Front Wheel Lockups

[chris.hevey]

(Sorry, this might be a total noob question as this is my first Porsche)

I've noticed my SC is prone to lock the front wheels under heavyish braking.

I was wondering if this a "feature" of Porsches of this era and therefore something I need to adapt my driving to, or if there might be something up with my particular car - i.e. is this what everybody gets if they hit the anchors too hard.

I don't expect it to brake in the same way as a car with ABS, but I do seem to have to brake a lot sooner than I would expect to considering it's a 911 - 29 years old notwithstanding.

I need to roughly double the braking distance in comparison to my 2003 2 litre petrol VW Passat to bleed off the same amount of speed to avoid needing cadence braking - does that sound right?

New pads and disks all round within the last 1,500 miles, tyre brand / size as specified by Porsche with plenty of tread, shocks seem to be OK, laser alignment about 5-7k ago.

 

[chris.hevey]

Thanks Phil. Sounds like I need some driving lessons, or a lot more practice. (Or do they sell auto-pumping shoes somewhere?)

 

[Pete917]

You should be able to brake quite heavily and slow alot before locking up. Are both fronts locking at the same time or just one of them. Under heavy braking all te load moves up front to help with braking (lots of fuel in the tank can also help as these cars are very light at the front.

Corner weights, balancing and geometry are all vital too to get the best out of the brakes.

 

[chas3.2]

Are the brake pads from Porsche if not. ? are all the caliper piston cutouts set to 20' as in your workshop manual. are all the brake caliper pistons free to slide in and out.? do you have dot 4 brake fluid and when was it last changed.?

Charles

 

[George Elliott]

Charles,
My SC was just as you describe. Its some years back, was completely std, and had 50k miles.
Your ref to the Passat goes to show how cars have progressed but the SC will put a smile on your face
There is a quite famous saying which applies to 911's up to 1990 - "slow in - fast out" - you may have heard it.
I have great memories of my SC, a bomb-proof sports car with character dripping off it.
Good luck with yours
George

944 turbo
964

 

[chris.hevey]

Thanks for the info gents - it's given me plenty to think about.

Either both fronts lock up, or if only one it tends to be the offiside.

Good point re. the fuel - I've noticed the car generally handles better on a full tank. Running on vapours even makes the front slightly "bouncy?" Just a shame it costs £100 to fill it these days![]

I actually don't know provenance of the pads and disks. I had RPM replace them last year as well as do a caliper re-furb and fluid change, during which I assume they set the cutouts correctly. They seem to know what they're doing, have a good reputaion in R10 at least, and are Porsche nuts themselves, so I tend to leave things to their judgement. I'll ask next time I see them.

Slow in, fast out. Jackie Stewart claims to have pioneered that. Being a chicken, it tends to be my style anyway - it's much safer for on-road "spirited" driving, particularly when you encounter a tractor or pedestrian on the bend! To be honest, I probably get the lockups more when I'm attempting fast-in, very-fast-out, so back to the driving lessons / practice idea![:-]

Regarding the Passat, it was a bit of unfair comparison really. It does have phenominal brakes considering it's such an otherwise boring 'dad car.' I particulalry enjoy it when I lend the car to people not used to VAGs - watching them get slammed against the belts the first time they drop anchor....

Smile on the face? Hooo yah! The look goes: smile, smile, terrified, smile, grin, big grin, utterly terrified, relieved, massive grin....

 

[sailor]

In my opinion, dear boy, the SC is a pig to handle unless you maintain at least half a tank of petrol. It is amazing the difference it makes.

Sod the cost []

JohnC
993turbo

 

[chris.hevey]

Sailor:

I like the cut of your jib sir. I shall repair to the Shell emporium first thing in the morning and take on 80 litres of their finest vintage optiwotsit (it being cheaper than Moet & Chandon - just about,) and therefore excellent value) I shall then proceed to thrash about the Buckinghamshire countryside, grinning all the way, in the pursuit of obtaining quantitive analysys to prove your theory. If I die in the process, then let it be known I did so with a smile on my face, and that I absove you, dear matelot of any responsibilty in the matter. Happy days!

 

[Gary C]

I was just thinking at the weekend that modern brakes were the thing that had developed the most over my 3.2

But it was stability not braking force I miss from cars like my old EVO.

If it takes you twice as long as a Passat to stop, then there must be something wrong !, unless you are exaggerating, thats an enormous difference.

