# PMT Rear Control Arms



## bkellis1 (Jun 30, 2009)

Anybody have any experience with PMT as a company, and/or their products? I'm looking at their rear control arm kit with adjustable uppers, but never heard of them. Looking for advice. Here's the site:


1964,1965,1966,1967 CHEVELLE SS CUTLASS GTO SKYLARK REAR TRAILING ARMS | pmtfabrication.com


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## bondobill (Oct 24, 2011)

Don't know anything about them but...........
Bear turned us on to these folks for my sons rebuild on his 68 .......

http://www.spohn.net/shop/1964-1967-GM-A-Body/


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## PontiacJim (Dec 29, 2012)

They look OK, but have no experience or knowledge of them. Seems they have different levels based on costs.

I went with Spohn parts myself. Got the upper adjustable trailing arms and their front & rear sway bar. Quality seems good, but have yet to install or try them out. I have not yet decided on the lowers.

My thinking on all this, and its just my thinking, is that if you go with the stronger and improved stuff, you are giving up some of the flex built into the factory control arms and shift it to the frame brackets. Are the frame brackets and/or crossmember really that beefy to take up all the twisting without doing something to stiffen them up? So all the twisting seems to me to be concentrated at the bushing, heim joint, or Del-Sphere bushing (Spohn) end of things. Just saying and I'm no suspension expert on this.


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## 1968gto421 (Mar 28, 2014)

PontiacJim said:


> They look OK, but have no experience or knowledge of them. Seems they have different levels based on costs.
> 
> I went with Spohn parts myself. Got the upper adjustable trailing arms and their front & rear sway bar. Quality seems good, but have yet to install or try them out. I have not yet decided on the lowers.
> 
> My thinking on all this, and its just my thinking, is that if you go with the stronger and improved stuff, you are giving up some of the flex built into the factory control arms and shift it to the frame brackets. Are the frame brackets and/or crossmember really that beefy to take up all the twisting without doing something to stiffen them up? So all the twisting seems to me to be concentrated at the bushing, heim joint, or Del-Sphere bushing (Spohn) end of things. Just saying and I'm no suspension expert on this.



Good points. I've noticed Ames sells reinforcements for the crossmember/mounts so I think you have some very valid thoughts on this.


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## 1969Judge (Mar 12, 2012)

I'm using the PMT rear arms on my car. Well made and solid IMO. Used the adjustable uppers as my car is a little lowered. Next is to add the brackets mentioned as they make sense to add rigidity and support to the rear.


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## 1968gto421 (Mar 28, 2014)

I think Jim mentioned Dick Miller racing for parts. From Miller's website I copied these suspension/crossmember supports pieces. Hotchkis makes similar ones for the A-bodies.Here's the info:

DMR-5029-A-E A must for any GM coil sprung performance car whether using
a DMR rear suspension system or stock. If your car hooks you will eventually
twist or break the frame crossmember that the rear end upper control arms are
fastened to. These bolt on support pieces will help eliminate this dangerous problem
by triangulating both corners of the crossmember. Fits 64-67 GM intermediate
including Cutlass & Chevelle.
DMR-5029-A-L Same as DMR-5029-A-E excepts fits 68-72 GM intermediate
including Cutlass & Chevelle.

Oldsmobile experts, Dick Miller Racing Inc. Science Hill, KY Catalog

Going to this page and clicking suspension will give you a picture of the supports. Hope this helps.


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## PontiacJim (Dec 29, 2012)

I was undecided myself as to which type/style of lower control arms I wanted for my build.

I think it depends on the level of horsepower you plan to put into your engine, whether a stocker or bigger cubes/higher HP & torque levels. The following is *my opinion* from what I researched for my car.

The factory lower control arms (as well as uppers) are fine for the stocker. The next option is purchasing a set of boxed lower control arms as you begin to increase HP. Generally, when you go this route, you are also adding the rear sway bar as well. You can purchase these ready to bolt in from an assortment of vendors or buy the weld-up kit to box and add the bushings to your existing lower control arms, and then add a rear sway bar. 

Before going any further with any other choices other than factory style control arms, it should be pointed out that I think every build should at a minimum install the bolt-on upper/lower control arm supports. The factory began installing these in 1967, and I believe these came on the Ram Air, HO, and HD frame options and on cars with the 3.90 & 4.33 gearing (no expert on this, but think it to be correct. My '67 covert had 3.90's and had them). These supports are readily available and are made aftermarket. They range from a stock reproduction to the custom adjustable tubular bar style.

I purchased the UMI set from Summit in black for my '68 Lemans 1968-1972 GM A-Body Control Arm Reinforcements/Frame Braces [4028] - $129.99 : UMI Performance, Inc. Why? They are a bolt on tubular bar that is adjustable. Thinking was that adjustable might be the way to go just in case there was some variance in lengths (maybe it was Friday at 5 PM quitting time when my frame brackets were welded on:yesnod and I think I can add a little pre-load to the bars to get them tight/snug as opposed the the factory bolt-on style which could allow for some movement should the bolt holes be oversized a bit to help installations (but this is just guess as I don't have a set of factory style to compare).

