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GT6 Mk3 4-pot caliper conversion


Gordon Dickens
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Trying to improve my late (chassis KE14086) Mk3's braking I have eventually sourced a 4-pot conversion by BCC on a Rossini disc which fits beautiful and promises a significant improvement in stopping power.  The kit is advertised as suitable for all GT6 models but....the original 13" steel wheel binds on it.  Even with 5/16" spacers there is still contact.  I'm happy to consider replacement wheels but they must look the part for 1972 car and I would prefer to stick with 13" rims.  Has anyone else met this problem and are there any wheels other TSSS members would recommend?  Gordon

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Dont know, the 4 pot bcc alloy ones the club shop sell are shown to be a direct swap with no modifications required amd can use the std disc   how does  that compares with your selection ???

What do you feel is  wrong with the  std braking ???should be quite effective with decent pads and  linings

Just some toughts 

Pete

 

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I have not gone down the 4 pot route on my mk1 as I can lock up the front with decent pressure on the brake pedal. All I needed was decent pads and I did not have to go to the mintex pads which would have been my next step. Can you not send them back as they don't fit?

Aidan

 

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Hi Pete thanks for that.  I think the BCC calipers I have are the same and will fit the standard disc.  Everything looks fine until I try to fit the standard 13" steel wheel which binds as it has an internal shoulder.  The braking beforehand was as good as it could be.  Excessive pedal pressure for only average retardation in spite of new standard pads and fresh brake fluid.  I think the 4-pots should improve that, just need a wheel without a shoulder!  The old 2-pot caliper is shamfered to allow for this shoulder, the 4-pot is a more square design with no shamfer.

 

Gordon

4 minutes ago, AidanT said:

I have not gone down the 4 pot route on my mk1 as I can lock up the front with decent pressure on the brake pedal. All I needed was decent pads and I did not have to go to the mintex pads which would have been my next step. Can you not send them back as they don't fit?

Aidan

 

Hi Adrian,  I think that might be the next step if I can't source a compatible wheel.  Shame though....

 

Gordon

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Hmm, not exactly a good fit if you can't get a wheel over them. Were they sold as suitable for 13" wheels?

If you wish to make the pedal "easier" there are a few ideas. As above, using good pads makes a huge difference. Mintex 1144 excellent, any of the cheap pads are the wrong material (fine for modern cars with huge servos)

However, I think your car was fitted with a servo from the factory. If that has been removed it may still have the 0.75 (3/4) master cylinder, and that would make the pedal feel very hard.

So the questions are (1) is there a servo fitted and (2) what sized master cylinder is fitted. Size is cast on the side.

All the issues may have been caused by somebody "playing" and getting it wrong! Please report back.

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Gordon,

What is it about your brakes that you are trying to improve?

For road use, the OE brakes properly maintained are very adequate.    In competition, they suffer from fade, but pads for a higher temp range (eg Mintex 1155) and vented disks (several options - see past threads) have made mine fade-proof.     4 pots can 'improve' braking, IF the less tall caliper can allow a wider disk, so more leverage on the wheel, but that needs wider wheels too, and narrower, lower wall ratio (more expensive!) tyres.

You should be able to lock up all four wheels at moderate speed, even with the OE brakes!

John

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I have Mintex 1155s which made a surprisingly big difference. They are now however quite expensive, around £60? 

KE14086 would be a 1972, at that point servos were an extra, they were not fitted as standard until 1973 along with the larger brake cylinder. Servo or not, the car would have had the smaller brake cylinder. If there is a servo it will be a Girling and probably by now not very effective. Worth fitting a Lockheed type.  And before anybody else says it, servos don't make braking better. Just easier, less scary and more like a modern.

I also tried some dimpled and grooved disks that I got cheap in a Rimmer's sale, they didn't make any difference! But then I'm not in competition like John. Also they were noisy so I took them off. Now they sit in the discards drawer. :(

Doug

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4 hours ago, dougbgt6 said:

I have Mintex 1155s which made a surprisingly big difference. They are now however quite expensive, around £60? 

