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MG Midget and Sprite Technical - Clutch pipe diameter

Ordered a new solid clutch pipe , for master cylinder to slave cylinder . The new pipe is the same diameter as brake pipes 3/16 inch diam ?. The pipe on the car looks like 1/4 inch Diam ..What is correct and what needs to be altered to solve it.. Thanks Roy
R Mcknight

Roy, Depends on the year. 948, 1098 cars had the smaller 3/16 pipe plumbed directly into the slave cylinder.

1275s have the 1/4" pipe plumbed to a rubber flex hose with a 7/16 fitting into the slave. If you have a 1275 1" slave cylinder, then you need the hose, and thence the larger pipe which gets reduced at the master to the usual 3/8 fitting.

If you have an early car with a 1275 engine/transmission/slave cylinder, not uncommon, then you should use the larger tubing. Helps with pedal effort.

Peter
Peter Caldwell

but fitting it directly to the slave instead of through a hose saves the hasel of replacing hoses!

just coil up the last bit to dampen out vibrations and you will be fine
Onno Könemann

I don't believe the larger bore hose helps with pedal effort and in fact the BBS had a long debate about this a while back (unless it was the Spridgets list). I converted my car from the 1/4 line to the 3/16 without problems but can't give a specific comment on the pedal effort as I undertook other conversions at the time (co-ax slave on a type 9 box). The pedal effort should be directly related to the master/slave though I'm open to being proved wrong and learning something new.

Daniel Thirteen-Twelve

I am also of the same opinion as Daniel on this one, how do you think that a larger bore pipe helps the pedal pressure Peter?

The effort required must be directly proportional to the master/slave cylinder diameter ratio isn't it?

To get back onto thread what is the problem with your clutch Roy that makes you want to change the pipe?
Robert (Bob) Midget Turbo

Roy at you at Silverstone Friday or Saturday - I might still have my 1/4 pipe that I don't plan on going back to.
Daniel Thirteen-Twelve

Hi .Thanks for the replies , No will not be at Silverstone as i spend my summers in Spain ..I am converting the car to LHD . It has a 1275 and a 5 speed conversion . The clutch pipe goes straight to the slave with no Flexi . Ordered a LHD clutch pipe and the small size arrived , Think i may have problems getting a new large bore pipe made up in spain so i may have to stick with a small bore and make it fit . Is there an adaptor on the master cylinder that can be removed to allow the fittment of a small bore hose ?.
R Mcknight

Roy if I remember correctly yours will be a tandem cylinder. That I think takes a 3/16th normal brake pipe directly into the fittings at the rear. However some have an adapter fitted that converts that to 1/4 pipe. Some also have banjos fitted that can either take 3/16 or 1/4 pipe. What is yours fitted with, a picture will help.
Robert (Bob) Midget Turbo

Clutch systems move more fluid than properly set up brake systems. The large bore pipe has no effect on pedal effort, but it does affect the speed of fluid motion in the pipe, thus the clutch release rate. The theory was that the clutch should release and engage instantaneously. If you push the pedal down very quickly it will feel harder than a slow push with a smaller pipe, and on release will allow very fast clutch engagement. It is questionable whether most drivers would ever notice the effect, but some manufacturers now use a big pipe for quick clutch release, but fit a return restrictor to limit driveline shock on quick engagement. (found that whilst researching aftermarket high performance hydraulic systems) So, guys with high power, heavy foots, and weak drivelines (Spridget half shafts?) might want to consider such.

FRM
FR Millmore

So with the bits i have .I need to use a tandem cylinder with a 1275 slave , can i use a 3/16 pipe and a flexi into 1275 slave cylinder. Or will 3/16 pipe go direct into the slave .. Is the pipe size different on 948 /1098 cylinders to 1275 cylinders? .It all worked ok before i took it apart.
R Mcknight

Roy I assume you have the tandem master cylinder that you must have removed? mot sure if all the slave cylinders took the same size fitting. My MGA takes the 1/4 inch pipe so perhaps an early Spridget is the same? however test the fixing in the slave to see if it is for 3/16 or 1/4. It is better to have a flexable pipe to the cylinder but if the cylinder sizes vary then you will need to specify the correct size. Do you want to put a photo up of your cylinder?
Robert (Bob) Midget Turbo

Hi Robert ..Stripped out master cylinder and there is a union to go from 3/16 to 1/4 pipe ..Taken it out and 3/16 pipe goes in Ok ..So just need to match up slave cylinder end .
R Mcknight

The 1" slave cylinder on a 1275 takes the flexi hose fed by a 1/4 pipe. The fitting into the hose for the 1/4" pipe is 1 7/16-20 thread with the 1/4" single/bubble/ISO flare. The other end of the flexi hose is a straight thread into the slave cylinder utilising a copper gasket.

The earlier 948/1098 7/8" slave takes the rigid 3/16" pipe and uses the common single/bubble/ISO flare.

In short, the small pipe will not fit into the late slave cylinder, nor will it fit into the flexi hose.

The best solution is a new 1/4" pipe with a 7/16"-20 thread and bubble flare on each end.

Why not just get the right one?

Peter C
Peter Caldwell

Hi Peter ..I am trying to make do with the parts i have , i cannot source 1/4 tube locally , it means sourcing from the UK with the time implications of ordering and shipping .Roy
R Mcknight

This thread was discussed between 08/07/2009 and 11/07/2009

MG Midget and Sprite Technical index

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