Clutch Hydraulic Problems

[bobinyelm]

I just got my car on the road (well, sort of-I am awaiting a new non-binding steering rack from Reg before I can have it inspected), and after only two 10 minute test drives in the neighborhood, the clutch went out.

No external leaks, and it was bled perfectly. I suspect the master is bypassing the fluid, though I need to investigate further.

I am reading a LOT of old posts about hydraulic problems, mostly due to heat.

My 351W engine only has maybe one hour run-time on it (half idling w/ the hood open). Is this enough to cook the master cylinder?

I have the factory heat shield and the push-type slave cylinder on mine.

If it's heat-related, has anyone explored a small blower mounted somewhere and ducting cool air at the brake and clutch master cylinders?

I tried reaching in there, and even though the hood was open the entire time I had the engine running (maybe 5-8 minutes) the air and cylinder temperatures were more than what a human hand could stand.

Most of the clutch posts are over 2 years old. Does this mean there has been a "fix" I am unaware of? My MSO has "C/N 661" in red at the bottom, so I guess this is my chassis number?

Any insight much appreciated!

BTW, I read the master is from a 1985 Mazda truck-is this true if I need another one?

Bob

[Cashburn]

Usually not a master issue but a slave. Who did the engine install?

[bobinyelm]

Originally Posted by Cashburn

Usually not a master issue but a slave. Who did the engine install?

A friend* and myself installed the engine (we've both owned and operated shops so are not bad wrenches).

In what regard is the slave usually at fault? It's currently mounted on the 2-piece factory bracket (aluminum stock and steel angle, which doesn't offer the ideal angle, unfortunately), and is as much of an in-line-push for the slave as I could get it. I see there are after-market one-piece ones available now that bolt to the bell housing bolts (rather than through the bell housing itself).

The slave doesn't seem as subjected to heat as the master, so I made the (possibly incorrect) assumption the problem was heat-related.

Personally, given the heat, it would seem a cable would be not such a bad idea, though most all of my past cars have used hydraulically activated clutches without problem.

Eager to hear your suggestions.

Bob.
*He's a former Hurricane and BDR dealer who flew down to give me the hand.

[Gun Doc]

Bob,

I also have a BDR with 351W. I too, had clutch problems. Mine was the slave...It started leaking after a couple of months. I screwed with it for a year or more. Bleeding, adjusting, etc. I finally grew tired of messing with it and contacted Bill Littleton at Greater Cincinnati Performance Cars and bought one of his slave/mount set ups and have not had another problem. I can't remember how much it cost ($100.00 or so), but it has been some of the best money I have spent on this car.

Gun Doc

[bobinyelm]

New development:

Saturday when I could not disengage the clutch, it was odd that with the pedal to the floor, higher RPM forced my foot up, which it did not do when working properly. I remember an old '60 Ford that did this as well (though it worked properly otherwise), and attributed it to centrifugal force at higher RPM on the pressure plate messing with the release levers (it didn't have a diaphragm pressure plate) forcing the throw-out bearing back.

Anyway, I put the car on jack stands last night (everything at room temperature), and had my bride actuate the clutch. Son-of-a-gun, it appeared to work perfectly, with 1" travel forward of the slave cylinder pushrod, and the clutch felt normal.

I put the trans in gear, and verified that the driveshaft was free to turn w/ the clutch pedal at 1/2 or more throw, and began engaging at 1/2 or less pedal depression.

Is this how these things act when heat is messing with the master cylinder?

Unfortunately, I didn't have time to start the car and try to drive it to see how it would act hot again.

I am hoping that Reg will have my new steering rack in soon so I can actually "drive" the car.
It's tough having it sit there for a month after completion!

Bob

[Fletch189]

I have had my Backdraft for almost 7 years now and I have replaced the Master cylinder about every 8000 miles and the slave every 15,000. I have added a heat shield but haven't driven it enough to tell if it is going to make a differance. I have chalked it up to a bad design and just keep extra cylinders around just in case. I would have thought Backdraft would have fixed the problem by now.

[bobinyelm]

Hey, I'd be grateful to get 8000mi.

Under 10 miles is a bit depressing!

