QuestionQUESTION: Hi,
I own a Landrover 90 from 1988. The brake has been making trouble ever since I bought the car one year ago.
These are the symptoms:
When the engine gets hot, the brakes on all four wheels start dragging without any pressure being applied to the brake pedal. This leads to further heating up of the engine and worse brake trouble, up to the point that I have to stop and let the engine cool down.
The available local experts and I have done the following to cope with the problem:
- check and exchange the brake servo and master cylinder
- adjust the rear brake pads (this is where the symptoms are worst)
- (later) renew seals in the master brake cylinder and slave brake cylinders
- adjust the length of the push rod that comes out of the servo.
When adjusting the length of the push rod, there are two possible symptoms: if the push rod is too long, the brake answers immediately to the brake pedal when the engine is cold, but it will start dragging if the engine gets hot. If the push rod is too short, it will be possible to depress the brake pedal completely with only a minute effect; one has to depress it a second time in order to be able to brake. This will get better when the engine gets hot, but it will not come to a level where it feels safe to drive. Between the two states is less than one turn of the push rod adjustment screw, so I haven't been able to find an intermediate setting, yet.
In order to check whether the master cylinder piston gets stuck, I tried to disconnect the master cylinder from the servo while the brakes where stuck. When I did that, the brakes came free immediately.
Another test we did was to see whether it made a difference when the vacuum hose that powers the servo was disconnected. It didn't seem that way. I didn't notice any "automatic" movement of the push rod, either, when the master cylinder was disconnected and the vacuum applied.
I might have to add that I live in a third world country, so that original spare parts and professional help are not easy to get. I noticed that a former owner must have had the upper part of the brake pedal welded, where the push rod from the brake pedal into the servo is connected to the brake pedal. Another thing is that I saw the local experts fill dot 3 brake fluid into the system, while the workshop manual says it should be dot 4. I don't know the difference myself, but posts I found elsewhere on the internet seemed to suggest that mixing the two might create trouble.
Our next idea is to insert U-washers in order to adjust the length of the push rod from the backside of the servo. However, I haven't understood the workings of the servo enough to really grasp why adjusting the push rod so little makes such a big difference, and through all our tests we still haven't figured out what actually goes wrong. So, any help would be really appreciated...
ANSWER: I think your main problem is the length of the push rod. It really should never have been touched in the first place. Check for wear on the clevis pin from the brake pedal to the booster. If this is worn, this may be why they were trying to adjust the pushrod length.
I would definitely not recommend using U-washers to adjust the length of the push rod. The brake pedal being welded at the wrong angle could be causing your problem. If your problem persists, I would locate a new brake pedal and adjust the push rod length back to what it should be after replacing the pedal.
Mixing the DOT3 and DOT4 is probably not causing your current problem, but DOT3 will corrode the rubber components in the brake system. You would be well advised to flush out the brake system and replenish with DOT4.
---------- FOLLOW-UP ----------
QUESTION: Thanks for your advice, I will definitely change the brake fluid as soon as possible.
However, I'm not even sure whether the different brake components match each other. Could you point me to a list or something that allows me to find out exactly what make of components (servo, master brake cylinder, master brake cylinder pistons, brake pedal) should be in this car, and how I can make sure that this is really what I get? The problem here is that the people tend to sell you anything that remotely fits the description of what you want... so some identifying numbers which I could find on the things themselves or their package or so would be really helpfull.
Another thing: you mentioned resetting the pushrod to its original length. Can you tell me how much that should be, measured from the end of the servo pushrod, where the pushrod adjustment screw goes into the servo on the master cylinder side?
Thanks very much for your support,
Hans
AnswerYou can check various online catalogs for pictures of many of the various parts for which you are looking. Here is a link to Defender 90 brake parts on Atlantic British's site: http://www.roverparts.com/Nxt/search.asp?page=1&Dropdowndescription=Defender+90&
It is just a starting point. They do have pictures of the calipers, pistons and master cylinder. It may not be easy to find pictures of the brake pedal, but if you don't find it on any sites, I would recommend trying some of the Land Rover, and, in particular, Defender forums.
From the face of the servo to the end of the push rod measures 26.5mm with no pressure on the booster.
