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MG MGA - Swivel Pin - Play

Today while having the car wheels raised I check the play.
I found that the right wheel has play in the upper attachment of the swivel pin.
The must be a play of 1/2mm-1mm I would estimate.
Is this something easy to repair?
I understand there is a bushing that can be replaced? But I also understand the upper part is threaded.

You thoughts are welcome as usual!
Regards,
Gonzalo
Gonzalo Ramos

Depends where the play is coming from.

The swivel (trunnion) is threaded onto the upright. If these are not regularly greased according to the service manual, they wear out, and sometimes even break (I knew a Spitfire owner as a student, and helped him repair two such breaks).

The trunnion has a steel tube that passes through and through which the bolt for the shock absorber passes. This also suffers if greasing is not regular. It also often also rusts to the bolt. Then the upper arrangement doesn't work as designed, and things start to wear oval. This is even more pronounced on the bottom link.

To investigate, jack up the car and support on stands. Take the wheel off and use a jack under the lower spring pan to jack up and take the pressure off the bolt at the upper trunnion. Loosen and remove the bolt. The whole assembly can then be swiveled outwards. To take off the top trunnion you have to remove the inner distance tube, then the trunnion will just unscrew. If it slops around on the thread as you unscrew it, you have found your play. If the bore of the tube in the trunnion for the distance tube is worn and the tube is not a fairly tight push fit, the problem is there. Otherwise look at the arms of the shock absorber - if not round, the problem is there.

To check the lower trunnion you have to remove the hub and backplate on a disk braked car. Then the principle is the same - distance tube out, then unscrew the trunnion, which rotates in the opposite direction to the one on top. Never done any work on front drum brake cars so others will advise you here, or correct me if I the upper trunnion can't be removed so easily as on a disk brake car. On the bottom check that the holes in the end of the A pan arms are round. Ovals here are dangerous.

If you have disk brakes and remove the backplate, don't lose the little spacers for the backplate - they are made of unobtanium.

dominic clancy

As Dominic says, it depends on where you find the play,and how much it wiggles.

For the horizontal trunnion bolt, steel distance tube and bronze bushing (top and bottom), the play should be nil and the bolts should be captured solid in the arms. If you have play between the bolt and the swivel link, the bronze bushing would be worn and needs to be replaced. It is common for the lower bush to wear more than the top one. The lower link carries weight of the car while the top link holds the wheel upright and takes load of the shock absorber resistance.

Threads between the swivel link and swivel pin can also wear, especially if not greased regularly. Again the bottom one may wear more than the top one. According to the Workshop Manual a little play here s not critical, although it does not precisely define how much play might be tolerated. One half mm wiggle at bottom end of the swivel pin might be okay, but one mm wiggle there may be too much.

Motion of the wiggle is amplified more than 3 to 1 by height of the tire compared to height of the swivel pin. One mm play or tilt of the swivel pin would translate to more than 3-mm or well over 1/8-inch wobble at bottom of the tire. I'm pretty sure that would be bad on the road as the slightest bit out of balance could cause the wheel to shake badly. Some years ago I changed one of my lower links for that exact reason, but the other three links are still original after 380,000 miles.

On a drum brake car the top swivel link can be unscrewed after removal of the bolt and the distance tube. To remove the bottom swivel link also requires removal of the cross over brake pipe, the bearing hub and the brake backing plate.
Barney Gaylord

I can see the play where the swivel pin goes into the up (damper arm).
There does not seem to be any play in the bottom attachment point. Maybe the other seals had not failed hence keeping lubricated.

I was looking in the parts catalogue (like moss) but I can't see the bronze bushing piece that I would have to replace.
I understand that if the play is in the threads I would have to replace the whole swivel pin ($$$), right?
Gonzalo Ramos

If the play is in the threads it can often be fixed by replacing only the swivel link. Some very early MGA swivel links may have been bronze like the TD and TF parts. Most MGA swivel links will be cast iron, and those parts wear faster than the original forged swivel pins. Modern replacement swivel pins are likely to be machined form rolled bar stock. I don't recall which supplier, but some of the new swivel pins were hardened and too brittle, more likely to break than bend.

The horizontal bushing in the swivel link is actually bi-metal with a bronze layer inside of a steel shell (Moss Motors part #330-140). The bi-metal material is initially flat stock, cut to a rectangular blank, stamped with a oil groove (big "X" inside), then rolled into a tube form. For replacement the old one can be removed by hacksaw cut through one side (from inside of course), then press the new one in with a vice or arbor press (prefer no hammer). After installation it needs to be reamed to 0.7500-inch ID. This can be done in a home garage with a standard chucking reamer (cheap enough tool). See here: http://mgaguru.com/mgtech/suspensn/fs201.htm
Barney Gaylord

The bronze bush is rarely worn on its own; usual failure mode is that it doesn't get greased and the hard chromed distance tube gets rough and tears the bush up. And, if it has been running loose, it beats the thrust washers and seal supports up. These many parts including bolt, nut, and seals, are sold as a "lower trunnion kit" by Moss, but only listed as such (kit) for MGB for some odd reason. 263-455 per kit, for one trunnion (link). Same parts TD through MGB.

FRM
Fletcher R Millmore

I am going to look at where ther problem comes exactly tonite and take some pictures so I can report more accurately.

If I do have to change the swivel pin, it will be expensive ($135), or the link ($219), unless I get a second hand one as Barney suggests...

I guess if it is the bushing it will be a big job for me. Not sure I am capable of doing the reaming...
Why is the bushing not supplied with the right ID?

