TR7/8 270 x 13mm discs

[A TR7 16V]

Does anybody know if the big Princess 270mm discs fit the TR7/8 or if there's an easy way to fit some other 270mm solid disc?

Graham

[Howard]

They sound much to large. My 7 has EBC dimpled TR8 discs fitted which are 244mm diameter along with princess calipers which fit under the original steel wheels.

If you have swapped to MGF 16" wheels possibly you might be OK.

Howard

[Beans]

If you want to use the original wheel dimensions (13") ø245mm is about the maximum you can get, depending on calliper dimensions.
For ø270mm you'll need a minimum rim diameter of 14", maybe 15. But that depends on the type of wheel and again the calliper.

And spent some extra money and fit vented discs ...

Edited April 25, 2021 by Beans

[A TR7 16V]

I once had a set of unmodified Princess calipers on a TR716V with std alloy wheels, and I don't remember any spacers. But they were on TR8 discs. And the problem was that about 6 or 7mm of the pads hung over the edge of the discs, and the disc were worn, so that the pads met before they wore out. At which point the braking got a bit funny (funny peculiar, not funny ha ha). So, I had the caliper mounting holes doweled and re-drilled.

So I'm wondering whether, if I get bigger discs I can use the princess calipers without the faff of moving the holes. The assumption is that if the unmodified calipers fit 13mm out from where they should be so 6 or 7 mm of pad overhung (assuming the pads should run 5 or 6 mm from the edge of the disc), then discs that are 13mm larger radius, i.e. 244+26mm diameter, should fit the calipers. And if my memory is right, and the unmodified princess  calipers fit under the 13" alloys, everything will be hunky-dory.

If the unmodified calipers only fit 7 or 8mm out from where they should be (As I remember the holes were moved less than 13mm) and the pads are supposed to run right up to the edge of the disc, then the 270mm discs will need to be turned down by 6 or 7mm in radius. But I know a man that says he can do that cheap. Next time I needed discs, I'd then have to decide if I wanted to modify discs or calipers.

So, I suppose the implicit questions were do 13" alloys go over unmodified princess 4-pot calipers (so the only problem really is the overhanging pads, as I remember it) and are the TR7 mounting holes the same distance from the hub center as the princess's or 7-8mm closer?  

Graham

 

[RobPearce]

I had the modified Princess calipers on my 16V TR7 at one point (a Rimmers conversion kit) and my recollection is that they were a tight fit in the standard wheels, so I'd be surprised if you could get the unmodified ones in there. But it was a good few years ago that I had that car so my memory may be fuzzy.

[A TR7 16V]

It was 30 yrs ago for me too, but I do know I had the unmodified calipers fitted when the pads met, and that it was me that had them modified by a local engineers to move the holes. 

My memory is that it was on one of the drop-heads I had that were all on standard 13" alloys. But I did have an FHC on 14" monty go wheels at about that time, but I think that had TR8 brakes and took stag pads.

[A TR7 16V]

11 hours ago, Beans said:

And spent some extra money and fit vented discs ...

I don't drive in a way that I need the brakes to stop that hard more than once in a while. So I have no problem with fade, ever, and no need of vented discs. I'm running a Doly Sprint on standard calipers with a 1500 servo, and that seems adequate to me - rather, the wife's PT Cruiser with ABS feels really fierce. Maybe when I get really old and frail, I'll need better brakes and power steering. But I'm hoping infernal combustion engines will be banned before then.

Moreover, the coefficient of friction for normal brake pads is roughly proportional to temperature of the interface, right up to the point of fade. So brakes that run cooler will be less efficient (require more peddle force) for any given stopping force at any pair of temperatures less than the point where the hotter running ones fade.

So, if all you want is more stopping power for the same pedal force, not prevention of fade, vented discs actually have the opposite effect. That effect may be small, probably very small, but it's not none.

Graham

[A TR7 16V]

Actually the issue's gone away, because I just got a pair of nearly new TR8 calipers for little more than the cost of the princess ones (about £160 including pads and p&p and all), and probably less if they would have needed modifying to go under the 13" wheels.

Graham

Edited April 26, 2021 by A TR7 16V

[Beans]

32 minutes ago, A TR7 16V said:

I don't drive in a way that I need the brakes to stop that hard ...

