IRS Urethane Bushings - Lots of questions [Renamed]

[Evil_Fiz]

I just received a new set of Red urethane IRS pivot bushings.
- The urethane inserts fit the trailing arm snugly
- The metal sleeve fits inside the urethane inserts snugly
- BUT... it feels like there is TOO MUCH play in the fit between the bolt and the new metal sleeve

- The OD of the bolts is ~21.94mm
- The ID of the new metal sleeve is ~22.43 and feels sloppy
- The ID of the metal sleeve in the OE bushings is ~22.1mm and feels much better
Is .5mm (19.7 thousandths) clearance too much?

I looked online for a suitable replacement sleeve. I can find bronze sleeves with the correct OD and ID but not long enough to replace the one-piece unit.
Does anyone have a source for sleeves of appropriate dimensions?

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Emil

[Bruce.m]

~0.1mm is a nice engineering slip fit, so no surprise for the stock parts but consistently making the tube to that ID is more expensive than a more generous ID tube with variable tolerances.

In use the acceleration & braking could shift the tube but it will be clamped each end by the washer &/or chassis.

If you can’t get a suitable tube (ideally in stainless unless you live in a dry state), there is a somewhat hacky fix.

You could lightly peen the bolt OD with a sharp centre punch in straight, offset rows. This will create a tight dimple and a donut of raised steel around each punch mark. That will grow the OD of the bolt very slightly and reduce the slop. Whether you are comfortable with that approach however is up to you.

[Evil_Fiz]

~0.1mm is a nice engineering slip fit, so no surprise for the stock parts but consistently making the tube to that ID is more expensive than a more generous ID tube with variable tolerances.

Thanks. Suspicion confirmed.

- For NON-RACE use, will geometry stability be significantly affected by two well-fitting sleeves vs a single full-length sleeve?
(This design was good enough for VW but I want to improve the suspension if possible.)

I also thought of using three sleeves per side; one short one on each end and a longer one in the middle to bridge that gap between the urethane inserts. Is this a bad idea?

Of course, I could go "Captain Overkill" and use a Porsche spherical bearing instead. But that would fall in the "more money than sense" category for a street car.

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Emil

[Evil_Fiz]

I renamed this thread to reflect its expanded purpose.

Next question:
- Are urethane spring plate grommets supposed to fit so tight they need to be horsed into place?

Today I did a trial installation of the spring plates with the new Energy grommets. They fit into the torsion housings and spring plate caps perfectly. They seated with minimal effort and did not require longer bolts to get them started. The fit onto the spring plate is another story.

last week I sanded the spring plate mounting surfaces to smooth metal and applied a thin layer of all-purpose grease to one of them to prevent rust. Before installing the grommets I wiped as much of the grease off as I could with a paper towel. The grommets slid onto that plate with a fair bit of resistance on the bench (not compressed). When I tried to get the smooth grommet onto the sanded, ungreased plate, I was able to get it to slide about 1" before it stopped. I then used the supplied grease and got the grommet seated but I had to put the plate on the floor and push down with both arms and a fair bit of body weight to get it seated. The grease is more like glue than lubricant.

- Is this normal or do I need to ream/clearance the grommets for a more relaxed fit?
- If so, what is the best way to do this?
-----
Emil

[AdminSteve]

I renamed this thread to reflect its expanded purpose.

Next question:
- Are urethane spring plate grommets supposed to fit so tight they need to be horsed into place?

Today I did a trial installation of the spring plates with the new Energy grommets. They fit into the torsion housings and spring plate caps perfectly. They seated with minimal effort and did not require longer bolts to get them started. The fit onto the spring plate is another story.

last week I sanded the spring plate mounting surfaces to smooth metal and applied a thin layer of all-purpose grease to one of them to prevent rust. Before installing the grommets I wiped as much of the grease off as I could with a paper towel. The grommets slid onto that plate with a fair bit of resistance on the bench (not compressed). When I tried to get the smooth grommet onto the sanded, ungreased plate, I was able to get it to slide about 1" before it stopped. I then used the supplied grease and got the grommet seated but I had to put the plate on the floor and push down with both arms and a fair bit of body weight to get it seated. The grease is more like glue than lubricant.

- Is this normal or do I need to ream/clearance the grommets for a more relaxed fit?
- If so, what is the best way to do this?
-----
Emil

Its normal, they have never fit very well. Use lots of grease, its gonna be a squeak fest once assembled.

AdminSteve

[Piledriver]

Use the silicone grease supplied with the grommets or a drop of liquid dish soap, I like Dawn.
(I guess it doesn't matter if the bushings don't slide on the trailing arm)

IIRC the expensive Porsche versions from Elephant Racing the center bush over the TA also has rubber on the ID and the OD is correct clearance for the "race", all is greasable.
I suppose you could duplicate that with the right sealant like the 3M window urethane...

I recently fought with fitting new boots to some new 8mm plug wires for ~30 min before remembering the soap trick.
all 8 wires effortlessly slid right through after that.

