Searching around on the internet I’ve found people both for and against this upgrade. There are several companies offering it and claiming considerable braking benefit. The detractors say the benefit isn’t great and anyway needs servo assistance (which the suppliers deny). Can anyone who has actually done this upgrade advise on their experience? I’d be most grateful
I upgraded my XK140 front brakes to discs, very much needed here, as traffic here is intensity and always very high, and not much straight roads.
I also added a brake booster, and a brake pressure regulator for the rear brakes, as they will lock up way to fast without.
It already saved me a few times to avoid a collision.
By the way I used the kit from SNG Barratt.
Regards,
Peter Jan
I was confused as you are but a trip down Cypress Mountain here when I couldn’t get into second gear and a hairpin was coming up caused me to slam on the drums. The car swerved right and the locked up brakes put me in a spin out. Very scary. I opted for the Coopercraft disks which they made up to fit my 1/4 inch brake lines and supplied everything needed. These are engineered for the XK140. I later fitted a servo as I’m getting old and the knees are giving out. I have modern car braking and no rear whell lock up issues. Go for a 5 speed too.
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XK150 brakes fit straight on and work well.
Calipers same as MKII 3.8 E Type
I put discs on the front of my 120. It’s the 150 setup. You really should (must in my opinion) install a servo on the front brakes only.
Before I converted back to drums, someone had fitted my car with Mk IX front discs. After I removed the servo in the interests of reducing clutter in the engine bay, I discovered you needed thighs like Usain Bolt’s to stop the thing…!
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That sounds like needing shoe adjustments. It should stop straight.
You guys are spoiled by modern cars. I don’t really give much thought to pedal effort, I think it is reasonable, and I have noticed improvement in my 120 with radial tires.
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I think it depends on where and how you drive it. If it’s UK motorways, track days or Alpine Passes then you definitely need discs and absolutely need a servo unless you have super powerful leg muscles.
If its for tootling around pleasant country roads then I really wouldn’t bother, drums in good order and correctly set up will work fine or even better than discs. I have a 140 FHC and have driven it many miles on drums, on discs (Willwood callipers) no servo, discs with servo and most recently discs with dual master cylinder, servo and balance valve. Worst of all combinations by far for normal driving was discs with no servo.
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Thanks for the replies - all helpful. Coventry Auto Components, who specialise in XK’s offer a front disc conversion kit about which they state:
“NOTE : REQUIRES NO SERVO ASSISTANCE TO GIVE GREATLY IMPROVED BRAKING OVER DRUMS.“ Has anyone got experience of their kit?
Yes, I got front discs for my 120 from Stuart at Coventry Auto Components. I’ve never noticed any need for servo assistance. Stops better than my daily runner.
I once had a Daimler SP250 which had discs all round and no servo - I don’t remember any particular effort to make it stop. I find that now the XK120 is back on drums they work quite well, and after re-lining will probably be further improved. Any tips on re-lining brake shoes? I’ve never done it before.
Interesting difference of opinion regarding servos. I certainly respect Stuarts from CAC - so why? Could it be that different makes of calliper require different degrees of effort (piston size?) or perhaps our perception of leg effort required differs significantly - or perhaps a bit of both. Adding a servo is pretty straight forward so the obvious route forward I would think is to see how the conversion works without then add if required.
As this is a safety issue, I would also suggest that you talk to Nick Green at www.xkbrakes.com about dual master cylinders.
Very helpful, Bob. I see from your excellent book that on your 120 you repaired the brake master cylinder. Have you gone ‘dual’ subsequently? My worry is not the servo but would be a loss of fluid from the single system and having to use the handbrake. Happened to to me once many years ago in a series 1 Morris Minor which I think used a similar system to the 120. For some strange reason I’ve not forgotten it.
Unlike drum brakes, disc brakes are not self-energizing.
The big difference in drums v. discs, is the latter cool better and are not as affected by moisture.
On 120/140, with properly adjusted/fitted to the drums, and appropriately-lined shoes, they work pretty well.
Unless I was canyon carving, Id personally not swap drums for discs, on an XK.
When Sir Stirling drove the Silverstone, in 1963, he told Dad, “whatever you did to the bloody brakes, they bloody well work better than they used to!”
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I installed disks on my Wife’s treasured 120 FHC earlier this year. We had an endless number of leaking front wheel cylinders that caused very dangerous pull when applied. I changed to disks not for better braking performance, although the disks work MUCH better than drums with soaked linings, but to avoid the continuing problem of leaking cylinders.
That was an issue with the quality of the rebuild/poor manufacture of the cylinders, not an inherent design issue.
Wiggles - My question was not really the comparison between drums and discs but why we have such disparate opinions about discs with or without a servo. Another consideration / variable could be pad material.
Canary – my 120 has retired to the lake district but I do get the occasional email from its new owner usually after an exhilarating drive. I have fitted the XKbrakes dual circuit upgrade including servo to my 140 fixed head and set up the front rear balance as 66% / 33% at my local MOT garage, providing 300Kgf and 150Kgf average per wheel respectively. Apart from the increased safety aspect the pedal has a really nice progressive feel to it.
Interestingly I have seen over 370Kgf front average per wheel on this car with drums (cold). The MOT guy said cold drums would invariably outperform cold discs.
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An interesting question, indeed!
Ill be installing front discs on my Jeepster hot rod, and am anticipating using a power booster, but may try it w/o, at first, to see if it’ll be acceptable.
If all you are used to is modern servo assisted brakes, non-servo discs are going to feel very heavy. As Wiggles points out, there is no self-energizing geometry present in disc brakes, so everything has to be humanly generated.
First time I drove a Skip Barber formula Dodge I thought “Holy s#!t, that takes a HUGE amount of effort! Can I do this for 30 minutes at a time?” And I was a pretty fit guy. Got used to it pretty quick and drove the things a couple of times a year for about 10 years without issues. Had to be careful leaving the track in the rental car afterwards. 
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Yea… chances are high, Ill be lookin’ in the breakers, for some cylinder/booster combo to fit the Jeep.
Imma gonna have to do maths.
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