Improving track stability under braking / down shift

[kiwi 911]

I am finding the car has a slight lock up in the rear when under hard braking and changing down gears to 3rd or 2nd on the track .

It's kind of alarming as it gets the car briefly unsettled and I find myself braking slightly early in anticipation................

How do I solve this? Is is my driving technique (i.e. off the clutch too fast) or do I need to install an LSD to solve?

Advice from more experienced hands would be appreciated please?

[GaryR]

What is the car? What are the brakes? Stock, Big Reds, Wilwoods? What pads are you running? Are you braking in a straight line or trail braking into a corner at the end of a straight? Could be anything from a sticky caliper to an out of balance car, need more info.

[Tom '74 911]

Assuming your brake bias is correct. . . smooth inputs, smooth inputs, smooth inputs. . . you can threshold brake w/out stabbing at the pedal and locking up tires. Also, it's important to be smooth not only in initial application of the brakes (0-100%), but also in how you release the pedal (100%-0) . . .

All that said, a properly set up LSD not only helps put power down, but also settle the car during heavy braking. . .

Smooth is fast though. . .

[trak ratt]

Originally Posted by kiwi 911

I am finding the car has a slight lock up in the rear when under hard braking and changing down gears to 3rd or 2nd on the track .

You need to raise the revs before letting out the clutch! Your rear tyres are actually dragging a bit because the engine/trans speed doesn't match the rear wheels. Try practicing gunning the engine a little as you let out the clutch. Best doing this when there is no one behind you. It will become 2nd nature after a while.

[schumicat]

exactly. you need to lean to heel-toe. there are many threads on this. you really don't need to gun the throttle, just blip it is a little with the edge of your foot (area below the little toe) with the clutch depressed and while braking with ball of your foot.

Originally Posted by trak ratt

You need to raise the revs before letting out the clutch! Your rear tyres are actually dragging a bit because the engine/trans speed doesn't match the rear wheels. Try practicing gunning the engine a little as you let out the clutch. Best doing this when there is no one behind you. It will become 2nd nature after a while.

[kiwi 911]

Thanks for the feedback guys.

I have a 76 Carrera 3.0.

[GrantG]

Yep, good heel/toe downshifting technique and a good clutch-type LSD will help.

[ivangene]

this is the exact reason you have a 76 and not an 06'

learning this takes time....and practice, but once you have it down you can stop hella fast AND you will stop faster in a newer car too...

if the car is getting upset try to release SLOWLY

and as stated...heel and toe, the only way to go!

Have fun -

[NY65912]

How's your corner balance?

[Quicksilver]

Heal-toe will only work smoothly enough to allow extreme threshold braking if it is completely natural and automatic. If you have to think consciously about it you won't be smooth. To get to this point you need to have something that forces you to do it so it becomes second nature.

To get to this point I offer the solution:
"The Crappy Car!"

Get a manual transmission car that won't stay running unless you keep a foot on the gas. You will figure out how to keep it running pretty quick and you will become natural at it fairly quick. If you live in cold temperatures and have an older car just reset the idle down or disconnect the auto choke.


Just found out my wife can heel-toe because when she was younger she had a series of really bad cars 60 miles north of Anchorage. (Most people give up on rusty Escorts after the first one...)
She hasn't been using the knowledge because she didn't see the need for this technique on cars when we live in a warm climate. But now that I know I'm going to get her double clutching correctly on "The Crappy Truck" that has no syncros.

[69911e]

Most people downshift too early in a braking corner..... Try doing it later.
+ Heel and Toe

[tctnd]

Before doing anything too serious you might want to check the condition of the trailing and a-arm bushings. The factory rubber can get pretty squishy with age and allow a lot of toe variation which leads to the sort of sketchy handling you are experiencing.

regards,
Phil