Loose front end
10-03-2016, 11:30 PM
#16
Rennlist Member
Rake for a street car should be @ + 0.75 deg measured on the rocker.
If you haven't replaced your a-arm bushings (there aren't any trailing arms on a 993) then absolutely that should be done. Upgraded replacements are inexpensive but the work/labour is a PITA.
At more than 100k mileage with a 20 year old car unfortunately most if not all of the suspension rubber needs to be replaced.
If you haven't replaced your a-arm bushings (there aren't any trailing arms on a 993) then absolutely that should be done. Upgraded replacements are inexpensive but the work/labour is a PITA.
At more than 100k mileage with a 20 year old car unfortunately most if not all of the suspension rubber needs to be replaced.
10-03-2016, 11:40 PM
#17
since all the bushings are checked off here's something else to just cross off the list, very tiny chance someone set the front caster different side to side.
like 4.8 left and 6 right. just feel under the a-arm for the position of the eccentric, usually on a 993 it will be centered on both sides.
also possible you have zero toe and max caster. that would make the front end go in a straight line easily but any steering input would be quick with zero toe and make the front end feel like it lifts and rolls over as it turns.
like 4.8 left and 6 right. just feel under the a-arm for the position of the eccentric, usually on a 993 it will be centered on both sides.
also possible you have zero toe and max caster. that would make the front end go in a straight line easily but any steering input would be quick with zero toe and make the front end feel like it lifts and rolls over as it turns.
10-04-2016, 01:04 AM
#18
Three Wheelin'
Thread Starter
Wow, lots of great responses here and excellent advice, thank you. I'll try to answer each question in order.
Alignment numbers:
- Toe: 1/32 inch front left, 1/32 front right, 1/16 rear left, 1/16 rear right
- Camber: -.4 degrees front left, -.3 front right, -1.3 rear left, -1.2 rear right
- Caster: 4.8 degrees front left, 5.4 degrees front right
- Cross Camber: -.1 degrees front, -.1 rear
- Cross Caster: -.6 degrees front
- Total Toe: 1/16 inch front, 1/8 rear
- Thrust Angle: 0 degrees
For the bushings in the rear suspension, I tested by jacking the car and getting an assistant to work the wheel at 12 and 6 then at 3 and 9. I noticed no movement at 12 and 6 and a very small amount of movement at 3 and 9. I don't have another car to compare to but the movement was in the range of a few millimeters and I could feel the bushing moving on the lower rear toe link. I figured this was the kinetic toe in action.
The alignment mechanic told me that the rear bushing on the lower A arm as well as bushings on all the rear links had some wear evident but he didn't feel like it was enough to cause significant problems. I don't know if he's right about that or not, so take it for what its worth.
Regarding road surface. The smoother the road the more I notice the problem. On grooved or crowned roads the car doesn't exhibit much tramlining and the wandering is reduced. I'm guessing that the suspension or steering loads up a little in the groove and the looseness is less evident as a result.
Regarding rake, the car looks like it has a good stance and it was set up on RoW M030 springs to specified RoW height, six or seven years ago by a reputable shop, so unless something has settled, I think that's ok. Is there a way I can measure this at home?
Alignment guy said that KT was maxed out on one side when he started the alignment so he evened them out and got them both into what he said was correct range. He mentioned hanging the tool off of caliper mounts and said he set it to 6 on both sides. So I think he was using the aftermarket tool, not the factory tool. Handling in corners is predictable and good as far as I can tell. I feel confident pushing it in both higher and lower speed corners. In a tight turn with throttle application I get a nice bite in the front with just a bit of tail sliding at exit if I push hard enough. To my butt it feels really good when the suspension is loaded it up, its just in straight-line cruising that I notice a problem.
Interesting statement on the caster. Alignment guy did set it with a .6 difference, as you can see above. He said he's done this with lots of 993s and people have been happy. He feels the roads are crowned enough around here that its warranted. I asked him to set them equal both sides (after I'd learned what he did) and he told me it was a full alignment to get it equalized. I figure I should wait till after replacing rack bushings and front ball joints before re-doing the alignment.
