small(ish) calipers with large(ish) discs. will it work?

HairbearTE · Post by **HairbearTE** » Tue Oct 14, 2008 7:27 pm

I am looking at the possibility of using the Aluminium rear calipers from a mk4 golf on a volvo rear axle. The volvo disc is 9.6mm thick new compared to 9mm for the golf and the golf calipers are designed for mounting behind the axle as are the Volvo I believe. A light skim of the volvo discs would bring their thickness into line and still within spec (min thickness for the volvo disc should be 8.4mm) but the overall diameter of the volvo disc is quite a bit larger than that of the std golf disc (281mm vs 232mm). Assuning caliper brackets can be made up it should all work together but will the larger diameter of the discs have any negative effect that will either can the idea totally or that I can possibly work around? Or should this set up be fine for what will afterall be a lightweight car, a lot lighter than a mk4 golf for sure.

JSF55 · Post by **JSF55** » Tue Oct 14, 2008 7:37 pm

If your going to have the disc skimmed down to 9mm why not have the O/D turned down too the required diameter at the same time?

Ian Anderson · Post by **Ian Anderson** » Tue Oct 14, 2008 8:03 pm

My estimate is that with the larger diameter the braking force would be multiplied.

as these are on the rear it could cause the rear to lock up first and cause the tail to try and overtake the front in a skid situation

Using proportion valves / balance bars it should work

Ian

HairbearTE · Post by **HairbearTE** » Tue Oct 14, 2008 8:06 pm

JSF55> Well I thougt about that but the hub of the disc is about 35mm larger on the volvo disc than on the golf disc. I may still be able to take off a little of the overall diameter from the volvo disc but only a little. My main concern would be the area of the pad being inadequate for the area of the disc leading to pads wearing too quickly or brakes overheating. I don't think this should be a danger but I if someone on here who really knows would like to comment i'm all ears!

HairbearTE · Post by **HairbearTE** » Tue Oct 14, 2008 8:10 pm

Thanks Ian. A regulator or bias valve of some sort sounds like a good idea.

JSF55 · Post by **JSF55** » Tue Oct 14, 2008 9:57 pm

As both radii aren't going too match, it might be wise to mock it up to see how much over lap theres going to be off the pad into free air, obviously thats going to cut down on the contact area, this will help with the biasing of the rears and probably have no other effect ?

kiwicar · Post by **kiwicar** » Wed Oct 15, 2008 10:21 am

Big diamiter discs with small (er) calipers (reduced pad area big torque moment) should be good for frequent heavy use from moderate speed, big calipers (and pad area) smaller discs are better for sustained use from high speed (but used infrequently). So you should end up with a set up that takes little warming up, will have good bite and provided you don't want it all at once is resistant to fade.
Hope that is of help
Mike

ian.stewart · Post by **ian.stewart** » Wed Oct 15, 2008 10:58 am

I would think a good quality Antifade pad would be an Idea, Greenstuff??

The surface speed of the disc increases as you get larger, but the ability to add torque to the wheel when braking increases with the larger disc, because of the larger disc, it also actsas a bigger heat sink to take heat away,
Im not sure about the Pad size in comparrison to the disc. but its a common thing on Escorts to use a 285 disc with standard 16m calipers, how do the golf pad sizes compare to the 16m size, the next question-------dont the golf calipers have a built in handbrake mechanism, , just curious, cos I was thinking about these calipers for the cortina to save a bit of weight on the back of my car, dont suppose you have the bracket bolt pitch size to hand and the calipr floating pin pitch as well, you never know they may either bolt on or even fit my Granada brackets,

HairbearTE · Post by **HairbearTE** » Wed Oct 15, 2008 6:16 pm

Yes Ian, they do have a built in handbrake mechanism. I haven't bought the calipers yet but I got loads of 'em on the shelf at work, I may take them this week. I too wanted to use them to save weight. Any old volvo axle I get would probably benefit from new discs and calipers anyway so it makes sense to make the switch if possible. When I get the calipers Ian i'll measure them up for you.

HairbearTE · Post by **HairbearTE** » Fri Oct 17, 2008 6:42 pm

Ok Ian I got the calipers but the carriers for them are not available in the aftermarket and I don't have any genuine in stock at work so if I want new ones I'll have to go to VW

Fortunately I know a few VW trade club members who can get good discount. Alternatively if I can get a good deal on used carriers that are in good nick then I might take that route. I took your advice and picked up some greenstuff pads (£15 to me

) and also some ATE discs for the volvo axle (£9ea to me

). I figure if I can't make this swap work there's no way I can't shift this stuff anyway. Some rough dimensions are centre>centre of bolt holes 118mm, diameter of bolt holes 7mm, thickness of mounting at bolthole 13mm. If you've got access to VW slides such as ETKA you can view the arrangement of the caliper and carrier. I am gonna pick up the haynes for the mk4 golf and any other books on the subject of braking while i'm at it since I am not particularly well versed in the subject. If anyone would like to recommend a good title please do.

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kiwicar · Post by **kiwicar** » Sat Oct 18, 2008 7:31 am

The GT40 website/ forum used to have a breakforce calculator on it, if that is of any use.
Mike

minorv8 · Post by **minorv8** » Wed Dec 17, 2008 8:19 am

I have VW calibers in the rear with Peugeot discs. I believe the discs are 247x10 mm and largest that I could fit. I would have wanted even bigger discs but the wheel size vs. location of the caliber in relation to the body dictated otherwise.

I would leave the discs as is, bigger diameter gives more leverage to stop the car. In the rear it may cause excessive stopping power. Like already commented (depending on your front brakes) you need to fit adjustable brake bias valve or twin masters/balance bar to dial in the proper brake balance. I don´t see any point in skimming the disc since VW calibers are the same but various models have both 9 mm and 10 mm thick discs.

You did not mention which car or which front brakes you have. Volvo has originally twin piston calibers in the rear so simply replacing them with single piston sliding caliber may actually be a downgrade. Volvo axles have a forged (?) flange where the caliber is bolted on so you most likely have to get creative with the adapter for VW caliber.

I have a pair of VW caliber so if you need measurements from the VW carriers I can provide them.