Rover Vitesse, Brake Servo Testing

After rebuilding the calipers an issue that was slightly noticeable before, was very pronounced now. The brake pedal was sinking. This was not ideal.

The pedal had been soft and a little sink-y before I rebuilt the calipers, and I was hoping that the calipers may have been the cause of it, but clearly not. If anything, having all the pistons working properly had made the issue more evident, and holding pressure on the pedal would now cause it to gradually sink to the floor.

Unfortunately having just reassembled the calipers days before the car had to be moved into storage due to losing our house, there was nothing I could do at the time, and I had to drive her to storage. Needless to say driving down the hill from home was interesting; having to keep pumping the pedal to build pressure back up. I got there OK, and I got her to her new home again later.

A sinking pedal, with no fluid loss, means the master cylinder for the braking system was leaking fluid internally, passed the seals. Whether this was from the car sitting for so many years, or if it had just worn out, I’m not sure.

The other issue I had noticed, was that when shutting off the car there was a hissing noise coming from under the bonnet. I tracked this down to coming from the brake servo (or brake booster as its otherwise known as). This would indicate it was leaking vacuum, so that wouldn’t be helping at all.

I was initially going to just rebuild the master cylinder, but once I narrowed down the noise to the servo I knew it was going to be a bigger job than just the master and started looking for other options. I would need to at the least, replace the servo (as rebuild kits are NLA) and rebuild the master.

Rimmers has both, and even do them as a pair for a discount, but the freight made the parts rather unattractive. I was wary about getting an old used one that had been sitting on a shelf somewhere for years, so wasn’t too keen on getting something locally from a wrecker (if there was even anything still around).

I did end up going for a secondhand pair of servo and master, from a car that had been driven at speed into a tree, and came worse off. The seller claimed the servo was only two years old, and the master worked well (maybe too well…) and wasn’t leaking. It was cheap enough to take a punt and hope it worked.

The replacement parts arrived the other day but I haven’t had a chance to unbox and inspect them until today.

It’s a bit dirty and covered in polystyrene from the packing, but there are no signs of fluid leaks or peeling paint on the servo under the master (like my current one does).

There aren’t may ways to test if the servo is OK or not, but one of them is to see if it will hold a vacuum. I happen to have a small vacuum hand pump, so I plugged it into the vacuum line and drew a vacuum. Being such a big unit it took a while, but eventually I drew a decent vacuum, and sure enough to held it for a few minutes without dropping. Great success.

Of course I did the same test to the one on the car…. the results were uh… different.

I checked and double checked all the connections, but no matter how much I squeezed, I could not draw any vacuum at all. I guess that confirms that then, the servo is poked.

I can’t really test much of the master, but I did split it from the servo to see if there were any signs of leaks.

Plenty of grease, but no brake fluid. Excellent. It will be interesting to strip down the failed servo and master and see how it compares to this one. I’ll tidy up the mating faces, and then use some copper grease before reassembly as they were a little seized together this time.

I still need to drain the brake fluid res, and removed the failed parts and fit these replacements, and then bleed the whole system. First though, I need a new, very expensive addition to my workshop tools, just to make my life easier.