As I think you will have gathered as an avid reader of my blog- I have never been too impressed with the standard of brakes on this car. By all accounts they never were up to much even when new, but although mine do work and have passed the MOT twice - I think they should be better. The brakes don't "pump up" so I'm dismissing air in the system and the servo does work, giving additional pedal travel once the motor is started.
I also have to report a second (related?) problem in that Miles Wilkins did comment on a vibration from the rear and a possible warped disc many moons ago when I had my rear bobbins fixed. Since then I have been intending to replace the discs when I got around to it- and I'd already done the fronts, but my hand was forced when descending a hill. Braking produced a loud thumping sound followed immediately by a metallic graunching and grinding - clearly something amiss. Braking efficiency decreased still further but I was able to limp home. Examining the rear brakes I found the the bolts securing one torque bracket were missing!
At first I though that they had sheared off but later it became obvious that they are simply absent! I am assuming that I put these bolts in (of course I did) and the car had passed 2 MOTs since I last visited the rear hubs. So assuming that no one has removed the bolts then I'm forced to conclude that perhaps they can unscrew themselves! Maybe any slight movement of the torque bracket when the brakes are applied can eventually unscrew the bolts? It seems far fetched although I do note that many cars have these bolts attached with tabbed washers that prevent the bolts from unscrewing- and presumably this wouldn't be necessary unless there is a risk of that?
I had no tabbed washers, my torque brackets were secured to the hub carriers with M12 bolts. These were fixed through both a flat and a spring washer on all 4. However, I can't tell if this is the correct setup because the bolts themselves are simply not illustrated in the Lotus parts manual; neither under "Hubs" nor "Brake's and calipers".
I will try to find out if tabbed washers should be present but in the meantime I clearly need two new caliper mounting bolts. The rear caliper bolts are unusual in that they are M12 fine (1.25) thread and although they are only 1" or 25mm long, they are threaded for only half their length. These are now very hard to obtain although PNM do sell a fully threaded bolt for this purpose. I suspect the unthreaded part is significant or Lotus would not have used such an odd bolt so I researched on the internet and found that this size is common for motorcycle brake calipers which are secured with titanium bolts, and at least some of these have an obvious unthreaded shoulder section- although shorter than those of the Lotus original. I need to rebuild my calipers with something so I ordered two of these.
Use blocks to chock the front wheels and the opposite rear wheel. Release the handbrake and jack up the car. Support on an axle stand and remove the road wheel.
This gave me my first idea of the source of the graunching noise as the thin metal "flinger" (?) plate on the disc backplate had been bent over when the bolts fell out and the caliper moved. I've no idea what this part is for- I assume if deflects road muck but I don't know.
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| something is amiss behind the brake disc! A piece of metal from the "flinger" has been bent over backwards and probably accounted for the metallic graunching sound when the bolt failed. |
Release the swivel lock bolt and remove from the caliper.
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| Removing the swivel lock bolt. |
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| Lifting up the caliper |
Hinge the caliper up and slide it off the slider, securing it with a bungey tie so it doesn't dangle from the brake hose.
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| ... and suspending it from a bungey. |
Loosen the two caliper mounting bolts (hub carrier to torque bracket) 17mm heads (in my case these were missing) and remove the torque bracket- the pads will probably drop out at this point.
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| Yep- pads drop out! |
I checked the torque bracket carefully- it wasn't cracked and the threads for both missing bolts were clear and un-stripped.
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| Torque bracket seemed OK, pad clips all in position. |
As the handbrake is off, the wheel should turn freely and the rear combination drum and disc should just pull off. To my surprise it did!
My first thought was that the handbrake shoes seem to have worn quite a lot since I fitted them... but they were probably rather thicker than the OEM shoes anyway. However the handbrake is working well so I'm not going to worry.
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| Disc/drum removed- shoes look very thin??? |
I could then straighten the bent part of the "flinger" and remove any loose sections before filing and bending it back into position.
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| Flinger section fixed- its going to be shorter than the original but is neat and out of the way. |
The new discs had been obtained from Germany at about £70 for the pair which I thought was good value. I thoroughly de-greased these with carb cleaner, thinners and methylated spirits, cleaning both the discs and the drum sections.
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| I ordered these- described as Toyota Lotus discs. |
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| Comparing them- they look right |
The new discs slotted right on, I positioned them centrally with two wheel nuts before I adjusted the shoes and finally swapped the rubber cover plugs into the new discs.
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| New disc held in place with two wheel nuts prior to adjustment. The rubber plug was transferred from the old disc after the shoes were adjusted. |
I refitted the shoes to the torque bracket which was, as ever, very fiddly before offering up the bracket to the hub carrier.
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| Fit the rear pad before offering the bracket to the wheel, insert the front pad when the bracket is on. |
It helps if you fix the bracket loosely with the lower bolt so that you can swing it out from the disc and slip the caliper onto its slider (apply some corrosion block grease).
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| Both pads in |
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| This shows why you must pivot the bracket on the lower bolt. Access to the slider is blocked until you pivot- or let the suspension hang to clear the obstruction. |
You can then fold the torque bracket back up over the disc and swing the caliper down over the pads before fitting the top bolt. I found that if I fitted the caliper to the slider first the whole assembly was too heavy and awkward to position well and I tended to knock the pads out again. Similarly, if I fitted the bracket with both bolts I couldn't get the caliper onto the slider because it was blocked from behind by the suspension. (Probably easier if you are not supporting the car under the suspension arm so that the wheels hang and give more room... although I am still unsure of how best to support the car like that). Finally I refitted the swivel lock bolt and tightened it before tightening both caliper retaining bolts to 45Nm and refitting the road wheel.
The other side was much quicker since I didn't need to worry about changing the bolts or repairing the "flinger". I fitted a new disc to that side too and job done. I'm pleased to report that my braking is now much smoother, both the vibration and the graunching sounds have gone. I realise that the pads will take some time to adjust to their new discs so things should improve. However pedal travel still seems very long and I can still not lock the wheels at any speed. I think whatever is responsible for the inefficient braking was in all probability a second problem unconnected with the bolt failure. I will tackle brake pedal rod adjustment tomorrow.
Just adding that the poor braking efficiency was down to servo pushrod adjustment. It needed to be screwed out about half a turn... A small extension but one which had great effect. Braking vastly improved! It's a simple adjustment to make and I have described how I did this in my post on swapping the Girling bmc for a Land rover unit. I don't know why the Girling literature is so down on anyone trying this, it's really no big deal.
