Only tighten bolts after car is on the floor?

[sgtBerbatov]

I was talking to a friend about the car I've been working on and I told him I had installed new bushes on the whole rear suspension of my Corolla (about 8 in total). He said he was having to do the front of his car and asked me if I only tightened the bolts when the car was on the ground under its own weight.

I told him no, I had tightened them while it was up on axle stands then dropped the car. He wasn't sure, but he felt that he had heard that after installing new bushes on a car you should let the car rest on the ground and then tighten the bolts.

I've never heard of this, but I'm not a master mechanic either. Is this something that has to be done or does it not make any difference?

[robinessex]

That's how they do it when they make the car. Tighten the bolts fully long before it’s on it's wheels.

[justinio]

Probably good practice as the joints will be under load and could affect the torque settings of the fixings, due to the weight resting on them.

I wouldn't lose much sleep over it though.

[robinessex]

The explanation I've heard, is that with the car resting in it's unladen status (no passengers ), then tightening the bolts, ensures that the bushes have no residual torsional loads applied. Maybe some logic in that, but it would require quite a bit of testing to establish if that was correct. Or worth worrying about.

[stevieturbo]

robinessex said:

The explanation I've heard, is that with the car resting in it's unladen status (no passengers ), then tightening the bolts, ensures that the bushes have no residual torsional loads applied. Maybe some logic in that, but it would require quite a bit of testing to establish if that was correct. Or worth worrying about.

Many bushes are round, rubber...bonded.

If they are tightened into the chassis wheels off the ground, when load is applied they're already twisting the rubber quite a bit nevermind once loaded.
It will undoubtedly shorten their service life.

[robinessex]

stevieturbo said:

robinessex said:

The explanation I've heard, is that with the car resting in it's unladen status (no passengers ), then tightening the bolts, ensures that the bushes have no residual torsional loads applied. Maybe some logic in that, but it would require quite a bit of testing to establish if that was correct. Or worth worrying about.

Many bushes are round, rubber...bonded.

If they are tightened into the chassis wheels off the ground, when load is applied they're already twisting the rubber quite a bit nevermind once loaded.
It will undoubtedly shorten their service life.

Er, that's what I said. Never seen the manufacurers bother about it though.

[GreenV8S]

The advice to put weight on the wheels before you finally torque up the bushes is widely repeated and the reasoning behind it seems pretty clear. I think it's good advice. Ignoring it is unlikely to cause a disaster though.

[S0 What]

stevieturbo said:

robinessex said:

The explanation I've heard, is that with the car resting in it's unladen status (no passengers ), then tightening the bolts, ensures that the bushes have no residual torsional loads applied. Maybe some logic in that, but it would require quite a bit of testing to establish if that was correct. Or worth worrying about.

Many bushes are round, rubber...bonded.

If they are tightened into the chassis wheels off the ground, when load is applied they're already twisting the rubber quite a bit nevermind once loaded.
It will undoubtedly shorten their service life.

This /\ prelaoding the bushes can cause them to rip from the outer tube (if they are that typre of bonded bush) there's no hard and fast rule though, some need to be done on the floor some don't but the method of only tightening once on the ground is the safest and how every prof mechanic i know does it and the way i have allways done it, do them all that way and avoid protential issues, simple i've changed a few home changed bushes that were ruined because the owner didn't follow that simple method.
It's the best practise is all and it has been established over the years that it does happen, hense the advise to cover all types of bush used.

Edited by S0 What on Wednesday 2nd August 13:44

[The Wookie]

Normal practice as far as I'm concerned, done because (as said) preloading the bushes can cause premature wear and non-spec behaviour due to the risk of being wound up. Easily done with a 4-post lift or a pit, not so easily done without.

[sgtBerbatov]

Thanks for the answers. I never knew about it, and I've told my friend what's been said here.

I'll have to re-do my rear bushes now then! That should be fun.

[Andy 308GTB]

The Wookie said:

Normal practice as far as I'm concerned, done because (as said) preloading the bushes can cause premature wear and non-spec behaviour due to the risk of being wound up. Easily done with a 4-post lift or a pit, not so easily done without.

I did this without a lift, with the car on jacks, by supporting/raising each corner in turn using a jack on the A-Arm to compress the shock/spring.
Obviously some common sense is required to ensure that if anything moves the car doesn't fall off the jack, i.e. there is a support/stand very close to the jack that will take the weight should the worse happen.

[AW111]

sgtBerbatov said:

Thanks for the answers. I never knew about it, and I've told my friend what's been said here.

I'll have to re-do my rear bushes now then! That should be fun.

You don't need to disassemble anything.
Loosen the through bolts, bounce the suspension once or twice, then tighten again.

[steveo3002]

can roll the car up onto a couple of planks of wood to help you reach under and nip the bolts up

[anonymous-user]

Its a common thing mentioned in kit car build manuals - if you assemble the suspension with the car off the ground, don't tighten the bolts until the full weight of the car is on the wheels, to avoid suspension bushes being clamped at a rotation that is twisted away from their normal rest position.

[Arnold Cunningham]

The manufacturer's workshop manual for my Audi definitely says bolts must be tightened with the weight on the wheels.

robinessex said:

Er, that's what I said. Never seen the manufacurers bother about it though.

[TooMany2cvs]

robinessex said:

Never seen the manufacurers bother about it though.

Don't forget that the subframes are assembled separately from the bodyshell, on jigs/frames. The arms are sitting at the right ride angle relative to the subframes. The only things that are torqued "dangling" when the subframes are mounted into the shell are the frame-to-body mounts, and they don't go through the same rotational movement over suspension travel.