by admitting that I tackled the job with my favorite mechanic who really knows what he’s doing and is very capable when it comes to turning losing battles … He has no clue about older Jags though; this is my part of the job. Anyhow, I doubt it would even be possible to do this job alone as there is so much wiggling from the back to ultimately find holes and threads or pulling on springs while hooking them on tiny holes etc. that you really need that extra person.

We started well prepared with your information. As my problem related only to the lh brake we limited our efforts to this part. Things got a bit tight with the pulling of the fork and the pushing rearward and out of the handbrake calipers. Fortunately the brake pads were as good as new and looked perfectly well. Less so the outer face of the rotor. After some sanding - one person with the emery paper, one person turning the wheel - everything had to get back in. Doug was right: in is a lot trickier than out. It took us quite some time to get the mounting bolts through the locking tab sheet, the fork, the upper part of the brake calipers, then the hand brake calipers and back into the brake calipers until we found the threads - and got the “hooks” of the fork aligned as well.

Much to our dismay the entire action hadn’t helped at all, as subsequent tests showed. Only now;-( I remembered Peter’s advice: we didn’t hear any clicking of the adjusting mechanism. So everything out again - admittedly a lot faster - and dismantling the handbrake lever. Again everything went super easy. Inside, however, we found dirt, grime and crumbling rests of grease filling up the entire cavity. Buried in it was the adjusting mechanism, obviously completely apart. While I initially thought it had broken, it turned out that only a tiny axle had wandered away and released a spring-laden part of the mechanism. Restitution took us the best part of one more hour.

Putting it back in was not much quicker than the first time - still fiddly. Unfortunately, we got the distance between the brackets a bit tighter which made the final assembly not easier. For the moment, however, I’m quite confident that the handbrake will pass the MoT now.

Famous last words for those up to the same job:

  • The documentation doesnt reveal, but for a start all you need is Aristides’ description: the locking tabs are turned outward, the bolts (7/16") go out easily. Even the mounting bolts come out easily. They should be cleaned and greased well for reassembly.

  • What the ROM calls “retraction lever” (70.55.04, #8) is the characteristic “fork” (parts catalogue 1J 15R, 9750). As I reused my brake pads I decided to reuse also the fork. The “hooks” of the fork go into holes on top of the two parts of the handbrake caliper.

  • The loosened caliper can be wiggled backwards around the rotor. One good thing: we were able to pull out the handbrake caliper sideways to the outside. So it was not necessary to remove the tie plate (as per ROM 70.55.04, #2).

  • One key message: the description of the internals of the handbrake caliper, in particular the adjustment mechanism in the parts catalogue (1J 15R) hides an important issue: part 8836 in fact is composed of four parts: a basis that is mounted to the lower side of the lever, an upper part that actually engages into the gear ring of part 8990, connected with an axle and spring-laden by a tiny coil spring. This thing had come apart in my car and thus rendered the adjustment mechanism dysfunctional.

  • Make sure the adjustment mechanism operates properly prior to reassembly. It requires not only the functioning ratchet mechanism, but also free movement of the main bolt in the gearwheel and the fixation of the gearwheel by the outer cover of the lever. The cover plate comes with a slight hump indicating the location of the gear wheel and probably designed to “center” the gear wheel. If the adjustment doesnt work any more, braking power is directed at the outer cover and the small hump becomes a bulge big enough to let the gear wheel move away from the ratchet.

  • Take very good care to get the distance between the two parts of the caliper right. It is determined by the number of turns of bolt 8845 into the gear part 8990. If you get it wrong, you’ll have to start anew.

  • As a starting point you may lay out the whole shebang before you, put the bolts through the fork holes and the holes of the caliper parts (this is the fixed distance). Then push the tips of the fork into the respective holes and based on this parallelogram check the distance between the pads: Too big will be easy to install, but might not be adjustable. Too tight is extremely hard to install. As a starting point you might take the measure given in the ROM: 0.75" (19.05 mm).

