Jeep Front Brakes Disk Conversions Project
By Nigel Hudson – Weald Group
Back in the mid-eighties, I bought a Big Twin Harley and after the year’s warranty had expired, the first thing I got was not a big-bore kit, performance exhausts, high lift cams or up-rated ignition module but a 6 piston performance front brake calliper so the darned thing would stop! Even defensive riding, scanning the road way ahead and staying a healthy distance from the vehicle in front did not make up for the bike’s lousy stopping ability on today’s highways. In 2012 when I got my Hotchkiss jeep, I had a similar sense of déjà vu. Sorry guys, 9″ drum brakes all round do not inspire confidence. I figured a decent braking set up could potentially transform the whole jeep driving experience and for that I was going to need a disc brake conversion.
So I started doing some research on the internet. Via different Jeep owners’ club forums, I discovered 3 ways to go about this.
- Buy a ready-made kit from the States that could be bolted straight on. Hmmm……….expensive and what happens if/when any of the components fail or need replacing.
- There are a few YouTube clips from the USA of owners using callipers and discs from later jeep models sourced from the scrap yard. Unfortunately these callipers are quite big and seem to require a sizeable chunk of metal to be ground off the steering knuckle for clearance. Also, there doesn’t appear to be a surplus of old CJ’s in UK breakers yards.
- Use the disc brake set up from a Suzuki jeep. Readily available over here, I liked the idea of sourcing all the components from within the UK. This seemed like the choice for me.
In the classifieds on Milweb I found a few jeeps being sold with front disc brake conversions fitted. Unfortunately, none of the vendors had fitted the conversion themselves but had acquired the vehicle with it already set up so they could shed no light. Then I discovered an operation in Scotland that had developed and fitted their own disc set up. When I called them though, they said that they no longer supplied the conversion to customers. Apparently somebody had not followed their fitting instructions correctly, had an accident and tried to sue them! When I asked if they could tell me what donor vehicle the parts were sourced from just to give me a starting point, they refused and said ‘You’ll have to figure it out for yourself!’
So with plenty other jobs on the jeep to keep me busy, I put the brake project on the back burner. Forward to Autumn 2015 and I got to thinking of a project to see me over the winter months. I dived back again into the internet forums and in December after many hours of research, I’d finally ‘figured it out for myself’.
Confusingly, the American forums suggested using the brake callipers from a 1990’s Suzuki Sidekick, a model that was never imported to the UK. After much cross-referencing, I discovered that the same callipers were fitted to the Suzuki Vitara 1.6L 3dr 1989-2000. However there were 2 types: Tokico and Lucas/Girling. Either would work but they were not interchangeable although both used a 48mm piston. Their own specific calliper carriers and pads were required for each type.
I found a pair of the Lucas variant in a breakers via eBay and before agreeing to buy them, I asked the yard to send me a photo just to check whether they weren’t too corroded and more likely to be seized. I also asked them to leave on the brake hoses and include the axle mounting bolts. Having stripped the callipers, expecting to have to renew all the seals and rubber boots, I found everything in good condition so they were re-assembled. I also fitted Goodridge Speedbleeder nipples to the callipers as these make bleeding brakes a one-man operation.
I managed to find the correct part number for the brake discs/rotors from the Suzuki Sidekick (I’ll include a full list of components at the end) which I knew from other forum postings would fit. These discs were readily available in the UK as they were also fitted to UK vehicles such as the Suzuki Jimny and Samurai.
The old drum brake backing plate had to be removed from behind the hub and the disc was to be mounted in front of the hub. This would mean that the front wheels would be spaced further apart (by the thickness of the 2 discs) than with the original set-up. There was sufficient thread on the rear wheel lugs to add 2 thick washers behind the rear wheels bring them out almost back in line with the front ones. However, as we’re talking about a jeep not an F1 car, the effect on its handling would be negligible. The existing 10 front wheel lugs weren’t suitable for this new disc set up. The knurled section was too long, it needed an un-threaded section to bear the disc and finally a long enough threaded section to hold the wheel and nut. The forums suggested a pack of 10 Dorman 610-080 lugs would do the job and although I tried my best to source all the kit components in the UK, I ended up having to send off to the US for these from eBay. I was lucky having a younger Hotchkiss jeep in that the old lugs came out of the hubs quite easily with penetrating fluid and a hammer. Those of you with older wartime jeeps might have more ‘fun’ in removing the old lugs! In any case, the Dorman lugs have ever so slightly larger diameters than the originals so I wasn’t worried about enlarging the holes when removing the originals. In fact, pressing the new lugs in almost broke my bench vice so I ended up taking the hubs round the local garage where the friendly mechanic used a hydraulic press to install them for the price of a pint. It’s worth mentioning here that all 10 new lugs are right hand threads so I also needed 5 new wheel nuts for the driver-side wheel (wheel nuts for the 2 wheels on the driver-side are left hand threads and right hand on the passenger-side). Another advantage of the Hotchkiss was that it was fitted with non-combat wheels. This meant that there were no nuts/bolt ends protruding from the split rims which could interfere with the calliper body as the wheel rotated. The forums suggested that those with combat wheels would need to have 1/2″ spacers made up to provide effective clearance.