That's a lot of information all at once. To summarize my questions:
- How do I measure rake to confirm its OK?
- Does it sound like I should refresh all the bushings in my rear suspension? If so, should I do all the arms (to get balljoints as well) or go with bushing replacements only? I've read lots of BillVs posts so I am interested in going for sport bushings RS-style in the rear.
- How important are subframe mounts? They are expensive (parts and labor) and I've read in other posts that they aren't that important to do for a street car. I'm ready to do it if it'll make the car drive better though.
- What do you think of the cross-caster? I will definitely get it equalized in the next alignment but I haven't convinced myself that this is the root cause of the issue.
Alignment numbers:
- Toe: 1/32 inch front left, 1/32 front right, 1/16 rear left, 1/16 rear right
- Camber: -.4 degrees front left, -.3 front right, -1.3 rear left, -1.2 rear right
- Caster: 4.8 degrees front left, 5.4 degrees front right
- Cross Camber: -.1 degrees front, -.1 rear
- Cross Caster: -.6 degrees front
- Total Toe: 1/16 inch front, 1/8 rear
- Thrust Angle: 0 degrees
For the bushings in the rear suspension, I tested by jacking the car and getting an assistant to work the wheel at 12 and 6 then at 3 and 9. I noticed no movement at 12 and 6 and a very small amount of movement at 3 and 9. I don't have another car to compare to but the movement was in the range of a few millimeters and I could feel the bushing moving on the lower rear toe link. I figured this was the kinetic toe in action.
The alignment mechanic told me that the rear bushing on the lower A arm as well as bushings on all the rear links had some wear evident but he didn't feel like it was enough to cause significant problems. I don't know if he's right about that or not, so take it for what its worth.
Regarding road surface. The smoother the road the more I notice the problem. On grooved or crowned roads the car doesn't exhibit much tramlining and the wandering is reduced. I'm guessing that the suspension or steering loads up a little in the groove and the looseness is less evident as a result.
Regarding rake, the car looks like it has a good stance and it was set up on RoW M030 springs to specified RoW height, six or seven years ago by a reputable shop, so unless something has settled, I think that's ok. Is there a way I can measure this at home?
Alignment guy said that KT was maxed out on one side when he started the alignment so he evened them out and got them both into what he said was correct range. He mentioned hanging the tool off of caliper mounts and said he set it to 6 on both sides. So I think he was using the aftermarket tool, not the factory tool. Handling in corners is predictable and good as far as I can tell. I feel confident pushing it in both higher and lower speed corners. In a tight turn with throttle application I get a nice bite in the front with just a bit of tail sliding at exit if I push hard enough. To my butt it feels really good when the suspension is loaded it up, its just in straight-line cruising that I notice a problem.
Interesting statement on the caster. Alignment guy did set it with a .6 difference, as you can see above. He said he's done this with lots of 993s and people have been happy. He feels the roads are crowned enough around here that its warranted. I asked him to set them equal both sides (after I'd learned what he did) and he told me it was a full alignment to get it equalized. I figure I should wait till after replacing rack bushings and front ball joints before re-doing the alignment.
That's a lot of information all at once. To summarize my questions:
- How do I measure rake to confirm its OK?
- Does it sound like I should refresh all the bushings in my rear suspension? If so, should I do all the arms (to get balljoints as well) or go with bushing replacements only? I've read lots of BillVs posts so I am interested in going for sport bushings RS-style in the rear.
- How important are subframe mounts? They are expensive (parts and labor) and I've read in other posts that they aren't that important to do for a street car. I'm ready to do it if it'll make the car drive better though.
- What do you think of the cross-caster? I will definitely get it equalized in the next alignment but I haven't convinced myself that this is the root cause of the issue.
10-04-2016, 08:41 AM
#19
RL Community Team
Rennlist Member
Rennlist Member
Could be poor alignment. If rear tow is out a 993 will do this. I had the same issue at or above 70 MPH it felt like it wanted to wonder.