Note that the factory rubber grommets do not slide on the TA: they flex in shear as well as compress and stretch.
On 944s the OG bushings I think they were glued to the TA, had to be cut/sanded off.
Urethane doesn't like shear. It crumbles.

[Evil_Fiz]

Use the silicone grease supplied with the grommets or a drop of liquid dish soap, I like Dawn.
(I guess it doesn't matter if the bushings don't slide on the trailing arm)...

Thanks for the info. Yes, I used the Energy Suspension Formula-5 lube with the bushings.
I managed to get the TA and spring plate urethane bushings installed after many BLUE words were uttered. I made life difficult for myself by removing the OE outer meta shells (before I ordered the bushings) and the rubber inserts on the pivot bushings. I had to buy a new set of rubber bushings from CIP1 only to destroy them to get the metal shells. None of the vendors say you need to use the outer shells with urethane bushings. Oh well, problem solved now.

The .05mm clearance between the pivot bolt and the inner sleeve does not appear to be an issue. I am considering wrapping the bolt in PTFE tape to take up the slack.

One more question, how freely should the spring plates move with the urethane bushings? I had to shim the retaining bracket with 1/16" washers to keep the plates from binding.

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Emil

[Piledriver]

Teflon has ~zero mechanical strength, don't bother.
The cap should tighten down on the washers/torsion housing. Nothing will move if tight.
Use a bit of blue locktite if concerned.

Did you take pics?
Still confused as to the outer shells you speak of, all the rear bushing I have used fit in the steel covers and the torsion housing.
---rear, have never needed to do front torsion bushings on a T1. my 74 and 68 T1s didnt need them replaced, my sons 71 was a Super, and my daily until recently was a T3.

[Steve Arndt]

The spring plate bushings need to be hand fitting to the covers and also honed to fit the OD of the spring plate. They need to cycle smoothly without torsions installed.

[Piledriver]

Had to do that on some hard urethane rear bushing I got from SACO.
The black ones from Energy Suspension have fitted well and pass the free cycle test when lubed up.
(using stock covers) may have needed a little clearancing for the covers, been awhile since I did it last.

[Evil_Fiz]

Teflon has ~zero mechanical strength, don't bother.

10-4

The cap should tighten down on the washers/torsion housing. Nothing will move if tight.
Use a bit of blue locktite if concerned.

I am unclear. Are you saying the grommets should fit properly without the need for washers as shims?

Did you take pics?
Still confused as to the outer shells you speak of, all the rear bushing I have used fit in the steel covers and the torsion housing.

I will take pics and provide a better description of what I am facing.

---rear, have never needed to do front torsion bushings on a T1. my 74 and 68 T1s didnt need them replaced, my sons 71 was a Super, and my daily until recently was a T3.

Up front I am using OE bearings on the outside and Delrin bushings on the inside. I will need to massage the Delrin OD to get them to fit the tubes and ream the ID to get a good fit on the arms.

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Emil

[Evil_Fiz]

The spring plate bushings need to be hand fitting to the covers and also honed to fit the OD of the spring plate. They need to cycle smoothly without torsions installed.

What is the best approach to hone the ID and shape the outside of the grommets? These are Energy Suspension parts, appear to be properly sized/shaped, and fit well. The knobby inner grommets seem to have a more relaxed fit than the outer smooth ones. I suspect the outer grommets are the ones causing the binding. When everything is fitted properly, how much force should it take to cycle the trailing arm assembly?

Had to do that on some hard urethane rear bushing I got from SACO.
The black ones from Energy Suspension have fitted well and pass the free cycle test when lubed up.
(using stock covers) may have needed a little clearancing for the covers, been awhile since I did it last.

I applied the provided lube but the resistance level feels a bit high. If I sit with my elbow level with the axle and try to "bicep curl" the assembly, it fells analogous to about a 40 - 50 Lbs. curl.

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Emil

[Piledriver]

Sounds like they need to meet a sanding drum on a drill.

[Steve Arndt]

Should only take a couple pounds/finger force to cycle them.

I use a big belt sander and just shaped them slowly to fit the cover and make witness marks with a sharpie.

For the ID I use a sanding drum and drill

[Evil_Fiz]

As promised, here are the pictures and updated description of the issue I faced.

This is the "shell" I mentioned. It's the metal insert that fits into the pivot eye of the trailing arm. The rubber bushings on sale at many vendors include this shell as part of the assembly. The shell, rubber isolator, and inner sleeve are bonded into a single unit. Since the urethane bushings are never shown to include the shells, I incorrectly assumed they were not needed. When I painted the TAs I mangled the shell when I removed them. I had to buy new rubber bushings only to destroy them to get the shells.




Here are some pictures of the spring plate grommets installed.

In this pic, you can see the washers I used as shims on the grommet cover. They are against the torsion bar housing between it and the cover stand-offs.


Here I tried to show the outer, smooth grommet pressed against the spring plate.


Here I tried to do the same for the inner, knobby grommet.


And a clear shot of the entire assembly


Please point out anything I missed or am doing incorrectly. Although I have been around ACVWs for many years, this is my first full restoration and I am doing most of this work for the first time.

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Emil