Will continue reporting...
Gonzalo Ramos

Bushing ID is a matter of production tolerances (as used in the 1950's). When the bushing needed to be reamed it was least expensive to do it just once after the bushing was installed in the swivel link. If the rolled up tube was to be reamed to size before installation, it would have to be held securely in a split collet exactly matching the OD of the bushing, The swivel link would also have to be machined to exacting tolerances through the bore. Reaming the bushing after installation allows for looser tolerances for machining all of the parts prior to assembly.
Barney Gaylord

Any decent automotive machine shop can press the old bush out, new in, and ream - or better - hone the bush in about 10 minutes.

FRM
Fletcher R Millmore

Well it seems that the MGA can sometimes give you good surprises.
I took apart the swivel bolts and bushings and inspected them (top and bottom). In fact the bushings are fine, they are not worn at all. They are concentric and a good fit.
What is better event is that the swivel pin threads are also tight.
See some of the pictures and the video I took.
http://picasaweb.google.com/gramosgarzon/SwivelPin10May101027PM?pli=1&gsessionid=L5N8tqcL-EF7zp7NujLYEQ#

In fact the play is coming from 2 places.

TOP; The PO must have disassembled the this bolt before and for some reason the washers on each side are different. In any case, the damper arm is slightly too wide for the bolt to tighten up on the steel bushing, when the play at the top.
I guess I would need to add a proper thickness washer on the right side to make it all tighten up properly.
I tried tightening up the bolt a lot to make the arms come closer together but could not take up all the slack.
No seals found on the top swivel. I will need to order those to keep the grease in.


Bottom; The lower bolt did not seem tight enough. In fact with the top attachment off I could move the swivel pin forward an back about 5mm.
This went away by tighten up the nyloc nut on the bolt as much as I could, and a bit more. I guess this is even dangerous...
The A-arm holes seem to be round and not oval.

I also took advantage to grease up links.
BTW the bump stop is non-existant. ; )

I guess not so bad after all... saves me having to replace bushings. Question is why has is it like that... :S

Next time I will check the LH suspension.

Any additional thoughts on this issue?
Gonzalo Ramos

I mean to say;

TOP; The PO must have disassembled the this bolt before and for some reason the washers on each side are different. In any case, the damper arm is slightly too wide for the bolt to tighten up on the steel bushing, this is why there is play at the top. (see the video)
Gonzalo Ramos

Gonzalo -

Check with Apple Hydraulics 800-882-7753. They specialize in rebuilding British car shocks, brake master cylinders, A-Arms and swivel pin assembles. They will completely rebuild your swivel pins, including reaming,etc.

www.applehydraulics.com
F Valenzano

Well the first video took 20 min to get, so I'll not look further. Have mercy on we who are condemened to dial up please!

Look at the book, or Moss web page. You should have 2 seal supports, 2 thrust washer, 2 seals, 1 distance tube, 1 bolt, 1 nut, 1 spring washer per link. The seal supports and thrust washers are not hardware store items. Replace the distance tubes if the surface is not perfect - you can keep the old bush if it is not worn.

The arms top and bottom are dead tight against the distance tube when all parts are in place and correctly tightened. The link should have .008-.013 endfloat on the distance tube when correct, but a bit more is OK.

FRM
Fletcher R Millmore

That looks like good news Gonzalo,

Pity about the living room carpet though!!
Neil McGurk

From your pics, it looks like the PO removed the link seals and seal support for some reason. He may have even done a botch job on replacing the thrust washers. He may have done a similar botch on the lower trunion too. Based on his misassembly, I'd recommend getting a full set of seals, seal retainers and thrust washers and then start from there. see what else may be missing.

It also looks like you need new pin seals. All totaled about $35 ala carte from Moss (of one of the disty's)
Chuck Schaefer

Coming into work this morning I found the car now pulls to the left when I brake which driving at speed.

It did not use to do that before I took off the swivel pin yesterday.
Is it possible I didn't put it back together as it was?
The only thing I can think of is the turns in the upper swivel link. Maybe I turned it too far in on the swivel pin threads, and causing the geometry to change?
I turned it all the way and then backed it off half a turn.

Do you think this is related or unrelated to this?


BTW: the carpet is my mechanics rug that I use order to keep the parking floor clean. I works great at absorbing pints of brake fluid!
Gonzalo Ramos

Just reading on another side that the cause of my brakes pulling to the left is that fact that indeed yesterday the brake disk got greasy from messing about with the swivel pin...
I did clean it but obviously not well enough. will have to do that again tonite!
That would explain the uneven braking (i.e pulling to the left) cos the right front wheel is not braking as well....

Do you recommend cleaning the brake pads too?
Bummer!
Gonzalo Ramos

Gonzalo, you should check the end float - the distance tube should be about .005 longer than the link is wide, so you can safely tighten the bolt all you like. When I ordered mine (Moss) they were not so equal and I had to carefully match the tubes and even file the link face in one case to get the right clearance.
Art Pearse

Gonzalo, sorry for highjacking your thread...
I had a similar problem some weeks ago. First I thought it was the wheel bearing, but than I realised that the play between swivel pin and top link was not right.
I turned the Top link a few times and the play is gone.
Now I have the feeling the car is lower on that side.
Is that possible?
Or should I replace the swivel pin and link?
Thanks

Patrick
PP Radermacher

Patrick,
My opinion is that the height of the upper link will not change the ride height. This is determined by the position of the A-arm+ length of spring. If you however turned the lower swivel link, that would change the ride-height.

Turning the top one would change only the geometry on 'wheel-bump', but no affect the ride-height.
Gonzalo Ramos

This thread was discussed between 09/05/2010 and 11/05/2010

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