Replacing pistons in front calliper

[RichT]

Hi I am dealing with a stub axle issue but have discovered a seized outboard piston in the calliper is it permissible to change this piston only as the other 3 seem ok I haven't tried to free it off and look inside but previous experience with other cars tells me re sealing the unit will unlikely to be cost effective

All help gratefully received

Regards

Richard

[Martec]

Hi Richard,

Which calipers do you have, The original MkII calipers were the very early type made by 'Dunlop'. It consisted of a carrier bolted to the unright and two piston and cylinder units bolted to it. These bolts (4 per cylinder) are an odd size, the head is smaller than normal for the thread to get them in, and they can easily snap off.

Aftermarked units were made, not necessarily with 'Dunlop' in raised letters on them.

As these were the very early disc brake arrangement, the originals were back to front compared to modern day calipers. The original 'Dunlop' piston and cylinder units had a flat seal secured to the bottom of the piston and a dust seal at the top. This dust seal fails and road muck gets in and corrodes the CYLINDER. They have been sleeved with SS before now, but are best regarded as scrap.

20 years ago I tried to source a cheap supply involving made in Japan, shipped to USA and then to UK!!! I fitted 420 uprights to take the 3 pot girling caliper which are like hens teeth now.The 420 route was cheaper and vastly superior braking.

You maybe able to buy individual units but you need to be sure the piston diameters are the same.

It would be better to force the offending piston out (brake hydraulics and servo on the car) to see what you have got, the aftermarket units may have the seal in the later place (top of the cylinder) in which case it is probably corrosion bubbling the chrome on the piston and pistons maybe available.

There are I believe a couple of companies that make aftermarket 4 pot calipers that bolt direct to the original MkII upright.

You pays your money and takes your choice. I was overjoyed to get rid of the dunlop brakes.

PS The MkII pads were small and square and called 'quick change pads'. An XK150 I worked on had the same arrangement but round button pads and you HAD to take the units off to change the pads.

Brian

[RichT]

Hi Brian

I have the early Dunlop types with easy fit pads (easy fit if they were not crushed out of shape due to I suspect being rubbish pattern parts, this car is weird it was sold as a dry state car reimported in 1990 paper work tends to suggest that only did 10,000 miles in 20 years

Quite a lot was refurbed 1999

Looking at the pistons I have lifted the rubber boots and the metal is all bright, I think it has stuck because some wrong sized after market pads have been fitted I will post some photos at some point, anyway I have left it all soaking in releasing fluid and will get back to it in a few days

If I can fix it I will as hate to have the car off the road for any left of time, the four pots look like a good idea long term but I am still in that "honeymoon" period where I am waiting to see what is going to go bang or drop off before I spend a lump on any one thing, strangely even with a stuck piston the car was pulling up square and stopping ok but then my main car is a Landrover so anything else seems good

If the bores are not too bad I may risk a rebuild kit

There is a 420 front beam at the minute but 500 squids seems a bit steep without seeing how well it is refurbed also I guess ongoing pads etc for the cooper craft types may be easier to come by


Cheers

Richard

[Martec]

Hi Richard,

The 420 front axle overcomes a number of the MkII shortcomings, assuming you are not bothered about originality, ie thicker discs to disipate the heat from heavy braking (in truth on the road the brakes are not used that much), a nice big brake pad with the 3 pot Girling caliper and power steering. IF all of this was in recon condition THEN the axle is worth it, but if it has to be reconditioned then you might as well fit something like a coopercraft caliper and thicker discs if possible and an aftermarket (properly engineered) rack conversion!!!

As you have the old 'Dunlop' brakes that you have been happy with then as you say you just want it back on the road for the summer. The square pads are 'hooked' onto the pistons and once the bolt on clip is removed, with luck the pads can be levered/knocked back out. if you then put a 1/4" thick screwdriver (the thickness of a worn out pad) in its place you can pump the piston partway out and push it back in again a few times until it moves freely (I do this to all our cars at least twice a year). Also the caliper that locates the pad corrodes, so I also use a small file or scraper to remove the rust (you can't get much purchase in there so if you are careful you are unlikely to do any damage) so the pad is a rattle fit in the caliper.

