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Clutch Losing Pressure After Highway

My Mazda has been losing the clutch after exiting the highway going about 80 for anywhere from 45 minutes to 2 hours. The clutch just goes straight to the floor and needed pumping to get any sort of pressure back to keep shifting. After some time on a normal road, the clutch recovered.

Is this something that could have been caused by Jiffy Lube changing the manual transmission fluid at the end of July? There was some sort of leak so we are guessing they did not put the cap on properly. I had a guy at Tire Kingdom flush and repressurize the system and he couldn’t find any actual leaks and he said the fluid looked funny to him. After this the car still gave out after highway driving, but seemed to recover more quickly as we just stopped long enough to grab some drive through before returning tot he interstate. I took the car to AAMCO as well, and though he didn’t even LOOK at the car he said it sounded like the slave cyclinder? was acting up. I highly doubt that is the case as my car only has 56k miles on it, but I don’t know how to solve the problem. We have a road trip coming up and are conflicted about taking my car.

I have not had any problems driving around town, only after highway trips so far (3 times). Help! I have never had any car trouble before.

It sounds like the clutch master cylinder starts to leak internally once it gets hot. The master cylinder is mounted on the firewall in the engine compartment. As the engine gets hot, it heats up the master cylinder. The bore in the master cylinder expands from the heat, and hydraulic fluid bypasses the cup seals in the master cylinder where no hydraulic can be produced.

To confirm this, the next time the clutch hydraulic pressure is lost, pull the vehicle over, open the hood, and pour cold water over the master cylinder. If the hydraulic pressure is restored after doing this, you know what the problem is.


I could not recreate the problem this afternoon - I drove around for close to 45 minutes on the interstate near our home but didn’t lose the clutch on highway exit. I don’t know if this would be enough time to heat to the point of failure, so I am torn about taking my car to North Carolina versus the small sports car my husband has. Could it be coincidence that this problem happened after my fluid change? Could an incorrect fluid cause the same symptoms? They charged me an extra $30 for some synthetic stuff they said was required, but the other person said it looked dirty to him.

Thank you for the advice though - if it happens again I will see if the water helps.

Did Jiffy Lube or Tire Kingdom flush the clutch fluid? Or did they flush the manual transmission fluid?

A manual transmission doesn’t get flushed, you just drain the old fluid out and refill with new transmission fluid.

If the hydralic fluid was flush for the clutch system they may have refilled it with the wrong type of fluid. It seems you loose pressure when the clutch isn’t depressed for a long period of highway driving. This can be a leaky master cylinder, or leaking slave cylinder, but more likely the master because it is the part of the system generating the pressure. The wrong fluid could be getting hot and developing air bubbles.

You need to take it to either a good Mazda dealer or a good independant transmission shop. Stay away from Kingdom tire and Jiffy Lube for service period. It is not the norm for a master cylinder to fail at 56K miles, but it happens often enough that this could be your problem.

I don’t know actually - Jiffy Lube was first and drained the transmission fluid for sure but I guess they wouldn’t have messed with the clutch. I am completely ignorant as to whether these two systems are connected or if they would do both at the same time.

The Tire Kingdom guy may have flushed the clutch system since my issue is with the clutch pressure, but I don’t know that he drained the transmission fluid a second time. I will double check with him about it. He did tell me to go to a dealer if it happened again.

Since as you say the manual transmission fluid and clutch fluid are two different things, maybe it is a coincidence that the failure happened after a transmission fluid change. Will this type of problem get worse and creep into everyday driving and is it an urgent fix?

Thank you all very much for the prompt responses - I’ll have to see if it happens again after our vacation and I’ll come back to report in a little more than a week. I suppose we’ll be driving the sports car.

UPDATE: I took it to the Mazda Dealer in town after the same problem happened on the way to pick up my dogs. However it seemed to recover similarly more quickly like the last time I lost the clutch. I had been driving at a slower speed (50-60mph) for about half an hour so I guess that cooled everything enough to resolve the problem by the time I hit my first light. I am guessing the car has to be in the 3k RPM range for a long time for the cylinder to start malfunctioning, which in my car is anything over 70-75mph.

