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I have always had a brake pedal that travelled  further on the first push than the second, and 

I always put this down to pad knock back.

I now have the substantially thicker non tapered stub axles, and belive me, these aint flexing, yet the pedal remains the same.

Over the last two/three years I've changed, as a matter of course everything in the braking system, and the pedal is essentially the same,

so what causes this?

John.

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Hello ,
Is your pre-pressure valve working?
If not, install a new one. (Accessories willwood ect.)
And you already have a short pedal travel.

I wish you success
Ralf

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Afternoon John hope you fit and well and getting it in the TR. hope you get lots of helpfully answers to this post as I have the same problem. I first thought it may be my servo so by passed it but still had the same problem, I have had it since I got the car some 12 years now, and as you most things have been replaced ( but not the per-pressure switch) if you have not changed yours I’ll let you do yours  first, if works I’ll change mine. Hope to see you soon on an event.

Mike Redrose group (Brenda)

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1 hour ago, John Morrison said:

I have always had a brake pedal that travelled  further on the first push than the second, and 

I always put this down to pad knock back.

I now have the substantially thicker non tapered stub axles, and belive me, these aint flexing, yet the pedal remains the same.

Over the last two/three years I've changed, as a matter of course everything in the braking system, and the pedal is essentially the same,

so what causes this?

John.

John/Mike- if you have fitted repro new calipers, many people have found them to be the culprit - apparently the piston seals are not as flexible as OE ones and hence develop a "memory" of their earlier position so your first prod of the pedal takes this "gap" up, and then you are OK - some people have found pumping up the brake pedal as hard as it will go, and then wedging it in place to hold the pressure overnight or even longer appears to improve things, possibly because the continual pressure forces the cailper seals to adopt a new "memory " position - it doesn't cost anything so worth a try! Good luck

cheers Rich   

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3 hours ago, John Morrison said:

I have always had a brake pedal that travelled  further on the first push than the second, and 

I always put this down to pad knock back.

I now have the substantially thicker non tapered stub axles, and belive me, these aint flexing, yet the pedal remains the same.

Over the last two/three years I've changed, as a matter of course everything in the braking system, and the pedal is essentially the same,

so what causes this?

John.

Have you pressure bleed the system 

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Hello John

Are you still ‘ getting it’ in the TR as Mike ( Brenda) enquired? :lol: ( I’m sure that was a grammatical error- you’d certainly need to be fit and well!):lol:

I doubt very much if even standard stub axles would flex. Pistons don’t normally fall back as under the right circumstances there won’t be any reverse force greater than that applied by the retention of fluid against the piston or the resistance of the seal.

If you have play in the wheel bearing or run out on the brake disc ( doubt as you would experience brake judder), taking up adjustment could resolve it , as per workshop manual. 

As Pete says, rear brakes not adjusted or one of the blocks in the adjuster seized can be a culprit.

Another common reason is having the handbrake too tight, thus over-riding the footbrake adjustment. If the handbrake is holding the shoes out too far the cylinders could be travelling further than they need to each time you apply the pedal. Take off drums, service brakes/ check adjusters, slacken handbrake RIGHT OFF, check/ adjust footbrake to the last available ‘free’ turn then adjust handbrake to the footbrake.

Failing that, hydraulically, M/C may be faulty or air in system. Won’t hurt to bleed the system thoroughly anyway, just cost of a tin of fluid.

Hope that helps.

Kevin

Edited by boxofbits
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I queried this a while back on the TR6 slave cylinders, the spring in the slave seems to be omitted now, but is always shown in all the parts drawings, this would help the piston stay out and not creep back in, the clutch slave cylinder has a spring inside.

John

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9 hours ago, brenda said:

Afternoon John hope you fit and well and getting it in the TR. hope you get lots of helpfully answers to this post as I have the same problem. I first thought it may be my servo so by passed it but still had the same problem, I have had it since I got the car some 12 years now, and as you most things have been replaced ( but not the per-pressure switch) if you have not changed yours I’ll let you do yours  first, if works I’ll change mine. Hope to see you soon on an event.

Mike Redrose group (Brenda)

hi Mike,

firstly many thanks for your good wished, yes we are out and about in the Tr.