I located another thread saying that it's not unusual for them to act up when hot, only to work perfectly again when they cool.

I spoke w/ my BDR dealer and he said he's replaced cylinders on virtually all that he's owned (he kept one for himself) and sold, so at least I am not alone. He said my idea of a cold-air blower may be a permanent solution, though on another thread, someone fixed the problem by re-routing just the line from the master to the slave.

Just curious, my reservoir is on the master WAY under the fender (tough to reach to fill), but I saw one pictured with a remote reservoir. Did any of them come that way, or was that a mod?

Bob

Bob

[jhv48]

So, if I get this right.

Clutch operates fine when cold but fails when good and hot?

No visible leaks probably means one of two things.

1. Master cylinder or slave has an internal leak when the seals get good and hot allowing the hot (perhaps boiling) fluid to slip past the seals.
2. The fluid is boiling in the lines causing a loss in pressure. Try running with the electric fans on continuously. Does the problem persist?

Drain the hydraulic fluid first and see what color it is. If dark brown/black, it probably has been burned. Change to a high temp DOT 4 fluid such as Wilwood 570. If it has boiled, time for some custom heat shields.

Now drive it and see if the problem recurs. If so, then climb under the car (while the thing is still good and hot) and have a friend depress the clutch pedal. Observe the travel that the clutch fork makes (or doesn't). Is it the same as when dead cold? If not, then the M/C or slave are losing pressure internally. That will necessitate replacing first one then the other. Start with the one closest to the heat sources (headers). If that makes no change, then go to the other one. One or the other will prove faulty.

And this is not ONLY a BDR problem. I've been chasing my heat devils in an SPF for the last few weeks.

[bobinyelm]

Originally Posted by jhv48

So, if I get this right.

Clutch operates fine when cold but fails when good and hot?
Yep.

No visible leaks probably means one of two things.

1. Master cylinder or slave has an internal leak when the seals get good and hot allowing the hot (perhaps boiling) fluid to slip past the seals.
Yes, bypassing master seal was my first thought.
2. The fluid is boiling in the lines causing a loss in pressure. Try running with the electric fans on continuously. Does the problem persist?
Could be, but hood was open when this occurred, and car hadn't been driven that day-only idled for under 10 minutes. Another thread showed someone made new lines and routed them differently. I need to PM him to see if it cured his problem.

Drain the hydraulic fluid first and see what color it is. If dark brown/black, it probably has been burned. Change to a high temp DOT 4 fluid such as Wilwood 570. If it has boiled, time for some custom heat shields.
Color is normal (sample from master reservoir).
Fluid is DOT 4, and installed less than 10 miles and maybe 30 minutes engine-run-time ago (that's the total mileage on the Cobra since assembled). Is Wildwood DOT 4 fluid a much higher temp fluid than normal DOT 4?

Now drive it and see if the problem recurs. If so, then climb under the car (while the thing is still good and hot) and have a friend depress the clutch pedal. Observe the travel that the clutch fork makes (or doesn't). Is it the same as when dead cold? If not, then the M/C or slave are losing pressure internally. That will necessitate replacing first one then the other. Start with the one closest to the heat sources (headers). If that makes no change, then go to the other one. One or the other will prove faulty.
[color="red"]Yes, when I get it down from jack stands, I will drive it again. I no longer have a lift, so getting it up to see the fork move is time-consuming, but worthwhile.
I doubt the slave is the problem (if it's heat related) only because it likely did not get hot w/ the engine just idling under 10 minutes, especially w/ the hood open and cool air rising up past it.

And this is not ONLY a BDR problem. I've been chasing my heat devils in an SPF for the last few weeks.
A LOT of heat up under these cars! A small fan mounted behind the side grill blowing in continuously wouldn't hurt both master cylinders.
My car has the BDR heat shield, but hot air can rise past a heat shield.

Thanks-Bob

[CobraEd]

Replace all that mess with a cable and it will work perfectly forever !!!


.,

[jhv48]

Bob, don't sample the fluid from the M/C end. Open the bleeder valve on the slave and let it slowly drip into a glass bottle. Then check the color. That is where the heat will get to the fluid the fastest. You won't need to bleed the system if the bleeder is on the top of the slave and the master is higher than the slave. Gravity will cause it to flow without any air entering the system.

