Chevota clutch slave

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ijonesinsp

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Hello all,

So I have a '74 FJ40 I am installing a 350/SM420 into and have run into the clutch engagement/disengagement problems that have plagued many trying to use the stock Toyota hydraulics. My question is this: are any of you running a hydraulic throwout bearing on your setup? In the little research I've done, with the right throwout, you could gain enough stroke to allow you to use a stock Chevy clutch.

I also have read you can use a single stage brake master from a '70 or earlier rig, but I may run into potential over extension of the slave with the excess fluid.

Keep in mind I'm obviously not a purist and I am looking for the most reliable setup.

Thanks,
Ian
 
B y r o n

B y r o n

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"My question is this: are any of you running a hydraulic throwout bearing on your setup?" Yes!

But before going to my present setup I was running the factory hydraulics with my 350 factory 3 spd and it worked fine once I solved the clutch fluid boiling in the line. Using the right parts will allow it to work. You didn't post any info on the parts you're using or provide any photos to allow others to see where things might be going wrong for you.

My current setup is 350 and NV4500 and hydraulic throwout bearing. It requires additional fluid to get enough throw/movement and I used an early single brake reservoir to accomplish it.

Show/tell us what you have and what problem(s) you are having.
 
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ijonesinsp

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"My question is this: are any of you running a hydraulic throwout bearing on your setup?" Yes!

But before going to my present setup I was running the factory hydraulics with my 350 factory 3 spd and it worked fine once I solved the clutch fluid boiling in the line. Using the right parts will allow it to work. You didn't post any info on the parts you're using or provide any photos to allow others to see where things might be going wrong for you.

My current setup is 350 and NV4500 and hydraulic throwout bearing. It requires additional fluid to get enough throw/movement and I used an early single brake reservoir to accomplish it.

Show/tell us what you have and what problem(s) you are having.
Perhaps I left a critical part out: I am still in the research phase of this conversion and I’m trying to do it once instead of assemble/disassemble/repeat. I have all my parts ready to go together minus the clutch setup and I’m trying to figure out what throw out would allow me to use a stock Chevy clutch.
 
Downey

Downey

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Stock Chevy clutch requires .500" of travel (at the bearing) to disengage, the stock Toyota hydraulics only produces .420" of travel, that's why Downey makes a Chevota specific clutch that only takes .375" of travel to disengage- - -just saying.
 
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bikersmurf

bikersmurf

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Downey’s clutch would be a sale bet, and avoid possible problems. Since this clutch didn’t come with my DOWNEY conversion kit in ‘96, I followed the instructions that were with that kit and it’s still reliable & going strong in 2021.

In 1996, I used an 11” low diaphragm LUK clutch. With the stock master & slave in my July ‘74 Fj40, and a braided SS clutch line, I’ve never had any problems.

My pedal is reasonably light, and 25 years I’ve never had any problems with throw out clearance/adjustment. Years ago I found all the different bore specs, and discovered that the ratio in my ‘74 was biased to allow slightly more travel. Meanwhile, it doesn’t have a heavier pedal feel than stock.

Based on what I’ve read, the pedal is significantly heavier if a 1” brake master is used in place of the clutch master. Now for some an extra 30-40% more force wouldn’t matter… but my left knee was described as that of a 95 year old in 2002. I’ve got at least another 11 years before they’ll replace it, so lighter is definitely better.


My $0.02 on a hydraulic throw out bearing:

1) if it fails you’re going to have to pull the trans or engine to fix it and it’ll likely spill oil on the clutch. Whereas, a conventional slave will need to be replaced every 10 years (or so), but it is quick and easy to repair in your driveway or the side of the road.

2) if it doesn’t work out, you’ll need to pull the transmission to change it to something different.

3) initial cost will be much higher… although the design is simpler.

4) I have no personal experience with one… just know that stock can work for 25+ years behind a 350 on one clutch.
 
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Downey

Downey

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^^^^^bikersmurf got away with the LUK because it only takes .400" of travel to disengage, and the Toyota hydraulics produces .420" of travel (at the bearing). Problem with the LUK is you are out at the ragged edge should the hydraulics have any wear/leakage/damage/loss of travel, sooooo congrats on your 25 years with LUK.
 
h82crash

h82crash

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Stock Chevy clutch requires .500" of travel (at the bearing) to disengage, the stock Toyota hydraulics only produces .420" of travel, that's why Downey makes a Chevota specific clutch that only takes .375" of travel to disengage- - -just saying.
It depends entirely on the lever ratio of the throw out fork and total throw at the cylinder. I don't know for sure, but the travel could vary from vehicle to vehicle. My stock hydraulics give me a full inch of travel at the cylinder. If your fork has a pivot ratio of 2:1 which is the factory fork for the NV4500, it will give you 1/2" of throw at the bearing. It takes some measuring and simple math to figure out. Then some fabrication to get it all to fit. I wouldn't expect everything to be a bolt on approach for my custom application. But, if money is no object...

BTW, mine is also a 74, maybe Smurf is on to something for longer throw.
 
bikersmurf

bikersmurf

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^^^^^bikersmurf got away with the LUK because it only takes .400" of travel to disengage, and the Toyota hydraulics produces .420" of travel (at the bearing). Problem with the LUK is you are out at the ragged edge should the hydraulics have any wear/leakage/damage/loss of travel, sooooo congrats on your 25 years with LUK.
Which year and combination of parts produced .420” of travel?