If your tyres are good and the fronts both generally lock at about the same force, then that would suggest they are ok. Possibly sure the bias is not correct and the rears are not doing their fair share ?, I know almost all road cars have the bias heavily up front, but I imagine the 911 has more than most to the rear given that the weight is to the back ?

 

[sailor]

ORIGINAL: chris.hevey

Sailor:

I like the cut of your jib sir. I shall repair to the Shell emporium first thing in the morning and take on 80 litres of their finest vintage optiwotsit (it being cheaper than Moet & Chandon - just about,) and therefore excellent value) I shall then proceed to thrash about the Buckinghamshire countryside, grinning all the way, in the pursuit of obtaining quantitive analysys to prove your theory. If I die in the process, then let it be known I did so with a smile on my face, and that I absove you, dear matelot of any responsibilty in the matter. Happy days!

Bless you , my boy. Are you still alive? Yes? Then my advice worked. Ooooh... gives you a warm feeling all over .... another one saved .... aaah ... life is good.


JohnC
993turbo
Used to be The Stig

 

[usermjg]

Or failing the heavy petrol, stick a slab in the front [] Just make sure its fastened down []

 

[chris.hevey]

I shall have the bias thing looked at next time it's in for a service - sounds promising. (Unless there's a foolproof way of DIYing it? Knowing me, I'd adjust it the wrong way. Assuming you can even do that on an SC - sounds a bit 997ish to me!)

I must say the slab idea had occurred to me - friends of mine used to do that in their Mk 1 Escorts to to get better grip under acceleration. It mostly worked!

Sailor: Regrettably I was not let out at the weekend. Memsahib's birthday, preparations for moving house, and the weather conspired against me. Should be sunny tomorrow, so maybe a drive to work is on the cards. (I don't mind driving in the wet, I just can't be bothered to put the roof back on.)

Re. the Passat: I probably am exaggerating a bit. Of course a key difference is that between any two given bends at full chat, the Porsche will have achieved a much higher velocity, and therefore need more stopping!

One thing I'd forgotten was instruction I'd received on a day at Millbrook proving ground, where the instructor tried to get us to press the pedal more progressively rather than stamp on it as ABS lets you do (but still pretty hard eventually) then ease off the pressure as the car slowed down - you could kind of tell when the lock was about to happen. Oh dear, more practice needed. Ho hum...

Thanks all - I'll keep you all posted as to developments.

 

[Laurence Gibbs]

from what i remember of driving pre abs 911's, it was fairly difficult to get the fronts to lock except on greasy or wet roads, in which case it was fairly easy. Pedal should need a fair shove but the car should feel like somethings happening when you do hit the pedal. slow(in comparison to a newer car) progressive retardation is how i'd describe it. As others have recommended worth checking for a sticking caliper, fairly common and shows up sometimes when new pads fitted. Particularly if pad was a tight fit !
also as mentioned technique helps. You want to aim to get the weight over the front wheels quickly intially . This allows grip to tranfer from the rear to the front and the more grip the less chance of the front locking. Think any good driving book would describe this much better than i ever will.

 

[Pete917]

ORIGINAL: chris.hevey

I shall have the bias thing looked at next time it's in for a service - sounds promising. (Unless there's a foolproof way of DIYing it? Knowing me, I'd adjust it the wrong way. Assuming you can even do that on an SC - sounds a bit 997ish to me!)

I must say the slab idea had occurred to me - friends of mine used to do that in their Mk 1 Escorts to to get better grip under acceleration. It mostly worked!

Sailor: Regrettably I was not let out at the weekend. Memsahib's birthday, preparations for moving house, and the weather conspired against me. Should be sunny tomorrow, so maybe a drive to work is on the cards. (I don't mind driving in the wet, I just can't be bothered to put the roof back on.)

Re. the Passat: I probably am exaggerating a bit. Of course a key difference is that between any two given bends at full chat, the Porsche will have achieved a much higher velocity, and therefore need more stopping!

One thing I'd forgotten was instruction I'd received on a day at Millbrook proving ground, where the instructor tried to get us to press the pedal more progressively rather than stamp on it as ABS lets you do (but still pretty hard eventually) then ease off the pressure as the car slowed down - you could kind of tell when the lock was about to happen. Oh dear, more practice needed. Ho hum...

Thanks all - I'll keep you all posted as to developments.

Im not sure if the SC is supposed to have a bias valve or not. I'm not sure when Porsche started fitting them. I know the 3.2 Carrera's had them. If your brakes are the same size front and back, then my view would be that you need one. Its a thought and something to look into....