Discussion
On my Innocenti I have a strange hydraulic issue. The braking system has been largely re-built with new pistons and onversion to LHD. However I am experiencing a brake pedal which 'pumps-up' and has slightly excessive travel on the first application. Of course, I have bled large quantities of fluid through the system and it appears to be 'air-free'. But still it takes two quick pushes on the pedal to bring the pedal travel to be correct.
So, this morning I tried to isolate each corner in turn. I clamped off the LH front caliper hose and, bingo, the pedal was firm with no 'pumping action'. Hooray, thought I, it's air in the LH caliper. So, to be thorough I repeated the exercise on the RH front hose after removing the clamp from the LH hose. Again, with the RH hose clamped this time the pedal had no excess initial travel. That has exhausted my logic, as if there was air in the RH one as well, the pedal would still have been soft with the LH clamped, and vice-versa.
So illogical did it seem that I repeated the whole procedure with the same results.
Thoughts anyone?
So, this morning I tried to isolate each corner in turn. I clamped off the LH front caliper hose and, bingo, the pedal was firm with no 'pumping action'. Hooray, thought I, it's air in the LH caliper. So, to be thorough I repeated the exercise on the RH front hose after removing the clamp from the LH hose. Again, with the RH hose clamped this time the pedal had no excess initial travel. That has exhausted my logic, as if there was air in the RH one as well, the pedal would still have been soft with the LH clamped, and vice-versa.
So illogical did it seem that I repeated the whole procedure with the same results.
Thoughts anyone?
Has this been like this since everything was rebuilt? Were any replacement parts fitted eg the master cylinder?
My thought being is the master cylinder bore size is too small (small bore, long pedal and vice versa) this would give a long pedal which will pump up, isolating one corner of the front brakes would give a smaller overall fluid displacement and the pedal will have less travel as there is less fluid to move, is it a harder pedal again with both front hoses clamped?
My thought being is the master cylinder bore size is too small (small bore, long pedal and vice versa) this would give a long pedal which will pump up, isolating one corner of the front brakes would give a smaller overall fluid displacement and the pedal will have less travel as there is less fluid to move, is it a harder pedal again with both front hoses clamped?
Another thought, has it got drum brakes on the front? If so are the piston to shoe springs still there? The small ones that fit through the end of the shoe and into the small locating hole in the cylinder piston, if they're missing the pistons will often creep back into the cylinder giving a long initial pedal, and will harden up by clamping either side for the same reason as i mentioned above.
It' definately the correct master cylinder as it's unique to the Innocenti 1300 Export. The brakes are basically the 7.5" Cooper 'S' brakes as I have on my other Cooper, the difference being that it's a front/rear split system with, again unique to the Inno, the splitter/pressure limiting valve on the bulkhead not on the sub-frame.
I converted it back to LHD and re-built the calipers, so it has new brake pipes across the car, but apart from that everything is as it was when I restored it.
The brakes atually work fine and it passed the MoT. It's just that they do 'pump-up' with just one extra pump. It's the fact that having isolated one side and got a good pedal, it was natural to assume that air was in the isolated caliper. However, when i repeated the test on the other side I got a good pedal again. Mysterious!
I converted it back to LHD and re-built the calipers, so it has new brake pipes across the car, but apart from that everything is as it was when I restored it.
The brakes atually work fine and it passed the MoT. It's just that they do 'pump-up' with just one extra pump. It's the fact that having isolated one side and got a good pedal, it was natural to assume that air was in the isolated caliper. However, when i repeated the test on the other side I got a good pedal again. Mysterious!
Doesn't sound like air though to me, is it worth checking the 1300 export master cylinder size, maybe it's not entirely compatible with the 7.5 set up, i'm working a little in the dark here as i really haven't had much to do with Innocentis but would it have been fitted with drums as standard with this master or even the 7" cooper system? If it had discs would it have been fitted with a remote servo which could make a difference.
If so would these have smaller pistons in the calipers than the 7.5" calipers which would give this problem? Daftly, and probably not the fault but are the hoses ok?
If so would these have smaller pistons in the calipers than the 7.5" calipers which would give this problem? Daftly, and probably not the fault but are the hoses ok?
pete
when you rebuilt the calipers did you make sure that the outers where refitted to the correct side calipers - so that the drilling hole is lined up?
a mate of mine did this and had all sorts of brake issues - it passed the mot fine, but only half the caliper was working it made the pedal do all sorts of strange things, the brakes where terrible as well!
when you rebuilt the calipers did you make sure that the outers where refitted to the correct side calipers - so that the drilling hole is lined up?
a mate of mine did this and had all sorts of brake issues - it passed the mot fine, but only half the caliper was working it made the pedal do all sorts of strange things, the brakes where terrible as well!
The brakes are all as standard for the Innocenti Mini Cooper 1300 Export which has Cooper 'S' 7.5 diss and calipers as standard. The only difference from the original Cooper 'S' set-up is that it has a front to rear split dual system and the different master cylinder (GUD159?) as standard on the Inno.
