Hi to alls
My mechanic replaced the original Jaguar brake servo (very large: at least 20 cm in diameter and 15 cm in depth).
He told me that the one he installed is smaller, explaining that replacement brake servos today are generally smaller.
The result is that the brake pedal has become very hard, and it feels like stopping the car is difficult.
Everything else has been replaced: pistons, master cylinder, brake pads, and discs.
Could this pedal hardness be caused by the brake servo ?

The prices of brake servos range from 250 euros (SNG Barratt) to 1500 euros for a reconditioned Jaguar servo (Limora).
Is it absolutely necessary to have a brake servo with the same diameter/depth as the original one (to match with the original Jaguar specs)
My best regards
Gérard

 

if i found the amount of effort was alarming, i would question whether or not the servo was working at all. as i recently installed a new one that was supposed to apply less force per foot effort than the original yet the cars stops well. OTOH, i did drive it ten miles to the shop that did the new installation with absolutely NO brake assistance and it was difficult to stop, but i'm sure i could have still locked them up if i needed to.

to test whether working at all or not, you can pull the small vacuume line off the servo. if it's working i would think one would feel a major difference.

 

I think we discussed this a few months ago. The original Mk2 brake slave cylinders are fairly small diameter and so require more pressure than a larger cylinder to produce sufficient force on the brake disc. The original servos (boosters) provide a greater assistance ratio than the smaller, cheaper versions that are often added to classic cars, which is why they cost more. Given that when everything is original the pedal needs a fairly hard push, a downgraded servo is not a good idea. It's better to keep the original if it's working or buy the upgraded (slightly more assistance) from SNG.

The original Mk2 brakes work well. With a hard push, you can lock the wheels (usually rear first). Unless you're adding wider, stickier tyres, the only reason to change anything is ease of and reduced maintenance.

 

As mentioned, I would first check that there is vacuum going to the servo. I would put on a vacuum gauge and see what you get.