If the cylinder is corroded then it will leak when the piston is pushed home, so you then have no choice in the matter of replacement.

Really any pad should be removed and all cleaned up once a year to get the best from the system, but there again maintenance was a high priority for continued efficiency in my old job.

I drove series 2 and 3 long wheelbased landrovers as works vehicles and loved the controllable slides you could get on mud, until you met a big earth mover coming the opposite way, magic machines.

Brian

[RichT]

Hi back off hols now and had a chance to look at pistons, as expected are knackered looks like water has got in and have some interesting snotty deposits, I suspect brake fluid has been long term neglected by previous owner, serves me right for not taking all this apart when I first got the car

I will probably go with cooper craft four pot conversion and try xj calipers on rear if they need to be changed do you know which ones fit? And what mods need to be done

Also if I need to remove uprights to replace a stub axle I take it that it is safe to separate both upper and lower ball joints as long as the spring is compressed by jacking under the spring pan


All the best

Richard

[piman]

Hello Rich,

I would say that it depends on the jack, and how stable it is. Ideally a spring compressor would be best but a sensible approach to supporting the car under the spring pan should be safe. If using a jack set it to it's lowest setting would be best once the wheel is removed.

Alec

[RichT]

Hi Alec thanks for that, I will drop it low so the spring can't go anywhere have heavy duty trolley jack so should be ok
Any tips for separating tapers other than wacking it with hammer ie any good tool tips, I don't want to destroy ballpoints if poss

Cheers

Richard

[piman]

Hello Rich,

yes that sounds safe enough.

I prefer to use a screw type ball joint splitter rather than the tapered fork which you hit with a hammer, they normally destroy the boots. For the stub axle, I would guess that will be very tight. However it should knock out if you don't have access to a press. Just ensure that what it is resting on is solid or you lose a lot of the hammer's momentum. And use a heavy hammer, e g. a 4 lb club hammer.

Alec

[RichT]

Hi Alec what type of ball joint separater fits in the axle carrier the scissor type or the simpler type which looks like a g clam with a forked end that hooks under the ball. also I was going to use the sng Barrett stub axles and bearing kits have you used these as some sng Barrett stuff is no good

Cheers

Richard

[Martec]

Hi Richard,

Can I suggest you use a proper spring compressor before you remove the upright, with my attempts to find the ideal spring they have been taken out more times than I wish, they are extremely powerful and if the get loose you don't want to the there!

I spent time making my own compressor and then modifying it again and it still eats an M18 stud iron on each spring change, for safety contact Anne Jenkins to hire the clubs compressor.

I've had to replace my stub axles (very strange braking noises and actions), I contacted Ken Jenkins and ended up using a good secondhand set from him rather than 'New Repro'.

I took my uprights out, undid the nut, laid it on the vice and smacked it with one clean blow and it came out. I fitted the unworn side to the top and refitted the wheel hub with locktite to stop the bearing turning again (the reason for the wear).

As Alec says the taper splitter that is hinged in the middle and has a bolt to jack it apart works well, it has for me (I spent years doing it the old way with two hammers as my dad showed me).

Better to be safe than sorry!

Brian

[piman]

Hello Brian,

What are you using as the screw, the normal threaded bar is very soft but is available in high tensile grade, you need to go to an engineering factor rather than a general farmers or builders merchant. Also use the connecting nuts as they are double the length of standard nuts, both of those will help.

Alec

[RichT]

Hi Alec and Brian

I supported the front cross member on low wooden blocks then raised the side I was working on a low entry jack via the spring pan, the pan being almost on the floor and the two hammers approach to the tapers which has worked ok on side 1 so far. I supported the upright on two bits of sleeper with metal on the top. The stub axle needed gentle persuasion with a sledge hammer used more for weight than anything else, a few taps and it was out. side two tomorrow. I have already ordered some new stub axles and bearing sets from sng Barrett they say the more expensive stub axles are supplied by jaguar I am naively hoping this is a good thing coopercraft brakes coming next week


This raises another question I didn't really take much notice when I took it apart but once the ball joint nuts are tightened the movement of the steering upright feels smooth but quite stiff is this right as I expected it to be a more free there is a std ball joint top and sealed for life job bottom, this all worked fine with no play before I started messing with it

I appreciate the safety lesson and I will be careful

Cheers

Richard

[Martec]

Sorry Richard, I'm a little confused by your comments.

