Rear subframe lock bolts - wow
17 April 2012, 08:30 PM
#1
Rear subframe lock bolts - wow
What a huge difference these make. Makes the rear feel totally connected to the car.
No increase in NVH, so it's all positives. Highly recommended
The Whiteline ones can be used, but for a super cheap solution, try this:
2 - M12x1.25 Bolts 50-60mm long (must be grade 8.8 or higher! I recomend 10.9 if you can find them.)
2 - 3/4" OD x 1/2" ID Bronze Flange Bearing
Brilliant mod for any Scooby. Enjoy
No increase in NVH, so it's all positives. Highly recommended
The Whiteline ones can be used, but for a super cheap solution, try this:
2 - M12x1.25 Bolts 50-60mm long (must be grade 8.8 or higher! I recomend 10.9 if you can find them.)
2 - 3/4" OD x 1/2" ID Bronze Flange Bearing
Brilliant mod for any Scooby. Enjoy
18 April 2012, 01:28 PM
#3
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I have recently fitted these too. Made a nice little difference - might as well do it considering how cheap they are! Pics can probably be seen on my project thread.
18 April 2012, 02:10 PM
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Ah excellent good to hear positive reviews on these I still need to fit mine. Were you able to just install the bolts straight into the holes or did you have to loosen the subframe bolts either side of the holes?
18 April 2012, 02:30 PM
#7
It's very unlikely the shoulders of the lock bolt will slide straight in, without first loosening all 4 subframe bolts. You can try it, you might be lucky.
Also advisable to get the rear alignment rechecked once fitted
BTW - you might also need to chase out the thread with a m12x1.25 tap before inserting the bolt
Also advisable to get the rear alignment rechecked once fitted
BTW - you might also need to chase out the thread with a m12x1.25 tap before inserting the bolt
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18 April 2012, 03:29 PM
#8
Just my take on it: I'd keep an eye on your trailing arm and wishbone bushes with these are fitted.
As what happens when locking the subframe is it prevents the trailing arms pulling on the wishbone and in-turn pulling the subframe (rubberised) mounts. Without the locking bolts, the trailing arm normally creates a passive rear-steer effect under hard cornering. This can get worse as the suspension rubbers detriorate with age (anything above five years old depedning on how much its driven on salty roads without being washed off underneath IMO ).
Locking the subframe obviously eleminates the sloppyness caused by perishing subframe mounts, but it does put more strain on trailing arm bushings and more importantly the wishbone bushings (all located by rubber).
So IMO, if you do see a remarkable improvement after fitting these, I think the rest of your suspesnion rubber bushings are past their prime....another excuse to get more whiteline stuff
The rear suspesnion setup on old Jaguars is very similar in this respect apart from the wishbones are solidly bolted to the frame (the Impreza is rubberised - hence the issue). And when those are modified for racing/fast road, they rigidly bolt/brace the subframe to the chassis, by doing this the rear trailing arms can be removed entirely (infact later cars, like the XK8 did exactly this). Its pretty well documented with regards to this and the effects it had on rear-steer geometry.
In theory you should be able to do this on Imprezas (except the hatch), BUT I think the wishbones and subframe/mounts would need to be made much stronger and the wishbones would need to be solidly mounted to the subframe. Not impossible for a good fabricator though, and would give an awesome fast road/track setup
As what happens when locking the subframe is it prevents the trailing arms pulling on the wishbone and in-turn pulling the subframe (rubberised) mounts. Without the locking bolts, the trailing arm normally creates a passive rear-steer effect under hard cornering. This can get worse as the suspension rubbers detriorate with age (anything above five years old depedning on how much its driven on salty roads without being washed off underneath IMO ).
Locking the subframe obviously eleminates the sloppyness caused by perishing subframe mounts, but it does put more strain on trailing arm bushings and more importantly the wishbone bushings (all located by rubber).
So IMO, if you do see a remarkable improvement after fitting these, I think the rest of your suspesnion rubber bushings are past their prime....another excuse to get more whiteline stuff
The rear suspesnion setup on old Jaguars is very similar in this respect apart from the wishbones are solidly bolted to the frame (the Impreza is rubberised - hence the issue). And when those are modified for racing/fast road, they rigidly bolt/brace the subframe to the chassis, by doing this the rear trailing arms can be removed entirely (infact later cars, like the XK8 did exactly this). Its pretty well documented with regards to this and the effects it had on rear-steer geometry.