The brakes are absolutely fine if you give the pedal a quick second dab and it passed the MoT with no faults noted. In fact, the pedal feel is a bit like the old drum braked ones when they needed a bit of adjustment, OK but not perfect.
What I cannot get my head around is the fact that isolating either caliper, but not both at the same time, will give the right pedal travel. It defies logic really.
The brakes are absolutely fine if you give the pedal a quick second dab and it passed the MoT with no faults noted. In fact, the pedal feel is a bit like the old drum braked ones when they needed a bit of adjustment, OK but not perfect.
What I cannot get my head around is the fact that isolating either caliper, but not both at the same time, will give the right pedal travel. It defies logic really.
pete
i wonder, if cam suggests, that the new seals are pulling the pistons back when the pedal is released - that would explain the pedal having to be pumped.
in the past ive had this problem with alloy four pots - you have to make thinner 'fake' pads from plywood (to make sure the pistons dont come out) and pump the pistons in and out brushing a little brake fluid on to them to free the seals up.
i wonder, if cam suggests, that the new seals are pulling the pistons back when the pedal is released - that would explain the pedal having to be pumped.
in the past ive had this problem with alloy four pots - you have to make thinner 'fake' pads from plywood (to make sure the pistons dont come out) and pump the pistons in and out brushing a little brake fluid on to them to free the seals up.
guru_1071 said:
pete
i wonder, if cam suggests, that the new seals are pulling the pistons back when the pedal is released - that would explain the pedal having to be pumped.
in the past ive had this problem with alloy four pots - you have to make thinner 'fake' pads from plywood (to make sure the pistons dont come out) and pump the pistons in and out brushing a little brake fluid on to them to free the seals up.
Now that's worth a try. I guess i ould use a set of very worn out pads to get the pistons to come well out without 'popping'. i wonder, if cam suggests, that the new seals are pulling the pistons back when the pedal is released - that would explain the pedal having to be pumped.
in the past ive had this problem with alloy four pots - you have to make thinner 'fake' pads from plywood (to make sure the pistons dont come out) and pump the pistons in and out brushing a little brake fluid on to them to free the seals up.
I guess isolating one side would sort-of halve the excess pedal travel and make it seem acceptable, maybe. I'll give it a try next weekend as I have an engine to finish building this week and no assistant to pump the pedal for me. Cooperkid will be here on Saturday so we an try it all again then. I may get grumpy and just change the calipers again.
I had that problem with my new 4 pots, really annoying having to pump the brakes to get a decent high biting point. Have a look and see if you can wobble the pads around in the calipers (before pressing the pedal) indicating the new seals are sucking them back away from the disc. The solution i found was to push the pistons out on to thinner / dummy pads as suggested by Guru, clean and lube them with brake fluid, then with the pistons out a little, so that its a very tight squeeze put the pads back in.
It's just so odd and in 49 years b*******g about with Minis I've never had this problem before and especially never with an 'S' 7.5" system with standard calipers/discs.
Still, I'll keep on trying and will do as is suggested with the pistons. I only wonder whether brushing fluid onto the exposed part of the pistons when they are pushed well out may cause the wiper seals to remove the fluid before it gets to the main pressure seals. What do you think about that?
Still, I'll keep on trying and will do as is suggested with the pistons. I only wonder whether brushing fluid onto the exposed part of the pistons when they are pushed well out may cause the wiper seals to remove the fluid before it gets to the main pressure seals. What do you think about that?
Peter, my relax and see method, have you tried just using the car for a couple of days/weeks to see if everything sorts itself out.....i've had brakes where they needed serious pumping up one day and next day after leaving them overnight they are perfect.
Another thought, rather than the seals pulling the pads back, are the pads tight in the caliper and actually flexing rather than sliding.
Another thought, rather than the seals pulling the pads back, are the pads tight in the caliper and actually flexing rather than sliding.
I didn't get around to it today as I had to deliver a rebuilt engine to a customer, then make a trip to Mini Spares at Potters Bar. All-in-all a trip in the wife's Mondeo of around 140 miles towing my small trailer.
Probably do it at the weekend after another trip to MS to buy a shed load of body panels for Cooperkid's 1997 MPI which is to be his first car when he can drive. Just 18 months until he's 17.
Probably do it at the weekend after another trip to MS to buy a shed load of body panels for Cooperkid's 1997 MPI which is to be his first car when he can drive. Just 18 months until he's 17.
Well, 'kill-or-cure' seems to have worked! I just took the Inno out and gave the brakes a 'good hiding' I sat stationary and pushed the pedal down as hard as I could a few times. Then I drove it flat out in 3rd and left foot braked it until the brakes got hot, and I mean HOT'. After then driving a mile or so without using the brakes to allow them to cool down, they now seem to be much better and don't appear to 'pump-up' much, if at all. I suspect that any pump-up now is because the new pads are still bedding in and I've taken a bit off the new rear linings. My 'S' was about like this when I changed all the brakes and re-built the calipers.
Thanks for all the advice and encouragement.
Thanks for all the advice and encouragement.
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