MGB & GT Forum

1980 MGB - Steering rack damper. I have an occasional vibration / shimmy in my front steering that I'm trying to trace down. In checking the steering rack damper, what I have does not match MOSS catalog or other pictures I can find. Based on catalog and pictures I should have from top to bottom ( the cover plate, gasket, shims, a metal free floating plug, a spring and the copper damper pad - which should ride on the rack shaft (terminology?) and provide pressure.

What I have from top to bottom is (the cover plate, no gasket, 3 shims, spring, a white plastic_nylon plunger_damper that is not very free moving in the hole - but must be riding on the rack shaft with some pressure based on the wear marks).
Questions:
1. Is this a correct alternative set up?
2. Should the white plastic_nylon plunger_damper be free floating?
3. Is 2 is yes, what is a good method to "buff" it down? It has rough / scuff / gouge marks on the sides.

thanks for any and all help.

I bought a new rack from Sussex Clasic about a month ago. It also have a plastic plunger. But without the hole.

You say occasional vibration/shimmy in the steering. Is it usually at around 60 MPH?

BTW, many have chased this same issue and there are many possible causes.

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Check the bolts on your A-arms.

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Jim K is a grease-stained wretch

Also wheel balance. Wire wheels are a PITA, you need special adaptors, for the older style wheels.
I had this until I bought the adaptors and ha my tyre shop balance with them. Fixed problem.

Herb

Is there any play in the wheels?

Side to side, up and down, fore and aft (twist) - then tire balance

I don't think the rack is responsible for shimmy. Although and shimmy is fed back via the steering arms, rack and steering shaft.

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I removed almost all the free play in my rack (still with the copper part, not your later, plastic one), but still got vibration at certain speeds. Even selecting the best (read the most round and evenly turning) Rostyle wheels for the front did not help. Peak in vibration around 120-130kmh (75-80 mph), but the steering wheel already started shaking slightly as off 100kmh/60mph

2 Weeks ago I had all my tires renewed with new Michelins and the front wheels dynamically balanced: no vibration left at all on ANY speed

PS Of course wire wheels can be a PITA, but the best, most knowledgable tire shops can immediately tell you whether better balance is a wheel or a tire issue!

I agree with Don, check the tyres then wheels then tie rod ends and lastly steering rack. Sounds like a alignment or balance issue to me.

Update.

Couple points while rebuilding the front in addition to items listed below, I have new A arms and bolts, new king pins and rebuilt shocks.

From yesterday (07/03) evening.
More info. The shimmy / vibration I have is not constant. Does not always happen at the same speed. I may go for a long drive and it not happen at all. it may start at a slower speed (40s) and go away at a higher speed (60s). Or may not start at all until 60s. Seems like always though it is has started, when I go into a curve it stops and may not come back. Oh by the way I have wire wheels. In trouble shooting I have moved the wheels around (side to side, front to back etc.) This has had no affect. I have had the wheels balanced (although I have not yet had them balance with the proper adapter or on the car). However, I have checked all four wheels / tires by mounting them on the rear and running the car up to about 70 (on jacks - pointing toward clear space) with no vibration. No fool proof, but I think showing wheels are at least balanced close. All rubber in the front has been replaced. New outer tie rod ends. New wheel bearings. No slack that I can feel any where in the bearings / front end - shaking / yanking etc. Checked the u-joints being in proper phase. Also, for slack in u-joints. I have also have new / non-leaking gaiters. I'm down to slack in the steering. After pulling and cleaning the nylon pressure plug, spring etc. I put it back without any of the 3 shims. Steering is much tighter to turn (actually too tight). Went for a drive anyway (between thunder storms yesterday. I'm in Benton, AR by the way). Steering is too tight but no hint of vibration or slack. When I got back, put 2 shims back in. Plan on test driving today. Thanks for all the comments and feed back.

From today (07/04):
Follow-up after putting the 2 shims back. Steering has acceptable tension. No vibration / shimmy. Ran up to 80 mph. Hopefully fixed. Again does not happen on every drive. But better than it has been since I bought the car years ago.


Thanks for all the feedback and suggestions.

The only thing missing from your story is the check on your wheel alignment. Toe-in (by memory) should be between 0 degrees 15 minutes and 0 degrees 24 minutes (I've chosen 20 minutes). I once put a table on MGE on the various definitions and the values that go with them. Unfortunately it is not so easy to follow, so I leave it out. Most tire shops have better, easier to read databases, whether in degrees or in (fractions of) inches

Sometimes the setting is wrong because of free play in the bearings, wire wheel to hub etc
Toe-in set too low, let alone near zero gets you quite a lot of steering wobbles. Toe-in, together with the proper tires assures wheel stabilty and elimination of certain tolerances in the front wheel suspension



Edited 4 time(s). Last edit at 2015-07-05 11:19 AM by Donthuis.

Thanks for suggestion. I'll give that a check.

Minor tracking errors - either way - do not normally cause vibrations or shimmying, especially intermittently, and gross errors will make the car dart in response to the steering, make it difficult to steer a straight line, and very quickly show up as uneven wear on the tyres.

FWIW I do not recognise the rack you have, it's not OEM nor is it one of the common Argentinian after market affairs so where did it come from ?

TBH the arrangement you show gives me little confidence in it doing a proper job and may itself be the source of the problem and I'm not sure I even see how it works, either the spring is providing the pressure on the rack or shimming the top cover is, it can't be both.

This is the damper from an OEM rack and below is an Argentinian rack which is adjusted by the stud on the top cover not by shims.



Edited 2 time(s). Last edit at 2015-07-05 01:12 PM by ErnieY.

The intermittent nature confirms, to me, that it is wheel balance. What I have surmised happens is that each wheel has a heavy spot, and when these heavy spots are aligned you get the shimmy, as they reinforce each other. When not aligned they tend to cancel out.

Herb

I don't know Herb, the wheels are independent and one out of balance should evidence itself on it's own, two might exacerbate a problem and give you some sort of cyclic effect as the imbalances fell in and out of synch but individual imbalances would remain.

Hi Ernie,

You may be right, I'm only guessing as to the mechanism. Maybe when out of synch neither is enough to notice, but when in synch they add and become noticeable.

Herb