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Old 21st January 2011, 20:04   #11
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In theory yes but you'd need to do this several times over and over
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Old 21st January 2011, 21:54   #12
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Interesting read folks!!! My ZT has a soft pedal compared to other cars I have driven. My ZS was one of the worst for brake fade.
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Old 21st January 2011, 22:02   #13
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With almost all cars now fitted with ABS, does this mean any DIY brake fluid maintenance on them is ill advised? Are the brake fluid replacement instructions given in the Haynes Manual incorrect?

EDIT: The other manual (that dare not speak its name) describes brake bleeding exactly like Haynes does. Even when the ABS modulator unit has been removed and refitted, the procedure for fluid bleeding then links directly back to the earlier description using rubber tubing and a jam jar. The only reference to T4 in this section is to clear fault codes. The hydraulic flow diagram shows that there are several 'loops' within the ABS unit which are opened/closed by solenoid valves according to instructions from the ECU. However, all are connected directly to the master cylinder via the primary and secondary circuit pipes. Adding fresh fluid to the master reservoir will allow the pedal to pump it through the ABS modulator, but only those connections which are normally open. In other words, the loops which are opened during ABS activation will not receive the fresh fluid during the bleed. Having read through the manual, I can only conclude that these loops need not be bled (using a T4 to open them) unless the hydraulic fluid has more or less drained away leaving the ABS unit full of air. This could obviously get into the loops if the brakes were applied under conditions that would activate the ABS system. However, the details on refitting an ABS unit makes no such reference. I wonder therefore, what the routine is for fitting a brand new, 'dry' ABS unit? I would have expected that to be covered in the brakes maintenace section, but I can't see it.

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Old 22nd January 2011, 07:28   #14
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Bleeding with T4 gives the system a complete bleed purging any air within the system.
The factory were using this method for other models R8/concerto/200/400 25/45 years ago albeit not a T4 but a purging tool all the same,
Haynes manual sorry don't regard their advice as anything but a guide for general diy jobs.
This bleed function is not unique to Mg/rover as other manufacturers require it too with their dealer diagnostic equipment too
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Old 22nd January 2011, 08:32   #15
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So With almost all cars now fitted with ABS, does this mean any DIY brake fluid maintenance on them is ill advised?

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Old 22nd January 2011, 09:00   #16
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Its extremely unusual to get air trapped in the ABS modulator. If you have a spongy pedal I would make sure that you have bled the brakes conventionally first and properly & checked everything else out first. You may get air in the ABS if when bleeding you do not top up the fluid and air gets in the system. If the car has been regularly serviced and brake fluid changed there is no reason air can get trapped.

If your sure air is trapped in the ABS, the first step would be a power bleed that has more chance of getting it out.

If you have a car with lots of miles, then you get the same affect when all the seals get spongy. I've had dozens of cars and never had air trapped in the ABS.

Change brake fluid regularly and all the components will outlast the car! Its the most unserviced item on lots of cars.
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Old 22nd January 2011, 10:46   #17
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If I can add my twopennyworth, I am friendly with the owners of an MOT station who say that they have received official notification that the sinking pedal on a Rover 75 diesel is NOT a failure point when the engine is running. It is a failure point if the pedal sinks when the engine is off.
I don't profess to know why, and they didn't elaborate, but it may have something to do with the fact that the diesels generate the brake vacuum by way of a pump? i.e. anything powered by a pump will have a fail safe valve which might be the reason? OR,at tickover only, the pump cannot maintain the vacuum?

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Old 23rd January 2011, 13:07   #18
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Quote:
Originally Posted by T-Cut View Post
So With almost all cars now fitted with ABS, does this mean any DIY brake fluid maintenance on them is ill advised?

TC
You should still be able to bleed brakes the conventional way but if you still have a soft pedal then you know you probably have air in the abs unit so your have to use T4
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Old 23rd January 2011, 15:49   #19
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Quote:
Originally Posted by T-Cut View Post
I wonder therefore, what the routine is for fitting a brand new, 'dry' ABS unit? I would have expected that to be covered in the brakes maintenace section, but I can't see it.

TC

There are two bleed methods on the menu system on T4 one of which is for use when the ABS modulator has been replaced.

I don't know why they didn't mention this in the brake maintainence section

Even using T4 you need to manually depress the brake pedal as well to ensure that all the air is out of the system.

As others have said it's not unique to MGR, a lot of other manufacturers require the use of the diagnostic system to effectively purge the system of air.

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Old 23rd January 2011, 18:18   #20
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Quote:
Originally Posted by wuzerk View Post
I am friendly with the owners of an MOT station who say that they have received official notification that the sinking pedal on a Rover 75 diesel is NOT a failure point when the engine is running. It is a failure point if the pedal sinks when the engine is off.
That tallies with my research on SPP.

Quote:
I don't profess to know why, and they didn't elaborate, but it may have something to do with the fact that the diesels generate the brake vacuum by way of a pump? i.e. anything powered by a pump will have a fail safe valve which might be the reason? OR,at tickover only, the pump cannot maintain the vacuum?
The diesel vacuum pump explanation of SPP is a myth IMO. The source of vacuum in the servo is immaterial. I've yet to read a convincing explanation, so until I do, here's my own,superficial theory (copied directly from another discussion on SPP).

It's not a 75/ZT exclusive behaviour, many other makes of car do this including Ford and Jaguar. Personally I don't go for air in the ABS module as the explanation. I'm not saying that air in there doesn't require a T4, what I'm saying is SPP isn't directly related to air in the ABS unit. SPP is far too widely reported to be explained by air in the hydraulics. The brakes wouldn't operate as well as they do if that were the issue. Again, I personally think it's an effect of the electronics trying to 'understand' what's going on when you have the engine running, you're pressing down the brake pedal, but the wheels aren't rotating. How does the ABS system interpret that? And many MOT stations are indeed aware of SPP and do not regard it as a fault. As stated above, SPP is only apparent when the engine's running. That also would require explaining.

EDIT: It would be an interesting experiment to use an external vacuum pump to run the brake servo and see if you get SPP without the engine running and with the ignition off. My gut feeling is you would not. You'd need something like a small Edwards Speedivac pump to pull the servo pressure down enough.

TC

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