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Old 02-04-2018, 07:41 AM   #1
FreeEMSFred
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Default Volvo 740/940 Torque Rod Bushing Questions

Hello all,

Some time ago I bought a 1990 Volvo 940 GLE wagon for its B234F heart, quite cheaply. I drove it for a while, but it was unreliable, and running on borrowed time on a dodgy safety inspection. I pulled the engine, cut the front off, and converted the rear half to a caravan.

Today I removed the G80 axle assembly from it and installed my "indifferent differential" in it (no pinion/ring gears, no flange for the ring gear, no nose on the diff, cut/shut. Running Penrite 70w75 synthetic oil for lower friction on the inner bearings, etc. A good weight saving and friction reduction, then!

In the process of having it way up in the air and apart I noticed the frame that the two torque rods bolt to was forward of where I expected, and it was impossible to align the top torque rod bolt (lower removed for weight savings). I pulled the front two bolts and wiggled the alloy piece and bushing out, they looked OK and complete. I reassembled it with a little grease in the front to ease pushing it in and had the same issue. So I poked a small bar in the front and levered off the chassis and managed to push it all back about an inch until the two rear "spikes" seated into the little bushes up under the boot floor. This allowed the bolt to line up and insert easily. However with the handbrake (relocated to right inner guard, just behind pillows) applied, you could push/pull on the whole thing on the jockey wheel and feel it slide forward and back, rotating the diff in the bushes on the trailing arms. The default position of this arrangement was forward with the nose of the diff facing down more than I would have thought normal.

Then I remembered that when it was a car it had a horrible driveline vibration at any speed over about 25mph. The driveshaft had been DIY balanced, so I put it down to a bad job of doing that. However they were trying to balance it for some reason in the first place... Pinion angle! This explains it completely. What has me stuffed, though, is that from diagrams I've seen online, the bush situation is correct. I expected there to be a spacer bush missing from the front hole, but the diagram doesn't show that. Does anyone else have experiences of this nature or knowledge on the correct bush/position situation? I stuck my head under my 740 sedan and the frame is sitting back where you'd expect it to and all is aligned perfectly. Hmmmmm.

The beast in question:








Diagram I mentioned showing only what I saw, and nothing more:







Situation under the 940 caravan with the thing still forward before I stuck the crowbar in and pushed it back 25mm or so:














Any thoughts/comments welcome! :-)
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Old 02-04-2018, 03:18 PM   #2
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Quote:
it was impossible to align the top torque rod bolt (lower removed for weight savings).
You don't have the lower torque rod any more?

Quote:
and feel it slide forward and back, rotating the diff in the bushes on the trailing arms.
So, when the diff rotates, the upper rod pushes the subframe, but there's no lower rod to counteract by pulling it, keeping everything "in phase"?

Quote:
I stuck my head under my 740 sedan and the frame is sitting back where you'd expect it to and all is aligned perfectly.
With both torque rods in position.

This isn't a typical "4-link" suspension, where the upper rods attach to a fixed point on the body. The subframe floats for noise isolation.

Volvo designed it to have both rods there. Put the lower rod back in. Problem solved.
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Old 02-04-2018, 03:41 PM   #3
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Seems SO obvious now! I was looking at it very naively. Thanks!

The whole lot is going away, minus one rod from the upper (lower bracket removed from indifferent differential axle) to a new fixed mounting point, maybe tomorrow some time. There's no pinion angle to worry about anymore, anyway.

Flattening the floor through where the front mount currently resides is a larger priority than maintaining original geometry when there's no engine torque to transmit.

It only has to take braking forces from the handbrake when accidentally left on and attempted to tow, or intentionally left on to assist with steep descents at low speed, and dynamic ones once I get a braked coupling on it and refit the calipers.

If I don't get a chance to fold up and bolt on a new bracket, then I'll probably stuff a spacer in to reduce play and keep the thing uprightish.

You learn something every day. I can just imagine you sitting there shaking your head while writing that post Thanks again.
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Old 02-05-2018, 01:42 AM   #4
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Just the first thing that comes to mind..got the torque rods in the wrong location. Different length between the top and bottom.
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Old 02-05-2018, 02:23 AM   #5
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Nah, long/lower one was removed months ago, and upper one was still at the top - it fitted fine as soon as I levered the frame backward. For my purposes the frame is going away, possibly as a base for a welded up version for my 740 sedan so I can keep a stock one in case the WOF man complains. I just didn't realise it was a sliding mechanism, and has assumed wrongly that it was fixed in nature. The sliding mechanism makes perfect sense once someone (MasterBlaster) points it out to you! I should PM you about your sig, though.
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Old 02-05-2018, 11:37 AM   #6
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Yeah, for the tow vehicle at the very least!

Usually that subframe doesn't slide much at all when all the parts are in place.
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Old 02-06-2018, 10:01 AM   #7
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those bolt that fix the 2 dogbones to the diff housing are notrious for working lose over time.
Back when i did service on a 740 rally car i always made sure i checked those bolts for tightness during each service. I have seen them working lose, both on the rally car and on my 940 daily. I did apply loctite to those bolts before torqueing them down. Need lots of torque too. And tighten them only when the weight of the car is on the springs.
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Old 02-06-2018, 10:50 AM   #8
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^^^^^ nailed it. With poly in there you can tighten in the air, but locktite and a lot of torque is a must. I've had to retighten mine a few times over the years.
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Old 02-06-2018, 06:13 PM   #9
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Like how much torque are we talking here?
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Old 02-07-2018, 04:24 AM   #10
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i don't really remember, sorry. it's now 10+ years ago form me. But it's more then the final stage of a headbolt. 150Nm? 200Nm?
The bolt size is larger then that of a headbolt and made of similar tuff steel so it will take some serious torque. You may want to use an impact wrench with a torque stick or at least a 1/2m length torque wrench for proper leverage.
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Old 02-09-2018, 09:03 PM   #11
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I just rattled it in place on the medium setting of my large-bolt-breaking rattle gun for a second or so. Highly unlikely to come loose with that :-)

/me wanders off to post some carnage photos in his 740 thread...
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Old 02-13-2018, 01:51 PM   #12
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