Matter of fact we had 14 cars on a group run to a members home above Ullswater for a BBQ just yesterday, quite a magical, 'Thats what its all about' day.

 

I'll keep you posted on the brake pedal travel, thingy. Trying the held down pedal overnight, tonight, as you say cheapest I.E. free ideas first.

John.

DSC04792 At The Hill, Ullswater, 25th July 2021.jpg

DSC04791 At The Hill, Ullswater, 25th July 2021(1).jpg

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If you put the handbrake on so that it's just not stopping the rear wheels, does your pedal feel improve? (just try it in an empty parking lot).

If yes then rear brake shoe pull-back is the issue. (Adjust rear brakes)

Single circuit brake pedal travel is heavily influenced by the slack in the back end.

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If there really is a need to make an adjustable pushrod, it is easy to make one

P1250345-b.JPG.3c0ddd9ffaa5e4cb8c5e4d40173855d9.JPG

The part left is called "Gabelkopf" (fork head) at Germany, thread is M8

Edited by Z320
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Being short in both legs and arms, I have always had problems in fully depressing the clutch. 

Revington offers RTR4136K, which I fitted in 2009, and this has solved my problem (well, that particular problem!).

Ian Cornish

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15 hours ago, Chris Hubball said:

I have to admit to my ignorance were is the pre-pressure switch that Ralf & Mike refer to situated, as I have the same problem ?

Cheers Chris

Only fitted to 3a/4 but only occasionally on a 4a  mounted on the 4 way brake union down on the chassis.

Stuart.

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Do the later TRs with a servo have a larger bore master cylinder?

I was thinking that would be a way of firming up the brake pedal as the a larger bore m/cylinder would push more fluid through and the servo would compensate the increased pedal pressure.

Ralph

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Ralph,

The earlier cars had a larger bore master cylinder, changed during the TR4 run from 0.75" to 0.70" . Rear wheel slave cylinders were changed from 0.75" to 0.70" around the same time. This wasn't related to any servo fitment, but to reduce pedal pressure I believe.

Mike

 

Edited by mike3md
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Many thanks all, for th ereplies.

It seems that we are looking at three areas;-

100% good brake bleed, tried allsorts in the past, and the pedal is hard, once it commes 'On' so we'll see.

Play at the pushrod, never considered this, and there is a couple of mm rock there now, which I guess translates to 10mm or more underfoot.

Back brake adjustment, I've always adjusted until solid, then backed off two clicks, but I'll certainly look again.

Cheers,

John.

 

 

918089438_holdingdownthebrakepedal..jpg.8eb8346f9c823f039cb12bf094062492.jpg

 

 

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10 hours ago, John Morrison said:

Many thanks all, for th ereplies.

It seems that we are looking at three areas;-

100% good brake bleed, tried allsorts in the past, and the pedal is hard, once it commes 'On' so we'll see.

Play at the pushrod, never considered this, and there is a couple of mm rock there now, which I guess translates to 10mm or more underfoot.

Back brake adjustment, I've always adjusted until solid, then backed off two clicks, but I'll certainly look again.

Cheers,

John.

 

 

918089438_holdingdownthebrakepedal..jpg.8eb8346f9c823f039cb12bf094062492.jpg

 

 

What number Churchill tool is that John ?

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Morning all, leaving the foot brake pushed down has not helped things, popping down to see Hamish this morning so when I get back I’ll look at the brake master cylinder push  rod to see if we have play in that area. She passed her MOT with no advisory’s, the Pedley has been like this for a long time so may just continue with it, it still stops ok.

Mike redrose group 

 

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Mike I have this problem on my own TR5 and despite doing and changing things time and time again I am just going to live with it.

On new Moss callipers I have fitted (not on my TR5) I now fit ply blocks in place of the pads and at half the thickness.Jam the brake pedal down with the ply pads in place

and leave overnight or as long as you like. This brings the pistons further out and fools the dust seals memory.After that the brake then works as it should. The seals do not seem to have the elastomer of past seals which is more of a problem of rubber or whatever they are using today.

Try it!

Regards Harry

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