KE14086 would be a 1972, at that point servos were an extra, they were not fitted as standard until 1973 along with the larger brake cylinder. Servo or not, the car would have had the smaller brake cylinder. If there is a servo it will be a Girling and probably by now not very effective. Worth fitting a Lockheed type.  And before anybody else says it, servos don't make braking better. Just easier, less scary and more like a modern.

I also tried some dimpled and grooved disks that I got cheap in a Rimmer's sale, they didn't make any difference! But then I'm not in competition like John. Also they were noisy so I took them off. Now they sit in the discards drawer. :(

Doug

how much did you pay for the discs and do you want to part with them ???

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1 hour ago, ludwig113 said:

how much did you pay for the discs and do you want to part with them ???

It is a 72 and does have a servo. I'm quite happy to see how the drilled and grooved discs go so not for sale- yet!  Thanks for your advice about the Lockheed cylinder. I'm also.haply to try Minted but not keen on green/red/yellow stuff

Gordon

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7 hours ago, JohnD said:

Gordon,

What is it about your brakes that you are trying to improve?

For road use, the OE brakes properly maintained are very adequate.    In competition, they suffer from fade, but pads for a higher temp range (eg Mintex 1155) and vented disks (several options - see past threads) have made mine fade-proof.     4 pots can 'improve' braking, IF the less tall caliper can allow a wider disk, so more leverage on the wheel, but that needs wider wheels too, and narrower, lower wall ratio (more expensive!) tyres.

You should be able to lock up all four wheels at moderate speed, even with the OE brakes!

John

Hi John, my brakes were never better than low average on the standard set up and faded frightningly recently.  I'm happy to try Mintex etc but would like to give these 4 pots a try if I can get a wheel to fit. Not into green/red/yellow pads. I'm trying to keep 13" wheels rather than go to 14s...still looking!

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Fading is caused by the pads getting too hot. Fitting bigger calipers without changing the disc type will not help. A higher temperature pad would, better is a vented disc.

My old vitesse had std calipers, old stock pads (better coefficient of friction than the cheap modern grades, similar to Mintex 1144) and std discs, and stopped very quickly indeed. So GT6  brakes should also work very well. 

Worth checking the type of pads currently fitted. And I have no idea what pads come with the 4 pots, or indeed the cross sectional area of the caliper pistons (if it is the same as the std calipers, there will be no advantage at all)

My spitfire with "adequate" power (180+bhp) runs GT6 calipers with capri vented discs. At the moment I am on Ferodo DS2500 pads, which are a bit down on bite until warmed up. They didn't fade at all coming down Stelvio at speed, nor any problems on tracks. I can report back in 2 weeks after Silverstone trackday, where I believe the straights are long and fast, therfore the brakes WILL be tested as much as anywhere, but not expecting any issues.

If you really want to keep the calipers, a set of 14" minilite alloy wheels would work. I have them in my spitfire,and the wife has them on her spit too. Both with 185/60 tyres which are reasonably priced, and if your car is a rotoflex version, the 60 profile will be OK.

 

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And poor condition discs can make the brakes feel terrible. 

A herald I owned years ago cameto me with terrible brakes, one reason the PO sold it cheap:)

Some fresh brake fluid, new discs, clean and correctly adjust the rears, the breaks were superb. The main issue was the discs, scored, worn, probably warped a bit too.

But if you really want those 4 pots on the car (think you do ) then there are no wheels that give more clearance than the std steel wheels. I should add that some wheels seem to be riveted together, but most are spot welded. The rivet heads can be an issue as they reduce clearance by a few mm.

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20 hours ago, Pete Lewis said:

When you say they fadded frightlingly .... what happeded

You lost the pedal 

You had a good pedal but the pads lost grip 

Pete

Hi Pete, on a long descent lost pedal and braking completely, fortunately at the bottom of the hill!  Brakes were very hot.  Recovered a bit on cooling

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if you lost some pedal thats water  content absorbed in your brake fluid nothing to do with fade which is loss of friction

you need to replace brake fluid every 2 years max.  

brake fluid like Dot 3 or 4  etc  absorb moisture like a sponge  via the beather  hole in the resv. cap.  

Pete

 

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5 hours ago, Pete Lewis said:

if you lost some pedal thats water  content absorbed in your brake fluid nothing to do with fade which is loss of friction

you need to replace brake fluid every 2 years max.  

brake fluid like Dot 3 or 4  etc  absorb moisture like a sponge  via the beather  hole in the resv. cap.  

