TR2/3/3A TR3 clutch slave cylinder

[TFB]

I didnt get a slave cyinder with my car,and have seen 7/8" new repalce ments and 1" bore "original type".
Was the bore originally 1",and are the 7/8" a suitable relacement?
Thanks
Tom

 

[Geo Hahn]

Moss shows a 1' slave for the TR3-4 (p/n 580-760) and a 1 1/8" for very early cars (p/n 580-750). Both are item 53 here:

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29130&SortOrder=70

Yes, I seem to recall someone has a 7/8" for sale (VB?) though I see no advantage in that.

 

[TR3driver]

The 7/8" will give you a softer clutch pedal, and more travel (possibly even so much travel that the clutch does not release fully). Unless that sounds attractive to you, I'd stick with the original size. The 7/8" cylinders are from later TR6, and they have all sorts of clutch problems.

 

[TFB]

Randall and Geo,
Thanks forbreplies and link.
Tom

 

[Moseso]

It's so rare for Randall to miss on one, that I just have to comment...

Smaller bore slave cylinder = harder pedal, longer excursion at the slave piston, more CLUTCH movement.
Larger bore slave cylinder = easier pedal, shorter excursion at the slave piston, less CLUTCH movement.

Worth mentioning, also, are the three holes where the slave rod clevis can attach to the clutch throwout lever. I found they're not all really usable, due to the angle that this can create where the rod enters the slave cylinder, but:
Lowest hole = easiest pedal, least clutch movement.
Highest hole = hardest pedal, most clutch movement.

Mine is in the lowest hole and there is PLENTY enough movement to release the clutch.

 

[TR3driver]

It's so rare for Randall to miss on one, that I just have to comment...

Moseso is, of course, entirely correct! I must've been tireder than I thought ... was thinking of what happens with a smaller bore <span style="font-weight: bold">master</span> cylinder rather than slave.

But I still feel this is a bad place to be making "improvements", since the stock setup works quite well.

Also, my opinion is that the hole in the lever should be chosen strictly to get the best alignment between pushrod and slave cylinder bore. Misalignment here will cause side force on the slave cylinder and lead to more rapid wear; plus the extra friction will tend to negate any advantage from the slight change in ratio.

 

[TFB]

Again,Thanks for all the replies.Lots of good info here.
Tom

 

[luke44]

Hi guys, see my other thread I have going on this topic. https://www.britishcarforum.com/bcf...tion-Adjustment-of-TR3A-Clutch-Slave-Cylinder

I just crawled back up from the car, I didn’t shorten the rod. My problem is I need to have the throw out bearing preloaded quite a bit before the clutch action disengages and allows easy shifting. Regardless of rod length the throw - ie amount of movement- has to be controlled by the fluid being displaced. It appears to be a 1” dia cylinder. Wouldn’t a smaller bore result in more movement?

ive been working the pedal with the boot off. The piston travel (system is well bled, good pedal feel) is about 5/8”. This just isn't enough to release the clutch unless I have the preload.

So so the idea of somehow getting more movement seems to be exactly what I need. Step one is to move to the center hole from the bottom one. That still isn’t enough.

And maybe step 2 is the longer throw slave cylinders? I honestly don’t know wht else to do. Could this be related to the faulty clutch master cylinders of a few years ago?

 

[CJD]

So, the next question is, what year/style master are you running?

Randall would know the actual diameters, but, from my limited experience...

My TR3A had a smaller MC diameter which went to the longer (and smaller diameter) slave cylinder.
My TR2 uses a larger MC bore and a fat, short slave.

Either of the above arrangements gives about the same throw, but if you mix a later MC with an earlier slave, you cut the throw.

 

[luke44]

I was also wondering if that’s where I should look, and not the slave.

In that regard, if I lengthen the master cylinder rod length will that cause more travel to take place in the slave when the pedal is depressed? It looks like I have a 1/4” of longer throw I can adjust in.

 

[STeve 1958]

My clutch engages at about half way. If you're at full pedal and not disengaged, there is something wrong. That 1/4" at the master cylinder will give you a couple inches at the end of the pedal, so I'd try that first. Just make sure you still get fully disengaged when your foot is off the pedal.

 

[TR4nut]

Jerry (texasknucklehead) may chime in on this - but beware using a longer throw slave. On a car he recently worked on clutch disengagement was a real mystery. Until he studied it and found the slave was actually moving too far and doing that the pressure plate was actually recatching the clutch disk. A real headscratcher until he sorted it out.

I believe the 3A master cylinder is 3/4", the slave is 1". Steve's thoughts sound good to me, especially if you've adjust to the specified free play at the slave.

 

[luke44]

Just to bring this thread full circle for those who may search later, I finally got everything working, with my original parts.

I moved the slave back onto the engine side of the mounting plate - the trans side mounting I'm pretty sure is for the TR2 Lockheed setup. Then after a full bleed, I selected the center hole for mounting the clevis instead of the bottom hole. That combination seemed to do the trick, albeit just barely, there is still a slight bit of fight mainly going into non syncro first.

I did speak to BPNW who make the extended throw slave. It's all about fluid displacement, so cutting rods etc really doesn't help you. They achieve the longer throw by going to a 7/8" dia bore, which moves the rod 30% further. So why would you ever need this I asked? He asked if I had a new pressure plate and clutch - yes. So the needed distance to disengage is at its greatest after all new parts. Then he asked if I'm using silicone fluid - yes. They believe silicone is more compressible than Dot 3-4, and hence needs a bit of a further throw. Add in the tolerance of all the repro parts today and there are enough variables that it may be right on the edge. All in all, it made sense to me. I'm going to order the longer throw slave - it's very quick to install so I'll know pretty quickly it's effect. As the car gets broken in, it should all come together. Thanks as always for the great feedback.

 

[CJD]

Thx for the update! My TR2 disengages in the last inch of travel. My Vette in the first inch. It drives me nuts switching between the 2.

 

[Snowkilts]

I'm going to order the longer throw slave - it's very quick to install so I'll know pretty quickly it's effect. As the car gets broken in, it should all come together. Thanks as always for the great feedback.

Hey, did you try the 7/8 bore slave? I just got my clutch back together with all new parts and I'm having a similar issue of the clutch failing to disengage.