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MG Midget and Sprite Technical - Midget brakes
|I have just inheried 1973 1275 midget, it was fully restored 20 years ago but then placed in storage never getting on the road. I have been working through the jobs on it and have now come to the brakes or should I say the lack of them.|
I have bled them 3 times with no luck, you have to be pumped 3,4 times to go hard, these are the things I've tried and noted so far.
1, After market servo
2, All new brake pipes all round although flexible pipe are black rubber I have purchased S/S braided ones but yet to fit them.
3, New pads and shoes and new back brake cylinders
4, New master cylinder
5, Callipers seem to be working ok and no leaks in the system that I can see
6, Adjusted back brake drums so shoes are slightly rubbing when the wheel is turned cylinders went in and out ok and no leak
should I replace to rubbers in the M/C and drum cylinders.
One thing I noted today where I could normally get a hard brake after 3,4 pumps, I had the rear of the car on ramps and could get no brake at all no matter how many times I pumped the pedal, but when it was back to 3,4 again once the car was back on the ground.
Any Ideas please
|Bypass the servo - it's not standard and it's not needed.|
As you have them, fit the braided hoses then re-bleed.
Which method of bleeding are you using?
- pressure (Easibleed or similar)
- 2 person using the pedal?
IMO easibleed is the better method.
|I suggest you clamp off the hoses then release one by one to isolate where the problem is.|
I had a similar problem once drove me mad. It turned out to be the lube for the pistons in the calipers was a bit tacky, and on pushing the pedal the pistons distored the caliper seals rather than slip through them. When the pressure was released the seals recovered their shape and pulled the pistons away from the disc. Only half mm, but enough to occupy the whole stroke of the m/cyl.
|Nice (previous) post from Paul Walbran - illustrating how an (almost) unimaginable 'trifflingly small' scenario can cause brakes not to work. |
Although not my Midget, I had a scenario where, after a full bleeding, my brakes would work for approx 150 miles, and then go soft. No visible loss of fluid - I changed all components (including the BMC, twice), except the front hoses. Eventually I discovered one of the front hoses had a tiny nick which was very slowly letting air into the hydraulics - the nick acting like a one-way air inlet valve. Before I found that, I was one step away from being admitted into a 'medical facility'.
Unfortunately with brake faults, the servo (if fitted) seems to be 'the obvious culprit' with 'excessive pedal travel' or 'pedal needs to be pumped' faults. But with such faults, it is physically not possible that the servo can be to blame.
As Paul suggests, something to check is the action of the cylinder seals. And as a last port of call, don't assume that new parts are working properly.
|I see you have adjusted the rear brakes which is good as correct adjustment of the rears is critical to getting the front callipers to work. But when adjusting the rears did you ensure that the handbrake was completely free first? If the handbrake mechanism is not freed off properly, then the correct adjustment cannot be achieved.|
Another possibility: I am unsure of the details but on some versions the master cylinder actuating rod is adjustable and needs to be set with clearance when your foot is off the pedal, to allow the M/C piston to return fully to its at rest position. I am not sure how this could make the brakes spongy, but might yours be of this sort?
|I'd go around and check all connections, I have had the same problem with the peddle going soft twice, both times I found that the front flexible pipe connection could be nipped a little tighter.|
|Sanity check the calipers are fitted the right way around, bleed valve uppermost.|
|I had a problem long time ago with the bleed valves during bleeding|
They were worn in the treads and had a lot of slop so added ptfe tape and that cured it
i agree take the servo out of play and install the new ss hoses
also take apart the porportion valve it could have a worn out O ring
i always like to bleed from the farthest wheel working towards the closest to the master cly
|Thanks for all the replies, the methods I've used are the two person and a one person one that connects to my air compressor. The previous owner (my Dad) told me the brakes were fine until he removed the m/c he also told me that he had split one of the callipers.|
I did try to clamp the flexible hoses but they were hard as rock and didn't seem to have any give.
