Why Hydraulic Throw-Out Bearings?

[tkb289]

OK ... got a dumb question ... why hydraulic throw out bearings? It seems like something that would be prone to leak, and not in a good place either.

Are there some motor / bell housing / clutch / transmission combinations that require hydraulic TO bearings? Are there others that don't? Do all Cobras need hydraulic TO bearings?

I am still somewhat new to this site and to be honest had never heard of a hydraulic TO bearings until recently.

Please advise ... thanks!


- Tim

[Clois Harlan]

Good morning Tim,

I wondered the same thing for awhile but I run a hydraulic throw out bearing in my 427 with a toploader transmission and I love it. The main reason I run one is space limitations for the release fork. Some of our kits are more confined than others and mine is one that probably has the most room for a release fork. I have had mine in place for over six years now and the only problems I had was with bleeding the clutch and that was my fault due to the thickness of my firewall. I was not allowing enough travel for the piston in my master cylinder. No leaks for over six years.

The other reason is effort to engage the clutch via your foot. The hydraulic throwout bearing makes it much easier to push in your clutch. Expensive little set up but I wouldn't have it any other way.

Clois Harlan

[RICK LAKE]

tkb289 It's about choice in some cases. In others it's about having room. In my ERA I have the originial setup from them with a Master and slave cylinder for the clutch system. A modified clutch fork is used in my car with a Lakewood bellhousing. Depending on the size of the clutch, 12.0" - 7.5" single or multi plate setup, it's also about how much pressure needs to be applied to release and have the clutch engage. The new clutches that are coming out are having a softer pedal and hold power of 800HP. Twin disc is the way to go. It has to be setup right or you will have the same problems as any other clutch. Quartertime has a lighter bellhousing then Lakewood by 20 lbs. They are having the bellhousing certified for SFI at this time. There where problem with some of the older HTBearings with leaks that would soak the clutch assembly and cause slipping and a bad smell. To the best of my knowledge this is a problem of the pass. Bleeding the HTB is the only problem I have heard of. The mastercylinder bore needs to be able to supply the slave with enough fluid to disengage the disc from the pressure plate cleanly. Your Car should have a pedal limiter as to not over extend the bearing. You can blow out the seals if extended too far. Again another mess. IMO HTB is better with less moving parts, easier if running certain bell housings, it automaticly adjusts to the clutch. If setup right will last with no maintainence for many years of driving. If you go racing that's another story. Rick L.

[convincor]

i'm using a CJ/Boss429 fork and TO bearing with a external slave with my top loader.
Going third season with out having to touch it.

[Mac VABCH]

I have been running a HTO bearing and will never use a slave again. Some make have better setups for there Slave cylinders but the HTO bearing has fewer parts and pieces to setup. As for leaking you have to install a pedal stop so that you don't over stroke the bearing. To bleed them most brands have a remote bleeder hose that can be routed outside of the bell housing. I replaced 4 slave cyclinders before I switch to a HTO bearing. As for how they handle the abuse of track events, my car is strickly a track car...Mac

[4pipes]

I have this Pull type slave and haven't had a problem since replacing the Mcloed 3 years ago.

http://www.wilwood.com/Products/006-...1-SC/index.asp

[convincor]

see post #9 here McLoed Hyd bearing problem...

[Roscoe]

I love my Tilton Racing HTOB. I've over 26k and ten years on that unit and it still works great. Pedal is like a VW clutch....nice and easy. Setup is critical...so is pedal stop....but once it's installed it's fuggedaboudit. BTW, I have a Centerforce Dual Friction 11" clutch.

Roscoe

[tkb289]

Originally Posted by convincor

see post #9 here McLoed Hyd bearing problem...

convincor

Read that ... Jamo does have a way with words

- Tim

[tkb289]

Originally Posted by 4pipes

I have this Pull type slave and haven't had a problem since replacing the Mcloed 3 years ago.

http://www.wilwood.com/Products/006-...1-SC/index.asp

Dave ... sounds like an interesting set-up. Next time I see you car, would like to take a peek underneath and check it out. Seems like a pretty clever solution.

- Tim

[tkb289]

To All,

Thanks for all of the info about hydraulic TO bearings, it makes a lot more sense now. Sounds like trade offs between space constraints, pedal pressure, clutch fork / throw out bearing range of motion and design philosophy.

- Tim

[David Kirkham]

Just to stir the pot a little.

We had failure after failure after failure with the McLeod throw out bearing units. We were changing them in our customer's cars at a rate of 1/month for a while. I will NEVER use one again.

