guykay Posted September 6, 2014 Share Posted September 6, 2014 I know this question has been asked before, but I couldn't find a solution to my problem, so here goes: my lightweight brakes work fine when I first press the brake pedal, even locking up the wheels. But if I keep pressure on the brake pedals it slowly goes down until it is fully depressed. Releasing the pedal & then pressing again the pedal is at first firm & then again starts to go down. I have replaced all fluid in the system & bled it thoroughly. There are no obvious elks anywhere & the fluid level in the master cylinder stays at the full level. I am inclined to think it might be a leak on the vacuum side of the servo. Is this likely? Quote Link to comment Share on other sites More sharing options...
Tony B Posted September 6, 2014 Share Posted September 6, 2014 (edited) Change all the flexible pipes for a start, they may be balloning. Also try bleeding again. The term is very apt on Landy brakes. As a test get some brake clamps and clamp each of the flexis in turn. If the problem dissappears that is the offending flexi or cylinders. If with all three pipe clamped off, then it is fluid seeping back past the master cylinder seals. Also adjust brake shoes on the snail cams. If there out all sorts of weird things can occur. Edited September 6, 2014 by Tony B Quote Link to comment Share on other sites More sharing options...
guykay Posted September 6, 2014 Author Share Posted September 6, 2014 If the flexible brake pipes were ballooning, would the peddle just be spongy rather than initially hard and then slowly settling to the bottom of its travel? I think that the master cylinder passing fluid is a possibility. Can the master cylinder be rebuilt? And if so does anyone know the part number(s) for the rebuild kit? Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 6, 2014 Share Posted September 6, 2014 (edited) First , possibly it would be best if you posted a photograph of the Master cylinder , with the S3 Lightweight - depending on age there are two types of Girling MC depending on vehicle age. There are pattern MC around - I would not use one. You say you are not getting a loss of fluid - from front & rear compartments of the MC ? It is possibly to get fluid loss from the MC , a bad case you would get it running down the pedal box - look for dampness. The Girling Supervac (genuine) at the mounting flange , there is a small drain groove , feel underneath with tissue - check for fluid loss under bolting flanges. Where the MS sockets into the booster can get corroded , so rust can choke up this drain-way - the only check is to remove and examine. You can get seal recon kits , depends if the MC is worth salvage. Basically there are early & late vacuum check , manual or the later auto on ignition start , often these don't work. Doing the standard pedal check , vacumm exhaust - pedal should drop abt. 1" and then be rock solid. ------ Look at the pressing between , pocket for the MC mounting spigot - you will see a very small vee groove impinge (above vacuum switch) - this is the fluid drain if seals are worn. Edited September 6, 2014 by ruxy add photograph Quote Link to comment Share on other sites More sharing options...
guykay Posted September 7, 2014 Author Share Posted September 7, 2014 The master cylinder (mc) fitted to my lightweight is shown below On close examination the paint on the servo has bubbled somewhat and it is quite damp. I think I'd put this down to the usual combination of damp & rust that permeates the rest if the vehicle. can you identify the mc from the photo? Is it likely to be recoverable with an overhaul kit, or should I cough up for a new one ( are they available) Also as you can see. the vacuum switch is not connected to anything & the lugs have broken off. At the risk of sounding stupid, is this important, or just an indication if some sort? Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 7, 2014 Share Posted September 7, 2014 The MC & reservoir have the appearance of a 569671 , that would be correct on a truck up to approx. manuf. date of June 1980. This would have a Supervac unit using a manual "Test" button on the dash (this is just to check the warning bulb has not blown -Ign on). Obviously non-functional, if it were operative and tests out correct, then if the lamp illuminates - indicates loss of vacuum or loss of fluid in front or rear lines (or both). It should be restored & shuttle valve also tested. Without a operational Supervac , there is still braking , you just press harder LoL . There could be some spongyness , esp. if the footpedal height (from floorplate) is not correctly all set up right from scratch. If you don't have fluid weepage from the bleed at Supervac , then the spongyness is probably by-pass across worn seal set. Hose balloon , possible I suppose , my experience is more the opposite , as hoses deteriorate they restrict and then shut off all fluid flow , first indication is when your brakes start pulling to one side. ----------- A problem is that the cylinder (it is Girling manuf) , you can't identify from the casting No. & the plastic or ally bracelet bench test band is missing. It is possible that it is the wrong MC - such as the one used on a 109" of same period , this had front rear flud compartments the other way fore/aft & pipework thread sizes different way - as warning not to use & cross-pipe ! This is a possibility. --- After abt. June 1980 - there were many changes to brakes , the MC NRC6096 was used , this was also rationalised so as to use on 109" with dual-circuit from same time. This is more or less identified in first blush stage - the reservoir is affixed with two Mills pins .. Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 7, 2014 Share Posted September 7, 2014 btw , if your bonnet is original to truck , you have the later windscreen washers from abt. 1980. Engine obviously much earlier manuf. due to side filler pipe. What is your vehicle mil. no. probably something like --HF-- or --HG-- , or chassis No. ? Do you have 10" or 11" front brakes ?? , often axles get swopped and it is a total mix up of parts that are then obviously wrong to application , this also affects front & rear slave cylinder sizes. It would probably best to date the truck as starters. Quote Link to comment Share on other sites More sharing options...
guykay Posted September 7, 2014 Author Share Posted September 7, 2014 Reg no is as on photo. I have also got a photo of the front drum brake drums, hopefully you can tell me if they are correct for the vehicle. Number on side of mc casting is 64676942Q26. As I said fluid appears to have seeped down the front of the servo steel pressing from the mc. So I guess this is the most likely culprit. Cost of a new mc is about £200.00 guess I'll just have to cough up. Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 7, 2014 Share Posted September 7, 2014 Actually , the condition of your MC looks quite good external , often the plating strips off the cast iron early. It is probably changed in recent , very recent years. I will find the part number for the recondition seal kit for the MC , this evening. Actually , I have 23HF86 (95105276A) a little newer as Contract FV.22A/87 Item 3 (a Suffix Item is more or less a bolt-on to a main contract). DIS. July 1979 Your brakes are correct for period - 10" all , front + rear . Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 7, 2014 Share Posted September 7, 2014 90606422 http://www.lrseries.com/shop/product/listing/2219/90606422-MASTER-CYL-REPAIR-KIT.html?search=90606422&page=1 ---------- The Girling No. was / is SP2361 , could be S/S by TRW Quote Link to comment Share on other sites More sharing options...
guykay Posted September 9, 2014 Author Share Posted September 9, 2014 Ordered mc and servo overhaul kits. Arrived today, fitted this evening. Brakes now spot on. No fade on the pedal. That's the brakes sorted, rear chassis replaced, front outriggers repaired, exhaust centre replaced. Just the dreaded zenith carb to sort out now! It pops & bangs on full throttle, like a misfiring Merlin, with gouts of black smoke pouring from the exhaust. I think I can see light at the end of the tunnel, or is that just a torch from some other lost soul. Quote Link to comment Share on other sites More sharing options...
ruxy Posted September 9, 2014 Share Posted September 9, 2014 Always something LoL , if not buy another. Quote Link to comment Share on other sites More sharing options...
Tony B Posted September 9, 2014 Share Posted September 9, 2014 Just remember the old adgage! A bu**er if they don't go . A disaster if they don't stop! Quote Link to comment Share on other sites More sharing options...
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