  • When reinstalling the handbrake caliper, take care to first align the handbrake calipers into the slots of the rear brake calipers, so you can fit the mounting bolts. Then take care of the inner part of the “fork”, as the inner part of the brake caliper has less play. Finally, prise the fork into the hole on the outer side.

  • To balance the brakes without having to try and repeat you may try to install the handbrake a bit on the loose side and tighten up by hand. The split pin 3752 can be pulled with the handbrake in place. A well-functioning adjustment mechanism can then be adjusted manually by tightening the main bolt 8845. It is accessible with a very small ratchet.

Good luck everyone and apologies for the text wall

Jochen

75 XJ6L 4.2 auto (UK spec)

Jochen!
When I had my 69 E type long ago I had a fantastic parking brake,
I never touched it.
Now on my 78 xj6 I have a problem, its not holding the car when I park.
I know that the long rod that goes into the center of the calipers is not
adjusted properly.
You might look at the mechanism and might be able to adjust it.
Let me know.
Walter

**
The ‘retraction lever’ deforms as pads wear, Jochen, but retains enough elasticity to slightly retract the pads from the discs.

This ensures that the retraction gap is constant throughout pad life. If worn pads are replaced by new ones, the ‘forks’ should be replaced - the metal looses its properties if bent back. But, as you say, if the same pads are reused so can the forks…

However, to ensure proper initial clearances, it is advisable to fractionally re-bent the forks - they will deform as appropriate. If the forks are too narrow, there will be no clearances between pads and disc - but the fork metal is to weak to exert much pad/disc friction. And as pads wear the proper clearances will be re-established…

A beautiful write-up - no need for any apologies…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

Walt,

in fact I didn’t have any reasons to complain about my handbrake - it was always up to the job, until - as I had to find out, the adjusting mechanism virtually fell apart leading to the total loss of the left handbrake. For the moment I seem to have regained full braking power - Monday morning the test bench will hopefully confirm this.

As to your problem: it could be just about everything from disintegrated pads to a loss of the adjusting mechanism - as in my case. I’d start with an examination on a lift: have one person operate the hand brake and check smoothness of operation of all wires and simultaneos operation of both levers. By asking the person to pull the brake just one click each time you can check which road wheel is subject to which braking power.

If you’re lucky, you’re done with some greasing, if not, you’ll have to get into the same job as I. A significant loss of braking power may be caused by the usual suspects, ie brake pads and rotor surface, or by the handbrake mechanism itself. In that respect there can be only three problems: one, as I described, is the free movement of the two handbrake parts around their mounting bolts. So, if you take it apart, clean and grease the holes and the mounting bolts. The second is the alignment of lever and the two handbrake parts over the bolt 8845 - this may be what you referred to as “the long rod that goes through the center of the calipers”. In my case it was obvious that there was no issue about free movement of this part. The third one is the internal of the lever with the ratchet adjustment mechanism. This indeed takes care of the adjustment of the two sides as you write. Peter advised that the grease may gum up and block this mechanism; in my case it had fallen apart. So, if you decide to go in, you better put that mechanism (handbrake pawl 8836) and the critical springs (8940 and 8837) on your shopping list before to be prepared for the worst case. One of the usual suspects carries an aftermarket replacement part for the handbrake pawl at UKP 4.20 - it took two of us one hour to restore function of the original one … you may do the maths!

Good luck and keep the faith! As I wrote - both physically and mentally this is a two-person job

Jochen

75 XJ6L 4.2 auto (UK spec)

Thanks Frank,

upon removing the hand brake mechanism I found that the original brake pads were pretty much as thick as the replacement parts I had purchased before, so I decided to keep the originals. That made my decision easy to keep the original fork. And as we quite carefully made sure not to change the distance of the two parts of the handbrake the original fork’s hooks found the holes in the two handbrake parts with minimal need of deformation (<2 mm) and rather fore/aft than left/right. It was still tedious enough.

Now, I’m just wondering when our examiners will tell me to replace these rear rotors …

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

If one drives ‘by the book’, handbrake shoes should last longer than the driver. Setting the brake after coming to a halt and releasiing it before moving off means no rubbing friction, only static clamping. No wonder the grease congeals if it is repeatedly warmed by the main calipers but never stirred by a moving/working adjustment mechanism.

