Front End Dilemma

[David53]

Having now run the car for a few hundred miles since the rebuild I have a dilemma.

You might recall after rebuilding the suspension and setting the torsion bars to the correct height I found that the front end was sitting a little over an inch higher than the rear of the car, which was due to the rear springs having sagged a little over the years. So I lowered the front about and inch to match the rear. Car looked good and seemed to drive and ride perfectly.

However, on inspection it is clear the front end is too low, as the lower RH trunnion is pressing against the brake backplate. I think this is also due to the modern trunnions being a little larger than the original MM stryle trunnions fitted to me car. The suspension arm is clearly too "flat", there is not enough difference between inner and outer pivot points - It should be 1.625 Inch, instead it is only about 3/4 inch.



So.......the question is. Do I

(a) Return the front end to the correct height by raising it approx 1 1/4 inch, thus giving greater clearance between trunnion and backplate, but making the car appear "nose in the air"

(b) Do the above and try and find replacement rear springs to raise the rear of the car

or

(c) Leave all as it is. There does not seem to be any real damage on the backplate from the trunnion, but obviously there is meant to be some clearance there. BTW also not thrilled with surface rust already appearing on a brand new trunnion!!

What does everyone think?

[chrisryder]

i think that the back plate will always be bolted to the swivel pin, and the swivel pin will always have that trunnion on. so no matter how high or low the front or back are. that brake backplate will always hit that trunnion!

the only explaination for that could be that the trunnion is, as you say, a slightly different shape, or you may not have the trunnion screwed all the way up the swivel pin (although it looks pretty far up in your picture so i don't think that's it).

there's no real movement going on there. only the slow turning when you steer. the suspension crashing up and down will not damage the back plate.

have you tried looking at the clearance when the steering is on full lock? if it's clear when steering either way, you could just get away with removing a little bit of material off the trunnion. not ideal (it should fit!) but it keeps your mind at rest.

[mike.perry]

I would set the front suspension at the correct height. If your roads are as bad as the roads over here then you need all the suspension movement you can get.
Have you still got the original thin seven leaf rear springs? If they are sagging, mine were almost flat, then they will need changing eventually, there is no point in setting up one end to compensate for the deficiencies of the other end. If you are not too bothered about originality then M1000 five leaf springs are fine, do not fit seven leaf Traveller springs (you probably can' get them over there anyway) as they jack the back up too high and spoil the handling.

[David53]

i think that the back plate will always be bolted to the swivel pin, and the swivel pin will always have that trunnion on. so no matter how high or low the front or back are. that brake backplate will always hit that trunnion!

As the height of the inner eyebolt is raised the angle of the swivel pin changes and the bottom trunnion will move away from the backplate. My concern is that when I hit a bump or a pothole the opposite will occur and the trunnion will be pressing harder against the plate. I am thinking the only real option is to replace the rear springs and raise the front again to factory spec. Is there any way to easily assess the condition of a set of leaf springs when they are off the car?

[rayofleamington]

i think that the back plate will always be bolted to the swivel pin, and the swivel pin will always have that trunnion on. so no matter how high or low the front or back are. that brake backplate will always hit that trunnion!

The comment is correct - the suspension height will NOT affect the clearance between trunnion and backplate. The trunnion should be unable to move in any way apart from rotating on the swivel pin thread. The swivle pin and the brake back plate don't move relative to each other.

Either the trunnion or the backplate (or even the swivel pin) is faulty. My guess would be the trunnion but anything is possible if the parts have been made recently.


as regards sligfhtly lowering the front suspension - this can improve the handling a little but reduces clearance to the top bump stop - this will give a bigger impact in extreme conditions (e.g. driving over speed bumps at the same speed as modern cars).
That's not a major issue unless your inner wings have some corrosion around the top bump stop (you can end up with the bump stop breaking off or through the inner wing!)

[newagetraveller]

I would like to see a picture of the same thing on the other side of the car.

[MarkyB]

I think the trunnion has been threaded wrong, I received one recently that hadn't been threaded at all!


As it's a nut on a bolt effectively, I can't see any way that changing the ride height will alter the relationship to the back plate.

The other option would be that the king pin is bent or badly made, the second is possible but the first almost unthinkable.

[bmcecosse]

The important thing is - how much clearance is there between bump stop and inner wing ?? It does appear the trunnion is not screwed on the king pin sufficiently - there should be good clearance, and i can't see lifting the front end will make it any better. On the plus side - the suspension won't be able to 'pull out' when the trunnion wears...........

[David53]

Thanks for the replies. I was under the impression that as the angle of the lower suspension arm increased the trunnion would swing away from the plate slightly as it pivots on it's eyebolt....Not at the car now but will check when I get home.

I can guarantee that the trunnion is screwed in correctly, all the way to lock and then back one and a half turns to allow it to swivel through 180 degrees. I do believe the trunnion is a little "fatter" than the original ones for the car (MM style). In answer to your question "newage" the other side has a small clearance between plate and trunnion.

I guess bottom line is I'm not doing any damage?

[bmcecosse]

I would only turn back half- a turn........ I think that's the problem.

[David53]

Half a turn wasn't enough - I turned it back only as far as it needed to be to swivel.....

[bmcecosse]

Well - that would only be half-a-turn back - since it then only has to swivel only about 1/6 of a turn in each direction. Check again.........

[David53]

Possibly a difference in the older MM style swivel pins and modern trunnions, but I definitely turned back only as far as was required to allow the eyebolt to clear the groove in the swivel pin. I really do think the modern trunnions are "fatter" than the originals. Any MM owners confirm this?

[mike.perry]

The only difference between the front suspensions on the Series MM / early Series 11 and M1000 is the stub axle. The swivel pins on the M1000 can be identified by the circular boss above the steering arm. Series MM swivel pins are difficult to find so there is a conversion to M1000 swivel pins on the Series MM website. Early MM trunnions were brass but are interchangeable with later trunnions. The lower trunnion should be fitted and wound down so that the fulcrum pin lines up with the recess in the swivel pin thread and the trunnion turns freely

[David53]

Thanks Mike. Yes that's exactly what I did. Hmmm... will have another look tonight and take a few more close up shots.

[David53]

Sorry about the fuzzy picture, but this might give you a better idea of the position of the trunnion.



I can confirm you are all correct - raising the chassis leg makes no difference to the angle of the trunnion. It does not seem to be pushing hard against the backplate, just touching. When I reassembled it I could not have had the trunnion screwed any further on to the swivel pin or the eyebolt shaft whould have pushed against the swivel pin.

And re: concerns about bump stop - I measure four fingers easily between top trunnion and bump stop on the RH side and just a small amount less on the LH side. Is this OK?

[bmcecosse]

4 fingers is surely a lot? Are the bump stops cut down at all ?

[David53]

No, both appear to be original conical shape...