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TR 4A brakes - Slack on Pushrod


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Hi all, having just finished fitting a new rear brake pipe (dont ask) I have been attempting to bleed the brakes. This has never been easy on this car and I have always had more travel than I would like however this time I resorted to the eazybleed as the manual method did nothing. So I now have brakes but still with excessive travel so I currently have I piece of wood holding the pedal down as per Stuarts suggestion on an old post with the rear adjusters tightened right up.

We will see if play is less tomorrow.

My question is, the pedal moves the pushrod about 5-8mm before it touches the piston so can a stop be put behind the pedal shank to eliminate the dead zone or could an adjustable pushrod be used as I have on the clutch master cylinder.

The car has an aftermarket Servo fitted.

Thanks in advance.

Chris

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I think there should be no dead zone. The pushrod should be in contact with the piston when the pedal is fully released (held by the spring hooking the pedal to the the box) and the pushrod isn't adjustable. You may have a problem with worn pedal shaft and bearings...

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I think there should be no dead zone. The pushrod should be in contact with the piston when the pedal is fully released (held by the spring hooking the pedal to the the box) and the pushrod isn't adjustable. You may have a problem with worn pedal shaft and bearings...

Hi the only springs I can see are "pedal return springs" IE they hold the pedals up inside the car which pulls the pushrod away from the piston.

Pushrod Pivot has been rebushed and pedal pivot bushes are ok.

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Hi Chris

 

You might just find the Master Cylinder is not as good as it was. If you have followed Stuart's advice of locking the rear brakes up, then there is very little scope for movement especially if your discs and pads are good.

 

It might be worth fitting a new seal kit to the M/C and see how it goes from there. Many classic cars have had copper brake pipes fitted and some of the shapes and lengths of replacements people put on leave much to be desired,many can have unnecessarily high loops in them that trap air. Also, If you have a brake pipe clamp go round the car and close off each brake hose in turn to see if it makes any difference to the pedal.

 

If you have a servo fitted I was taught to running the engine when bleeding.

 

Kevin

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Hi Chris,

 

If the m/c is sound, and there is little wear in the clevis/pedal hole, you might want to consider fitting an adjustable pushrod & clevis:

 

https://www.merlinmotorsport.co.uk/s/brake-clutch-parts/master-slave-cylinders/page:2

 

I did this to eradicate some of the free movement between the pushrod and the piston. The extra long pushrod can be fitted without removing the m/c, but first needs to be cut down and additional 5/16"unf thread cut to fit the TR4 setup. Remember to fit a locking nut ( half nut is best) to the back of the clevis. Don't be too enthusiastic with removing the play, or you could end up with locked brakes!

 

:rolleyes:

 

Mike

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Hi all, thanks for input.

Kevin, mast cyl is only a couple of years old as are, discs & pads & rear shoes & drums.

Anyway, the car has stood since yesterday with the rear adjusters tightened up tight and a piece of wood between the pedal and the seat jamming it down, this morning went out to car removed wood jam and adjusted rear brakes. Most of travel has gone!

That Stuart knows his stuff, sounds like smoke and mirrors but it works!

Mike,

An adjustable pushrod would remove the last bit of slack but its less than 2mm at the master cyl so will leave it for now. Maybe put on winter list. I have had an adjustable rod on clutch mast cyl for 5years+ and it works fine.

Chris

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Hi Chris

 

Glad you've got it sorted. I think a lot of the problems we get with brakes is due to the cars not being used as much as modern cars.

 

I had a problem with handbrake grip when I went for an MOT a couple of years back, and it was sorted just by de-glazing the rear shoes and drums.

 

Kevin

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Chris

I had a similar problem, found the piston was not fully returning.

Paul

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This clearance problem often comes about by the pushrods not actually being the correct one. Often when master cylinders have been replaced they arent necessarily exactly the same as the original spec which is why its always better to re-use the push rod from the original. If you only have a small amount of play and the clevis holes in the pedal and the pushrod arent oval and the clevis pin has no wear then what you can do is build up the ball end of the push rod with weld and then file up to suit. As stated though you must always make sure that the master cylinder push rod does return to rest or you will end up with the brakes jamming on.

Stuart.

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Hi Stuart, I did wonder about adding some weld but was waiting for someone else to confirm this was ok. I have an old Pushrod somewhere, I will find it and compare lengths.I put some brass bushes in the pedal holes and fitted new pins about 8 years ago and there fine.

The other thing which is a pain is the difference one click on the rear shoe adjusters makes. As I have the rh side its well free but I tried it up just one flat and although I could turn the wheel fairly easily after a 5 mile run the drum was too hot to hold your finger on.

LH side was warm but touchable.

Chris

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Get your drums checked by someone with a lathe for any ovality and if required just have them skimmed slightly.Check your back plates for a wear spot where the handbrake lever pivots and if required weld up and grind flat again as it will stop the cylinders sliding properly.

Stuart.

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Hi Stuart, the drums were new about 3 years ago can i assume they were round then?

I did try moving the cylinders back and forth by hand and they seemed to move smoothly but I did not dismantle from the backplates. The brakes now are better thank they have ever been and ive driven about 65000 miles over the last 20 years with them not quite as good as they are now. They will do.

Thanks Chris

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  • 2 weeks later...

This clearance problem often comes about by the pushrods not actually being the correct one. Often when master cylinders have been replaced they arent necessarily exactly the same as the original spec which is why its always better to re-use the push rod from the original. If you only have a small amount of play and the clevis holes in the pedal and the pushrod arent oval and the clevis pin has no wear then what you can do is build up the ball end of the push rod with weld and then file up to suit. As stated though you must always make sure that the master cylinder push rod does return to rest or you will end up with the brakes jamming on.

Stuart.

Hi Stuart, I found the original master cyl, been in scrap bin for nearly 2 years, and removed the pushrod, its thicker a full 5/16" and about 1.5mm longer than the new one. Its now back on the car and freeplay at pushrod is now minimal.

Lesson for everyone, dont rush to throw anything away!

Chris

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Hi Stuart, I found the original master cyl, been in scrap bin for nearly 2 years, and removed the pushrod, its thicker a full 5/16" and about 1.5mm longer than the new one. Its now back on the car and freeplay at pushrod is now minimal.

Lesson for everyone, dont rush to throw anything away!

Chris

Its always the first thing I look at when changing them, glad you kept yours.

Stuart.

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