Viel Glück für TüV Montag! It took me three attempts.

Viel Glück!
I‘ll look into what I can do to make my handbrake work in the next weeks going by the above and from then on I expect reliable operation of everything. I guess there’s no way to determine if I should shop for the replacement parts right away, so I better get them now?

David

Thanks, Pete and David!

On Monday morning I’ll just check on my mechanic’s bench whether the handbrake now performs as it should - last Thu his test bench was blocked by another car. In the afternoon I have an appointment with someone else with an exhaust analyzer to tune the carbs leaner - that was the second objection. On Tue I’ll hopefully pass the test:-)

Peter, you’re right, of course - that is if the car is driven “by the book”: no movement, no friction, no wear. The pads on the pic Aristides posted tell a different story though … wonder how that car was used …

Thanks again for your good wishes!

David, I purchased all I expected - pads, all the bolts necessary to fit them, the retraction levers and the locking tab retainers for both sides (all for approx. 80 EUR) -, but didn’t use any of those and instead would have desperately needed the handbrake pawl which I didn’t have at hands. Maybe the good thing is that I rescued a bit of mechanics - residing in an ugly handbrake lever, but resembling a Swiss watch movement - instead of throwing in a cheap replacement part that omits all of the ingenuity of the original. If you have a lift and an extra day I’d go in, check, order if necessary, and refit. All parts seem to be available and will be at your door in one day.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

Interim report:-(

We did everything right with the lh handbrake. In particular the restoration of that exploded handbrake pawl seems to have worked out. The lh handbrake showed very good functioning today on the test bench. Unfortunately, now it was the rh handbrake that was an almost total failure …

Initial test: LH 60 daN RH 260 daN
Today: LH 200 daN RH 80 daN

I’m aware that we got the lh caliper somewhat tighter than it was before, maybe one turn of the screw, and we only worked on the lh handbrake, but my understanding was that the load distribution was self-levelling between the two calipers.

Is there anything we could do short from pulling both handbrakes?

Thanks all and best regards

Jochen

75 XJ6L 4.2 auto (UK spec)

It is self-equalising because one cable pinches both levers in opposition. However, when some stiffness or distortion occurs in he levers and/or mechanism, an equal cable force does not always lead to balanced grip ‘downstream’ of the cable.
Even at my third attempt it was not perfect but the tester could see I got improvement each time and it was not safety-critical really.

Maybe the LH caliper got jealous and wants also some attention ?

You’re right, of course, Pete!

The cable pulls together the two levers. Equal braking power will be distributed, if the pivots of the handbrake parts, i.e the mounting bolts at the brake calipers move equally freely - yes, we cleaned and greased only the lh bolts, so some room for bias here - and the two handbrake parts move equally freely on the big bolts. Actually, the lh brake was absolutely open, so I have no reason to believe the rh side is much worse.

The place where my visualization of equal braking power is somewhat lost is the transfer from the lever over the bolt 8845 to the ratchet mechanism 8980, 8836. It is obvious that if the bolts aren’t screwed into the levers to the exact same depth the basic distance between the two handbrake pads is different, the travel of the pads to the rotor is different and ultimately the braking power on the (assumedly equally thick) rotors is different as well. That would mean you’d always have to make a perfect match of both handbrakes.

But then there comes the adjustment mechanism. I understood it compensates for the wear of the brake pads and readjusts the setting of each (!) handbrake. So it should also compensate for slight imperfections of the basic width of the distances between the handbrake parts.

When the tip of the lever in the pic is pulled “right”, it will - due to its geometry - compress the two parts of the handbrake. The bearing of the force applied is the head of the bolt 8845. The gearwheel 8990 is fixed against the lever by the brace 8840.

With compression the bolt 8845 will move further into the lever. As the bolt can’t turn with the locking pin 3752 in place the gearwheel 8990 will have to move clockwise which it can do with the ratchet. With every tooth turned the ratchet 8836 will hold the gearwheel in its position.

