muller@market.alliant.com (Jim Muller) (02/27/90)
Michael Sands writes: >...In taking appart the casting that holds the spindle, brake caliper, >and dust shield (the name of this part escapes me for the moment) Uhh, vertical link, in the usual parlance, I believe. >I find a strange >pivot joint on the bottom. This joint is what allows the spindle >to turn as you steer the car and attaches the bottom A arm to the >spindle. It seems to be made out of brass and is internally >threaded. There is a grease seal between it an the threaded bolt >like part of the spindle that screws into this brass part. That "strange pivot joint" is the trunnion and it acts as the lower ball joint. In fact, it isn't all that strange; *all* (or almost all) of our LBC's have them. At least Triumphs do. The fact that it is threaded allows the designer to have the wheel move vertically as it is steered, countering some of the undesirable vertical movement induced by positive castor. You will find that the left and right sides are threaded differently (I think it has right-hand threads on the left wheel, and left- on the right wheel, if I remember). It is brass so as to not bind on a similarly-metalled shaft. Lubrication of the threads is very important for the long-term life of the trunnion. On Spitfires and GT-6's, you are supposed to lube them with 90-weight oil in the grease fitting (which leads to the trunnion threads), but other TR's call for grease, I think (mjb, comment?). If they go unlubed then the force of the roadspring will strip the threads when they wear enough, and the suspension will drop the car onto the road. You see, all of the weight of that corner of the car is supported by those threads. You don't say what year your S.S. is. I mention all this Spitfire stuff because other builders, including Lotus, used those front-end parts, which were really just stock Herald parts, and probably stamped "Alford & Alder". Check it out carefully against a Spitfire, or maybe other builders, MG, A-H, etc. Trunnions are available if you can be sure of the original source. >Finally to my question, how far should the spindle be treaded into >this fitting. Obviously if I thread it too far into the bushing >during assembly, the spindle will bind when trying to turn the car >to full lock (right hand turn?). Should I turn it all the way in >and back it out a full turn, half, what? I can look this up in my manuals if it comes to that, but I'd guess your "Should I turn it all the way in and back it out..." is close. Turning full lock only rotates those threads by perhaps 45 deg. (?) or so from dead center, so you don't have to worry about a lot of rotation. More importantly: (1) if it is threaded more, you get more thread bearing surface; (2) the grease seal will fit poorly if it isn't reasonable snug; (3) the amount of threading affects the vertical positioning of the wheel on the suspension. Someone else want to take a crack at this? I'll try to remember to look it up tonight, but I'll probably forget... Jim Muller
kent@wsl.dec.com (02/27/90)
My TR4A workshop manual just happens to be at work. It doesn't say how far to thread the vertical into the trunnion -- just to ensure that it moves easily back and forth. The point about the grease seal is well taken -- it needs to be fairly snug to fit well. (And yes, TRs take grease here.)
leger@sherman.alliant.com (Bob Leger) (02/27/90)
Jim Muller writes:
On Spitfires and GT-6's, you are supposed to lube them with 90-weight
oil in the grease fitting (which leads to the trunnion threads), but
other TR's call for grease, I think (mjb, comment?).
The factory recommended oil for the TR-250 and TR-6 trunnions as well.
When I rebuilt the front suspension of my TR-250 last summer, I found
grease in the trunnions, but filled them with 90-weight gear oil when
I reassembled everything. I'm going to have to buy an extra grease gun
and charge it with oil for the purpose of oiling the trunnions.
On the subject of how far to thread the vertical link into the trunnion,
I found nothing in the Bentley manual to guide me. I stopped when the seal
was snug but not too tight. On my car, the trunnion hits something else,
the brake backsplash I think, before the vertical link bottoms in the
trunnion. The right side had been assembled a thread too far and I had
to remove the caliper, rotor and backsplash in order to remove the trunnion.
Bob Leger