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Question about fitting a larger bore clutch master cylinder


A TR7 16V

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While I've got some clutch movement back by replacing the pedal, bracket, and clevis pin, I would like to see If I can get just a little more. So I was thinking of a bigger bore master cylinder then the 5/8th (0.625)" one I have in, which will get more slave travel for the same pedal movement, but stiffen the pedal a bit.

Pete Lewis suggested a 3/4"e LR one as a cheap option, which they are. But they don't have the fork for a clevis pin. They aren't expensive either, but I don't know what thread is on the piston pushrod on the LR cylinder. The good thing there is there's an opportunity to use the thread to set the position of the pedal. But I recon that 3/4" bore will take 1.44 times the force to move the pedal, but, obviously, 1.44 times as much clutch movement. 1.44 times sounds a fair bit more force, but it's leg work and the pedal is light enough now. So I wondered about a 0.7" bore TR cylinder, which would only take about 1.25 times the force and still give me a bit more clutch movement.

So, has anybody done any such thing and/or got opinions? And if anyone's used the LR one, can they give details of the clevis pin fork I would need and how much heavier the pedal becomes? 

Graham

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I've not done that as such but when my Vitesse clutch was a bit like yours I replaced the 1" slave cylinder with a 7/8" one (1600 spec), giving about 1.3 times the movement and pedal effort. I haven't really noticed the extra effort, to be honest, but the improved operation is definitely nice.

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Ive used a 0.75 Land Rover clutch mc on my Vitesse brakes and well pleased especially with the price. The push rod thread was 5/16UNF and getting a clevis is a bit of a faff as the mc suppliers dont seem to do them! However I like being able to adjust it to take up any play. Youll lose a bit of sensitivity but I wouldnt have thought enough to affect normal clutch control...

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The last two posts seem to suggest that increasing the pedal force by 1.44 won't be that big an issue. 

In which case the next problem is to find a fork with a 5/16th thread? Lots of M8 x 1.25mm pitch.

Don't suppose anybody knows the thread on a Land Rover S2/3 handbrake link?

Graham

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4 minutes ago, Nick Jones said:

Just swap the push-rod from your original master. 1 circlip, takes under a minute…..

Nick

But then I lose the ability to adjust the pedal height. Will it naturally come to the same height with the same rod in a different cylinder?

Graham

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1 hour ago, A TR7 16V said:

The last two posts seem to suggest that increasing the pedal force by 1.44 won't be that big an issue. 

In which case the next problem is to find a fork with a 5/16th thread? Lots of M8 x 1.25mm pitch.

Don't suppose anybody knows the thread on a Land Rover S2/3 handbrake link?

Graham

These are the cheapest I can find and in long or short versions. Still annoyingly expensive when compared to metric so I was tempted to drill out and tap one of those...

https://www.ebay.co.uk/itm/370861670549?hash=item5659140095:g:cskAAOSwP4lbWcN0

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4 hours ago, Pete Lewis said:

its easy enough to swap pushrods   so long as the one you add is round holes not pre worn 

Pete

I still want to know if swapping the master cylinder and keeping the push rod will move the pedal up or down. And the holes in mine are a bit worn - the 8mm clevis I think got sold is only tight in the pedal arm, and quite slack in the fork. I do see that replacement rods with forks are available, but I think I want a slightly bigger bore. However, I'm still worrying a bit that 3/4" is a more bigger than I want.

I got a reply on the 5/16 UNF thread fork to fit the LR 0.75" cylinder, and it takes and comes with an 8mm clevis pin. I really do like the look of the pin clip it comes with. I feel like the R clip on the one I got to replace the one in the car sticks out too far and might split the boot in time.

Graham

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55 minutes ago, A TR7 16V said:

nd keeping the push rod will move the pedal up or down

on the M Clys the end cup and circlip control the foot off pedal position apart from on the brake you might use the brake light swtich and its nut 

what ever the  push rod  must let the cyl to be fully OFF regardless of where the pedal ends up without any pressure applied to the cyl.

the cyl relies on the small seal in its end closing and opening the feed to the reservoir or you dont refill after application or if its not seating loose the pedal and you just suck and blow into the resevoir , 

there are adjustable pusrods  that can be used to fine tune but normally not needed 

Pete

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On 22/08/2021 at 12:50, A TR7 16V said:

But then I lose the ability to adjust the pedal height. Will it naturally come to the same height with the same rod in a different cylinder?

Yes.  It will be the same.  I've tried most size combinations over the years and always just swap the pushrod over.  As long as the holes are not worn oval - all is good.

Nick

 

PS Current state of play in my fleet

 

Vitesse:
0.625" Brake master (std 0.7") to reduce pedal effort (at expense of a bit of extra travel)
0.75" Clutch master (std 0.625") because Toyota gearbox and hybrid clutch

GT6:
0.75" Brake master (std 0.7") because remote servo
0.7" Clutch master (std 0.625) because MX5 gearbox and concentric clutch

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15 hours ago, A TR7 16V said:

I still want to know if swapping the master cylinder and keeping the push rod will move the pedal up or down.

Graham

It shouldn't provided the body of the master cylinder is the same size as the original, and the push rod the same length. The pedal will come to rest at the same position; only the amount of travel will vary with different bores.

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