And, yes, Wilwood fluid will boil at 570 degrees dry where normal DOT 4 fluid can boil at 446 degrees dry. Big difference.

[Gatorac]

The heat related issues most common are not a first start issue. They are a long term issue. You may have a bad M/C from the get go or something is wrong with the clutch itself. When I had my clutch issues the first year, it started gradually over the course of a 30 mile trip. The master was leaking inside. The fluid was cooked. I replaced the M/C and slave. I have over 12k miles and 5 years on that same M/C and slave now. All I do is bleed every 6 months. I have no heat shield. Reg moved my line to the top of the foot box a couple of years ago and it made no difference in the color of my fluid at my normal 6 month bleed interval.

To get the right angle (or non-angle) on the rod from the slave, I welded a washer onto the clutch arm in the correct spot.

The slave is from the Mazda pickup. The M/C is a Wilwood part available from any Wilwood dealer. I don't remember the size but it should be stamped on the M/C itself.

[bobinyelm]

Originally Posted by jhv48

Bob, don't sample the fluid from the M/C end. Open the bleeder valve on the slave and let it slowly drip into a glass bottle. Then check the color. That is where the heat will get to the fluid the fastest. You won't need to bleed the system if the bleeder is on the top of the slave and the master is higher than the slave. Gravity will cause it to flow without any air entering the system.

And, yes, Wilwood fluid will boil at 570 degrees dry where normal DOT 4 fluid can boil at 446 degrees dry. Big difference.

Man, if the fluid boils and is destroyed after 10 miles and a total of 30 minutes engine run-time, it would see, that there are more design problems present than
switching to a new fluid type will cure.
Reaching over 446 degrees where fluids are present is pretty shocking, not to mention the brake master cylinder parts and fluid!
Do people suffer brake failure frequently as well, or is that why DOT 5 silicone fluid is used for the brakes?

[bobinyelm]

Originally Posted by Gatorac

The heat related issues most common are not a first start issue. They are a long term issue. You may have a bad M/C from the get go or something is wrong with the clutch itself. When I had my clutch issues the first year, it started gradually over the course of a 30 mile trip. The master was leaking inside. The fluid was cooked. I replaced the M/C and slave. I have over 12k miles and 5 years on that same M/C and slave now. All I do is bleed every 6 months. I have no heat shield. Reg moved my line to the top of the foot box a couple of years ago and it made no difference in the color of my fluid at my normal 6 month bleed interval.

To get the right angle (or non-angle) on the rod from the slave, I welded a washer onto the clutch arm in the correct spot.

The slave is from the Mazda pickup. The M/C is a Wilwood part available from any Wilwood dealer. I don't remember the size but it should be stamped on the M/C itself.

What fluid are you using (Regular DOT4 or Hi-Temp Wilwood DOT4) when you you mention no difference in the fluid color now.

When you first changed the components, was your fluid black as JHV says to possibly expect?

Bob

[Gatorac]

I use Wilwood 570 as it is what I have on hand from my race car.

Fluid is always very nasty after 6 months. My "no difference in fluid color" reference was to that fact that moving the line had no effect and the fluid is still just as nasty after 6 months.

You won't cook the fluid in 10 minutes. Something else is up.

[jhv48]

So, just how long does it take to boil the hydraulic fluid?

Just sitting and idling with no air circulating in the engine compartment is more than enough time to boil the fluid. The headers can reach temps much greater than the boiling point of most brake fluids if not shielded from radiating their heat directly onto a metal hydraulic line. Shoot a laser temp gauge directly onto the line after the car has been idling for ten minutes and see what the exterior temp reads. You may be surprised.

And, once the fluid is boiling, your clutch becomes useless until the fan comes on and blows some air on the lines to reduce the temp or you take the car for a drive and the air circulating around the engine brings the temp down.

That's why so many of these cars have troubles when stuck in traffic but operate fine once on the hiway.

Don't rule out the m/c just yet either.