In theory you should be able to do this on Imprezas (except the hatch), BUT I think the wishbones and subframe/mounts would need to be made much stronger and the wishbones would need to be solidly mounted to the subframe. Not impossible for a good fabricator though, and would give an awesome fast road/track setup
Last edited by ALi-B; 18 April 2012 at 03:33 PM.
18 April 2012, 03:46 PM
#9
The downside of poly bushes, whether whiteline or other, is that they dry out. When this happens they bind and squeak or crack while trying to move. You may not wish to have to service your bushes, particularly the hard to get at one's. new OE rubber bushes would give an improved feel without the issues IMO.
18 April 2012, 03:54 PM
#10
Yeah, I have mixed feelings about the polys. This is why I like the idea of solid mounts with sealed rose joints. Probably not so nice for isolation/vibrations, but the poly bushes can be just as bad.
For certain keep the trailing arm bushes as standard rubber.
For certain keep the trailing arm bushes as standard rubber.
18 April 2012, 05:14 PM
#11
Ali - Thanks for coming in. Quite a few of the mid 2000 year STi's have solid rear subframe mounts. (so if you have one of these you don't need the bolts)
Here's a pic of a 02-07 WRX subframe mount, allowing the subframe to float.
Here's a 2005 STi. The 04-05 STi's, have non-rubber isolated mounts. In other words, they are solid metal. These mounts do not allow the subframe to translate relative to the chassis, therefore lock bolts are useless. Here is a picture of a 2005 STi subframe.
HOWEVER, having said this, Whiteline state the bolts should be installed before / removed after "race meetings", because of potential premature chassis wear.
BUT, Scooby folk have been using the lock bolts for years and I cannot find one instance of complaint
As for trailing arms, pillow ball bushing are the way to go
Here's a pic of a 02-07 WRX subframe mount, allowing the subframe to float.
Here's a 2005 STi. The 04-05 STi's, have non-rubber isolated mounts. In other words, they are solid metal. These mounts do not allow the subframe to translate relative to the chassis, therefore lock bolts are useless. Here is a picture of a 2005 STi subframe.
HOWEVER, having said this, Whiteline state the bolts should be installed before / removed after "race meetings", because of potential premature chassis wear.
BUT, Scooby folk have been using the lock bolts for years and I cannot find one instance of complaint
As for trailing arms, pillow ball bushing are the way to go
18 April 2012, 05:37 PM
#12
Now, that I didn't know LOL. 
I need to pay more attention when I'm looking under a Sti 
I think when whiteline say premature chassis wear I think they they are covering their ***** saying its anything chassis related, but I think its the arm bushings that are taking the brunt of it.
I need to pay more attention when I'm looking under a Sti I think when whiteline say premature chassis wear I think they they are covering their ***** saying its anything chassis related, but I think its the arm bushings that are taking the brunt of it.
18 April 2012, 07:23 PM
#13
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Its the type r/ra that have fixed mountings, is it not? mine certainly is.
I wouldnt recommend anybody to loosen rear subframe bolts on an old uk classic without being aware that the captive nuts can break loose.
I wouldnt recommend anybody to loosen rear subframe bolts on an old uk classic without being aware that the captive nuts can break loose.
19 April 2012, 12:52 PM
#14
[QUOTE=ALi-B;10583989]Yeah, I have mixed feelings about the polys. This is why I like the idea of solid mounts with sealed rose joints. Probably not so nice for isolation/vibrations, but the poly bushes can be just as bad.
[QUOTE]
I've used rose joints before and they work well up to the point they wear out. Keeping them clean is key (with rubber boot covers) and also lubricated.
[QUOTE]
I've used rose joints before and they work well up to the point they wear out. Keeping them clean is key (with rubber boot covers) and also lubricated.
19 April 2012, 01:39 PM
#16
Ali-B .... the passive rear steer found on the rear is dialled into how the subframe flexes, the nvh from cornering is dialled into the lateral link bushes, and the nvh from rough ground is dialled into the trailing arms.
Ive done a quick rough and ready FEA looksy on the standard subframe before beefing it up and its pretty clever what subaru did with this as it seperated the nvh to handling compromise into the 3 distinct areas. i had no idea about the passive rear stability in the subframe till i did this, but what they did here was pretty bloody clever! As the loaded side directs force into the subframe, the forward lateral point is designed to flex more than the rear most lateral point, therefore toeing in the rear and adding stability!