According to the dealer it’s the slave cylinder that’s the problem. They recommended replacing both the slave and master since once one goes out the other usually follows, as well as a clutch fluid flush because mysteriously the fluid was dirty looking again (the Tire Kingdom guy DID flush the clutch fluid a couple weeks ago and he had said the same thing). They also mentioned part of the hydraulic pump maybe being an issue. I am going to get clearer details when I pick it up after the flush the fluid again. That’s all I can afford at the moment.

Now, the price shocked me because these parts seem relatively inexpensive based on what the AAMCO guy said. $1375, because apparently in my Mazda Tribute they have the remove the transmission to get to what they need to replace. Is this reasonable??

Do any of you know any good transmission places? The only one I know of is AAMCO that would be all over the country. I am in Gainesville, Fl.

Part of the problem is this: Jiffy Lube, Tire Kingdom, and AAMCO.

You need a mechanic, not a quicky-oil-change place. Tire shops are good places to buy tires, but that’s it. And don’t EVER go to AAMCO, not even to ask for directions.

I don’t agree with the dealer saying the master cylinder will fail just because the slave cylinder has. If the slave cylinder is the problem you only need to replace the slave cylinder, and you can save money by having this done by an independent mechanic. There is no hydraulic pump that I know of within the clutch system. Need more info on that one.

An independent mechanic is NOT the same as a national chain shop.

Consult the CarTalk home page for mechanic recommendations in the “Mechanics Files” section. You can search by zip code, make of car, etc.

Stop trusting your vehicle to the untrained, underpaid kids at these chain places and find a real mechanic to help you maintain your car.

I suggest you locate a good independent mechanic in your area, get another opinion about what’s wrong with the clutch, and what is required to repair it. Sort of like getting a second opinion form another doctor before a major surgery.

I have to concur with mcparadise.

People who rely on chain operations like Jiffy Lube and AAMCO for servicing their car invariably wind up with both inferior workmanship and higher costs than if they went to a reputable independent mechanic. I am not familiar with Tire Kingdom, but in general I would only recommend going to a tire dealer for tires and possibly for wheel alignment.

Yea I’m learning that those places are not the best to get anything other than an oil change. The Tire Kingdom guy was a family friend so he looked at the car and flushed the clutch fluid for free. He probably wasn’t a full service mechanic, but at least he didn’t bullshit us.

As for the second opinion, I did call a non-chain local family owned and operated place and he is looking at my car as we speak for free. I have already paid the Mazda diagnostic fee and caught them before they had a chance to flush the clutch again, so I hope I’ve saved some money on that point. The price the local guy quoted for the dealer’s suggested repairs were half of the dealer’s! We’ll see what his opinion is.

Thanks very much for all your help and advice. I will check out the CarTalk mechanics files as well. Will update with second opinion.

I seem to have randomly picked a pretty good place:

Just an update for anyone else with this problem - the place I took it to offered to replace the clutch, master, and slave cylinders for less than the dealer’s price for just the cylinders. Since my cylinders were difficult to get to, most of that cost was the labor for removing all the stuff that was in the way and they figured since they were in there it would save me another $400 in labor to get the clutch replaced later. So I went all in. There was also a 1 year warranty on the parts and work.

Anyway…So that fixed the problem for a couple of months. Then suddenly I lost my clutch completely in a grocery store parking lot. Had it towed back to the mechanic and after a couple days they discovered a leak in the tubing from one cylinder to the other or some part of the same system. This issue was more difficult to find and they had to order the replacement tube (I only paid for the part this time, yay warranty), but since then my car has been running reliably if not a little differently. Hopefully it will stay that way. Thanks for all the recommendations - I’ll definitely be taking my car to an actual mechanic more often than not from this point forward.