I’ve tried to find Clutch M/C & slave specs with limited success. SOR no longer seems to have them. All I found was there are at least two slave bores… 13/16” and 3/4”.

This would seem to indicate ‘74 had the smaller 3/4” bore (which is what I also remember):
EC2F5366 3D79 4AD6 B695 A821789ECC83


I found references to earlier ones having a smaller bore, but no specs as to which are which bores.

As far as I could tell, clutch M/C bores were all 3/4.

I believe the more rigid braided SS line also helps travel. I don’t remember the exact specs, but I had no trouble getting more than enough free play before the bearing touches the clutch diaphragm fingers. The clutch is also fully disengaged by the time the pedal is 1/2 way down.

I mention these things do that others can learn from my own experience. Also, because I get tired of being told I’ve done it wrong… when I followed the instructions given, and it has worked great for 25 years now. Back in ‘96, there were magazines, catalogs, and instructions that came with parts/kits. Aside from that, you were on your own to figure it out. Mud wasn’t around, and the internet barely existed. So we figured it out, and made it work with what we had.
 
h82crash

h82crash

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Yes, I remember doing custom mods before the internet. You needed to find very experienced, local, people who knew parts interchange like breathing, and magazine articles.
 
bikersmurf

bikersmurf

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If it only works with a LUK clutch, then I was very fortunate… the conversion instructions said to use a, “…standard 11” low diaphragm type Chevy clutch”. Back in ‘96 it took a lot of searching to find what that translated into. With no year, make, and model most parts desk jockeys were useless. It wasn’t until I found an older parts person that I found answers. He walked into the back and came back with the LUK clutch that’s still in there today. It outlasted the first $300 runner, and is now onto the next.
 
bikersmurf

bikersmurf

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I’m too tired to do the math, but 1/16 less bore = less area = more throw. My belief is that’s why my setup has worked so well. That and a more rigid line that doesn’t stretch has made it work.

My cruiser experience has been that way. The only good runner engine I could find in ‘96 had the right manifolds. The pitman arm from the donor car fits the P/S conversion I’m doing now, and the random Toyota pickup TRE that I’ve had in my parts pile for 15+ years fit said pitman arms taper. That TRE is about 5” longer that a 40 one, so it’s just the right length to connect to the stock 40 Tie Rod without modifications. And that’s how it goes… now I’ve got a TJ rear bench that will fit inside the tub with about 1/2” clearance on both ends.
 
h82crash

h82crash

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I’m too tired to do the math, but 1/16 less bore = less area = more throw. My belief is that’s why my setup has worked so well. That and a more rigid line that doesn’t stretch has made it work.
That would be true if the slave was the smaller bore. If the master is smaller, then less throw and less effort.
 
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ijonesinsp

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Well, I have the cast fork, pivot ball and bell housing that came with the SM420. The only hydraulics I have are the original Toyota, which I believe are 3/4" but I would have to check. I guess I am weighing out my options of whether I should:
(a) buy a low throw clutch and use stock hydraulics,
(b) buy an appropriately sized hydraulic T/O bearing and use the Chevy clutch I have or
(c) use a combination of Toyota/GM/whatever else to make it work.

I really appreciate your help on this!
 
bikersmurf

bikersmurf

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That would be true if the slave was the smaller bore. If the master is smaller, then less throw and less effort.
As far as I can tell the M/C are the same bore, and the slave bore for the three finger clutch is slightly smaller (and thus more throw).
 
bikersmurf

bikersmurf

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Well, I have the cast fork, pivot ball and bell housing that came with the SM420. The only hydraulics I have are the original Toyota, which I believe are 3/4" but I would have to check. I guess I am weighing out my options of whether I should:
(a) buy a low throw clutch and use stock hydraulics,
(b) buy an appropriately sized hydraulic T/O bearing and use the Chevy clutch I have or
(c) use a combination of Toyota/GM/whatever else to make it work.

I really appreciate your help on this!
If your Chevy clutch doesn’t have low fingers I t’s a no go for this application.

The easiest option would be to use a low throw clutch.
 
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ijonesinsp

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If your Chevy clutch doesn’t have low fingers I t’s a no go for this application.

The easiest option would be to use a low throw clutch.
It doesn’t and that was the main reasoning behind the internal slave. I always like using parts I can source locally, but it seems somethings gotta give no matter what route I take.
 
bikersmurf

bikersmurf

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Remember the KISS principle that these trucks are built upon. 95% of the work on them can normally be done with a 10mm, 12mm, 14mm wrenches, and basic hand tools. Get too far away from that principle and it’ll loose it’s charm.
 
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ijonesinsp

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Remember the KISS principle that these trucks are built upon. 95% of the work on them can normally be done with a 10mm, 12mm, 14mm wrenches, and basic hand tools. Get too far away from that principle and it’ll loose it’s charm.
I have a lifelong plague of overthinking things...at least I asked for advice first on this one!!!
 
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peesalot

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FWIW my stock 70 master & slave work fine on my 6.0/sm420 combo with LUK clutch. Don't know what the LUK clutch is spec'd for , I called Georg, told him what we were building and he gave me the part# for the LUK to ise, simple.
 

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