"Disappearing brake fluid means an internal leak..."

I had a question about a jaguar 2003 S-Type-R low brake fluid indicator.
-System checked and flushed in late January 2022. Also replaced the rotors and brake pads at the same time.
-Low fluid level on March 5th 2022, brakes were not spongy, I figured the mechanic shop may not have filled the system properly after the flush. Another mechanic (out of town) added some fluid.
-Low fluid level this week May 2022, I refilled the brake fluid yesterday with Super Dot 4. Couldn't compare to what the level was in March. I made sure to not overfill it.
-Pressed brake pedal hard 5x on a flat garage surface, no obvious signs of brake fluid on the floor after this
-Checked brake fluid level today, no drop in the last 24 hours

Any ideas?

 

Welcome to the forums JSCanuck,

I've moved your question from MKI / MKII S type 240 340 & Daimler to S-Type forum. Members here with the same model will be able to help.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some information about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

 

You might want to use a light and an inspection mirror and check the area of the brake servo beneath the master cylinder; this is to see of brake fluid is making its way past the seals/o-rings at the piston end of the unit.

 

Does the pushrod extend into the cabin? On some vehicles, you can get a leak on the aft side of the firewall, inside the cabin.

Also, inspect the interior of the big vacuum hose feeding the booster. Shine a bright light inside the hose and look for a shiny surface. Leaking brake fluid can make its way into this hose and be drawn into the intake, leaving no external clues.

 

Thanks for being so helpful GGG.

1) Inspection mirror: didn't see any leaks underneath the master cylinder
2) Pushrod: no leaks seen. The pushrod does extend past the firewall and is above the brake pedal.
3) Vacuum hose: have not checked. I was concerned I was going to break something so I didn't disconnect it.
4) Brake fluid level: unchanged since I refilled it last week.

At this point I am thinking the low level was due to the recent flush and new rotors/pads in January? Or maybe there is a slow leak I cannot see (vacuum hose)? Since the brake fluid levels have been unchanged for the last week and my commute is only 1-2 miles I'm going to watch it for a bit longer. I'll be sure to update this story for everyone as it happens.

 

Update: Leaking rear brake calipers were the culprit.

The mechanic says I can order replacement calipers from jaguar overseas (1 month deliver) or he can have someone build them for cheaper (1-3 months to deliver). I was wondering if anyone knew a cheaper or quicker source to buy these calipers from? Going through the forums I found someone had mentioned Rock Auto and I found this (https://www.rockauto.com/en/catalog/...b,caliper,1704). That website is saying the price would be around $100 which is more manageable than the quote (especially the overseas option). However, I don't know enough to know if that is even the right part.

 

That link brought me to calipers for a V6 model. Try this instead for the supercharged V8 model, although unfortunately the rear calipers are out of stock:

https://www.rockauto.com/en/catalog/...b,caliper,1704


If you decide to have your calipers rebuilt, ask if they will be sleeved. With low miles on your car, it's a pretty good bet the caliper bores will have some pitting due to minimal use. This is due to extended periods of inactivity, and moisture in the lines forms an acid that sits in one spot. Honing doesn't remove enough material to get rid of the pits, so sleeving is usually the only option. By contrast, calipers with high usage usually don't have much pitting. Most likely a pro rebuild will include sleeving if needed, but beware of the low-buck hone and hope method, which almost never holds up if pitting is present.

 

There folks do excellent work. We used them exclusively when I owned a piece of a service facility specializing in high-end Imports:

Brake Sleeving & Rebuilding Services – White Post Restorations

 

Thanks so much kr98664! How would I have known to ask without you?

Thanks S-type owner, really appreciate it. Checking that out now.

 

ISSUE RESOLVED:
The culprit was a leaking rear brake caliper. The options for fixing were to custom manufacture the part or to order it directly from jaguar.

 

HI, I guess what you need for your 2003 R V8 S-Type might be: CALIPER SEAL KIT
Part No: BPC165, Rear caliper seal kit - models with R performance brakes

• Jaguar X350 XJR supercharged
• Jaguar S Type supercharged 2002 to 2008 vin M45255>>>

Thus, looks like you need just some cheap seals...