TR6 TR6 front brakes Jack Drew

[rporter]

Has anyone seen or used the new kit for front brakes from TRF by Jack Drews. My brakes do have to be pumped twice sometimes which I thought was air in the lines but may be flexing. Anyone familiar with Jack Drews and his kit.
Seems like a good idea.

 

[SCguy]

How about a part number for the kit? That way I can find said kit in a TRF web search.

 

[vettedog72]

Gads, what part is flexing?

 

[Geo Hahn]

On some TRs the stub axle has a bit of flex. Hard cornering (really hard cornering) and the flex will wiggle the disc, pushing the pads back a bit. Next application of brakes will have a longer pedal throw to get the pads against the disc.

A problem that comes up in autocross.

rporter: If you are experiencing soft pedal/needing pumping in just everyday/straight-line driving then the problem may be more basic (flex in a rubber hose, partially failing master or slave, etc).

 

[Geo Hahn]

More info, from a message by Jack Drews (on the Triumph mail list) which I had saved --

[ QUOTE ]
3. The front spindle conversion. This is a stand alone project, almost. This provides front stub axles made of superior material by superior manufacturing methods. It includes a spacer and shims that get clamped between the inner and outer bearing, thus stiffening the front spindle. The purpose is to eliminate the flex of the front spindle, which causes the rotor to push the pads back during cornering, giving unpredictable brake action. This kit is produced by Mark Weathers and sold through Ken Gillanders (BFE). The cost is about $250. The only relationship with the aluminum front hubs is that since the aluminum hubs and stock hubs use different width bearings, a different length spacer must be used.


Ken Gillanders (British Frame and Engine) phone number is 626-443-0939.

[/ QUOTE ]

I believe Jack's role was that he was the inspiration for and possibly the designer of the product.

 

[Alan_Myers]

[ QUOTE ]
On some TRs the stub axle has a bit of flex. Hard cornering (really hard cornering) and the flex will wiggle the disc, pushing the pads back a bit. Next application of brakes will have a longer pedal throw to get the pads against the disc.

A problem that comes up in autocross.

rporter: If you are experiencing soft pedal/needing pumping in just everyday/straight-line driving then the problem may be more basic (flex in a rubber hose, partially failing master or slave, etc).

[/ QUOTE ]

I agree with Geo.

Unless you find yourself sliding off the original seats while cornering (ie., need to use a high-bolstered racing seat and 4- or 5-point harness to keep yourself pinned in place), it's very unlikely that axle flex is knocking the caliper pistons back and causing the low brake pedal/pumping problem you described.

As Geo said, look for any leaks or failing MC or SC, of course. And check that the calipers are tightly mounted and measure the amount of runout in the front rotors. This runout is the very likely cause, if all the rest of the system is up to spec.

DOT5 brake fluid can give a sofer pedal, too, especially if a lot of air got trapped in it when it was poured in (run it down a screwdriver blade into the master cyl, to minimize air bubbles in the fluid). DOT5 with a lot of air bubbles can be almost impossible to ever get bled properly.

Then see if there is a restrictor valve installed in your brake system. I think Triumph stopped using these valves on later cars (TR4A?), but don't know exactly when the change occured. The restrictor is essentially a simple one-way valve that keeps most of the hydraulic fluid out at the caliper, rather than letting the master cylinder draw too much back when you release the pedal. I've heard of folks retrofitting these valves with good successon later cars, including the front brake circuit of the latest, dual-circuit cars. See item #43 on Moss' page https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29151#top or #79 at https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29152. Factory part number is 116197, Moss part number 589-030.

Unfortunately, this valve seems to be N/A new from any of the U.S. vendors or Rimmer Bros., but might be bought used. It's simple and unlikely to fail or wear out, can be usually just be cleaned and used.

Yes, Geo is right that soft rubber brake lines that expand under pressure could contribute to the problem, too. New rubber hoses might restore a lot of the pedal, or upgrade to braded stainless steel for a firmer pedal. The later, IRS cars will see even more benefit changing to s/s braided hoses, since they have 4, where the earlier live axle cars have 3 hoses.

Finally, you might check the adjustment/wear on your rear brake shoes. That can have an effect, too.

