4a irs brake cylinders

[dpb]

Hello. 

 

Just been bleeding my brake system after renewing various bits, but not the rear brake cylinders.  On testing it seems that the cylinder is only pushing out one piston, the forward pointing one,  same on each side.  I'm assuming that a piston should push from both ends of the cylinder. otherwise only one shoe is moving. Is that right, or am I wrong again?

 

Cheers Dave

========

[stuart]

1 minute ago, dpb said:

Hello. 

 

Just been bleeding my brake system after renewing various bits, but not the rear brake cylinders.  On testing it seems that the cylinder is only pushing out one piston, the forward pointing one,  same on each side.  I'm assuming that a piston should push from both ends of the cylinder. otherwise only one shoe is moving. Is that right, or am I wrong again?

 

Cheers Dave

========

Theres only the one piston in the cylinder, the cylinder should slide in the back plate slot to equalise the effort to both shoes.

Stuart.

[dpb]

  I'm wrong again then!

 

Just had another look and there is no sliding anywhere.   And if it  does slide it must take the brake pipe with it, which seems odd.  

A bit of grease needed perhaps.

 

[stuart]

3 minutes ago, dpb said:

  I'm wrong again then!

 

Just had another look and there is no sliding anywhere.   And if it  does slide it must take the brake pipe with it, which seems odd.  

A bit of grease needed perhaps.

 

Yes they should slide, copperslip helps and also make sure that the handbrake lever cross pin hasnt worn a groove in the back plate as that will stop them moving and yes the brake pipe does move although its only a small amount side to side.

Stuart.

[RogerH]

Hi Dave,

as Stuart states the cylinder MUST be able.

If it can just about slide and you apply the brakes then one shoe may stay in contact   not good.

Take the cylinder out,clean the lock plates and ensure that things do move

Although it has solid pipes the movement is slight and it all works OK

 

Roger

[dpb]

Great advice as usual Stuart and Roger.   I'll have a cup of tea and have a good look again.

 

Dave

====

[dpb]

A bit of  sideways adjustment with a Brummagem screwdriver,   and I can see that indeed the handbrake pivot has worn a grove in both backplates.  New backplates I guess.

Thanks

Dave.

[BlueTR3A-5EKT]

2 minutes ago, dpb said:

A bit of  sideways adjustment with a Brummagem screwdriver,   and I can see that indeed the handbrake pivot has worn a grove in both backplates.  New backplates I guess.

Thanks

Dave.

No.
Splodge of Weld in the grooves and dress back the weld with linisher/grinder to give a smooth surface like a bought one.

New backplates (212058 & 212059) might be a tad difficult to locate these days.

[dpb]

Hi Peter

 

Yep I see a used RH one is available at Rimmers, but not a left hand.   I'll  have a go with the welder I think as you suggest.

 

Dave

 

[dpb]

It occurred to me that perhaps there is such a thing as a two-piston brake cylinder, which would on the face of it seem a good idea.   Is there such a thing for the rear brakes?

[BlueTR3A-5EKT]

7 minutes ago, dpb said:

It occurred to me that perhaps there is such a thing as a two-piston brake cylinder, which would on the face of it seem a good idea.   Is there such a thing for the rear brakes?

Yes twin piston single rear cylinders were on other Triumphs.  The nearest to fit your IRS car is from the back end of a big Triumph Saloon or Estate 2000,2.5 PI , 2500.   Stag which is slightly bigger also used that set up but is rarer in the used market.   You would need backplate assemblies and drums.  Same stud pattern as TR.   Same rear hub unit.  Handbrake cable is a tad of a challenge to adapt.

 

[keith1948]

Hello Dave

My wife's Ford Fiesta has double piston cylinders on the rear wheels. The main problem I have with those is that one piston moves first and then the second. If the car isn't subject to hard braking for a while then the second piston seizes. So having a double piston doesn't necessarily solve your problem. I have had no trouble with the standard 4A rear cylinders and sliding backplate because I check them annually and make sure everything that should move does and use brake grease or copper grease on moving parts. That includes the 3 raised bits that each brake shoe slides on at the backplate.