Andy
Andy
10-04-2016, 09:00 AM
#20
I would start with the basics. Check the rotors and wheels are flush. Someone on my car smeared so much anti-seize all over the wheel and the rotor it got hard and when the wheel was taken off and on it never sat flush and make my car wobble at slow speeds. I had to scrap it all off.
If the rotors has crud behind the mating surface it could do the same.
Are you wheels straight? are the tires the right size for the rim?
Just something else to think about..hard to diagnose your symptom on a web form.
You may want to take it to a Porsche specialist that knows what a 993 drives like not necessarily a dealer but a good Porsche suspension shop.
It doesn't say where you live but if your anywhere near this shop, he will fix it. http://fdmotorsports.net/
If the rotors has crud behind the mating surface it could do the same.
Are you wheels straight? are the tires the right size for the rim?
Just something else to think about..hard to diagnose your symptom on a web form.
You may want to take it to a Porsche specialist that knows what a 993 drives like not necessarily a dealer but a good Porsche suspension shop.
It doesn't say where you live but if your anywhere near this shop, he will fix it. http://fdmotorsports.net/
10-04-2016, 09:14 AM
#21
Alignment numbers:
- Toe: 1/32 inch front left, 1/32 front right, 1/16 rear left, 1/16 rear right
- Camber: -.4 degrees front left, -.3 front right, -1.3 rear left, -1.2 rear right
- Caster: 4.8 degrees front left, 5.4 degrees front right
- Cross Camber: -.1 degrees front, -.1 rear
- Cross Caster: -.6 degrees front
- Total Toe: 1/16 inch front, 1/8 rear
- Thrust Angle: 0 degrees
- What do you think of the cross-caster? I will definitely get it equalized in the next alignment but I haven't convinced myself that this is the root cause of the issue.
measure the ride height so you can cross rake off the list, then you'll have to go back to checking bushings.
10-04-2016, 10:24 AM
#22
Three Wheelin'
Thread Starter
I would start with the basics. Check the rotors and wheels are flush. Someone on my car smeared so much anti-seize all over the wheel and the rotor it got hard and when the wheel was taken off and on it never sat flush and make my car wobble at slow speeds. I had to scrap it all off.
If the rotors has crud behind the mating surface it could do the same.
Are you wheels straight? are the tires the right size for the rim?
Just something else to think about..hard to diagnose your symptom on a web form.
You may want to take it to a Porsche specialist that knows what a 993 drives like not necessarily a dealer but a good Porsche suspension shop.
It doesn't say where you live but if your anywhere near this shop, he will fix it. http://fdmotorsports.net/
If the rotors has crud behind the mating surface it could do the same.
Are you wheels straight? are the tires the right size for the rim?
Just something else to think about..hard to diagnose your symptom on a web form.
You may want to take it to a Porsche specialist that knows what a 993 drives like not necessarily a dealer but a good Porsche suspension shop.
It doesn't say where you live but if your anywhere near this shop, he will fix it. http://fdmotorsports.net/
I'm out in the middle of nowhere unfortunately, not close to FDMotorsports.
10-04-2016, 10:35 AM
#23
Three Wheelin'
Thread Starter
Front Left: 685mm
Front Right: 685mm
Rear Left: 667mm
Rear Right: 665mm
What do you think?
BTW - I've removed spare tire, compressor and tools from the front - thinking that weight removal would be a good thing. Could that mess up my rake?
Last edited by Tlaloc75; 10-04-2016 at 10:55 AM.
10-04-2016, 11:15 AM
#24
next time you are at a hardware store buy a small turnbuckle, remove the screw from one end and use it to measure the ride height from the factory measuring points.
fender heights can be inaccurate, but based on the numbers you posted you might not have any rake at all.
if you have a digital level you can place it on the door sill to get a measurement.
fender heights can be inaccurate, but based on the numbers you posted you might not have any rake at all.
if you have a digital level you can place it on the door sill to get a measurement.
10-04-2016, 11:19 AM
#25
Three Wheelin'
Thread Starter
Good tip, thanks I'll do that.
What do you think of the other questions I had above?
