CALIPER POSITION GTC

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Dennis Nicholas
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CALIPER POSITION GTC

Post by Dennis Nicholas » Sun Jul 28, 2019 8:35 am

Just put callipers back on after n/s overhaul of front suspension. A bit miffed to find that the disc in the inner gap is + 0.014" larger than the outer gap. This means there is no way of setting calliper in position with a shim. Last time I fitted them I had to put a shim of 0.025" between calliper and mounting bracket to move the calliper inwards to give an equal gap either side of disc.
I have fitted new vertical link and trunnion, new stub axle and new wheel bearings and felt grease seal (proper thinner size that fits) but same hubs, new wishbone rubbers and everything painted. The vertical link was the correct later type with the bearing shoulder/grease seal spigot machined into the vertical link so not requiring the spacer that went over the in-between set up when early v/ls were used up on the earlier 6s.
Looks like I will just have to live with this and don't think it will have any adverse affect?????
However my inquiring mind would like to know why this is happening.

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CALIPER POSITION GTC

Post by scimjim » Sun Jul 28, 2019 9:41 am

Surely just the different tolerances of the stub axle, upright and new bearings?

You can take a little material off the caliper mounts or upright, but at 14 thou difference, I wouldn’t worry about it.


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Post by Old and Slow » Sun Jul 28, 2019 9:43 pm

I agree with Jim, and I think that after a few miles the pad wear will probably be different side-to-side anyway.
Alternatively, can't you make a negative shim out of unobtanium? :?


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Post by Dennis Nicholas » Tue Jul 30, 2019 12:25 pm

Old and Slow wrote:
Sun Jul 28, 2019 9:43 pm
I agree with Jim, and I think that after a few miles the pad wear will probably be different side-to-side anyway.
Alternatively, can't you make a negative shim out of unobtanium? :?
All back together and washer tags bent to bolt heads so it is not coming apart again to file calliper or VL! I am happy it should be ok and pad wear, as you say, will be unequal anyway.
On that point I have seen that the inner and outer pads have worn unequally on both sides of the car. New pads fitted previously were Balco (asbestos free guaranteed 12,000 miles) and after 6,931 miles it is BOTH the inner pads that have worn more than outers:-
Amount of pad left (more or less in view of slight irregular wear top to bottom of each pad)
N/S..... outer.......inner.......difference
..........5.5mm.....4.5mm.....1mm
O/S......6mm.......4mm........2mm

Out of interest new stainless pistons (KITEC) and seals, all new cylinders/hoses (Goodridge)and master fitted at 54,000 miles. Seals in callipers rubbed well with Moly and Moly grease brushed onto exposed bits of pistons at the time. Pads renewed at 74,962 when exposed bits of pistons were cleaned, re-brushed with Moly grease and pushed in to receive new pads and ditto cleaning up when new pads fitted at 94,584 (now 101,505 miles).
Just curious as to what others have found?? Is it always the inners that wear quicker?

I did make some neg shims last time I encountered this problem (with a 6a) but found it was due to a previous owner or garage having put the spacer for the earlier vertical link spigot on the wrong way round so pushing the hub out too far!!! I thus didn't need the shims and being made from unobtanium and thus invisible I gave each a dot of paint so I could find them in the tin again. Imagine my horror on opening the tin only to find the dots of paint had separated off and were floating around sans shims. Eventually located one in tin and on getting it out to try on calliper bolt I dropped it and heard it roll away and being made from stainless unobtanium I couldn't use the usual trick of magnet wrapped in rag to locate it so it is still there somewhere in the dirt/dust on the floor/in the pit :( .

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CALIPER POSITION GTC

Post by philhoward » Tue Jul 30, 2019 12:43 pm

I’ve never experienced unequal pad wear unless there’s a seized piston (or slide pins on newer stuff) but then I only use regular brake fluid and red rubber grease...

I can only assume that the friction coefficient of normal pistons on normal seals with normal brake fluid is designed into the component and by changing the friction points has lead to the uneven wear?


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Post by Dennis Nicholas » Tue Jul 30, 2019 1:26 pm

I should have also added that with all being new hardware I used dot 5 silicone brake fluid at that 54,000 miles rebuild in 2004. Fluid Unchanged since and still all working well and clean. The pistons at this clean up/check were free and easy. I suppose I could just bleed a little fluid off to check for any dirt.

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Post by philhoward » Tue Jul 30, 2019 2:55 pm

The advantage/disadvantage of Silicone fluid is it doesn’t absorb water. Advantage being it doesn’t lower the boiling point over time. Disadvantage being it then sits in the lowest points of the system, namely the calliper/cylinder.. fine for vehicles in long term storage with no temperature fluctuation (I believe it was originally formulated for military applications?), but I’m not personally convinced for regular use. I know thousands are but not me.


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