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MG TD TF 1500 - Checked Yourv U-bolts Lately?

Another lesson from the rear spring work on the53. We all know about the benefit of installing a pair of MGA Buffer Plates to avoid having the U-bolts gouge a groove into the top of the rear axle housing. You might want to take a look at your U-bolts where they contact the upper and lower spring plates. All four on the53 show the same wear pattern. And, one of them broke there rather than give up the nut. Bud

Bud Krueger

Bud,

It seems I've read about loose U bolts more than several times on this site so it must be a problem area. Are the bolts inferior? If so it might be better to have some bent up at the local spring shop rather than source them at the usual suppliers. On other vehicles I've occasionally had them snap due to corrosion but rarely have I found them loose or worn like that.

Jim
JE Carroll

As a matter of interest, does anyone know how tight the nuts should be. I've yet to get my car back on the road but every time I hear about the U bolts I check mine and I always seem to be able to wind them up a bit more. I have nyloc nuts on them and I guess all I'm doing is compressing the rubber pads. The question is, when do you stop tightening them.

On the point of rubber, I drove my car around the block earlier in the week for the first time. The result was a leaking cylinder on the nearside brakes. I took the cylinder off but have yet to inspect it, I replaced all the rubbers before I re-fitted the brakes. I also noticed that the rubber grease seals and the bushes are already showing signs of cracking and they've not been on a year yet. It looks as though I'll need to overhaul the suspension again next winter. You just don't seem to be able to buy decent parts any more.

AJ
A R Jones

Where did you buy your rubber parts from AJ? I rebuilt the front suspension on my TD a year ago with parts from Brown & Gammons and after 500 miles they still look as good as new. Matt
Matt Davis

Moss Matt. I rebuilt the suspension last winter. They don't look too good and I haven't been on the road yet. One of the swivel seals already has a tear. I'm afraid to touch them!

AJ
A R Jones

Moss is not known as the supplier of high quality rubber parts among the members of this BBS. On this side of the pond, we seem to get better parts from Abingdon Spares. I dunno much about B&G.
Jim Merz

Jim, FYI these are probably the U-bolts that were installed in Abingdon. The car has about 88,000 miles on it and has not been on the road since 1972. The new rubber pieces being installed were purchased from Abingdon Spares. Bud
Bud Krueger

I had the identical experience with "Rocky"...every time I would let off the gas , the rear end would wiggle...
Folks here on the forum suggested the "U" bolts, and sure enough, they were either broken or shot....
I also bought the "saddles" when I replaced the other parts....
I just tightened until all the upper nuts felt reasonably snug, and made sure the ends of the bolts protruded the same distance from the plates, before adding the lock nuts.

E.B. Wesson

Does anyone know the answer to AJ's question above (torque or tightness of th U-bolt nuts). By the way, I purchased the nut set for the u-bolts from Moss and the threads don't seem to match. Suggestions?
Chuck
CR Frakes

The U-bolt issue has been around many years. The rubber pads rot and collapse, the axle starts moving, and the bolts wear just as Bud's did. Torque: See EB's post. Then loosen the lock nut and re-tighten after a few miles/weeks. Should be good to go long term after a retighten or two. New nuts: likely for the new repro bolts? Originals likely BSF thread. Have to call Moss and ask. George
George Butz

A couple of weks ago I took the53 out for its first run on the road in 40+ years. It's been almost a year since I redid the rear springs. This was also the first real run for the engine after rebuilding it. For break-in purposes I gave the engine a goose. It was as if someone grabbed the steering wheel and gave it a sharp spin to the left. Lifting my foot off of the throttle gave the opposite reaction. After we got back to the barn I was amazed at how much slack was in the u-bolts just from sitting for 10 months. Haven't had a chance to try it since then. Danged New England winter. Bud
Bud Krueger

The bolts wear like that because they were run loose.
They get loose over time from the pads settling, and from the bolts conforming to the actual shape of the axle, including any saddle plates etc that may be bridging nascent grooves in the housing.

They are tightened to a comfortable figure with a standard wrench of that size - not a long handled one. I use a standard 3/8 ratchet in one hand. Tighten evenly. Use the locknuts, either jamb nut or Nyloc, the jamb nuts are correct.

The bottom plates are often not flat, from overtightening. Once this happens, it is impossible to keep the assembly tight, as all the load comes on the corners of the spring leaf pack, through the pads. The overstressed pads then flow under pressure and it is loose again, so the dumpf tightens it more and makes it worse.

I always remove the plates and hammer them flat or to a faint negative arch. If, when you tighten them, they start to bend up around the spring - even a little - then you have overdone it. It is the load distribution across the entire face of the pads that keeps the local stresses low so that the mountings do their job of shock/noise/vibration isolation.

Retighten of these periodically is expected and routine, especially on rebuilds with worn and/or repro parts. I never even set the jamb nuts until I've retightened them a couple of times in the first few hundred miles. After that it is an annual check item. (cars in actual use).

