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-   -   740: Torque Rod Bushing Options (https://forums.turbobricks.com/showthread.php?t=356003)

FreeEMSFred 07-17-2020 11:07 AM

Torque Rod Bushing Options
The factory bushings in my early solid axle 960 torque rods are flogged enough to move quite a lot and cause some driveshaft vibration in 1st gear under load (only). I see IPD does OEM and aftermarket similar - are there stiffer/better options available commercially? I couldn't find any. I could get some made up but thought I'd ask around first.

What about rotating them 90 degrees? Or putting fresh ones in 90 degrees rotated? Bad idea? Common practice? Other?

Cheers! :-)

sbabbs 07-17-2020 04:40 PM


classicswede 07-17-2020 05:20 PM

I stock the poly bushes for them but as you are near the home of Super Pro they should be easy for you to get local

gsellstr 07-17-2020 06:06 PM

Honestly, I put in the Superpro stuff a good 8-9 years ago and have been quite happy with them, even while throwing some power thru them. I do have some adjustable torque rods to throw in the car still, haven't done it yet, but I wouldn't hesitate to run the Superpro stuff. Given you're on the same continent as them, hit them up or see if you've got a local distributor. SPF-4775K is a pair of the big ones.

Putting those in got rid of all that slop in the rear end.

FreeEMSFred 07-18-2020 12:11 AM

Thanks guys, that's exactly what I wanted to hear! And the part number, I feel spoilt! :-D

I will find a supplier and get a set or two, do you happen to know the part number for the front end ones? May as well tighten up that end at the same time.

I need to dig up the TIG-weld reinforcement strategy for those arms so I can do this once and it's ready for big power in future :-)

Ditto for the subframe thingy. Not a problem right now, but the internet says it will become one sooner or later :-D

FreeEMSFred 07-18-2020 08:38 AM

This appears to be the front ones: spf3120k

gsellstr 07-18-2020 06:07 PM

Yup, that's correct for the fronts. Usually the fronts aren't too bad, but if you're doing them, do them both.

Pro tip on the rear's. Once you have the old ones out, the torque rods cleaned up, grease the crap out of the bushing, put it into a piston ring compressor, tighten it down as much as you can, then press it into the torque rod. The spring compressor helps compress it but it also helps guide it in straight. Sadly I figured this out on my third set or so of these (friends cars), and after launching a few greased up bushings across the shop. lol

Honestly, if you can keep the subframe straight, chances are the torque rods will hold up fine. I don't drift, but I also don't behave in mine and it has seen a LOT of 1/4 mile passes, including a good number with slicks, and they haven't had an issue, but I boxed the subframe up a long time ago. There's external plating, plus a cross brace internally, so chances of it moving are pretty damn small. lol

tintintin 07-18-2020 09:47 PM

Are we talking about the dogbones, one large end, one small end? Bolts to the differential carrier?

FreeEMSFred 07-18-2020 10:13 PM

^ yes we are.

Thanks gsellstr, good to know. Best pass? Not keen to do work that's not needed, and TIG welding would weaken the metal around the weld while adding overall strength so that did bother me, plus WOF concerns with modified arms would mean I'd have to do a stealthy job and paint them if I did mod.

LOL @ launched greasy bushings :-D good tip - I don't own one, but have various engines to assemble so it should be on my shopping list and can move closer to the top now.

gsellstr 07-18-2020 10:49 PM

Best to date is 13.3 @ 105, haven't run in close to a year, done a good bit of work since, tune related, but hurt the motor prior to it.

tintintin 07-19-2020 02:59 PM

How can you tell if the bushings need replacing?

gsellstr 07-19-2020 07:59 PM

You'll see cracks and crumbling of the rubber. The front ones usually hold up a lot better than the rear, being a full bushing, where the rear ones tend to fall apart sooner, since there's so much flex in them during normal driving. Think square bushing in a round hold, with the gap being in the fore/aft direction, so every load change causes significant flex in the bushing.

The Superpro bushings are round, taking out that flex.

FreeEMSFred 07-20-2020 08:03 AM

Driveshaft vibrations from misalignment in my case, tintintin. Could be other causes, but it's a first gear and heavy load only thing, and you can see the wear marks showing the movement to be enough to cause an angular misalignement of the yolks.

I'll get this fixed first (after the broken rear window, that is) and if there's still issues after that then I'll keep chasing them.

13.3 is pretty respectable for sure. Guessing you're around 300whp with that time?

gsellstr 07-20-2020 11:27 AM

Yeah, right around that.

tintintin 07-20-2020 02:37 PM

Reverse was not affected?

FreeEMSFred 02-11-2021 10:59 PM

Reverse is affected if you floor it in reverse, which is a fairly brutal thing to do in most scenarios :-D

I just ordered 2 sets of these SuperPro parts, 1 set will be here "soon" coming on a courier from Aussie and the other with other orders in future to upgrade my 740 sedan.

It has been getting a bit worse, and I had to tow a trailer the other day and it was chronic until 40-50kph and lifting a bit. Annoying. Parts on the way, should be resolved soon.

FreeEMSFred 02-22-2021 12:51 AM

For the record, the SPF3120K kit is for one bar only, so the correct order for these for one car is as follows:

1x SPF4775K
2x SPF3120K

I now have one of each, but I can do the lower front ones later when the rest of the order arrives for my 740 16v sedan that isn't yet showing any issues, but gets a hard time :-)

gsellstr 02-22-2021 11:23 AM

Yup, that's correct on the part numbers. They combined the 3121's into a single 4775 a few years ago, but they haven't done the 3120's for some reason. Fun fact, that 4775 is the same bushing as the late 140 front trailing arm bushing. lol

FreeEMSFred 02-22-2021 05:48 PM

Interesting. I was guessing the 3120 had some other application as it is a very generic shape. Surprised the 4775 is though! :-D

FreeEMSFred 03-04-2021 02:03 AM

And I picked up some special order WLN14SP nordlock washers (8, for 2 cars) today, a little spendy for a handful of washers, but a really good product in my personal experience. Can't hurt, can help a lot. There is enough extra thread, just, for them on the front end, and I think plenty on the back end inside the diff casting.



Also collected my new ring compressor, and results are as follows:

32mm hole ID in free form
29x30mm oval hole ID as tight as I could get it without fear of damaging the tool

Is the below the right type of ring compressor and if so, how much were you able to squeeze them down? Urethane is at approx room temperature in case that was a factor.



I'm not happy with the supplied pins, though, they're very heavy, so I'm going to bore them out nearly to the other end and press in a bolt guide at the drilled out end so they're hollow in the middle and under half the weight. Currently 764g for the pair, or 1.7lb in them! Not including the urethane. Too much.


gsellstr 03-04-2021 12:06 PM

That ring compressor is the same as I use. It won't do a lot, but it's enough to shrink them a little and also help guide them and start them straight...the biggest issue when they are all slimed up.

The inner sleeves are indeed a little on the heavy side, not sure the reasoning for the added thickness over the stock ones. Superpro does tend to make their stuff a little beefier than stock in quite a few cases though.

FreeEMSFred 03-04-2021 08:16 PM

Thanks for confirming! :-)

As for the sleeves, the reasons are obvious, I think:

1. The OD has to be large to make the soft urethane reliable, and this is why the Volvo factory lower trailing arm bush has a layer of steel in the middle of the rubber, too
2. The ID has to be a hair bigger than the bolt to keep it centred
3. It'd be expensive to make it semi hollow manufacturing wise.

The end :-D

I don't think it's crap that they ship that way, I just want better, no biggy :-)

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