Solid mounting the sti subframe (which is alot stiffer in itself therefore has less passive rear wheel steer/deflection stability) must make a fairly significant difference!
Ive gone a bit further and have strengthened the hole subframe, while lifting the pickup points to help bring the roll centre back up, and theres a spider which ive yet to make which will go on after the diff goes in to hopefully massively reduce all this comfort compromise flex.
End result should be like this. Its a bit of an experiment and im half expecting it to be a bit too rattley for every day road use. This subframe, polybushed to the chassis, with lock bolts as well, and rose jointed laterals, plus a poly at the hub end of the trailing arm and rose joint the other .... almost definately wont be needing the locking bolts! :-)
Can sort of see the end result here.
Ive done a quick rough and ready FEA looksy on the standard subframe before beefing it up and its pretty clever what subaru did with this as it seperated the nvh to handling compromise into the 3 distinct areas. i had no idea about the passive rear stability in the subframe till i did this, but what they did here was pretty bloody clever! As the loaded side directs force into the subframe, the forward lateral point is designed to flex more than the rear most lateral point, therefore toeing in the rear and adding stability!
Solid mounting the sti subframe (which is alot stiffer in itself therefore has less passive rear wheel steer/deflection stability) must make a fairly significant difference!
Ive gone a bit further and have strengthened the hole subframe, while lifting the pickup points to help bring the roll centre back up, and theres a spider which ive yet to make which will go on after the diff goes in to hopefully massively reduce all this comfort compromise flex.
End result should be like this. Its a bit of an experiment and im half expecting it to be a bit too rattley for every day road use. This subframe, polybushed to the chassis, with lock bolts as well, and rose jointed laterals, plus a poly at the hub end of the trailing arm and rose joint the other .... almost definately wont be needing the locking bolts! :-)
Can sort of see the end result here.
Last edited by legacy_gtb; 19 April 2012 at 01:42 PM.
20 April 2012, 01:39 PM
#20
Ali-B .... the passive rear steer found on the rear is dialled into how the subframe flexes, the nvh from cornering is dialled into the lateral link bushes, and the nvh from rough ground is dialled into the trailing arms.
Ive done a quick rough and ready FEA looksy on the standard subframe before beefing it up and its pretty clever what subaru did with this as it seperated the nvh to handling compromise into the 3 distinct areas. i had no idea about the passive rear stability in the subframe till i did this, but what they did here was pretty bloody clever! As the loaded side directs force into the subframe, the forward lateral point is designed to flex more than the rear most lateral point, therefore toeing in the rear and adding stability!
Solid mounting the sti subframe (which is alot stiffer in itself therefore has less passive rear wheel steer/deflection stability) must make a fairly significant difference!
Ive gone a bit further and have strengthened the hole subframe, while lifting the pickup points to help bring the roll centre back up, and theres a spider which ive yet to make which will go on after the diff goes in to hopefully massively reduce all this comfort compromise flex.
End result should be like this. Its a bit of an experiment and im half expecting it to be a bit too rattley for every day road use. This subframe, polybushed to the chassis, with lock bolts as well, and rose jointed laterals, plus a poly at the hub end of the trailing arm and rose joint the other .... almost definately wont be needing the locking bolts! :-)
Can sort of see the end result here.
Ive done a quick rough and ready FEA looksy on the standard subframe before beefing it up and its pretty clever what subaru did with this as it seperated the nvh to handling compromise into the 3 distinct areas. i had no idea about the passive rear stability in the subframe till i did this, but what they did here was pretty bloody clever! As the loaded side directs force into the subframe, the forward lateral point is designed to flex more than the rear most lateral point, therefore toeing in the rear and adding stability!
Solid mounting the sti subframe (which is alot stiffer in itself therefore has less passive rear wheel steer/deflection stability) must make a fairly significant difference!
Ive gone a bit further and have strengthened the hole subframe, while lifting the pickup points to help bring the roll centre back up, and theres a spider which ive yet to make which will go on after the diff goes in to hopefully massively reduce all this comfort compromise flex.
End result should be like this. Its a bit of an experiment and im half expecting it to be a bit too rattley for every day road use. This subframe, polybushed to the chassis, with lock bolts as well, and rose jointed laterals, plus a poly at the hub end of the trailing arm and rose joint the other .... almost definately wont be needing the locking bolts! :-)
Can sort of see the end result here.