Bad rubbers are the curse of man!

FRM
FR Millmore

I have a set that looks like that.
Bruce Cunha

Here's an image of my rear u-bolts , after my rebuild (a little far away)...Anyway , all of the bolt-ends were adjusted to the same distance from the nuts...
Car has not been on the road much, but I'm sure I will have to retighten....Since there is a rubber pad, there is no torque value for these...The jam nuts hold everything in place.
Notice the "saddle" to hold the u-bolts parallel, and prevent wear on the axle housing.
Edward

E.B. Wesson

What I don't understand is why the springs are mounted in the rubber pads in the first place. It's just asking for the bolts to loosen.

I can just glance under my big trucks and see they're metal to metal so I climbed under my pickup truck and it's metal to metal. I can't recall ever working on anything with rubber pads. I checked my TF and sure enough the bolts are not more than finger tight. The rubber was replaced and obviously has settled.

In a higher horsepower application rubber pads would be squished out like toothpaste. Has anyone just removed them?
J E Carroll

Because it is a sophisticated car, with some nice engineering, despite the bean counters.
Because Nuffield/BMC was making something better. Because that's how it is.
It works fine if you put it together correctly.
If it was different it would be different.
Sure, take it out and make it like every other car.
Change the engine and the body and the nameplate.
Buy a Chevy.

FRM
FR Millmore

FR,

It seems I've touched a nerve.

My question is: What's the point? Is there a vibration with the high pinion speed? Is it a ride quality issue? Why mount the springs in soft rubber if the shackles are also in rubber bushings?

Jim
J E Carroll

Most likely NVH issues- noise/vibration/harshness, fine in a truck, but not a car. With the tiny contact area between axle mount and springs, likely movement would wear and cause squeaks, etc. With new pads, correctly re-tightened, the will stay tight for a long time. Someone has some urethane pads that will last years, don't remember where. George
George Butz

Jim-
Indeed; I don't mean to yell at you, but -
LISTEN DAMMIT!
It is the little idiosyncrasies of engineering that make different cars interesting.

If ye build them all the same,
Ye shall never garner fame.
Add some changes, try some stuff
Some roads are smooth, some are rough
Sometimes better, sometimes worse
Sometime genius' gift, sometime idiot curse
Days you walk, days you win
Change the car, do it agin'

A corollary of "when you find yourself in a deep hole, first quit diggin' " All races are won by designers and mechanics before the driver gets a shot.

We could all be driving electric golf carts - and soon will be if some have their way. Huge commotion when Issigonis designed the Austin 7 (Mini) and put the engine in crossways, now look what everyone's driving.

The rear leaf spring mountings are unique to BMC,at least in my experience, but originated pre BMC as Nuffield. They may in fact be also an Issigonis design, as he did the Morris Minor (one parent of the Spridgets) as well. He was a great friend/co-conspirator with Alec Moulton, the genius in the application of rubber to cars - who did the rubber biscuit (and later hydrolastic) Mini suspension as Issigonis did the rest of it. Or they may be a Gerald Palmer design; I believe he did the Y suspension, which is what the TD/MGA-B suspension is based on, plus the 4/44 Wolseley-Z Magnette, which is the driveline basis for the MGA/B.

These guys, along with a few others - Edward Turner, Phil Irving etc - were in and out of various companies in England from the 30s through the 60s, and are responsible for an astonishing web of innovation and design; do some searching.

I've never seen any documentation re the spring mountings, but would really like to find the story "from the horses themselves". Given the genius of these three men, and the fact that BMC carried it through to the very last leaf spring MGB, and used it on every car from about 1950 to 1980, You can be certain that they could convincingly argue the benefits of the system to the bean counters - all those bits and assembly labour ain't cheap.

A principle of noise/vibration control is to provide more than one break in the vibratory transmission chain, such that they will not be resonant with each other. So, an acoustic wall might have one skin of 1/2" drywall (resonance one), an air gap, and a second skin of 5/8" (resonance two) drywall. This is a similar situation, the rubber at the axle, some spring, and the (different frequencies) rubber at the ends. Might by one reason all MG are notable quieter and more civilised than any of their Triumph counterparts were - and why pieces do not fall off nearly as often.
There are similar factors involved in details of the actual suspension motion under load; it is possible that some subtleties are dealt with by the compliance of the rubber, which would otherwise cause binding or harshness and possibly less grip. The genius is in doing this with $2 worth of rubber instead of $500 worth of linkages (see "German Engineering"!).

Today we have the "NVH" buzzword, and "compliance" in reference to suspensions. These are the some of guys who did the early work in those fields; the little oddities of design like the spring mountings are what lead us to the stories - treasure them.

FRM
FR Millmore

This thread was discussed between 04/03/2012 and 07/02/2013

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