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Post by ahaugland on Apr 16, 2019 17:03:15 GMT
Hello! We're just finishing up recommissioning my P5 Mk3 which has been off the road for 23 years. To that end we completely replaced the brake hydraulics on the car with parts purchased from JR Wadhams. The brakes do work but the pedal falls almost all the way to the floor before stopping and there is a lot of travel before any engagement is noticed. Clamping the hoses to the rear brakes or the front brakes to isolate the two sides of the system doesn't yield any significant improvement. The only non-stock part of the system is an aftermarket brake booster we installed, which is also new, but different from the stock unit. We are certain that the brakes are sufficiently and correctly bled as we've bled them multiple times via different methods to try to sort out this problem. The master cylinder in the car is the 3/4 inch bore 3 bolt cylinder that Wadhams lists as being correct for the 3 Litres. They also list a 1 inch bore cylinder for the P4 with either open or closed ports that looks like it could be used and would push more fluid, though I have no idea what they mean by open or closed ports.
Does anyone else have any suggestions or recommendations they could give me? Thanks!
--Alex Haugland
Eugene, OR USA
1966 LHD Rover P5 Mk3 Automatic
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Post by Phil Nottingham on Apr 16, 2019 20:57:18 GMT
Introducing a non-standard servo has created an unknown variable so this needs bypassing hydraulically to eliminate it.
However excess pedal travel not down to rear brake adjustment or balooing flexis may just be down to the brake pedal pushrod adjustment.
3/4" is the correct bore and using the 1" bore should not be necessary
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Post by ahaugland on Apr 16, 2019 21:50:20 GMT
The flex lines are also all new, so I doubt that's the problem. I've thought about bypassing the servo as a test but haven't tried that yet as it would be an involved process and require rebleeding the brakes again and I will need a servo fitted in the long run. Refitting a standard servo would be difficult as the car had an old American made aftermarket servo fitted and in doing so, the original mounting bracket was cut off completely. The servo we fitted is a Lockheed style 4.25:1 ratio. Thanks for confirming the size of the master cylinder. To try to eliminate brake adjustment, we tried turning the rear adjusters to full lock and put on the hand brake, which doesn't improve the pedal height at all. The brakes also don't change in travel with the engine running or the engine off. I'll take a look at the adjustment of the pushrod again and see if there's anything that can be done to eliminate any play in the pedal.
--Alex Haugland Eugene, OR USA 1966 LHD Rover P5 Mk3 Automatic
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Post by enigmas on Apr 16, 2019 22:45:15 GMT
From what you state it sounds like the system is full of air. Another area of issue could be the pushrod free play to the master cylinder. If this has been altered to allow too much free play.
NB.You can also bleed the brake system by loosening and tightening any unions at any high points in the system...such as the brake booster, even if it doesn't have a bleed nipple. Air rises to high points. Bleeding the system at the wheel slave cyls alone may not evacuate all the air.
PS. (I have a P5 MK3 Coupe with an extensively modified brake system including a non standard dual brake booster in line with the original master cyl)
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Post by lagain on Apr 17, 2019 10:27:23 GMT
It sounds like air in the system. When I replace seals and have to refill the system I start with a Gunson Easibleed to fill up and then use the pedal to get any more air out. That usually works, it does seem difficult to get the brakes right on the P5.
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Post by Phil Nottingham on Apr 17, 2019 17:44:39 GMT
Quite a few seem have trouble bleeding these brakes but if you follow the correct procedure it takes only minutes even from empty.
However the servo assistance is too high - 3:1 is more than adequate.
Is the servo mounted so its outlet is at a least a shade pointing upwards? If not it wil never purge the air. It is quite easy to bypass the servo an bleed the system again (starting at the futherest nipple and with the rear raised if poss) and would pinpoint the problem quickly.
A vac or air bleeder should do it but it should not be necessary
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Post by djm16 on Apr 18, 2019 0:33:57 GMT
Been there and done that!
You will be chasing your tail unless you start eliminating things.
I would begin here by plugging the servo output with a welded over ferrule. The pedal should then be rock hard and very little different with the engine running.
Assuming the MC / servo setup is now proven to be OK, there are only two common possibilities:
1) there is still air somewhere, despite your multiple bleeds.
2) the rear brakes are a VERY long way out of adjustment.
When I am struggling a little with bleeding brakes on my P4, I go around all 4 wheels before I start and lock all four wheels with the adjusters. This makes it very clear whether I have a hard pedal or not.
If with the servo output plugged you pedal still goes to the floor, then the cause can be hinted at by whether the brake pedal seems to pump up.
Pumps up: probable cause - air leak in MC.
Does not pump up but goes steadily to floor: - leak in servo (even though it is new) in which case your brake fluid level will progressively decrease, or defect in recuperating seal, or damaged / missing recuperating seal shim.
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Post by ahaugland on Apr 30, 2019 14:41:13 GMT
I believe we've identified the problem, which is that J R Wadhams shipped me the wrong rear wheel cylinders. The wheel cylinders I received were larger than the 3/4 inch diameter cylinders that are supposed to be on the P5 Mk3. I now have the correct cylinders in hand and will hopefully get them installed shortly so the car can get back on the road Once I've verified the solution I'll post again.
--Alex Haugland Eugene, Oregon USA 1966 Rover P5 Mk3 LHD Automatic |
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Post by Phil Nottingham on Apr 30, 2019 15:44:10 GMT
Apart from early Mk1s 3/4" were used on all P5s and Mk1's were smaller. What size have you?
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Post by djm16 on May 1, 2019 0:51:14 GMT
I am puzzled. You said that you clamped the hose(s) to the read brakes and that made no difference. So I am puzzled how changing the size of the slave cylinders is going to help, except that you get to bleed the brakes again.
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