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MG MGB GT V8 Factory Originals Technical - XJS to SD1 Brake Swap??

I just saw this on e-Bay.....

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2457500609&category=27382

If this is a direct swap and if an SD1 caliper will bolt to a B swivel axle, will an XJS caliper work on a B?? Has anyone seen this done? We wouldn't be so lucky to have this work and have matching piston areas as well, now would we?
David
David

David,

Good place to start

http://www.mgbv8.co.uk/frontsus.htm

David- the brake issue is one of balancing front and rear.

Paul
Paul

David,

As I've raised the brake issue recently, I'll add a few more rambling thoughts on a general nature.

If you can lock front and rear wheels with OE system why change?

If you have pad fade try an uprated pad - may wear disc more
If you have fluid boil try an uprated fluid - may have to change more often

If you have a longer pedal travel than you like - increasing piston area increases fluid so longer pedal travel, reducing piston area achieves shorter pedal travel but pad is less stable - increasing disc size reduces pedal travel.

Increasing disc size or using vented disc (keeps same brake balance) improves heat loss so less of above heat problems.

If the uprated pads still fade then increase pad size which in turn means piston area to keep pad stable and if too much additional fluid a M/C change.

Adding larger discs and calipers increases unsprung weight so the lighter (more expensive) the better.

Maximising heat loss may mean pads now run too cool and are now less effective.

Lowering car reduces weight transfer - using sticky tyres on track increases weight transfer.

After all that balance rears to match as only approx 30% of work.

For the road OE system with good pads is cheap and effective?

Paul



Paul

David, that is a fine looking front suspension. It retains most of the stock crossmember which is about as good as you can do for torsional stiffness of the body and moves the coil-over attachment points both outward at the bottom and inward at the top for good shock geometry. I didn't look at the specifics but the appearance is the best I've seen so far.

Paul, good info but I think you got crossed up in a couple of places. Increasing the *slave* piston size will increase pedal travel but increasing the master piston size will increase fluid output thereby decreasing pedal travel and increasing pedal pressure. The disc or rotor has no influence on pedal travel and I'm not sure what you mean by pad stability but don't see where that would be an issue unless you are referring to fade. The pad size itself should not affect braking force and therefore should not affect piston size either, any more than rotor thickness does, as the same force is applied but over a larger area, giving a smaller loading for a given area and therefore less localized heat buildup and fade, but the same overall amount of friction, drag, heat production, and braking force. Stock MGB brakes are just fine except for two things, fade and wear life. Competition pad compounds may require heat to work optimally, but an OEM compound will work just as well cold as warm, so unless one is racing the route to a great street upgrade would be the lightest possible ventilated rotors of the largest available diameter along with the lightest available calipers giving the largest possible pad size and an OEM pad, at the best price in a bolt-on configuration. So far there's been no agreement on just what parts give this combination.

Jim
Jim Blackwood

Paul,
I simply need more rotor mass. Sure, My MGBs have always had decent brakes - until they get hot, which occurs the first time I haul it down from 85 in a hurry. I've been driving these cars (and I've had quite a few) for 30 years and their brakes are just not able to take abuse as I define it. Driving more modern cars has spoiled me, too. TR 2500 calipers are non-existant over here and I have had zero luck with the breakers anywhere willing to ship me calipers for a reasonable price so I'm always looking for an available caliper that will allow me to use a thicker rotor. Your statement about wheel locking is not really a valid assocation. You can stick a cricket bat in the spokes of a moving bicycle and it will lock the wheels but that doesn't mean that it has adeqaute brakes. If locking the wheels was a measure of adequate brakes then any, and I mean any, car on the road today would pass your test. Why did Leyland upgrade the brakes on the BGT V8? Why did TR upgrade the brakes from the TR7 to TR8? Why did the Mini Cooper S use uprated brakes? All of the cars I just mentioned could, and would, happily lock their brakes with their original systems.
Cheers,
David
David

Paul,
A nice web site and, wow, what a suspension!
David
David

David,
Email me off the board, I know where you can get either a pair of the V8 OE calipers or a hybrid set with the TR2000 calipers here in the states.
Jake

Jim,

Not sure I mentioned M/C change as trying to stick with OE M/C, apart from point re additional fluid and possible change, but agree with your analysis re change.
Large discs do not work in same way as pistons re travel, but you do not need to push so far to get the same braking effort, this effectively reduces pedal travel and therefore response time which could save 5-8 ft on a higher speed stop.

Increasing pad size was re heat , 4 pots provide more even pressure over the pad area, and you can use unequal to counter gassing?

OE compounds may have COF of .3 perhaps compared to Mintex/Greenstuff at .45 (still a road pad) this upgrade will increase braking power prob at expenses of more disc wear.


David

Back to my original theme - Tyres stop the car if your brakes can generate enough force for tyres to lock then the limiting factor is tyre grip which at 15% slip is say 1.2g compared to say 0.9 when locked.

Its difficult to compare cars without knowing M/c - piston areas and effective radius pad COF and tyre grip (whether this has changed from crossply days to radial and then wider). In addition a car 2 times more mass will require 2 x stopping power?

So rear pistons on GT larger than roadster although same as roadster on GTV8 and smaller rear drums on RV8? perhaps GT was overbraked at rear?

Reasons for uprating brakes

Pedal feel - larger discs improve this although too far and you have on/off brakes, and if the car was balanced to start with then you now increase stopping distance, apart from small respose time gain.

Heat - higher stop speeds increase heat dramaticaly as does multiple stops.

The simplest upgrade must be best pads for road use.

then a vented disc/rotor - same size using same piston area although prob 4 pots for stability

Wilwood have a kit for B in UK at £400 or say $600 should be cheaper in US comprising 4 pot road brakes choice of pistons but say 1.5ins and 270mm by 24mm vented disc which fits a 14ins wheel.

With other upgrades you may have to rebalance the cars brakes to retain present minimum stopping distance usually involving the rear drums and therefore handbrake and fitting at least a bias valve, unless the balance was incorrect to start with?

Paul
Paul

Paul
Have you had any experience with brake upgrades.
What have you done to your car?

Mark
Mark

http://www.mgbv8.co.uk/frontsus.htm

<<David, that is a fine looking front suspension.>>

Jim, that is Nick Smallwood's handiwork.
Carl

There's something a bit odd about the photos in that link. The small shots in the middle of the page appear to show a sharply angled shock, which is a good thing, but the top and bottom shots clearly show a vertical shock orientation which leaves something to be desired. I'm left wondering if these are the same suspensions or two different ones.

Jim
Jim Blackwood

Mark,

I am not Paul, but able to make short outline. Paul drives his B V8 roadster daily. It has a well tuned 4.6 that is very responive. Just looking at the throttle in any gear is just like engaging warp drive.
Brakes are vented Wilwoods.

With my own B GT V8 I tried a couple of combinations. The brakes were fine, but due to high speeds and holidays in the mountains with holiday luggage (and lpg tank in the back) heat build up was something to prevent.
OE discs with Greenstuff pads is a very good combination. X-drilled 604 discs with cheap pads (Ford Transit pad, unknown supplier) also do the job, but OE Lucas pad with the x-drilled disc is lots better.

It will be interesting to watch the other thread on the use of the Volvo caliper. With a bridge piece this will be able to use the 604Ti vented disc. If Jake can get it to work, it will be the budget way of getting rid of excessive heat build up.

Comments that front and rear should be balanced are very right.

Frank
Frank de Groot

This thread was discussed between 01/02/2004 and 03/02/2004

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