Anybody mess around with thrust angle on rear ends?

[hunt2elk]

Local shop got a new machine that measures this. One of my cars has a positive .25. I have to shim the drivers side from what I gather. Hotchkis makes a shim kit with six 1/32" plates. It is expensive for what you get, and I think I would need all of them to get close. I am leaning to just making a plate, kind of like what Cass sells for leaf spring reinforcement. Does anybody know what the .25 would correlate to shim thickness?

 

[Jc cooper]

If .025 maybe less than a 1/32

 

[toolmanmike]

Local shop got a new machine that measures this. One of my cars has a positive .025. I have to shim the drivers side from what I gather. Hotchkis makes a shim kit with six 1/32" plates. It is expensive for what you get, and I think I would need all of them to get close. I am leaning to just making a plate, kind of like what Cass sells for leaf spring reinforcement. Does anybody know what the .025 would correlate to shim thickness?

That .025 is probably in degrees. You may have to measure, install a shim and measure again to see how much it changes. I can see where cars may be different because of the wheelbase possibly.

 

[toolmanmike]

@Scott Engelhardt

 

[hunt2elk]

That .025 is probably in degrees. You may have to measure, install a shim and measure again to see how much it changes. I can see where cars may be different because of the wheelbase possibly.

Yes, the .25 is degrees.

 

[Scott Engelhardt]

.025 is a very minimal amount, over the road trucks generally do not adjust until .08. If you are shimming at the leaf spring I would start with 1/32.
Do you have a print out from the alignment machine? If they re using a rolling compensation procedure I have seen techs that will roll the vehicle to the wheel stop causing a false trust angle. If your quest is to get a 0.00 reading I would say there will be lots of time spent making very thin shims to achieve that goal. Please post a picture of your alignment print out, I am curious to see it.

 

[toolmanmike]

.025 is a very minimal amount, over the road trucks generally do not adjust until .08. If you are shimming at the leaf spring I would start with 1/32.
Do you have a print out from the alignment machine? If they re using a rolling compensation procedure I have seen techs that will roll the vehicle to the wheel stop causing a false trust angle. If your quest is to get a 0.00 reading I would say there will be lots of time spent making very thin shims to achieve that goal. Please post a picture of your alignment print out, I am curious to see it.

Thanks Scott. I knew you would have the right answer. How many years now?

 

[Scott Engelhardt]

25 with Hunter Engineering and 15 years alignments and Ford master tech before that.
I found my little calculator website that is very handy.
When converting toe or thrust angle from degrees to inches you need to take the tire diameter into consideration. Here is the calculator I use when I get questions from customers
https://robrobinette.com/ConvertToeDegreesToInches.htm

 

[Scott Engelhardt]

Im actually waiting outside a shop right now to go in and calibrate an alignment machine

 

[4mulas]

25 thou is 1/40 of an inch but why not just make the the shim the known .025 measurement you have. No need to convert? Caveat, there maybe a good chance I’ve miss interpreted what you’ve got going on here too. Lol

 

[hunt2elk]

.025 is a very minimal amount, over the road trucks generally do not adjust until .08. If you are shimming at the leaf spring I would start with 1/32.
Do you have a print out from the alignment machine? If they re using a rolling compensation procedure I have seen techs that will roll the vehicle to the wheel stop causing a false trust angle. If your quest is to get a 0.00 reading I would say there will be lots of time spent making very thin shims to achieve that goal. Please post a picture of your alignment print out, I am curious to see it.

I'm sorry, it is .25* not .025*.

 

[Scott Engelhardt]

I'm sorry, it is .25* not .025*.

Is this a shim between front spring mount and frame? Thrust angle is a live reading so you could loosen that mount then use a horse shoe shim just to find the thickness you need. Im guessing 1/8". You will need to have your front toe reset after you zero your thrust angle

 

[hunt2elk]

Is this a shim between front spring mount and frame? Thrust angle is a live reading so you could loosen that mount then use a horse shoe shim just to find the thickness you need. Im guessing 1/8". You will need to have your front toe reset after you zero your thrust angle

Yes, from what I gather I shim between the frame and spring hanger. I just want to get it close before getting it realigned next spring. Sounds like you have done this before?

 

[RemCharger]

Could you not also loosen up the axle u bolts and do a little grindy-grindy to the perch hole?

 

[toolmanmike]

Could you not also loosen up the axle u bolts and do a little grindy-grindy to the perch hole?

Not recommended. The pin and hole keeps the rear axle located. Slotted holes wouldn't work.

 

[RemCharger]

Fair enough.

Not recommended. The pin and hole keeps the rear axle located. Slotted holes wouldn't work.

I guess you could do a weld and drill as well.. just throwing out ideas

 

[wish4hemi]

Not sure if this how-to article is any help, but it does include some relevant details with the Hotchkis kit.
https://moparconnectionmagazine.com...mancini-racing-and-hotchkis-sport-suspension/

 

[hunt2elk]

Not sure if this how-to article is any help, but it does include some relevant details with the Hotchkis kit.
https://moparconnectionmagazine.com...mancini-racing-and-hotchkis-sport-suspension/

I read that over a couple weeks ago. They ended up using 1/8" of shims to correct .09 degrees. So my .25 degree will take almost 3/8" if I am figuring right. I don't think I have enough stud length for that. Unless I remove the stiffening plates....

 

[Nate S]

.025 degrees would offset the front end about .050”. This is nothing. Leave it alone. I’d question if that’s even within the tolerance of the measurement. Sure, when you see a car “crab walk” down the road and can visually pick out an inch or two, that’s a real issue. .025? I defy anyone to see it, let alone measure it twice in a row. Heck, change your front wheel bearings and it’ll move that much.

 

[Scott Engelhardt]

.25 degrees is worth the effort to make it better. I personally would start with 3/16, then I would shake down the rear suspension to relax the movement i made in the rubber bushings.
If the thrust line is .10 or less I would lock it down and adjust the front end.
I guess if you need perfection, then you will need to modify that front bracket.
There are 1000's of new pickups driving down the highway with a thrust angle between .10 and .15 I
My car was at .09 when I aligned it in my shop the last time. It drives straight and handles well. I will be replacing the 50 year old rear springs this winter and I am now anxious to see how far off it will be afterwards.
My hat is off to your alignment guy for mentioning your thrust angle though.