I'm liking that alot.
Is that all painted or power coated?Did you do anything to modify the front subframe too?
I agree there is definetely some engineered flex in the original subframes, I mean its pretty thin pressed steel, so its rididity comes mainly from its shape.
(Jags are the same as I'm currently rebuilding one, but unsure to go about strengthening it, its just a folded box of ~1.5mm thick mild steel, although it does use the diff and fulcrum pins to act as a brace to reinforce it).
20 April 2012, 07:11 PM
#21
Its all powder coated.
Yes matey, theres definately engineered flex there, if you look at that vid, at 15 seconds you can see the rear most point is on a wall with a folded edge, and the forward point is just a wall, so can flex for some toe in under load!
The bit that should do most of the work is the spider which will get fabbed on once the diff and exhaust are on.
Probably worth mentioning its a bit of an experiment handling wise stiffening up the **** end this much, but im reshelling an existing car so the standard ones coming out and getting powdered red just in case -the roll centre adjustment doesnt work -stiffening is overkill for the road. - effect isnt noticable enough to warrant the kg or two of steel and mig wire ive stuck into it.
Front subframe i left alone, on the last build i found the h brace and strutbrace into the firewall beefed things up quite alot.... Heres the hole shebang, h brace obviously thing on the left and strutbrace at the front of the black bit. Included a master cylinder stopper bar off this too which worked really well and is alot more discreet than the big chunky brackets that hang off the tower.
Really looking forward to reshelling the old girl now! :-)
Yes matey, theres definately engineered flex there, if you look at that vid, at 15 seconds you can see the rear most point is on a wall with a folded edge, and the forward point is just a wall, so can flex for some toe in under load!
The bit that should do most of the work is the spider which will get fabbed on once the diff and exhaust are on.
Probably worth mentioning its a bit of an experiment handling wise stiffening up the **** end this much, but im reshelling an existing car so the standard ones coming out and getting powdered red just in case -the roll centre adjustment doesnt work -stiffening is overkill for the road. - effect isnt noticable enough to warrant the kg or two of steel and mig wire ive stuck into it.
Front subframe i left alone, on the last build i found the h brace and strutbrace into the firewall beefed things up quite alot.... Heres the hole shebang, h brace obviously thing on the left and strutbrace at the front of the black bit. Included a master cylinder stopper bar off this too which worked really well and is alot more discreet than the big chunky brackets that hang off the tower.
Really looking forward to reshelling the old girl now! :-)
21 April 2012, 07:44 AM
#22
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Reading all this had got me wondering.... As I'm planning to rebush my car soon (2002 WRX) is it worth gettin an STI subframe, are they stiffer/stronger than the WRX on a 2002?
21 June 2012, 01:13 PM
#23
Hi
I've got the rear subframe off my 95 wrx, to fit poly bushes, and re-install it with locking bolts in place. Should I install any form of bracing while I'm at it? Either bolt on: I like the second link, as it picks up on the locking bolts - it's listed for a newage, would it fit a classic?
http://www.invoauto.co.uk/images/Pro...-ON-CAR-LR.jpg
http://www.invoauto.co.uk/images/Pro...sb-rtb-lrg.jpg
Or I could weld in some bracing. What would be the best areas to brace for a daily driver.
I've got the rear subframe off my 95 wrx, to fit poly bushes, and re-install it with locking bolts in place. Should I install any form of bracing while I'm at it? Either bolt on: I like the second link, as it picks up on the locking bolts - it's listed for a newage, would it fit a classic?
http://www.invoauto.co.uk/images/Pro...-ON-CAR-LR.jpg
http://www.invoauto.co.uk/images/Pro...sb-rtb-lrg.jpg
Or I could weld in some bracing. What would be the best areas to brace for a daily driver.
Last edited by 2pot; 21 June 2012 at 01:17 PM. Reason: spelling
23 June 2012, 05:01 AM
#24
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check these out from japspeed mate rear subframe t brace set
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
Last edited by GORDON GT SERIES 11; 23 June 2012 at 05:02 AM.
23 June 2012, 07:51 AM
#25
check these out from japspeed mate rear subframe t brace set
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
23 June 2012, 07:11 PM
#26
check these out from japspeed mate rear subframe t brace set
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
http://japspeed.co.uk/Subaru-Impreza...et/p-24-1-530/
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