The next reason, and the real reason I selected the UMI bars was because they have a slight bend in them that is specifically put there to clear the floor pan. It was noted that some bars hit the floor pan and you have to adjust this problem with the good old hammer. The assortment of aftermarket tubular bars do come in differing diameters, adjustable & solid, and some are big, so it made sense that big may be stronger, but big means it might hit the floor pan. Now again, nothing to compare it with, so that floor pan claim could be BS, but I didn't want to take the chance and have any problems -we all know how "fits like factory" usually almost doesn't.:cuss:

Back to lower control arm choices. After the stock style control arms there are quite an assortment of heavy duty rectangular control arms with/without sway bar mounting holes, and with various types of bushings & materials. Spohn exhibits some differing types that are available. http://www.spohn.net/shop/1968-1972...er-Control-Arms-Boxed-with-Poly-Bushings.html I purchased the Spohn upper arms with Del-Spere ends, but the lower arms did not have the holes for the factory style sway bar and you had to purchase their version of a sway bar. I actually purchased a Spohn factory type rear sway bar and wanted to bolt it on to the lower control arms like factory as well. All top quality parts, so don't be afraid to use Spohn. 

I wound up purchasing the UMI tubular lower control arms with the factory style mounting holes for the factory style sway bar. Again, lot of different styles to choose from All : UMI Performance, Inc. I purchased the double adjustable tubular arms with the Roto-Joints in black from Summit. 1964-1972 A-Body Double Adjustable Lower Control Arms- w/ Roto-Joints [4043] - $299.99 : UMI Performance, Inc. Why? First, I plan on raising the rear of my car ala mid-1970s look with wide tires hanging out the wheel wells slightly. Raising the car ride height means putting more angle on the lower control arms and I felt/assumed the factory or boxed lowers might be too bulky and actually hit the rear-end axle tube or frame brackets. Tubular arms are narrower and thus might provide extra clearance -should I need it.

Raising the car will affect the position of my wheels within the wheel well. Jacking up the suspension will put my suspension at a lowered arc and move the wheels forward a bit, and I want to fit the tires within the outer wheel well (not up inside it). With both ends being fully adjustable (as well as my adjustable Spohn uppers with their Del-Sphere ends) I should be able to center my tires IF I find there is a clearance issue at the front portion of my wheel well. I don't want my tires hitting and I really don't want to trim/cut the wheel wells to get them to fit.

Another feature is the Roto-Joint. It moves, yet is solid. With higher HP engines, the rubber bushings are too soft and can contribute to wheel hop, while the polyurethane can be too hard and doesn't offer a lot of flexing. Both bushing types from what I read, won't hold up so well under bigger HP or the "heavy foot". Racing type cars use the solid heim joint. Not good for a street car. The Roto-Joint appears to be the best of both. You get the "solid" for straight line acceleration, while getting side to side flex through the 28 degrees of movement built into the Roto-Joint. My concern then becomes the side-to-side movement of the rear axle within the body. So I will add a Panhard Bar (which came factory on the '65-70 Impala's) to keep the rear axle centered and from moving side-to-side, but still allow movement (body roll) for handling.

Yep, going with some "no-hop" bars to raise my upper control arms to change geometry, but it looks like I will have to fabricate a custom set to fit the Ford 9" I have.

In conclusion, I'm no chassis expert by any means, and I'm not even sure if what I'm doing will work.........but it makes sense to me and its what I am going with after doing a lot of reading and researching various products. I think any suspension mods are simply by choice of the owner or a recommendation by a fellow user of the product. Seems there is always the "new & improved" and 5 years from now, the hot set-up of today will be obsolete and something "new" will be the rage. 

Just sayin' :thumbsup:


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## ALKYGTO (Mar 29, 2010)

PontiacJim said:


> \
> 
> Before going any further with any other choices other than factory style control arms, it should be pointed out that I think every build should at a minimum install the bolt-on upper/lower control arm supports. The factory began installing these in 1967, and I believe these came on the Ram Air, HO, and HD frame options and on cars with the 3.90 & 4.33 gearing (no expert on this, but think it to be correct. My '67 covert had 3.90's and had them). These supports are readily available and are made aftermarket. They range from a stock reproduction to the custom adjustable tubular bar style.
> 
> \:


Jim, my 69 4 speed GTO came with the factory upper/lower control arm braces. I think all the 4 speed cars got them. They are better than nothing but pretty flimsy compared to the tubular pieces and I replaced them. 

My feelings on the stock suspension are that all the arms should at least be boxed even in a stock manual trans car or an automatic that shifts "hard". I use the old Southside Machine lower arms which move the IC forward by lowering the attachment points of the lower arms at the rear axle.

Also my car is equipped with a roll bar and this ties into the crossmember where the upper arms attach (my upper arms are stock, boxed by me, and use the hard urethane bushings with zerk fittings) and my lower control arm attachment points at the front are also tied into the roll bar. I can post pictures if anyone is interested.


