Correcting front / rear brake bias

[black11s]

Sevenman said:

When I bought the car it had old Toyo T1-S tyres on, which hadn't been made since about 2004 and I think the sidewall dates were 02 (front) and 03 (back) (See pic at this link if interested). The Tamora had only done 13'500 miles from new. So, despite having plenty of tread, I changed them for the new Toyo T1-Sports back in April, and have already put 3500 miles on them.

I am going to have to assess all the information, try to do a bit of looking at the car on a ramp, and come up with another plan to get it sorted. It might end up back at TVR Power as they are a lot closer to me than Track V Road, but are still 60 miles away. Having a specialist car is a bit awkward. I knew I should have gone for a Peugeot 206CC

It sounds like you can discount the tyres then. (God knows what it must have been like with those old ones on there before!)
Unless the garage had removed the pads to inspect them, they wouldn't have been able to tell what the surface was like.
Swapping the front pads may be your cheapest 1st option...

For the suspension, if someone like Dom (who I only know through reputation) has driven it, and doens't think there is anything wrong, I would assume all is well. Mine was such a pig I used to have to apologise to passengers as we went over pot-holes.

Good luck, and please let me know how you get on. Brake set up and balance is so important on these cars as there's no ABS.

[Targarama]

You could try another specialist and see if they have any ideas, nobody knows everything.

I'd try some new front pads first though. I've glazed a few sets on my T350 over the years.

[m4tti]

If you suspect the rear end lightening allowing the rearwheels to lock, could you not effectively ballast the rear to confirm?

[Sevenman]

Thanks for the replies.

Regarding the old tyres - they weren't too bad, but I never really pushed them that hard. The new Toyos are good though and have been tested in all sorts of conditions.

Another specialist is an option. Hopefully I can get as good an idea as possible of what to try before spending any money. It is a very expensive trial and error process so I just want it to be sorted.

Not sure about boot ballast - I want to get the car working as it is. The spring / damper settings should be ok for weight transfer. Unless there is something really wrong with the setup, and I don't think there is...

[m4tti]

I was thinking along the lines of eliminating one variable.

I guess really you need to understand first the pressure being delivered via the front brake line versus the rear.

Ive recently replaced all discs and pads. Ive used the sagaris front disc upgrade and the standard rear with DS2500's and can say I've never had the rears lock no matter how hard ive tried.

[Sevenman]

m4tti said:

Ive recently replaced all discs and pads. Ive used the sagaris front disc upgrade and the standard rear with DS2500's and can say I've never had the rears lock no matter how hard ive tried.

What is the Sagaris front upgrade? Bigger disks and calipers moved out? All the disks on my car look in good condition at the moment.

I have used DS2500s on other cars and they were good at handling trackdays.

[m4tti]

Yep bigger front discs and larger caliper spacers.

If I were you Id be tempted to start from the begining, and determine exactly what your brakes are doing.

http://www.stu-offroad.com/suspension/bpress/brake...

[Sevenman]

m4tti said:

Yep bigger front discs and larger caliper spacers.

If I were you Id be tempted to start from the begining, and determine exactly what your brakes are doing.

http://www.stu-offroad.com/suspension/bpress/brake...

That kit looks slightly useful.

I guess you need the engine running to get brake servo assistance, and then you can measure the pressure at up to 2 brakes at a time given an unknown pedal pressure.

But with a number of tests (needing to re-bleed for each) you could compare:

FR to RR, FL to RL, FR to FR - That should give you an idea of the relative front/back and side/side pressures, and would allow the effect of the variable proportioning valve to be tested.

[m4tti]

Yes, at least that way you could determine that the front has definitely got a pressure greater than or equal to the rear.

You could make the pedal pressure known by fitting a longer bolt to act as a pedal stop so both tests would have the same length of pedal travel or pressure applied. Not sure how easy it is to hit the standard pedal stop.

Until youve got some tangibles the rest is guess work and swapping parts out.

[ChrisPap]

Have you done a few (or had a few) simple manual checks? Have you retracted all the pistons and pushed them back out with the pedal pressure to make sure there are no siezed or binding pistons?

I'd recomend that you do that and while your at it check the front pads for glazing as mentioned above if you are in any way handy.

Is it the same side rear wheel locking every time? Is if both (with engine stall)?

Did any of the expereinced mechanics who had looked at the car provoke the same locking as you had at the skidpan? And if so did they comment that it happened at about the same pedal force as they'd expect to lock? I'd expect it's less likely to lock rear because the rear brakes are working too well, than it is to lock the rears because the front isn't working well enough.

[jrb43]

Reading through, it sounds as if you received the car with replaced pads all round. Given that they normally do their fronts before the rears and that you noted the front pads to be older, I'd suggested it's had the front pads replaced before the rears and now the front pads/discs have gone again - glazed as others have suggested. The majority of the braking force is achieved by the fronts (in any car) so the fact that you couldn't slow it down as fast as a Focus suggests more that there is a front brake problem than that the rears locking is the issue. As standard, T-series have a fair degree of squat under acceleration with softer rear spring rates to improve rear grip and I suspect subsequently transfer the weight forward more emphatically under braking - potentially leading to the rears locking.

The benefits of the Sagaris front brake upgrade (spacing the calipers out) is that the discs are subsequently cheaper than T-series (don't know why) and if that continues, it will pay for itself the next time round. Bigger discs also give more braking feel.

My personal recommendations would be Dom at TVR Power or Warren at Topcats Racing who has a private runway and therefore can safely simulate speeds above the legal limit. I'm sure there are plenty of others around too. Sorry you're having so much grief - it will be worth it!

[Sevenman]

ChrisPap said:

Have you done a few (or had a few) simple manual checks? Have you retracted all the pistons and pushed them back out with the pedal pressure to make sure there are no siezed or binding pistons?

