Beefy Brakes #706

[PeterTR7V8]

I'm having brake issues. As you know I like to have a thrash around the track whenever I can & the car's limits are quite well tested. Accordingly I've been tinkering with every aspect of the car over the last 3 years & for a road cruiser/club car I think my car is doing very well due more to luck rather than any engineering nous. But.. There's always a big but so let's talk about my ..er.. big but.

I keep on having issues with the brakes. I have the ABC of brake upgrades ie, Princess calipers over Capri vented rotors with a Sherpa/LDV master & booster. The stopping power is great & now I put the booster on (cheers Jolyon) the feel at the pedal is spot on (apart from a bit of a vacuum issue which is another story). The problem is the way the Princess calipers work with the Capri rotors. When I replace the pads I have to grind notches off the backing plate of the pads so they fit in behind the retaining pins of the calipers. This should've been my 1st clue that I needed to think about the set up a bit harder because the pads are sitting too far inboard & as a result don't sweep the outer 2-3mm of the rotor & rub against the centre when they wear down. They also wear unevenly & I sometimes get big vibrations just after, tho not during, a heavy workout. This happens typically on the warm down lap & is fine again for the next race. I never have a problem otherwise.

I've got people telling me I have sticking pistons but I don't believe it because it is the same on both sides. I reckon the problem is caused by the pads being in the wrong place & I need to move the calipers out by a few mm so that the pads sweep the outside of the rotor & leave the hub alone.

What I don't understand is that for such a copybook setup why I'd be having these problems. The calipers are supposed to be a bolt solution but it seems to me that the mounts are not in the right place. I could go to the Volvo 240 calipers but they are similar to what I have, yes? So why bother. I could buy expensive Wilwoods but I have enough stopping power already so really I just need to relocate the Princess calipers so they sit a bit further out from the hub.

Does sound right? And is it OK to slot the mount holes on the calipers or do they need to be filled & redrilled? We're talking about 3mm.



The map: http://tinyurl.com/wedgemap . The blog: http://www.forum.triumphtr7.com/topic.asp?TOPIC_ID=8548

[busheytrader]

Hi Peter,

When you get the "vibrations", what do you feel through the steering wheel and brake pedal? If the drums or discs were out of true, a pulsing brake pedal alone would indicate possible issues with just the rear brakes but both together brings the front into question.

I've got Capri calipers with Capri vented discs so don't have the issues with having to fettle the pads to fit you've got. Once fitted my pads can move about 0.5mm? all around in the calipers. Maybe your pads have got a touch too much or too less room and the heat is affecting their tolerance causing them to vibrate? Then again, your brakes will get more use in one race than mine get in a whole year...........

I thought that Princess calipers were a bolt on mod to our brakes as well, but maybe that's to std 7 or 8 solid discs. If you modified your disc adapters not to touch the pads, would that make the pads move even closer to the centre?

I've had to work through the night so hopefully the above is coherent.

Adam



Adam

[Vegas_M]

Peter,

So if I understand you correctly:

1. The outside diameter of rotor protrudes beyond the outside edge of the brake pads by 2-3mm.

2. The inside edge of the pads (perhaps their backing plates) wear on the hub of the rotor as the pads wear down.
3. You have uneven wear on the pads, on both wheels. But, you haven't said how they wear. ie: Is it a straight wear from the lower leading edge to the lower trailing edge (more material at the upper edge of the pads)? Is it only the inside or outside pad that wears? etc.

If these are correct, then re:

1. Should not be an issue. Many stock systems have this much rotor protruding.
2. I'm concerned that you have to grind the backing plate to fit them in the calipers. Are you sure you have the correct pads for these calipers?
Re the rubbing on the hub - You may want to go to a disk mfg site to check the hub diameter of the std Princess rotor and compare that to the Capri dimensions.

3. The centre line of the calipers may not be properly aligned with the centre line of the disks. Or, the calipers may not be fully sitting square to the rotors. Many things to check...


If you are going to change your calipers, you may want to check out ones from the smaller mid 80's - 90's Toyota pick-up trucks, 4-Runners and Land Cruisers (Casting #S12-8, with rotor cutout of 24mm (0.95â€￾)). Easy to get and cheap. You would either need to plug and re-drill the mounting holes (as you would with the Volvo calipers), or make up adaptors to mount them (probably a better route as you can make them align perfectly.

Here is a pic of my conversion using the Toyota calipers:


Martin

[Bendder]

Martin

Just curious to know what rotor you used withthat set up and what size wheel do you run to clear it.



Mark
1977 TR7 FHC
1978 TR7 FHC
1980 TR7 DHC
1980 Rover SD1 4.0L

[Vegas_M]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Bendder</i>

Martin

Just curious to know what rotor you used with that set up and what size wheel do you run to clear it.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

I used 1986-88 Toyota Cressida rotors. $30 for the pair.
Diameter: 272.0 (10.71â€￾)
Thickness: 22.0 (0.87â€￾)
Height: 40 (1.6â€￾)

I am using 15" rims, but 14" ones will clear as well. I made the below drawing when I was trying to figure out the clearances.



Martin

[PeterTR7V8]

You understand correctly, Martin. The pads wear so that the top is of different thickness than the bottom, I can't remember which end is wearing faster & can't check until Monday but I suspect the tops are thinner. I wouldn't be concerned about the unused outside edge if the inside edge wasn't being over-used.

The pads are correct according to the catalog but they are EBCs so... The back plate of the pads have tabs that sit against the retaining pins but that's all there is to stop the pads moving. Its these tabs that I have to grind bits off to make the pads fit & this has been the case for every change of pads. I suppose I could grind even bigger notches to get the pads to sit further out but it seems wrong to have to do this.



The map: http://tinyurl.com/wedgemap . The blog: http://www.forum.triumphtr7.com/topic.asp?TOPIC_ID=8548

[Jolyon39]

Hi Peter,

Wedge shaped pads.... great accesory for a wedge[:D]

It sounds like the pads get too close to the bell and consequently lever the pad to the outside, am I right?

You can buy brand new, 4 pot, Alloy Calipers for the Princess lug mount in various widths and using a different pad from Hi-spek. Their web site has dimensions on it and perhaps their different set up using a different pad will not rub agains the bell of the rotor

http://www.hispecbrake.co.uk/calipers/b ... ncess.htmt

(Go on, you know you want to reduce your unsprung weight anyway)


Have you considered the spacers in the callipers? Someone had to add a spacer to your Princess calipers to make them wide enough for vented callipers. Could the spacers have put the calipers out of true? Perhaps the faces of the spacers are not parallel and or not wide enough for your rotors.

If you end up needing a new set of spacers check out Ralley design in the UK, they have them off the shelf for Princess calipers. I can not remember if they are wide enough for the Capri rotor.

http://www.rallydesign.co.uk/product_in ... s_id=10503



Jolyon