I have noticed that MOSS have callipers on offer at the moment so I might replace them,
Do they do back brake cylinders with bigger bleed nipples, I also read about using 5.1 DOT brake fluid with the s/s pipes
I will try all your surgestions that will just leave me with the carb but that's for another day
|If the flex hoses are "rock hard", they shouldn't be. That may indicate the problem, if they have deteriorated internally and blocked.|
The other clue is that if they were OK until the m/c change, it may need the push rod adjusting before efforts at bleeding will work.
|I have had bad brand new master cylinders. I have found that with a servo everyting bleeds better with the engine running. Clamping any flexible brake hose can damage it permanently.|
i didnt catch that
I did try to clamp the flexible hoses but they were hard as rock and didn't seem to have any give
if they were not bad before ... they are now
|Yes I thought that Danial, I managed clamp them with g-clamps and they are well and truly trash now, but I do have replacements.|
Brakes were 75% better, still good with rear brake pipe clamp removed but soon as I removed either of the calliper pipes the brakes were poor again.
Thank you Fergus, the callipers were on upside down. I will see if they can be serviced while they are off the car.
I have new m/c rubbers on order for my piece of mind and will check push rod setting.
|Clamping does not damage hoses in good order when done with a soft edge clamp and not over-done, and provides a quick and effective means of isolating the problem.|
|They will damage if clamped with G clamps or Mole (Vise) grips. But properly designed hose clamps work well on rubber hoses. I have used them for years with no ill effects.|
|How can anyone be certain when clamping a hose that they are not over doing it?|
|If a tree falls in the woods but there is no one around, does it make a sound? :-D|
|Malcolm Le Chevalier|
|What order should the brakes on a 1971 Sprite be bled in?|
|P R Clark|
|I've always bled mine as follows: rns, ros, fns, fos based on decreasing distance from the master cylinder. I was having exactly the same problems as Mr Coulon and fitted new seals to the master cylinder which seemed to cure matters but I've got a horrible feeling the problem may start to be reoccurring.|
|When a new m/c is fitted, it can be difficult to clear air from the first upwards loop of the pipe as it leaves the m/c. Pumping sometimes pushes fluid through, but leaves an air bubble in the pipe at the top of the loop. I think what is happening is that a single stroke of the peddle doesn't push the air bubble far enough down the pipe and the air rises back up to that loop before the next peddle stroke.|
The solution is to start by bleeding air out at the incoming pipe at the 4-way brass junction unit where it is fitted to the front inner wing - crack it open just enough to bleed any air out of that first length of pipe following the same procedure as you would for bleeding via a nipple. (press, open, close, release etc.) It's a bit messy so have a rag handy to collect fluid as it leaks out. Bleeding doesn't have to be 100% but it is worth doing this before then proceeding with standard bleeding at each wheel following Matt's sequence.
|I guess, Guy, that would be one advantage of the Eezibleed in that there is a continuous flow to stop air coming back. Lots of disadvantages though, mainly resulting from a pipe coming off!|
|Yes, I guess so. I do use an Easibleed as I rarely if ever have anyone available to do the pedal pushing. |
(realising that my last message about selling goods doesn't make much sense!)
Touch wood, I have never had an Easibleed pipe come off and have so far been spared the excitement of DOT 4 being sprayed all over the paintwork!
|I always use a large towel over the bottle and the mc just in case a pipe comes off!|
|Yep the towel is a must for me too. I also double check every connection before pressurising! Years ago I had a pipe ping off a 1300GT and spent forever cleaning everything off.........and then discovering I missed the odd blob!|
|Brakes bled following guidance from here. All good. Thanks for the advice.|
|P R Clark|
|Did 'R Coulson' ever get to the bottom of his brake problem?|
|callipers where on upside down, I replaced the rubbers in the m/c and brake pipes. Now I didn't remove the servo even though it's not needed, it's working fine,touch wood |
Thanks everyone for the help
This thread was discussed between 22/04/2016 and 10/05/2016
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.