/ubbthreads/images/graemlins/cheers.gif

 

[rporter]

Everything is new including braided flex lines, MC, servo disks green pads rear breakes. About the only thing it could be is runout of the new disks but I had heard that there is some flex in the spindles which may show up as lost initial braking. I had thought about gettin the runout checked but would take a trip to a garge with a disk lathe to fix and I just have not done it yet. The brake work just some times especially on a hard street turn the pedal has to be pumped. I just expected better having gotten used to new cars. The kit is in the latest TRF internet special catalog I got today. Screw driver idea is good one. I will try that the next time I fill a MC.

 

[vettedog72]

I can't believe you front wheel bearings would have so much runout as to allow a brake problem without your notice; but, you might check the wheel bearings to see how the run out stacks up to specs.

 

[hondo402000]

if you installed a new servo, did you adjust the little screw inside the servo? I installed a new servo and did not think about adjusting the screw, it hits the piston inside the MC and you have to adjust it out. Be careful not to adjust it too far or the plunger inside the MC will not come back far enough to release the pressure and eventually your breaks will be on all the time I found this out. Pull the MC off the servo you dont have to take the lines loose if your careful, loosen the nut and screw the ball screw out one turn at a time and drive, repeat and see if this solves your problem

 

[rporter]

Interesting I did not know there was and adjustment to the servo. I don't think the bearings are loose but I will check.

 

[Alan_Myers]

Hi again,

On the street, I'd check for and eliminate everything else before suspecting it's axle flex.

FYI, the last set of brand new rotors (Brembo) I bought needed to be turned and skimmed before installing. They had quite a bit of runout right out of the box. It's pretty easy to check them right on the car, with a dial caliper if you have one.

Also, by any chance have you replaced wheel bearings recently, and especially the inner grease seal along with them? If so, I think that seal on TR6 is the same as on earlier cars, i.e. a sort of felt "donut" that gets soaked in oil before installation, isn't it?

The reason I ask is that all those seals I've seen lately - from the major Triumph vendors - are about twice as thick as originals. I've ended up carefully trimming them approximately in half horizontally with a razor blade.

If used without trimming, the extra thickness of the seal very often "fools you" into thinking that the wheel bearings are properly adjusted. It feels just like the bearings are starting to drag and the adjuster needs to be backed off, when in fact the adjustment is nowhere near right and the "drag" you feel is actually just the too-thick seal.

If this happens, as vettedog72 noted, then the loose wheel bearings in turn could cause the brake caliper piston knockback and soft pedal you describe.

Yes, as you heard there is a possibility caliper piston knockback sue to axle flex. But, again, this is not all that likely to show up in a street car simply because cornering forces/tire stickiness, etc, just aren't high enough to flex the axles very much.

However, if it does happen to be what is happening in your car, the kit from Jack at https://www.tonydrews.com/Jack_Parts.htm would solve the problem. His kit includes a replacement set of beefier axles (that need to be pressed into your car's vertical links), along special spacers and adjusting shims to keep the bearings in place. Spacers and shims alone might do the job with all but the most extreme street driving stresses. But, I don't know if spacers are made for stock size axles, or if they are sold separately.

 

[rporter]

Thanks a lot. Good ideas I never thought of. I don't remember what the seals looked like I did it in the garage in the winter and just wanted to get the job done. I don't remember soaking a felt seal.

 

[rporter]

I talked to a mechanic friend about my problem. He only works on American cars but he said a surpising amount of fluid is needed to move the rear brakes if they are not adjusted properly and that could be why I have to sometimes pump twice. My emergency brake handle does not grab until the top of the pull so I pulled it a little to preload the rear brakes but not actually activate the rear brakes. Voila now I have good hard servoed brakes. Not as good as modern car brakes but not bad either. When it is not so hot I will get under the car and adjust the rear brakes. I bet the problem will be solved.

 

[RomanH]

[ QUOTE ]
... then the loose wheel bearings in turn could cause the brake caliper piston knockback and soft pedal you describe.

[/ QUOTE ]
/ubbthreads/images/graemlins/iagree.gif
Couldn't figure out why my brakes wre soft and did not have good modulation. Decided to check the wheel bearing and re adjust them. On a whim I left them what I thought was tight. That did the trick. I now have fantastic brakes and after reading Alan's post I know why too! /ubbthreads/images/graemlins/grin.gif