Pete

 

Hi Pete, It was all new fluid, new pads and discs but old cylinders.  The fade was caused by serious overheating.  I've taken up the calipers not fitting the wheels with the suppliers who say BCC design them to fit steel wheels, so It's wait and see time.

20180303_135537_001.jpg

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2 minutes ago, Gordon Dickens said:

Hi Pete, It was all new fluid, new pads and discs but old cylinders.  The fade was caused by serious overheating.  I've taken up the calipers not fitting the wheels with the suppliers who say BCC design them to fit steel wheels, so It's wait and see time.

20180303_135537_001.jpg

Ps I take your point about Dot4 and water.  Considering silicone-based Dot5...but probably not!  Thanks again

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On 06/03/2018 at 7:32 PM, clive said:

And poor condition discs can make the brakes feel terrible. 

A herald I owned years ago cameto me with terrible brakes, one reason the PO sold it cheap:)

Some fresh brake fluid, new discs, clean and correctly adjust the rears, the breaks were superb. The main issue was the discs, scored, worn, probably warped a bit too.

But if you really want those 4 pots on the car (think you do ) then there are no wheels that give more clearance than the std steel wheels. I should add that some wheels seem to be riveted together, but most are spot welded. The rivet heads can be an issue as they reduce clearance by a few mm.

Thanks Clive.

All good advice, the suppliers say the steel wheel should fit (It's nowhere near) and have taken it up with BCC. I have to say the BCC calipers look well made and fitted the hub and disc perfectly.

Gordon  

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I've just received a new set of DS2500 pads for the standard 16P calipers, which will be going onto my Vitesse tomorrow to replace the previous set of DS2500s that went on there in 2009.  They've survived multiple Alpine/Pyrenean passes (5 x 10CRs), a flying lap of the Nordschleife and a couple of trackdays, but are now pretty much worn out.  £ 90 a set but still decent value I reckon.  Never faded, even at the 'ring, where they took a tremendous beating - think smoke, melting bearing grease and blue discs!  Usually get problems at the back first.

Before those I had Mintex 1144s, which are fine road pads with slightly more cold bite (as Clive says), but can be faded (pad fade) if used hard.  They were SO much better than the various standard offerings (including Green Stuff) I'd tried before - the car was downright scary until I fitted them.

I've never experienced fluid fade (loss of pedal due to boiling) on the Vitesse, with decent quality DOT 4, changed every year.  Have had it on my (1500) Herald with the type 14 calipers (not a good feeling), cured by upgrading to Vitesse brakes.

Nick

 

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Hi Nick, we're off to Nurburgring in June so looking for a big improvement in braking.  My "fade" involved blue smoke, molten bearing grease, warped discs and molten piston seals too. The set-up when that happened was completely standard, recently refurbished and not awfully efficient.  I hear lots of tales about how good the standard set-up can be, but although mine was fully refurbished it simply wasn't. I'll have a look at the pads you recommend if I'm forced back down the 2-pot route.  Currently BCC are researching why my 4-pots don't fit the road wheels they are designed for.  All I want now is wheels that fit!

Gordon 

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20 hours ago, Gordon Dickens said:

Hi Pete, It was all new fluid, new pads and discs but old cylinders.  The fade was caused by serious overheating.  I've taken up the calipers not fitting the wheels with the suppliers who say BCC design them to fit steel wheels, so It's wait and see time.

20180303_135537_001.jpg

Gordon,

That disk is massively thick!   A vented wouldn't be much (any?) thicker, and would promote cooling massively - just what you need on the 'Ring.

John

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OK, if you drive that hard, you are needing vented discs. And ditch the stoneshield to aid cooling. (may need to replace teh shield with 3 thin washers to compensate)

 

And I see John beat me to it!

Also worth looking at racing type bearing grease that is less likely to melt at high temps.

The steel wheels are likely to be be a bit restrictive on cooling the disc too, so worth a thought.You may need to bite the bullet and fit 14" wheels. (though I have Minilites, I am not a fan But needs must etc and function over form)

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