Within the forums I found a diagram (including dimensions) of a 1/2″ steel bracket to mount the calliper to the steering knuckle and contacted a firm who specialised in the laser cutting (it’s cheaper than a waterjet cutter) of steel plate to make 2 up for me. For anyone interested in fitting discs all round, these brackets will also work on the rear axles. To mount these to the knuckle, I also needed longer 3/8″ UNF bolts (old 3/4″, new 1 1/4″). These needed to be high tensile steel bolts due to the stresses imposed on them by a 4 X 4 braking application. I couldn’t locate any of these US standard grade 8 bolts of the right length in the UK, so I ended up using metric grade 12.9 (which actually exceeds imperial grade 8) cap head Allen bolts which also come in a 3/8″ UNF size.
To plumb in the callipers, I decided to use steel-braided hoses. These would have to be custom-made as I had to marry up the metric 10mm 20 degree-angled banjo fitting at the calliper to the existing imperial 3/8″ 24 tpi UNF female bulkhead fitting (with a convex seat). There are companies who will make you up new hoses if you input your requirements online but to be sure of a correct fit, I found a reasonably local operation, took the old rubber hose that came attached with the calliper along with the existing brake hose and asked them to make new ones combining both ends.
The discs were a snug fit over the threads of the new wheel lugs but once sitting on the un-threaded shoulder, they had a tendency to creep away from the hub. Using the two 8mm threaded holes in the disc (machined to aid in its removal) I drilled 2 holes through the hub and Loctited 2 short bolts to hold it back in place if ever the calliper needed to be removed or the pads changed.
The design of the original jeep set-up used front brake cylinders with 1″ pistons working in conjunction with rear cylinders using 3/4″ pistons. I figured that as the external dimensions and mountings are similar for both front and back cylinders, why not transplant the now redundant but more powerful front cylinders to the rear wheels. This way I would also get a slight upgrade to the braking at the rear axle.
The original set up has the brake master cylinder (MC) mounted on the chassis below the level of the drum brake cylinders. To counteract the fluid dropping back out of the drum brake cylinders due to gravity once the pedal has been depressed (and hence the brake pressure fading), a residual pressure valve (RPV) is needed. For a drum brake set up, where the shoe return springs are competing with the hydraulics to pull the shoes back away from the drum, a pressure of 10lb is required. To maintain this 10lb of pressure, an RPV is fitted within the MC assembly. A disc brake set up will also suffer from the same condition although less pressure (2lbs) is needed to prevent the brake fading because the calliper pistons are not competing against return springs. Unfortunately the 10lb pressure held at all 4 wheels by the RPV will cause the pads in the new front callipers to remain in contact with the discs for an extended period after the pedal pressure has been released making the brakes ‘drag’. The way round this was to remove the RPV (in the TM9-803 manual diagram of the MC it’s labelled as a ‘check valve’) and instead fit 2 separate RPV’s to the brake lines. A 2lb RPV was fitted inline between the MC and the front callipers and a 10lb RPV fitted between the MC and rear drums.
To plumb these RPV’s into the steel brake lines I had to buy myself a brake flaring tool and teach myself how to create ‘double flares’. Many thanks to the kind souls who have posted up the numerous ‘How to’ clips on YouTube. What I hadn’t expected though was the difficulty in using a non-professional flaring tool to try to create a double flare in a steel brake line. The tool could not grip the steel-walled pipe tight enough to prevent it slipping back when pressure was applied during the flaring process.
