Rear Subframe Bushings oddities

[alcyon]

I am in the midst of installing the rear RonnieK subframe bushings and found something odd.
The thickness of the rear 2 bushing mounts vs the 4 front bushing mounts are very different.
The front 4

and the rear 2

If the subframe thickness is not the same , why are all the 6 bushings the same dimensions ? Wouldn't we also need shorter spacers for the last 2 ? But all the bushings and spacers are the same length. In theory, if assembled as is,the subframe could actually slide up and down. I mean for poly bushings, isn't it supposed to be gripping the subframe above and below so that the subframe cannot move up and down ?
below are the bushings placed back to back, the minimum achievable dimension is 60.5mm so minus with 58mm, that is gap of 2.5mm!
I noticed for other brands like strongflex, the last 2 rear bushings are a different part number, this is also true for the OEM bushings.


Below are part numbers for the front 4s

and the last 2 diff bushings

What are your experiences with Ronnie K rear subframe bushings and with other brands like Strongflex. How are the strongflex ones different for the last 2 bushings ? Does anyone know the actual datum level for the subframe mounting points so I can be sure I am levelling the subframe correctly ?

 

[alcyon]

Looks like i was wrong, i used my pushing jig to get the bushings out and I placed a wood ruler above the rear bushing hole top surface on the subframe, and insert the caliper tail from the bottom, indeed the rear is also 65mm, NOT 58mm as I said earlier, I had difficulty measuring that area with a caliper and got it wrong last night. So indeed all 6 bushings are the same. I compared the pressed out OEM bushings and they all measure the same. A mock up placement of the new poly bushings however shows that the spacers that came with the bushing set is too long. at 75mm, the ends are same level as the bushing ends, that means the poly bushes will not be compressed. So i got some one to cut all 6 spacers down by 2mm. The original lengths are 75mm, they are now 73mm.
Here are some pics of the subframe with the OEM bushes pushed out, there are some surface rust so i am applying some CRC rust converter on these areas.



And here are the pics of the bushing pushing jig in action, the good thing about using this jig is no damage to the subframe holes. If any wants wants the technical drawings for this jig just ask.


Its almost midnight now, so will install the poly bushings tomorrow, hopefully I can finish up soon.

 

[mobes]

Nice, glad to see that you've figured it out. I was curious myself, I did not notice anything like that when I installed mine (though it's been ~10 years) but I have also heard anecdotes in the past of variations in the subframes and bushings.

 

[steve_mk3]

I needed to do the same on the spacers, both front and rear. 2mm.

 

[Piratetip]

All the Super pro rear subframe bushings I pressed in were dimensionally the same.
Had no issues with bolting/alignment up to the body.

There should be no difference between them.

 

[alcyon]

So today I managed to install the bushings. I figured I should add a stainless steel washer to spread the load from the center collars.


So I torqued all the bushings up and went for a test drive. I felt something was off. It felt like the subframe was shifting everytime i shifted from N to D, and whenever I accelerate hard or accelerate then let off . Could it be that this washer is causing the subframe to shift around a little because the metal washer to the chassis has low friction ? Do you guys think if by removing this washer, and letting the poly press against the unibody would prevent this shifting since this poly will grab the unibody ?
There is some diff whine on accel and decel, but I guess this is the nature of poly bushes even soft ones. I can live with that, but the shifting worries me.

 

[steve_mk3]

From above - this is why your subframe is moving around-

shows that the spacers that came with the bushing set is too long. at 75mm, the ends are same level as the bushing ends, that means the poly bushes will not be compressed. So i got some one to cut all 6 spacers down by 2mm. The original lengths are 75mm, they are now 73mm.

 

[alcyon]

From above - this is why your subframe is moving around-

shows that the spacers that came with the bushing set is too long. at 75mm, the ends are same level as the bushing ends, that means the poly bushes will not be compressed. So i got some one to cut all 6 spacers down by 2mm. The original lengths are 75mm, they are now 73mm.

Ok i removed the washers, it seems the 2 washers at the rear are deformed ! Now they are nice snug and tight, no way the subframe will move.
However the clunking is still there. It happens whenever the car isnt moving and i put it from N to D. It also happens when I let off the gas abruptly after acceleration, and as coming to a stop. As far as i know, once the wheel nuts are tight, the rotor cannot slip and move and engage the wheel studs like when the wheel is off. So I suspect the center bearing and or the diff backlash. When I leave the trans in D and just keep brakes on, as soon as i release the brakes and accelerate there is no clunk at all.

 

[destrux]

It's likely diff backlash. Even with a fresh diff in the car you still hear that clunk because of how much noise the poly transmits.

Make sure your diff is bolted tight to the subframe though and that the subframe isn't cracked at the mount holes near the diff yoke because that's pretty common.

 

[Piratetip]

At .005" backlash I have no more clunking in my rear.
For an old worn out diff, yes there will be an audible noise.

I have a manual as well so that may attribute to the difference.

@3p141592654 are you getting any noise from R to D or D to R on the new diff?

 

[Enraged]

what would cause a knocking only on turns to one side? diff? I think my diff needs a rebuild.

 

[Piratetip]

Could be diff.
Could be worn CV 's

 

[alcyon]

I just opened up my diff yesterday and sending the diff and prop shaft for rebuild, may also send the CV joints but they seem fine. Btw, the clunk isnt a one clunk, but a clunk clunk. Its like as soon as i engage D, one clunk then less than a second later another clunk as it "settles"

 

[NashMan]

i used a dead blow .....

 

[3p141592654]

@3p141592654 are you getting any noise from R to D or D to R on the new diff?

None. My shifts are clunk free but I have the OEM subframe bushings.

 

[Piratetip]

Nice