In which case why bother changing the original set up? (not that I promote using the original set up though 🙄)

[Matt306]

18 hours ago, Howard said:

They sound much to large. My 7 has EBC dimpled TR8 discs fitted which are 244mm diameter along with princess calipers which fit under the original steel wheels.

If you have swapped to MGF 16" wheels possibly you might be OK.

Howard

Howard, I have seen some repro princess calipers in Ebay (160) which seem good. I have stock TR7 calipers and while it will stop, there is plenty of travel on the pedal which alarms me despite bleeding. With the engine off i get a firm pedal.  I was wondering if the princess calipers are worth it. I have stock 13" alloys

[Beans]

1 hour ago, Matt306 said:

I was wondering if the princess calipers are worth it. I have stock 13" alloys

I have a set up using (vented) ø245mm discs and spaced M16 callipers. This gives good stopping power and fits inside the original alloys. For steel wheels you'll need slim (3mm) spacers. Biggest advantage of this set up is that all parts are readily available and there is a huge amount of pad material available.

The long pedal travel on my DHC is something that annoys me too. And in my case it is pretty random. I presume it is mainly caused by automatic adjusters for the rear drum set up. My Sprint powered FHC, which is fitted with discs on the back axle, doesn't have this problem.

[Matt306]

56 minutes ago, Beans said:

I have a set up using (vented) ø245mm discs and spaced M16 callipers. This gives good stopping power and fits inside the original alloys. For steel wheels you'll need slim (3mm) spacers. Biggest advantage of this set up is that all parts are readily available and there is a huge amount of pad material available.

The long pedal travel on my DHC is something that annoys me too. And in my case it is pretty random. I presume it is mainly caused by automatic adjusters for the rear drum set up. My Sprint powered FHC, which is fitted with discs on the back axle, doesn't have this problem.

 

 

I always liked your blog Beans, you do a fantastic job of your TR7.  Pleased to hear the long pedal travel is not just me! If i press hard enough the car comes to a stop, i rebuilt the brakes with new seals and caliper piston, new rear cylinder, green stuff brake pads up front.   

I have looked at varying ideas but would like to keep the stock wheels which limits stuff. The Capri M16 calipers seem a good idea then and the spacers readily available. 

 

[Howard]

6 hours ago, Matt306 said:

Howard, I have seen some repro princess calipers in Ebay (160) which seem good. I have stock TR7 calipers and while it will stop, there is plenty of travel on the pedal which alarms me despite bleeding. With the engine off i get a firm pedal.  I was wondering if the princess calipers are worth it. I have stock 13" alloys

I will defer to Beans for all advice on the subject of brakes, and while I managed to warp the standard discs after a quick drive down the Stelvio pass the stopping power with TR8 discs and decent pads (currently EBC) has never concerned me.

Cheers

Howard

[A TR7 16V]

8 hours ago, Beans said:

In which case why bother changing the original set up? (not that I promote using the original set up though 🙄)

It's for a TR7 Sprint. So it probably wants better than HA Viva front brakes.  And I do want to be able to stop reasonably well, which means I need to be able to lock the front wheels on the tires I have on a dry clean road (if I ever find one of them in West Lancs). I just don't want to do it many times in a row, like at every corner on a track. I only expect to get to the limit of breaking in a situation where the next step is to go straight home for a change of underwear. So vented discs are a waste of money for me. But slightly bigger brakes seems worthwhile.

I will be checking if TR8 rear cylinders are smaller than TR7 ones, because TriumphTune used to recommend going to 4-speed rear cylinders on upgrading a TR7. That may be just to reduce pedal travel. But it may also be in anticipation of better tires, i.e. more grip, on the front. In that situation it's necessary to reduce the effort at the back, because the extra weight transfer from harder breaking that better tires give (and better brakes allow access to) means the back wheels are more likely to lock first. And we don't want that, do we?

I was starting to despair of finding a pair of TR8 ones in good nick (I do have a pair, but they look like the Antikythera mechanism), and I knew the princess calipers would fit, at most for moving the mounting holes a few mm. But I need discs as well. So, I though, if it were possible to fit a slightly bigger disc with unmodified princess 4 pots, it would be simpler and relatively cheap - new repro princess ones being about £130 a pair plus pads, etc. And remembering (or misremembering) that I had had a set of unmodified princess calipers under std alloys, I though I'd ask. 