Are you saying that when the steering arm was disconnected from the suspension upright it swivelled easily, but when the steering arm was connected it was a lot harder?

The original top and bottom ball joints came with grease nipples and HAD to be greased very frequently or they became worn. The later type were sealed for life (Lemforden?) and are very good (I have them on top and bottom).

Once the steering arms are reconnected to the upright you are pushing against the worm in the steering box so naturally it will be hard work. This steering box needs to be full of thick oil/grease (a special type of fluid). Also the steering idler may have a grease nipple on it and the 4 ball joints on the two link arms.

It is essential that all these are greased frequently or you will be replacing them at each MOT. As I say I check and clean the brakes on all our cars at least twice a year and grease all the nipples at the same time.

I'm glad to hear you have got the stub axles out and some decent calipers on the way. The rears can be replaced with 'late series2/early 3 rear calipers and bolt straight onto the MkII mounting plate. I was given these by a friend from his scrap XJ6 but others may fit. I also fitted the MkII handbrake caliper above the XJ6 main caliper, but the gap/fit is a bit cockeyed so I used stick on production paper onto the disc and cut the handbrake pads back until they were parallel to the disc again!

They say the handbrake doesn't hold, mine does, and will pop the car off the rollers at MOT.

Best of luck,

Brian

PS I started our car up on 9 month old petrol tonight, first pull, it sounded glorious. Last coat of varnish tomorrow.

[RichT]

Hi Brian

What I meant was once the top and bottom ball joints were tightened up the upright seems stiff on its swivels I have not connected the steering arm yet. I guess it may be because of the lack of leverage just pulling on the upright or would it be that I haven't pulled up the tapers tight enough I guess I will just have to compare to the other side

This car has power steering I think the dreaded xjs conversion early 90s but it seems to work ok

Glad to hear you have it running, if I don't drive mine for more than three weeks I go insane

Cheers

Richard

[Martec]

I see, tightness in the ball joints of the upright.

If you look at the cross section of a ball joint, particularly the old adjustable ones, the taper pin has two curved surfaces with a loose bottom pad held intension by a very powerful but short spring. Adjustment usually required the setting of the top nut so the taper pin would only just move with the help of a spanner, then it was dismantled and refitted with the spring and was even tighter, but no slack to give a 'thump' over bumps, when the curved surfaces became worn, an old trick was to tighten the nut a little to take the slack out, but this made it very tight on full deflection (It could snap the pin).

As the sealed ball joint is not adjustable this will be fine or slack and knackered, when the taper is removed from the wishbone this should be tight but able to be moved by a ring spanner (not round and round but backwards and forwards).

Similarly the greasable ball joint, if it is the top one I don't think this one is adjustable either.

Due to the tension within the ball joints to remove slack there will be some stiffness of movement, but easily to swing the upright by hand when bolted into place. If it it lolls about then something is far to slack and you will hear a snap as you go over potholes.

Have you got similar stiffness on both sides? Ask at your local parts factor to feel the stiffness of a ball joint, you will be surprised that it will not move just with your hand (similarly a trackrod end).

Sorry Alec for not replying, I stick with the ordinary MS stud iron as I am now wary of High tensile bolts and stud iron. We have two local bolt and fixing suppliers in town (a steel town). I asked one for high tensile steel bolts to hold the girling calipers and XJ6 calipers on (a MS bolt came out of one of the rear calipers and the other one bent, but as we were 140 miles from home I managed to find bolts in the boot to resecure it). The owner of the bolt store did not recomment HT bolts as he said MS would bend, but HT would snap. He knew more about bolts than me so now I stick to MS bolts and drill them and use the old fashioned lacing wire to secure them (obviously the loctite didn't work previously).

So now I buy a handful of stud irons and weld two nuts together and clean the thread with a tap so a large thread area is in use. My compressor is a lot better now as I turned up a hemishperical swivel and matching base(45 degree bevel), so less damage to the threads (a copy of the JEC compressor).

Sorry for being a windbag,
Brian

PS Parked up under a motorway bridge at David Manners I checked and found all the other caliper bolt loose!!!!