- Does it sound like I should refresh all the bushings in my rear suspension? If so, should I do all the arms (to get balljoints as well) or go with bushing replacements only? I've read lots of BillVs posts so I am interested in going for sport bushings RS-style in the rear.
- How important are subframe mounts? They are expensive (parts and labor) and I've read in other posts that they aren't that important to do for a street car. I'm ready to do it if it'll make the car drive better though.
What do you think of the other questions I had above?
- Does it sound like I should refresh all the bushings in my rear suspension? If so, should I do all the arms (to get balljoints as well) or go with bushing replacements only? I've read lots of BillVs posts so I am interested in going for sport bushings RS-style in the rear.
- How important are subframe mounts? They are expensive (parts and labor) and I've read in other posts that they aren't that important to do for a street car. I'm ready to do it if it'll make the car drive better though.
10-04-2016, 12:08 PM
#26
Three Wheelin'
Thread Starter
I managed to measure at the factory locations with a flexible tape measure. This is what I got:
- Front 155mm
- Rear 125mm
It appears I'm at the correct rear height for RoW M030, but not correct in front, 10mm too high.
- Front 155mm
- Rear 125mm
It appears I'm at the correct rear height for RoW M030, but not correct in front, 10mm too high.
10-04-2016, 01:21 PM
#28
I would suggest that your ride height is 20mm off to get at least .5 degree of forward rake.
so either raise the rear or lower the front or some combination of both. if your roads are good you could go for 135mm in front. but you will need to have another alignment done, and there might be a reason why the ride height is set the way it is, maybe lack of threads on the spring collars.
take it back to the alignment shop and talk to the guy about measuring forward rake and trying to get at least .5 degrees of forward rake. see what he can do.
having the front so high seems like a good reason for the front end feeling wayward.
if you are looking for a winter project replacing the rear bushings is fun. remove the arms and check the ball joints, if they are good just replace the bushings.
rennline has sport rubber subframe mounts now. pretty easy job with an air chisel.
so either raise the rear or lower the front or some combination of both. if your roads are good you could go for 135mm in front. but you will need to have another alignment done, and there might be a reason why the ride height is set the way it is, maybe lack of threads on the spring collars.
take it back to the alignment shop and talk to the guy about measuring forward rake and trying to get at least .5 degrees of forward rake. see what he can do.
having the front so high seems like a good reason for the front end feeling wayward.
if you are looking for a winter project replacing the rear bushings is fun. remove the arms and check the ball joints, if they are good just replace the bushings.
rennline has sport rubber subframe mounts now. pretty easy job with an air chisel.
10-04-2016, 01:30 PM
#29
Three Wheelin'
Thread Starter
I see plenty of thread, so I think it should be ok to lower a little further. Alignment guy asked me to change it myself and then bring in for an alignment check. Should the car be on the ground to adjust the height, or can I do it jacked up?
How do I check the ball joints? I'm not sure how to tell if they are still good or not. Do I need to put them under load or is it enough to check boots and then rotate them by hand once off the car to see if they are still tight?
How do I check the ball joints? I'm not sure how to tell if they are still good or not. Do I need to put them under load or is it enough to check boots and then rotate them by hand once off the car to see if they are still tight?
10-04-2016, 01:57 PM
#30
Drifting
Matt had mentioned earlier, all the rubber in the suspension is far from optimal at this age and mileage. If you have the means to do it, then yes. Although since you mentioned driving thru corners isn't an issue, I'm inclined to think your immediate concern might not be related to the rear setup.
If you decide to re-fresh the rear, the lower A and subframe mounts, toe arms are typically the best options if budget is your limited. But ideally all new arms would the best option. Replacing just the rubber wouldn't be ideal as most likely the ball joints are on their way out too (these are not replaceable unless getting a new arm). As you can see this can be a very slippery slope!
If you decide to re-fresh the rear, the lower A and subframe mounts, toe arms are typically the best options if budget is your limited. But ideally all new arms would the best option. Replacing just the rubber wouldn't be ideal as most likely the ball joints are on their way out too (these are not replaceable unless getting a new arm). As you can see this can be a very slippery slope!