Diesel braking problem
 

When I'm driving around town at speeds no more than 30mph, but really usually much lower than that, and with a lot of stop start in traffic, my brakes work perfectly. 3 days ago I went out of town and after driving for a couple of miles at about 50-60mph I needed to brake approaching a junction.Not a hard brake, just gently to slow down, but the brake pedal felt hard and there was limited brake effect, as if the engine was off. Once I reached a slower speed the brakes came back. This happened twice more once I reached a speed greater than 50mph. Any ideas?

I don't really know why it would change with speed as it is dependent on vacuum but I would look at your brake booster.... That is the only thing that I see possibly changing on how fast you are going and being intermittent. Other people here will know much more than I though.

Post some info about your jeep. Year, engine, etc. itll help us help you. Also welcome aboard. When were the brakes last serviced.

Details of Jeep
 

Sorry, it's a 2000 XJ, a 2.5 diesel, manual (stick). My 4th Jeep so far since 1999.

More
 

Diesels have a vacuum pump built in to the front of the engine.

This ^^^ or at least inspected. Was this sudden, or gradually worse?

Check that pump works, no leaks in hoses.

braking
 

It happened suddenly and disappeared when I slowed down. The re-occurred again whn I sped up. This is the opposite of what you might expect? It was serviced a month ago and passed the annual MOT (safety test)

If it has a vacuum pump, it sounds like a vac issue. Looses vac at higher speeds and comes back

vacuum
 

Yes, I agree, but it's illogical because the pump is driven by engine speed, so I could be doing 30mph at 2000rpm in 2nd or 60mph at 2000rpm in 5th. It's a conundrum.

Im gonna report this thread for two reason. Too have it moved to advanced tech since you have a diesel and to get it more views. Im not sure personally how the diesel system works. Trying to think about the diesel vans I've driven. Well get you some answers yet.

wrong thread
 

Since I've been moved to 'other vehicles' there's been no more replies. It's a JEEP !

oh boy lol. I suggested advanced. Not sure how it got shifted to other vehicles. Ill see if i can find something out