I haven't done those checks myself - 2 garages have ok'd the brakes, but I don't know specifics.

I also don't know if the front pads have been removed and checked for glazing or just checked for pad depth.

I have put a lot of normally driven miles on the car that I would hope would work through glazing issues.

And I did get the fronts to lock first for a while using the adjustable valve, but then it stopped happening.

ChrisPap said:

Is it the same side rear wheel locking every time? Is if both (with engine stall)?

The driver's side rear has certainly locked up, not sure about passenger side. I am fairly sure it hasn't stalled and I come off the brakes very quickly as it starts to lock up.

I am not sure if having me in the driver's seat benefits deceleration grip on the rear driver's side tyre or not. Will help during acceleration, but on braking my weight is transferred forwards.

jrb43 said:

Reading through, it sounds as if you received the car with replaced pads all round.

The car came with Ferodo pads on the front and EBC Greenstuff on the back.Both at least a few years old, but I don't have a detailed bill history from the car's earlier days (just service stamps), so no idea how old either are. These cars if driven normally should be very easy on the brakes (like the tyres), so the front pads could be old.

jrb43 said:

My personal recommendations would be Dom at TVR Power or Warren at Topcats Racing who has a private runway and therefore can safely simulate speeds above the legal limit.

Use of a private runway and experience with race cars is good for setting up brakes.

It shouldn't be that difficult given there are lots of cars that work just fine, but it seems to be.

Somewhere with good test facilities would be a bonus. It is very difficult to judge how well it works without. Are Top Cats based on an old airfield?

Maybe I should just replace the front pads with new to eliminate that variable. I imagine they need some time spend driving to bed them in before more testing.

Each change is ££, and then the testing afterwards is hard to do and not fun.

[optimax sniffer]

Topcats are near Bicester:

Building/348B Westcott Venture Pk
Aylesbury
HP18 0XB
United Kingdom

[Targarama]

optimax sniffer said:

Topcats are near Bicester:

Building/348B Westcott Venture Pk
Aylesbury
HP18 0XB
United Kingdom

Topcats did my 'S'/Sagaris front brake upgrade. The caliper adapters needed some 'adapting' to fit properly.

[m4tti]

From the tests you've been doing, I'd be suprised if the pads are glazed. It sounds like the kind of braking you are doing would be enough to knock any glaze off the fronts.

Im presuming the front pads have been physically inspected. When I did the brake swap on mine the front pads had substantial pits.

This is a pretty simple braking system. If you eliminate the front pads (you've changed the rears) your really down to master cylinder, brake lines, and calipers.

[Targarama]

m4tti said:

From the tests you've been doing, I'd be suprised if the pads are glazed. It sounds like the kind of braking you are doing would be enough to knock any glaze off the fronts.

Im presuming the front pads have been physically inspected. When I did the brake swap on mine the front pads had substantial pits.

This is a pretty simple braking system. If you eliminate the front pads (you've changed the rears) your really down to master cylinder, brake lines, and calipers.

and suspension setup...

[m4tti]

Targarama said:

and suspension setup...

Yep true, thats why i wondered if you could balast the rear adding weight over the rear wheels, to stop the back end going light, on forward transfer.

Has the front and rear braking force been measured on rollers just to get a rough idea?

[Hollowpockets]

I think it will be something simple, you shouldnt need brake bias adjustment. Pad glazing is down to poor technique with braking on track IMO, grooved discs are better but they may not be available for TVR's.

Toyo T1-s or R are crap on track - I'd change them if your that worried about performance on track, get some Goodyear eagle F1's or better.

Pads- brand does make a difference, surprised people still think redstuff pads are any good, get a matching set of ferrodo's or Pagids are what I've used over the years and have always performed perfectly. Pagids RS29 are amazing!

Suspension set-up- get the ride height of the chassis checked and make sure your spring rates and damping are correctly adjusted.

If youve got the above all done it must be a wearing or failed brake system part.

[Sevenman]

Hollowpockets said:

Toyo T1-s or R are crap on track - I'd change them if your that worried about performance on track, get some Goodyear eagle F1's or better.

I don't have either of the above, but have their new T1-Sport tyre (very different to T1-S). For occasional trackdays (one/two per year planned) I am happy with using a respectable tyre. Since I only have one set of wheels, these tyres need to cope with winter days as well as the track and for a little track driving I don't want to compromise the rest of the year (888s...).

Hollowpockets said:

Pads- brand does make a difference, surprised people still think redstuff pads are any good, get a matching set of ferrodo's or Pagids are what I've used over the years and have always performed perfectly. Pagids RS29 are amazing!

Maybe I should have asked the garage to change the fronts regardless. Although the bill was large enough anyway... At least it would have removed a slight unknown. I would be happy with new Ferodos that match the compound on the back.

If it wasn't such a pain to do I would switch back to a standard proportioning valve as well for a test.

Hollowpockets said:

Suspension set-up- get the ride height of the chassis checked and make sure your spring rates and damping are correctly adjusted.

Spring rates - standard Gaz kit for Tamora, they should be correct. Dampers set as advised by Gaz.

Hollowpockets said:

If youve got the above all done it must be a wearing or failed brake system part.

Or my TVR is just messing with me to wind me up.

Or it is something as simple as the front pads are 'off' in some way or the standard valve was faulty and the replacement isn't adjusted right.

m4tti said:

Has the front and rear braking force been measured on rollers just to get a rough idea?

Not that I am aware of. It passed an MOT at the same time the brake work was done, but no test results and that was probably one axle at a time.

Edited by Sevenman on Thursday 6th September 13:59

[Walford]

My AP pads after 1000 miles of hard road use (on new discs) looked odd
AP said if it is driving OK which it was, carry on, so i did