View Full Version : brake caliper shims

02-01-2010, 01:09 PM
Any idea as to what the thickness of these shim are and how many are needed for correct caliper location?

02-01-2010, 01:26 PM
Depends. Didn't need any on my TR.

Andrew Mace
02-01-2010, 02:27 PM
Are you referring to these shims (https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29146#73) used "as required" to "...center the calipers on the rotors"? AFAIK, these were only used on the TR3A (and possibly TR3B). Sorry, I've no idea how thick they are, although I've a vague recollection of them being a bit rusty and crumbly on a then-12-year-old 1960 3A I was digging out of a friend's father's barn to put on the road for myself! :laugh:

02-01-2010, 04:00 PM
AFAIK, these were only used on the TR3A (and possibly TR3B).I'm pretty sure they were used on later TR3 (with Girling brakes); and both Moss & TRF have them listed for TR250/6 as well. They are also listed in the TR4A SPC I have handy.

Most people (including myself) just leave them off, as they are a PITA to install and, near as I can tell, don't make any difference. But without them, I suppose there is some chance that the rotor will rub the caliper, in a hard corner (when the spindles flex to some extent, allowing the rotors to effectively move sideways relative to the calipers).

Don't have one handy to measure, but I would guess they are about .010" thick (each, without the rust), and TS13571L had 4 of them per side when I took it apart.

Andrew Mace
02-01-2010, 04:25 PM
Randall, thanks for clarifying my post. I'd meant to surmise -- perhaps in error? -- that they were used on the earlier styles of caliper but not with the later 'split' Type 16 Girling caliper. I admit to having much less hands-on experience with TR4-6 Girling calipers, but I can understand why the shims might have been used throughout the TR3-6 range.

02-01-2010, 04:34 PM
I concur with Randall. I did put
them on My Six; a PITA; and they
seem to serve no purpose. I have
a bit of uneven pad wear but no big deal.

02-01-2010, 07:50 PM
The shims on the 4 and the 6 are designed to prevent chatter and squeal that can occur between the piston and brake pad. Acting like a bearing surface they allow the two components to move independently of each other. Other then that, the calipers are self adjusting.

02-01-2010, 08:17 PM
Two different kinds of shims, Ray. It's not entirely clear to me which ones BillJoBob is asking about, but the ones that go between the caliper mounting ears and the caliper bracket, item DP15 here (https://www.zeni.net/trf/TR6bluebook/123.php?s_wt=1920&s_ht=1200) are not about chatter and squeal.

02-01-2010, 11:12 PM
Your right randall,
I am talking about the caliper mounting shims. And yes, the calipers are Girling (split). they are not centered on the rotor which leads me to believe that there will be uneven wear and slow brake reaction. If I recall, these calipers didnt have any shims when we removed them. Still, I like good brakes almost as much as torquey motors, so I want to do this right. Thanks!

02-02-2010, 10:10 AM
Oh, those shims! I did not have them on my '73 TR6 which I have owned since '75. When I mounted my calipers following a rebuild, I noticed they were not centered on the disk and thought about the shims. But after some thought, given they were not present on the factory build, I left them as they were.

Perhaps the factory realized they were not needed, and by omitting them, they could cut one job from the assembly line.

02-02-2010, 06:10 PM
I can understand not shimming a single piston slide type caliper. But, I would think that since these calipers are stationary and only the pistons move, shims would have to be used to eliminate one brake pad from doing most of the work.(this might expain why the rotor was rusted on the inside only when I removed them) Im no rocket scientist, but im pretty sure that evenly applied pressure on the rotor from both pads would result in better brake performance and wear. Then again, I am complete new to these cars...and really clueless...:-). If I remember correctly, I read somewhere that later TR's were mass produced to such an extent that quality suffered from the factory, much like the MG's of the 70's and that such little things like shims were left off, not because they werent needed, but because they took too much time.

02-03-2010, 01:12 AM
The pressure and clearance (hence reaction time) is going to be the same on both sides, regardless of whether the shims are installed or not.

