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Brake Efficiency


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Hi,

Been out driving the restored TR6, trying to bed the brakes in.

Have done a few miles with lots of braking. Although they have improved slightly they leave a lot to be desired.

All the brake system was replaced with standard parts.

Should i be able to lock the wheels up when braking very hard, cant at the moment. Driving on 195 tyres.

No air in system as pedal doesn't 'pump up'.

Any thoughts greatly appreciated.

Thanks

Dave

 

 

 

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Did you clean the discs off properly first and what pads are you using, also what fluid?

Stuart.

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55 minutes ago, stuart said:

Did you clean the discs off properly first and what pads are you using, also what fluid?

Stuart.

The new discs were cleaned throughly with brake cleaner, fluid was Dot4. Cant remember the make of the pads but they were standard purchased from one of the frequently mentioned suppliers.

Dave 

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First question should be if the brake balance is okay.

If front locks and rear does not or other way round there

might be a problem.

 

If both axles do not brake as expected the brake booster may be the culprit

or simply the TR6 does not brake like a modern car.

Had similar problems with let driving my girl friend with the TR6. She comes from a modern

ABS brake Volkswagen and simply had no confidence if pedal must be pushed that hard.

 

I installed the double diaphragm Volvo brake booster, added vented discs at the front

and now the car brakes as it should.

 

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How many clicks do you get when you pull up the handbrake?  If more than four, adjust the rear brakes so that it takes three clicks.  The difference can be dramatic.  The front discs may get pad knockback after cornering.  Front bearing spacer kits will relieve this problem.  All in is four pot vented front brakes, rear discs, and dual master cylinders with balance bar.  Then, of course, sticky tires like Potenza RE-71's.  But, it's a lot money.

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Standard brakes if everything is working OK will happily lock the wheels and are certainly good enough for all but race conditions, you need to look closer at what you have.

Stuart.

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Lots of hard application can glaze new pads. Normal driving seems to be the best method to bed in normal road pads. 

Perhaps a light sanding of the pad surface and start again?

......ducks below parapet waiting for incoming contradictory opinions :-)

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Thanks guys. Going to start with the servo, then have the pads out to check.

Seen a few posts about testing the servo, starting the car with a foot on the pedal and should feel something also check the NRV.

Any other thoughts on the servo.

Am i correct in saying that both ends of the servo pipe have a Non return Valve.

 

Dave

Edited by cookie
added question
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The rear shoes will bed in quick, and require re-adjustment.

To mimic rear brake adjustment, you can drive with the hand brake lever say 2 or 3 clicks up for a short distance and see if this makes a difference.

But if your pedal is not on the bottom when pressing hard, the servo is a more likely cause.

Waldi

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2 minutes ago, Waldi said:

The rear shoes will bed in quick, and require re-adjustment.

To mimic rear brake adjustment, you can drive with the hand brake lever say 2 or 3 clicks up for a short distance and see if this makes a difference.

But if your pedal is not on the bottom when pressing hard, the servo is a more likely cause.

Waldi

Thanks Waldi, have adjusted the rear brakes handbrake is only just 2 clicks. 

Will be checking the servo, think i have just realised the connector to the manifold is also an NRV. This could be a problem as i didn't realise this when restoring so it is the original.

Will start by pulling the pipe off the servo with engine running to see if it affects tickover.

Dave

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The Moss book shows the Servo connector is an NRV and the inlet connector is an NRV, will check.

I cant lock the brakes no matter how hard i press the pedal.

Will have the pads out to check also.

Dave

 

 

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Hi Dave

brake pad, and to a lesser extend disk, material have a huge effect on braking ‘bite’ and power.

what pads and disks do you have?

steve

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Hello Dave

Try bleeding the brake system again starting at wheel furthest from master cylinder. I use an eezibleed which makes job easier. If you have replaced the braking system then it is easy to get air trapped somewhere. On the rear wheel cylinders push the piston in and clamp it in this position so there is little space in the cylinder itself for air to get trapped and do one wheel at a time. Take the clamps off the cylinders, refit hubs and press brake pedal to get the pistons back to "operating" position. On the front push the pistons in and clamp them and bleed them one at a time. Then release clamps and operate foot pedal. You will need to keep master cylinder topped up during all this. At the servo ensure that all the air is removed from the system. You can't always tell if there is air simply by pumping up the pedal. Also check brake fluid is ok using a brake fluid tester to make sure that the water level is less than 1%. Dot 4 fluid is fine but should be renewed every 3 years.

Secondly ensure all the bits that should move do actually move. Rear pistons should slide on the backplates, rear shoes slide on the 3 raised dimples on the backplate and should slide in the adjuster at the bottom. On the front the disc pad holders slide on flat faces on the callipers. Copper grease and white brake grease for lubrication on moving parts.

Good luck

Keith

p.s. check also that flexible brake pipes are in good condition and don't swell up when you apply footbrake (assistant required for this).

Edited by keith1948
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Hi Dave, 

      I also drive a TR6 with standard brakes. As Stuart says they are more than adequate if all is working ok. I can certainly lock up the front wheels on v heavy braking, unsure about the rears. In normal driving I have no confidence issues with the brakes.

So on the face of it something appears to be wrong. That said I believe your car is a fresh restore onto the road. It probably takes 200miles general driving to get all-new brakes bedded in. As others mentioned, if you've done lots of medium to heavy braking quite quickly you may have glazed the pads as they wouldn't have matched their surface to the new discs to provide a good heat sink. 

If you're happy with pedal position and you can brake smartly (if not yet lock up the wheels) I'd suggest just getting more miles in and see how they improve... 

Hope helps, cheers, J.

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Thanks for all the replies guys.

Had a quick look today and servo working ok.

Have probably only done around 15 - 20 miles so guess a few more required.

Will have the pads out tomorrow just to check.

Thanks

Dave

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Double check on servo operation as follows:

Engine off, pump the brake pedal several times to purge air from the servo. The pedal should go hard. 

Keep the pedal pressed down and start the engine. You should feel the pedal move away slightly if the servo is working. 

That said, as others have pointed out, you should be able to lock up without the servo. 

Edited by peejay4A
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Thanks for all your help.

 

Checked the servo today, all working fine.

Had the pads out, looks like they need more miles, gave them a light rub with emery cloth.

Had a nice drive round and jammed the anchors on and eventually managed to lock the front wheels.

Bit more bedding in required i guess.

Thanks

Dave

 

 

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