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MG MGB GT V8 Factory Originals Technical - 4 spot caliper conversion

I have heard of people using Volvo 240 4 spot calipers on Bs. I had a look at this last night and found that the mounting holes don't quite line up. Can someone out there explain how this conversion is done. Also what vented discs will fit to the wire wheel hubs
Matt

Matt,
Have investigated the Volvo option myself and found that the holes on the Volvo calipers are about 6mm too close. At the risk of offending a few readers, I believe that cross-drilling calipers is very half-arsed. There are a few options out there. One is to find Princess calipers from the UK which may be difficult. The second is to use SDI calipers which you would be able to get from Triumph Rover Spares in Adelaide (I know they had some a couple of months ago), however they may result in a spongy pedal due to the larger pistons (there is a lot of info in the archives). The third is to go for an aftermarket caliper like the Willwood which you can have with an adapter made up for them. All caliper options need a spacer or stepped bolt because of the metric holes in the calipers.
About the discs, Peugeot 505 are almost identical to the B except they are ventilated, 20mm thick, and definitely require a bigger caliper. Disc Brakes Australia have a website with more detail than you'll ever need. I haven't got the address anymore but start with www.dba and it should find you something. The Peugeot discs just need redrilling and you're good to go.
MG Workshops in Melbourne do a kit with 300zx discs and Volvo calipers but they cost a lot of money. Regards,
Stainzy
Stainzy

Matt, Volvo Brakes come in with spacing for solid disc and vented disc. Calipers required to be modify by enlarging the mounting holes to 3 1/4 MG mounting are 3"
Calipers also required a spacer to center with rotor.
The Volvo has a twin circuit system therefore half of the caliper has a separate hose meaning that the caliper uses two brake hoses. Three different ways of connecting the four pots. 1. Install a manifold connecting both metal pipes to the manifold and a single brake hose. 2. Cross drill one side of the caliper, connecting all four pots 3. Connect externally with steal pipe, this will required enlarging the bleed holes!

Wilwood calipers Dynalight II are great and required an adapter that is strong and cost is very reasonable, they are light 2.7 lbs and work great. This combine with MG drill rotors from Moss are a great combo. Wilwood pads are design to reduce fade under severe racing conditions with solid rotors, therefore vented rotor are just an added weight and cost.

MG’s do not weight over 2800 lbs so solid disc are used. Instead of vented.

MG brake caliper is very strong and capable of doing the job of stopping a V8 Larger pads are a big help.
Bigger pads can be made, by buying pads for a Volvo or Wilwood and cutting to size meaning to fill the caliper opening this will increase the braking area, or just buy the expensive V8 mintex pads.

R/Bill

Bill Guzman

I havehad the Peugeot/Princess solution fitted to my GTV8 for a couple of years. The other thing you should note is that you require slightly larger bolts to locate the disc. I seem to remember that Triumph GT6 bolts do the job.
Hi Spec Engineering made up brackets to fit mine after I sent them a stub axle to play with. Their tele number is 44-1-474-707733 ask for Geoff.
They work very well!
BobP
robert pulleyblank

I don't know much about the ATE(Volvo) 4 pot calipers-but here are some useful facts to consider during brake swaps:

1- MG stub axle bolt centres are 2.25 c/c

2-All girling/Lockhhed calipers went metric with 12mm holes-but on the same centres to ensure interchangeability with shouldered bolts as per GT6 Mk3 bolts.
3-Wilwood calipers might sound great on paper-but do they have the extra dust seals to stop dirt getting down the side of the piston neccessary on a road caliper. Are they designed for the 900 psi acheivable with a servoed system?
4-Most 4 pots were used a s safety feature on road cars esp Metro/princess/range rover with twin brake lines and different circuits for the different pots-ivestigate Sherpa vans for the single line versions.
5-Most of the vented brake kits seem to use the Peugeot discs-one thing is for sure-if you are seriously going to use the brakes-say on a track day at the Nurburgring-then you had better get some vented discs-as even 4 pots on solid discs will result in a pall of smoke and fried discs!

JB
London

John,
That's the second time I've seen the 2.25 inch c/c mouning hole figure used in threads about brakes. I can only say that mine appear to be 3.25 inches.
George B.

George,

I,ve beeen quoting this figure of 2.25" because that is what I remember Bob Green at BG developments-(and he ought to know)-quoted to me during my extensive discussions when I was building my braking system-But I've never actually measured it.....so after reading your thread I thought I'd better check-I toddled off to to my workshop-located the several stub axles I' ve got stashed and put some 7/16 brake caliper bolts into the lugs-got the Mititoyo Digitmatic calipers out and this what I came up with:

3.6865 overall the bolt shanks

Dia of the bolt shanks 0.434

3.6865 -0.434 =3.2525 which allowing for spring in the calipers etc means that the bolt centres must be 3.25"

Oh well- this what happens when you don't measure it for yourself!


I know that I am right about the vented discs though- a serious track day without vented discs in a v8 will result in fried pads....maybe you might get away with some fancy semi metallic linings-but having been on the V8 register tour of Germany recently and had the exquisite pleasure of tanking around the Nurburgring -and seeing some of the std V8 braking systems under stress-you need vented discs.........


Regards

John Bourke

John Bourke

Has anyone tried the 4-pot brake kit Victoria British sells?
Does it use ATE/Girling/Lockheed/etc. calipers redrilled for the MGB stub axle?
What about those vented discs?
Mario Funk

Robert,
The problem with using the Peugeot 505 disc / Princess caliper combination is that there aren't too many Princess's in North American scrap yards.
The four pot caliper from a Toyota Four Runner is popular with Datsun 240Z brake upgrades. Does anyone know the specs re bolt hole spacing, piston sizes for this caliper?
Im my mind you can never have too much braking performance, it's just a matter of how much can you afford to spend and what return can you expect for that investment? The Peugeot rotor with an inexpensive four pot caliper to me seems to give the best performance for the dollar/pound invested.

Regards

Andrew Worman
Andrew Worman

Roger is right about the vented disc for a hard day at the track.
Why solid disc? Solid disc weight less than vented,
Some racecars (2500lbs and less) used solid disc with proper cooling and perform great, Also alloy rotors work great with the proper pads less unsprung weight).

For the street the stock brake system with good oversize pads is all is needed, even with a V8. If really want to improve the braking system then increase the rotor diameter and also increase the pad area, and concentrate the braking on the extreme outer portion of the rotor. Clamping pressure is good with added area is better and complete.
A thing to compare is the rotor output pressure at the rotor. Some 4-pot rotors do not increase the pressure they just increase the braking area on the rotor. In fact some calipers put out less pressure than the MG units.

R/Bill





Bill Guzman

this mod seems to keep rearing its head so for what its worth gentlemen my comments.
I've gone the 505 + rover 4 pot twin line route.
problems encountered:the 505 disc and hub:i did not want to keep having to redrill rotors so modified the hub instead as the only machining was to have the bolt holes opened to suit the 505 metric bolts and slightly slot the hole about 40 thou all done on a milling m/c dividing head. before you all shout concentricity i machined the locating shoulder for the rotor and shrank on a sleeve to match the id of the 505 rotor, this is what the rotor should locate on not the bolts.the caliper fits dead centre the only head scratching at present is to pipe up the twin lines as i have the moss coil over set up to contend with.pads i shall use SDI mintex
regards adrian
adrian salisbury

This thread was discussed between 15/10/2000 and 18/10/2000

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