Keith

[dpb]

Thanks both.   I reckon I'll go down the weld and grease route first and see how it goes. I'm sure it will work.    I like the sound of two pistons though, seems to be more logical than sliding everything else. 

 

Cheers

Dave

====

[BlueTR3A-5EKT]

43 minutes ago, dpb said:

Thanks both.   I reckon I'll go down the weld and grease route first and see how it goes. I'm sure it will work.    I like the sound of two pistons though, seems to be more logical than sliding everything else. 

 

Cheers

Dave

====

You will not want a modern car then which might only have a single piston in its brake caliper, and rely on the whole caliper body sliding to enact force on both brake pads…..

Edited February 13, 2022 by BlueTR3A-5EKT

[Rob Salisbury]

Something else to watch out for, ... my guess is that the handbrake extenders that are offered these days will exert a greater force on the leavers pivot point and more readily form a bigger groove in the back plate, .... welding an annual event?!!

Cheers Rob 

[Z320]

You can imagine how much power is wasted with this construction for digging this grooves

[stuart]

13 hours ago, Z320 said:

You can imagine how much power is wasted with this construction for digging this grooves

And how many people have never heard of this problem and wonder why their rear brakes dont come up well on the brake rollers.

Stuart.

[dpb]

my brakes have never been good!   Now we may have found the reason.   Like Stuart says,   its a hidden problem.

[Z320]

As some of you might remember I made some modifications on my TR4A rear brake.

I fitted the wider brake cylinders from the TR6 (more force) for the hydraulic brake.

And a long handbrake lever inside the brake drum and automadjustment for the handbrake.

As it is still common on many cars, and used from the 50-ies for example by the VW Beetle.

This works very well.

Ciao, Marco

Edited February 15, 2022 by Z320

[RogerH]

Hi Marco,

 that does look very neat indeed.

 

Roger

[stuart]

27 minutes ago, Z320 said:

As some of you might remember I made some medifications on my TR4A rear brake.

I fitted the wider brake cylinders from the TR6 (more force) for the hydraulic brake.

And a long handbrake lever inside the brake drum and automadjustment for the handbrake.

As it is still common on many cars, and used from the 50-ies for example by the VW Beetle.

This works very well.

Ciao, Marco

When you say the wider rear cylinders from TR6 thats actually a bit confusing as the 0.75 cylinders were used on TR3 with 10" drums and again on later TR3a/TR3B and early TR4 its only on the late TR4/ 4a that use the 0.70.

0.75 were only used on N/American TR6.

Stuart.

Edited February 14, 2022 by stuart

[Z320]

At the Beaulieu Auto Jumble 2016 (?) I bought a set of little used „TR6“ rear brakes with 0.75“ cylinders from a NL guy.

It was the year when we visited you at your workshop btw

Edited February 14, 2022 by Z320

[stuart]

39 minutes ago, Z320 said:

At the Beaulieu Auto Jumble 2016 (?) I bought a set of little used „TR6“ rear brakes with 0.75“ cylinders from a NL guy.

It was the year when we visited you at your workshop btw

Yes it was good to meet you and your wife. They must have come from a N/American import then.

Stuart.

[ianc]

But having larger diameter slave cylinders at the rear, especially with 10" rear brakes, may mean that the rear end locks under heavy braking - not desirable as both braking and control is lost.

In the 1960s, my brother's TR3, with 10" rear brakes , could not stop as rapidly as my disc-braked TR2 with 9" brakes, because his car would lock its rear wheels.

He fitted smaller diameter slave cylinders to overcome the problem,

Ian Cornish

[Z320]

No problem here on my TR4A with the 0.75“ cylinders

Edited February 14, 2022 by Z320