When braking power is released the two handbrake parts move back to the position defined by the retraction levers aka forks 9750. Bolt 8845 moves backwards and forces gear ring 8980 to turn counter-clockwise. But wait: now the ratchet 8836 blocks the movement of the gear wheel, doesn’t it? Any clarification or enlightenment welcome!

Peter wrote that you can move the adjustment mechanism in both ways by forcing the lever in and out. For the moment I have got some hope left that by undoing the cable and moving both levers back and forth and finally to the same starting position I might achieve a better starting position for equal movement. Wishful thinking?

Thank you all!

Have a good night

Jochen

75 XJ6L 4.2 auto (UK spec)

You got it - that was exactly my initial idea, too! BTW, sometimes I really feel like any of my cars is trying to punish me for too much attention devoted to another car by acting up. But probably that’s just because I’ve got only one child;-)

Paul, how about your stable? Are your other Jags jealous over the engine bay work you did on the antelope colored car?

Keep the spirit

Jochen

75 XJ6L 4.2 auto (UK spec)

Jochen,
It is funny that you mentioned that. Following all the attention that I gave to our 1984 XJ6 Vanden Plas with the replacement engine and engine bay restoration over the past 8 months two of our other Jaguars did start acting up. I guess they were jealous. :wink:

The first was a failed distributor vacuum advance in our 1990 V12 Vanden Plas which I plan to tackle next week. Then the air pump failed in our 1990 XJ-S convertible and it started making a metallic chattering noise that I resolved last week when I removed and replaced the air pump with a rebuilt one.

I continue to drive our 1984 XJ6 Vanden Plas as I work off a few more items prior to selling it including installing new front brake rotors and pads that I just started working on.

With five Jaguars (four of them drivable) it is always something. :slight_smile:

Paul

The one thing that can fool people about ‘pincer action’ cable controls is the need for free cable outer movement as well as inner cable movement.

Normally a clutch or motorbike front brake uses an outer cable held between two fixed points, one at the control lever and the other near the clutch arm. The system works by transmitting a simple pulling force of the hand or foot from point A to point B. The outer is immobilized at each end and apart from guiding the inner cable like fluid in a brake line, the outer plays no part. Jag h rakes are different.

The outer and inner cables both transmit a clamping force to opposiing handbrake caliper arms, either directly (XJ) or via a cantilever mechanism (E-Type).

I have seen cars where the cable has been zip-tied or threaded through brackets or holes, because a floppy cable seems poor. Done to excess, this prevents the outer clampingshing its caliper arm enough and only the other side works, due to inner cable tension.

1 Like

Thanks Pete,

indeed the handbrake mechanism in the XJ works pretty much like a v-brake on a bicycle


The outer cable is fixed against one “floating” lever while the inner cable is fixed against the other. Any better v-brake will have adjustable springs though to compensate for differences in movement of one part vs. the other. That’s missing in the XJ …

See what I can do …

Wish me luck:-)

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

1 Like

I wanted to write about that type of bicycle brake but did not know anything useful to say.
The spring adjustability in these should only center the brakes so the pads don’t rub while driving. That isn’t needed on the car as they are more than powerful enough and the main pads aren’t pulled back either.
As soon as one side contacts the rim on the bicycle brake, the other will now be pulled in so the clamping force on the left vs. the right side (not necessarily the braking force, but close enough) is always equalized.
As long as the springs (not C.22690) hold the cable, movement should be sufficient. I would say that if the braking force is unequal it is not caused by the cable, nor by the return springs or by the pads (because now the other side is acting up if I’m not mistaken).

The only explanation I can come up with is that both brakes were binding. The now fixed one gave more resistance, so the braking force was distributed to the other brake.
Now that the one is repaired, the other gives much more resistance. The force on the levers is equalised, but the repaired, non binding brake mechanism transmits more power to the disc than the still binding caliper. Same pulling power on both, but one moves more freely, more braking reaches the disc.

Did the feel of the handbrake lever (the umbrella handle) change at all?