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Post by dmaxwell on Jan 13, 2021 13:48:07 GMT
Got a question about the clutch master cylinder. I've found in the service guide that the diameter is 3/4" but it does not say what the travel is. It looks like around 1.5" but without taking it out of the car I'm not really sure. Where would that infomation be? Of course, if someone here knows, that would be great!
Thanks,
David California
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Post by enigmas on Jan 13, 2021 20:42:39 GMT
Why do you need to know the travel or displacement of the master cyl? If it's original to the car...then no issues. Just ensure that when at rest the piston is fully retracted. ie. Allow a fractional amount of free play at the pedal.
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Post by Ken Nelson on Jan 13, 2021 22:30:40 GMT
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Post by dmaxwell on Jan 13, 2021 23:16:58 GMT
As I'm changing the engine/transmission in the car to an American set, it has occurred to me that if the master cylinder doesn't have enough travel to it, it won't work with the throwout bearing, hence my question. Crawling up under the dash with a measuring tape and pressing down on the clutch pedal, it looks like the rod travels about 1.5 to 2" but taking into account the thickness of the piston it may not push that much fluid down the lines.
David California
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Post by Ken Nelson on Jan 14, 2021 14:22:18 GMT
The diameter of the slave cylinder will also make a difference. Is it 3/4" as well?
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Post by dmaxwell on Jan 14, 2021 17:05:49 GMT
3/4" is correct I'm just not sure what the travel in and out is.
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Post by enigmas on Jan 14, 2021 22:46:04 GMT
This is going to be a trial and error exercise until you hit on the right combination. I went througn a similar exercise when I fitted a Triumph electric overdrive manual trans to my MG Magnette, Rover V8 powered, coupe project. To correct the mechanical/hydraulic pressure ratios, changes were made to the clutch master and slave cyls and the clutch fork ratios. Modified thrust bearing and clutch fork lever. Due to a mixed bag of components and leverages (clutch fork and pedal lengths, mechanical ratios of these, pressure plate type and hydraulic ratios of the clutch master and slave cyls which work in concert with the mechanical ratios of the various levers it's going to be an exercise requiring patience and fabrication as you vary the sizes of either the master cyl or slave cylinder to obtain the correct amount of movement through fluid volume displacement. In my view the focus should be initially on adjusting the size of the clutch slave cylinder bore incrementally rather than adapting various master cyls (which may also need to be an option to correct the fluid volume ratios.) This will provide increased movement and a slightly heavier pedal. Downsize the bore of the slave cylinder incrementally either by adapting other 'found' units or by have the bore sleeved down in size professionally. None of this type of hybrid modification is ever straight forward and it will test your resilience. Generally though, if you can mirror the hydraulic pedal and mechanical ratios of the transmission's donor car you'll be close to a viable outcome. Good luck.
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Post by dmaxwell on Jan 14, 2021 22:49:35 GMT
Thanks! It's been a long slog (much longer than I had thought it would be) but I think I'm close to the end. This coming weekend will see if I'm right or not.
David California
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Post by enigmas on Jan 14, 2021 22:58:43 GMT
Hi David, what engine trans combo are you fitting to the car?
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Post by dmaxwell on Jan 15, 2021 14:05:55 GMT
I'm putting in a Chevy 4.3L V6 with a 5 speed manual transmission. Some years ago I had hoped to used a Jag 4.2L inline 6 but it was too tall to fit into the engine compartment so I decided on the Chevy engine. As it is a Chevy 350 with two cylinders removed, parts will never be a problem. My P5 was a manual to begin with anyway so the clutch pedal and master cylinder was already there and I prefer a manual over an automatic.
David California
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Post by enigmas on Jan 15, 2021 23:33:35 GMT
All you need to do then is check the clutch pedal mechanical ratio and the clutch master cyl size to get the correct ratios for clutch disengagement and pedal apply effort.
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