But offhand, I can think of two reasons why the caliper needs to be centered over the rotor:

1) Some clearance is needed between the rotor & the sides of the caliper, because the rotor can move relative to the caliper under hard cornering. The spindles literally flex under cornering force. If the rotor was too close to begin with, it could hit the caliper, which would not be good.

2) There is a limit to how far the pistons can extend without risking seal failure. Brakes are intentionally over-engineered, to hopefully cover cases of severe neglect. If the caliper is not centered, it reduces the margin before the seals blow out, when the pads are worn totally away and so is the rotor.

I have literally seen TRs with the rotors worn to less than half their original thickness!

Don Elliott
02-03-2010, 07:16 AM
It's possible that one of the pistons is wedged, jammed or rusted to the point that it is not moving when you step on the brake pedal.

I got 43,000 miles out of the first set of front brake linings from new when I bought my 1958 TR3A brand new. And during those miles, I noticed that the wear on the pads was not the same for the inside and outside linings. So I was "rotating" the linings every 10 to 15,000 miles to even up the wear on the pads.

At 43,000 miles (about 1966), I put in new pads and never had to swop them. I got about 130,000 miles out of those pads before I put in new ones again in 2007. At 80,350 miles from new (1988), my neighbour skimmed the rotots on his big lathe to remove all the surface rust. He took off about 0.005" total. The rotors are not rusty or scored in the past 20 years (102,000 miles) since my restoration from 1987 to 1990.

TRs did not have any "dust sheilds" back then and I never had any shims or ever found a need for them.

02-03-2010, 08:05 PM
Interesting info gents. My TR came with dust shields, but no shims. So if I am understanding you both correctly, I need not bother with shimming the calipers. I have left off the shields for the time being mainly because they seem to be overkill ( and a PITA to install) for a car that might be driven 20 miles a month. I wonder....how can you tell the diff between a 3A and a 3B by looking at the parts. Our build started with two cars, one complete and the other in pieces. We have used most of the pieces and few parts from the whole car. Not sure what to call it when we are finished...lol.

02-03-2010, 08:11 PM
Wait, I just read Randall's reply again and you seem to be in definite favor of shimming the caliper. I will order them tonight. Thanks!

02-03-2010, 09:00 PM
Sorry to be so indefinite, Bill. I'm certainly not willing to say you <span style="font-weight: bold">must</span> shim the calipers, as I don't know how badly off-center yours are. On my own car, I removed the shims with no apparent ill effect ... of course I was also changing almost everything that would affect the alignment of caliper to rotor (calipers, rotors, hubs, vertical link, caliper bracket).

I was just trying to present some reasons why the factory may have felt it was important to shim the calipers. Oddly enough, this does appear to be something of an afterthought, as the shims don't seem to be listed in my TR3 factory Spare Parts Catalogue; but they are listed in the TR4 version.

Don't have time to check just now, but ISTR the VTR website has a fairly good list of the minor details that changed with the TR3B. There were actually two different series of 3B, if I recall correctly the later series even got the TR4 4-synchro gearbox. But since all of the distinguishing features can easily be installed on the earlier cars, I'd say go with whatever commission number plate you wind up with. If it's a TS- number, call it a 3A. If it's TCF- or TSF-, call it a 3B.

Andrew Mace
02-03-2010, 11:16 PM
IMO, a TR3B is only worth a premium price -- all else being equal -- if it is one of the fabled "numbers matching" cars. I wouldn't get too fussy about the gearbox, but the commission number should begin with TSF or TCF, the body number should be a TSF number (can be a prefix or suffix depending on ???? -- possibly the change from TSF to TCF commission series?), and the engine should be a TSF or TCF-numbered block, unless a build record says differently. I note that simply because, years ago in my local club, a member had one of the very last of the TR3A models with -- presumed to be original equipment -- a single-digit TSF engine number!

Beyond that, there is little to definitively ID a 3B, seeing as -- among other things -- the build run was a good excuse to use up 3A-related body and other parts stocks even as the TR4 was well into the product mix at Standard-Triumph!