[bobinyelm]

Originally Posted by jhv48

So, just how long does it take to boil the hydraulic fluid?

Just sitting and idling with no air circulating in the engine compartment is more than enough time to boil the fluid. The headers can reach temps much greater than the boiling point of most brake fluids if not shielded from radiating their heat directly onto a metal hydraulic line. Shoot a laser temp gauge directly onto the line after the car has been idling for ten minutes and see what the exterior temp reads. You may be surprised.

I am sure you're right, and maybe having the hood open was not a better way to try to encourage airflow. Maybe hood down with the radiator fan on would have been better.

I repeated the experiment tonight (engine idling, hood open) and tonight no problem-clutch as smooth as butter.

I did notice that even with the two BDR shields in place, the vacuum brake booster and the short brake line runs from the brake master through the inner fender were too hot to touch in 5 minutes flat.

The shields were burning hot, and despite being silver (low emissivity), were radiating an amazing amount of heat up at the hydraulic cylinders. I may try to find some of the thin wool insulation with silver foil on on side (often sold for firewalls, transmission tunnels, or undersides of hoods) to mount foil-up on top of the shields to cut down on the radiation.

The idea of putting some kind of fan in there blowing cool air in (or hot air out of the side grill) makes more sense than ever to me as well.

And, once the fluid is boiling, your clutch becomes useless until the fan comes on and blows some air on the lines to reduce the temp or you take the car for a drive and the air circulating around the engine brings the temp down.

That's why so many of these cars have troubles when stuck in traffic but operate fine once on the hiway.

I didn't know that was a problem until these postings, actually.

Don't rule out the m/c just yet either.

Yep. Nothing's off the table. Strange that whatever happened last time didn't happen tonight, though the outside air temp was 15 degrees cooler than the last time.

Bob

[jhv48]

I had to fabricate metal heat shields with reflective heat tape on one side to shield my hydraulic lines from the heat of the headers. Actually wrapped the last foot to the slave in a high temp sleeve.

You might have to do the same. A few pieces of sheet metal from Home Depot and a Dremmel with a cutting wheel can make great heat shields when covered with reflective heat tape on one side to reflect the radiant heat away from the hydraulics.

You might have to replace the m/c just because the heat has partially destroyed the rubber seals. Don't replace the master till you reduce the heat first, or you'll kill the new one too.

[bobinyelm]

I guess the slave gets more heat as the engine heat is sucked out of the bottom of the engine compartment when moving down the road, while the master gets more heat when the car is not moving and the heat is rising straight up at them.

I would maintain that it's a poor design if a master can be killed in 30 minutes of engine-run time.

I'm amazed that manufacturers haven't engineered this out by now. Cobra kits have been out there for decades.

Where did you find a small reflective sleeve for the slave flex-line?

Too bad they don't make master internals of hi-temp silicon rubber, then use DOT 5.1 (boils at 518 deg F), or the Wilwood EXP 600 Plus hi-temp fluid that they say boils at 626 degF ( http://www.wilwood.com/BrakeFluid/BrakeFluid.aspx ). Now I just need to find a supplier. Maybe call Wilwood and see what temp their master cylinder internal parts are rated at.

We can't be the only application where heat is such a factor I would think.

Anyone using the 7/8" Tilton clutch master cylinder for a shorter pedal throw w/ remote reservoir? Seems like having the reservoir where it would be easy to check and fill would be an improvement? http://www.tiltonracing.com/ins/98-1230.pdf

Bob

[jhv48]

It affects some, and others slide by without any problems. I think it depends on the engine and the tune of that engine. Higher performance engines tend to create more heat in the engine compartment.

I got all my heat shield material and Wilwood brake fluid from Summit Racing. They have the sleeves, and sheets of adhesive backed reflective tape and insulating tape. I have my new m/c sitting on my bench waiting to see if my heat shields and high temp fluid have solved my problem. Will know for sure tomorrrow. Supposed to be a hot day here in So. Cal so I'll go get stuck in traffic and see what happens. I do know that if I leave the radiator fans on while stuck, the problems disappear.

Good luck with yours. Solve it now, while the temps are relatively low in Texas or summers will be hell.