Rather than spending a few hundred quid on a professional tool, I decided to buy a 25ft length of 3/16″ cupronickel brake line and a slightly better flaring tool. The new flaring tool worked a treat on this more malleable tubing (first time, every time!) and it could be easily formed by hand without flattening. The design of the tool also allowed for the flares to be done even when the line was already fitted to the jeep. Wherever possible I tried to re-use the fittings by cutting them off the old brake line (for example, there are 4 male fittings that could be removed from the redundant ‘S’ pipes to the old front drums). However, I found that the short fittings on the original lines were not deep enough to seal inside the female bulkhead fittings of my new brake hoses so I ordered some longer male 3/8″ 24 tpi UNF fittings. The original short fittings worked fine on the RPV’s and the APV though.
So far so good. Now what about balancing the new braking system. Although the discs would create a much stronger braking force at the front of the vehicle (which was to be desired), I would need some way of adjusting the rear brakes to work in harmony with the new front callipers. Too little rear brake pressure and the drums would be ineffective. I would be just slowing the jeep via the front brakes. Too much rear brake pressure and with the weight thrown to the front of the jeep under braking, there was a risk of the drums ‘locking up’ causing the rear end to skid out. An adjustable proportioning valve (APV) plumbed into the rear brake line between the MC and the 10lb RPV was the solution. Time to dig the brake flaring tool out again.
After bleeding the system and making sure of a good seal round all the new fittings, it was time to test them out. The pedal seemed to be maintaining good pressure. While it was still up on the axle stands, I span the wheels by hand then hit the pedal. All the wheels stopped spinning so it passed the first test. Once off the stands, I tried it very slowly up and down the rear access track behind my garage. The brakes seemed to be doing just fine. After a last look once more round the fittings, I set off down the road.
Well the brakes work! It still requires quite a push on the pedal but there is a large improvement in stopping power. Fitting a remote servo would help to reduce the pressure needed at the pedal although I don’t think it’s necessary and this new set-up sure transmits plenty of feel from the brakes. With the APV dialled in just half a turn, I managed to lock up the rear wheels before the front so I backed it out to a quarter turn. The aim is to achieve the ideal situation of the front brakes locking completely with the rear just on the verge of locking or locking secondary to the front. This should coincide with the shortest ‘controlled’ stopping distance. I suspect the APV will need dialling to pass its minimum selectable pressure to the rear drums. This is probably in part due to the improved stopping ability of the front 1″ cylinders now relocated to the rear drums.
- Suzuki Vitara 4 X 4 1.6 3dr 1989-2000 Callipers
Girling/Lucas 48mm single piston from breakers £60
- Laser cut calliper to knuckle mount brackets out of 1/2 inch steel plate £40
- Rotors from Suzuki Vitara 4 X 4 1.6 3dr 1989-2000
Solid brake disc/hub hole centre=107mm/diameter=290mm/thickness=10mm £39
Various suppliers part numbers
- Brake Pad Set
Lucas type (spring on top)pad thickness=16.3mm £24
Various suppliers part numbers=FDB221/MDB1189/GDB1165/Motaquip VLX278
- Goodridge Speedbleeders 10mm X 1mm thread £28
- Braided steel brake hoses £70 the most expensive components of the project
- Brake Pipe Flaring tool £35
- Adj. brake proportioning valve w/2lb and 10lb residual pressure valves £50
- 10 X Longer Wheel lugs Dorman 610-080 or NAPA 641-1112 £16
- 10 X right hand thread standard MB jeep wheel nuts £17
- 12 X (3/8 UNF X 1 1/4″) knuckle to bracket longer bolts
- Grade 8 hex heads ideally, but very hard to find. I used Grade 12.9 cap head Allen bolts plus spring washers £9
- Cupronickel Kunifer Brake pipe 3/16″ 25ft roll plus 3/8″ fittings. £17
TOTAL = £405
You could probably knock a hundred quid or so off this depending on what tools and spares you have kicking around in your garage. If I had to repeat this project, I would probably have more confidence in ordering custom brake lines online and try and get a better deal on them. I suppose you could get the breakers to include some discs with the callipers too. However, although my callipers arrived with only slightly worn pads in them, I decided that I’d rather use brand new pads and discs.
Was it worth all the time, effort and expense? To know that I can stop in a hurry means a great deal to me, so that’s a yes. It does make quite a difference to your driving style in that I never quite trusted the old set-up to stop me in time and drove accordingly. Now it feels like it will stop no problem. Who knows, when the rear drums need replacing, I may even consider discs at the back. Oh and two more advantages of a disc set-up. No more brake adjustments and if you’ve ever forded a stream, it takes a dangerously long time for those drums to dry out. Just to sign off, I suppose I should take a leaf out of the Scottish Jeep outfit’s advice to me and finish with a disclaimer ………. mess with your brakes at your peril!