My next interesting option was going to be to wonder if it's possible to move the holes on Stag calipers, cos gRimmers are flogging new ones off for under £90 each, no exchange. 

But then, almost as soon as I asked I found a pair of TR8 calipers on eBay, slightly confused as being Stag/TR8 ones. Bit of checking that they ain't Stag ones, and they should be on their way even as I write. A bit expensive, but probably no more than re-conditioning the two lumps of bog iron in the garage.

Graham

[Beans]

3 hours ago, Howard said:

and while I managed to warp the standard discs after a quick drive down the Stelvio pass

That is the main reason why I choose vented discs. I had Princess callipers with solid discs fitted to 't Kreng many years ago.
I managed to warp the discs twice while still running in the engine. Fitted vented discs and never looked back.

[Beans]

2 hours ago, A TR7 16V said:

That may be just to reduce pedal travel.

That might be a solution to the problem, though on several long distance the brakes were absolutely fine. 

[Beans]

6 hours ago, Matt306 said:

The Capri M16 calipers seem a good idea

A word of caution here. Some callipers might need a little bit of material taken off to prevent the callipers touching the inside of the hub flange.

[Gt6s]

On 26/04/2021 at 08:17, A TR7 16V said:

But I'm hoping infernal combustion engines will be banned before then

Hardly likely. Even now dead electric cars are becoming a HUGE problem. Even the Chinese or the Indians DO NOT WANT THE BATTERIES as nothing can be done with them. Hydrogen is the answer. The internal combustion engine runs better on hydrogen than it does on petrol. Emissions, WATER.

[Gt6s]

4 minutes ago, Gt6s said:

Hardly likely. Even now dead electric cars are becoming a HUGE problem. Even the Chinese or the Indians DO NOT WANT THE BATTERIES as nothing can be done with them. Hydrogen is the answer. The internal combustion engine runs better on hydrogen than it does on petrol. Emissions, WATER.

Just to add to that.  How long do you think governments are going to permit electric car users EVADING ROAD DUTY ? With hydrogen, road duty can be collected easily JUST AS IT IS NOW.

[A TR7 16V]

13 minutes ago, Gt6s said:

Hardly likely. Even now dead electric cars are becoming a HUGE problem. Even the Chinese or the Indians DO NOT WANT THE BATTERIES as nothing can be done with them. Hydrogen is the answer. The internal combustion engine runs better on hydrogen than it does on petrol. Emissions, WATER.

A bit off topic, but IFAPIFAP:

Hydrogen, as in fuel cells, may be a better solution than batteries; though Elton Musk has much to say on them. But modifying a piston engined classic car to run on hydrogen as a fuel don't sound like a simple task, not even compared with converting to LPG. Don't think the SUs would cope well.

And there'd be more than pure water coming out of my exhaust, even if I were to modify to run on pure hydrogen. 

 

 

[Matt306]

7 minutes ago, A TR7 16V said:

A bit off topic, but IFAPIFAP:

Hydrogen, as in fuel cells, may be a better solution than batteries; though Elton Musk has much to say on them. But modifying a piston engined classic car to run on hydrogen as a fuel don't sound like a simple task, not even compared with converting to LPG. Don't think the SUs would cope well.

And there'd be more than pure water coming out of my exhaust, even if I were to modify to run on pure hydrogen. 

 

 

Christ I dont want to introduce any water at all to any Triump....

[Gt6s]

EFI works perfectly on hydrogen. Years ago BMW took two consecutive identical cars off the assembly line. One they converted to hydrogen with little more than a tank change. These two cars were put out to the press including Top Gear who did a spot on them. The hydrogen car came out on top.

[RobPearce]

2 hours ago, Gt6s said:

One they converted to hydrogen with little more than a tank change.

I find that extremely unlikely. A standard injection system isn't even close to being capable of running on hydrogen. You need a dedicated system like the LPG setup.

[Gt6s]

Toyota doing what BMW did years back with e36 press car.

Toyota Has Modified A GR Yaris Engine To Run On Hydrogen For Endurance Racing | Carscoops

[RobPearce]

52 minutes ago, Gt6s said:

Toyota doing what BMW did years back

And the article states that they are building a modified engine (so not even the same base engine!) with a completely new injection system. That's about as far from "little more than a tank change" as you can possibly get!