I did break down on the billet chassis car we are using because of extreme space constraints and used the Tilton unit. The clutch is like a bear trap and so we just did a massive redesign to handle the external unit. There is NO comparison between the pedal pressures--the external unit is far, far easier on the leg.

The Tilton would not release the clutch without a big master cylinder. After a day on the track, I said, no way am I going to deliver this.

David

[vettestr]

David,
I am sure you looked for the reasons the throw out bearing units failed. When the dust settled do you have a thought or two why or what failed. Thanks Jeff C

[ratsnst1]

Hydolic throw out bearnging are the way to go, none of you guys mentioned that every hyd, throw, needs to be calibrated, very important, mcloed will tell you this, its a very very important issue here. mcleod, will take you thrue the process, and, you have to take measur ments then send it back to them, and free of charge will do this for you, if you guys are getting a hyd, bearing and throwing it in, sorry its a crap shoot, just call mcloed they will explain it to you, I know I went thrue it.

[ratsnst1]

as far as being easier, dave, I dissagree, as long as you follow the steps no problem, you have to calibrate every single car. just call mcleod, they will laff when you guys drop these throw out bearings in with out the measurments. calibration is free, but must be done.

[David Kirkham]

Originally Posted by vettestr

David,
I am sure you looked for the reasons the throw out bearing units failed. When the dust settled do you have a thought or two why or what failed. Thanks Jeff C

All of the units failed with bad seals. McLeod told us we couldn't use DOT 4 brake fluid as that would eat their seals. I was dumb and believed them. We then used normal DOT 3 in the clutches and they still failed. No hope. I have seen that milky, dark, nasty fluid many, many times--too many times, in fact. Many of the seals were literally eaten, crumbling, and melting.

We finally called Parker and talked to a seal expert. He told us the seals had to be ethylene-propylene that is "sulfur cured" and that most people didn't do it because it was expensive. I can tell you the seals were not as expensive as pulling the transmission.

David

[David Kirkham]

Originally Posted by ratsnst1

Hydolic throw out bearnging are the way to go, none of you guys mentioned that every hyd, throw, needs to be calibrated, very important, mcloed will tell you this, its a very very important issue here. mcleod, will take you thrue the process, and, you have to take measur ments then send it back to them, and free of charge will do this for you, if you guys are getting a hyd, bearing and throwing it in, sorry its a crap shoot, just call mcloed they will explain it to you, I know I went thrue it.

ratsnst,

Perhaps you don't know us very well. Rest assured we "calibrated" (as you say) the hydraulic throw out bearing assemblies according to McLeod's instructions. We even made a few of them in a fit of stupidity (from solid bars of aluminum).

We know a few things about measuring piston heights and relating them to the distance of the pressure plate fingers (but we are always willing to listen to anyone who has any ideas to help us along).

Please see the following thread for a discussion of our measuring and machining capabilities:

http://clubcobra.com/forums/showthread.php?t=85278

Regardless, "calibration" (I assume you mean the measurement from the face of the bell housing to the clutch fingers has to match the height of the hydraulic throw out bearing assembly within specified tolerance) is not the reason the units failed. Bad seals is why they failed. As for crap shoots, we simply did the measurements first and ordered the right piston length from the start so we didn't have to send pistons back and forth too often--I don't like shooting crap.

I still have some of those dastardly McLeod units in the shop. Maybe I'll post a pic of the nasty seals as a warning...and now you have been warned.

David

[David Kirkham]

Originally Posted by ratsnst1

as far as being easier, dave, I dissagree, as long as you follow the steps no problem, you have to calibrate every single car. just call mcleod, they will laff when you guys drop these throw out bearings in with out the measurments. calibration is free, but must be done.

I think after you pull a transmission out of a car 3 times to figure out why the seals are failing then you might change your mind. We have not had a single failure with our external units--no matter what brake fluid we put in them.

As for putting things in without "calibrations" (measuring set up distances)--I am not sure why you assumed we did that???

David

[Jamo]

Originally Posted by ratsnst1

Hydolic throw out bearnging are the way to go, none of you guys mentioned that every hyd, throw, needs to be calibrated, very important, mcloed will tell you this, its a very very important issue here. mcleod, will take you thrue the process, and, you have to take measur ments then send it back to them, and free of charge will do this for you, if you guys are getting a hyd, bearing and throwing it in, sorry its a crap shoot, just call mcloed they will explain it to you, I know I went thrue it.

Awfully damn presumptuous ain't ya.

[vettestr]

David,
I caught that you have not had a failure with the external slave cylinders. Are these units Special in the sense they are manufactured to your specs or are they shelf stock parts?