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## PontiacJim (Dec 29, 2012)

ALKYGTO said:


> Jim, my 69 4 speed GTO came with the factory upper/lower control arm braces. I think all the 4 speed cars got them. They are better than nothing but pretty flimsy compared to the tubular pieces and I replaced them.
> 
> My feelings on the stock suspension are that all the arms should at least be boxed even in a stock manual trans car or an automatic that shifts "hard". I use the old Southside Machine lower arms which move the IC forward by lowering the attachment points of the lower arms at the rear axle.
> 
> Also my car is equipped with a roll bar and this ties into the crossmember where the upper arms attach (my upper arms are stock, boxed by me, and use the hard urethane bushings with zerk fittings) and my lower control arm attachment points at the front are also tied into the roll bar. I can post pictures if anyone is interested.



Yes, I can see it as well if you want to "use" the engines power - boxed control arms and the upper/lower control arm braces would be good insurance. I was not sure on which factory cars got the braces, makes sense to install them on all 4-speed cars.

I saw the UMI set-up that lowers the attachment points, but it also lowers the control arm closer to the pavement and I would be afraid clearance could be an issue in some instances out on the road. I have an old Alston Chassis manual I bought in the early 1980's that walks you through the chassis set-up and is fairly straight forward - squaring up a chassis and finding the Center of Gravity and Instant Center of your car using the factory rear suspension control arm angles, racing four link set-ups, or leaf springs.

YES, post those pics (as you didn't email me any:nonod Those pics would give a few of us an idea of a good roll bar set-up for higher HP cars and include a picture or 2 of your boxed rails you did yourself. :thumbsup:


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## BearGFR (Aug 25, 2008)

PontiacJim said:


> ... So all the twisting seems to me to be concentrated at the bushing, heim joint, or Del-Sphere bushing (Spohn) end of things. Just saying and I'm no suspension expert on this.


Exactly right. This is the reason for only considering arms that have some sort of sphereical joint on the ends that allow the arms to "twist" or rotate around their longitudinal axis. Without that ability, everything just tries to bind up whenever there is any sort of body roll (like in a corner). Making the arms stiffer (like with hard urethane bushings) just means that in order for the body to 'roll' like that something else has to bend - or break.

Also, the purpose of having the triangulated upper and lower arms (the lower arms run "sort" of parallel to each other, the upper arms are angled in towards the rear of the car) is to locate the rear axle side to side and prevent it from moving "sideways". That geometry principle (you can't compress a triangle without seriously bending or breaking one of the legs or attachment points) makes a panhard bar unnecessary.

Bear


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## ALKYGTO (Mar 29, 2010)

Ok here's a shot I just took( lol upside down sorry :blush2. Shows the bar that connects the front attachment point of the LCA to the frame and the roll bar ties into that from the top and the Southside LCA and the simple tab that lowers the LCA and moves the IC forward.


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## BearGFR (Aug 25, 2008)

ALKYGTO said:


> Ok here's a shot I just took( lol upside down sorry :blush2. Shows the bar that connects the front attachment point of the LCA to the frame and the roll bar ties into that from the top and the Southside LCA and the simple tab that lowers the LCA and moves the IC forward.


Thanks for posting the photo. I'm trying to get my head wrapped around what I'm looking at. Looks like what those tabs do, is to drop the rear of the lower control arm down so that it's lower than it was in the stock location . Am I seeing that right? So... if you were to draw an imaginary line through and parallel to the lower control arms, and another imaginary line through and parallel to the upper control arms, wouldn't that result in the point where those two lines intersect (the instant center) being moved closer to the rear of the car than it would be if the rear of the LCA's hadn't been lowered? (And also maybe higher, depending on whether the upper arms are angled "up" or "down" with respect to the front of the car)

I found this link that has some decent diagrams and stuff...
Tuning 4 Link Rear Suspensions for the Drag Strip

Bear


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## ALKYGTO (Mar 29, 2010)

Correct they move the IC of my car rearward (as would raising the rear of the uppers) putting more leverage on the rear. Unfortunately I haven't videoed any first gear launches but car leaves straight and hard when it hooks (hot tires).

"If your car wheel stands too much, you can angle the 4 link bars closer together at the front to move the 'Instant Center' closer to the rear of the car"

I never liked the looks or methods of raising the uppers and as they are shorter so it takes a greater amount of distance to effect the same change.


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## PontiacJim (Dec 29, 2012)

Yay!, pictures.:thumbsup: I downloaded mine to my "Documents" on my laptop and simply opened them up in Windows Viewer and corrected them so I could see right side up. OK, I got it. 

The link Bear included is pretty straight forward in explanation. I rolled my chassis out from under my car and could see right away where to tie the roll bar in to strengthen the upper control arm frame crossmember. Got some ideas working.:smile2:


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## ALKYGTO (Mar 29, 2010)

Jim, the rear down tubes of my roll bar tie in to the cross member right above the shock absorber. All but impossible to take a picture of that from under the car.


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