TR6 Lower A-arm trunnion bushings

[Ribbs]

I just received two new replacement lower A-arms from TRF, needed for a suspension rebuild on my 1973 TR6. I'm having quite a problem trying to get new bushings from a trunnion bushing rebuild kit pressed into the new A-arms. I finally forced one set in by using a vise and a lot of force, but it was such a tight fit that the metal sleeve just dug into the bushing when I tried to force it in. When I did the other side a few months ago (with original A-arms) I had no trouble whatsoever installing the bushings. Does anyone know what the ID of the A-arm hole (at the trunnion end) should be? I don't have the original A arms for this side and I was hoping not to totally disassemble the other side, just to find out.

 

[Tybalt]

The sleeved rubber bushing goes into the fulcrum end of the arm. The trunnion to lower arms joint use nylon bearings, a steel sleeve, steel cupped washers, rubber seal rings and flat thrust washers. Go to Roadsters on line TR6 catalog and take a look at plate DD.

 

[Ribbs]

The sleeved rubber bushing goes into the fulcrum end of the arm. The trunnion to lower arms joint use nylon bearings, a steel sleeve, steel cupped washers, rubber seal rings and flat thrust washers. Go to Roadsters on line TR6 catalog and take a look at plate DD.

It's the nylon bushings at the trunnion end of the lower arms that I'm struggling with. All I can guess is that the replacement arms from TRF have a smaller ID (at the trunnion end).

 

[Tybalt]

If you've got a set of calipers measure the OD of the nylon bits and the diameter of the holes in the control arm and see how they compare. I remeber them being a slight interference fit nothing that I struggled with to install. Probably wouldn't hurt to see how the sleeve fits those nylon bits as well.

 

[Ribbs]

Thanks Tybalt, the arm has an ID of 0.875" and the bushing has on OD of 0.890" - so negative 0.015" clearance! - too much! The metal sleeve had about 0.001" clearance which seems reasonable. Of course the sleeve doesn't have any clearance once I cram the nylon bushing into the arm. I don't think the problem is with the bushing kit - it has to be the arms I got from TRF, but why? And that's why I'm curious to know what the arm ID is that others have. I may have to have the arms machined out..

 

[Tybalt]

At the risk of turning this into a game of forty questions, I do have a few more in light of the nylon bearing/bushing OD. IIRC, the bolt through the trunnion and sleeve is 9/16" UNF (about as large as find on on a TR6) so the ID of the metal sleeve should be just over .563" to allow for the bolt to be a clearance fit. What I do not know off hand is the OD of that metal sleeve or the ID of the nylon bearing/bushing nor I know the OD or thickness of the flange and overall bushing length.

I ask all this silly stuff in that I have found some issues with parts being supplied that do not match original dimensions like trying to stick a metric hex section into a Unified sized fixture on TR6 heater cables. The .890" just sounds like a screwy dimension to me while .875" (nominal 7/8") sounds reasonable for the inch-pound world that existed when these cars were in production and I have to wonder if the issue isn't the bushing as opposed to the arm.

The bottom line out of all this is that it may be easier to find a standard bushing from someplace like McMaster-Carr, MSC, etceteras and so on that will work or can be made to work without too much difficulty. Just for grins, go to mcmaster.com and search on their part number 6389K621 and compare those dimensions to what you need. You might have to shave a bit of length or sand down the flange thickness and diameter a bit, maybe even open up the ID a bit but if you can't get a satisfactory answer out of Roadster something like that may be the way to go.

 

[Ribbs]

Well, I've about come to the conclusion that the two trunnion bushing kits I got have oversized bushing OD's. They had part#'s of QSK200SX and CQSK200S. TRF confirmed that the arms they sent were factory originals, so I don't know what else it could be. Further confirmation came when I tried a SuperPro bushing kit (SPF1844K) that I had but initially decided not to use. The SuperPro bushings were an easy press fit, just like what I would expect.

 

[Tybalt]

Glad that it is sorted out (short of having the correct bushings in your hand). Those look like they are Quinton Hazell part numbers. Quinton Hazell makes decent stuff as both an after market and OEM supplier but it looks like in this case they were misboxed or the wrong box was pulled to fill an order

 

[Ribbs]

Thanks for the heads up on 'Quinton Hazell' Tybalt. I wasn't aware they were out there. You're right, QSK200S sure sounds like one of their part#s when I look around their sight - for instance found QSK199S - but no QSK200S! So who knows, maybe just the wrong dang part.

 

[Ribbs]

Well, to put a wrap on this - turns out the problem was with the A arm I.D. after all. The I.D. on the new ones I purchased from TRF was 0.020" smaller than the original. Certainly enough to cause the problems with the trunnion bushing kit.

 

[CJD]

Bummer! I am a bit confused though. The trunnion side of the lower arms uses a steel sleeved bronze bushing which usually must be reamed after installation to 9/16" for the trunnion pin to fit through. There is a steel washer that crushes onto splines on the trunnion pins to lock the assembly together.

To my recollection, all the nylon is in the inner pivots, opposite the trunnion side.

 

[Ribbs]

I'm not aware of a bronze sleeve on the TR6 lower wishbone arms. The nylon bushings go directly into the arm and have a steel crush tube inserted in the center, along with some thrust washers on each side. Referring to the trunnion end of the arm here, although the fulcrum attachment end is similar.

 

[Tybalt]

Bummer! I am a bit confused though. The trunnion side of the lower arms uses a steel sleeved bronze bushing which usually must be reamed after installation to 9/16" for the trunnion pin to fit through. There is a steel washer that crushes onto splines on the trunnion pins to lock the assembly together.

To my recollection, all the nylon is in the inner pivots, opposite the trunnion side.

That would be for the TR2 through TR4 front suspension. Starting with the the TR4A and continuing through to the TR6 that whole lower arm/spring pan/trunnion set up changed. No reaming, no splined thrust washers, nominally a "more user" friendly set up although this case is defying that it seems.

I am going to take a spin through some spares that I have and see if I still have any lower TR6 front arms and get a measurement, but I might come up empty as I think they all got used/given away.

 

[Tybalt]

And that's why they don't pay me to think.....

Had a chance to start going through spares this afternoon and luck was with me. Not only do I still have a set of lower arms, they were sitting right on top of the bin contents of the first bin that I opened. These came off a car that I had bought as a parts car so are used factory equipment. The bore size for the nylon bearing/bushing at the trunnion end of the arm is .875" nominal. The actual range of measurements taken was from .870 to .877 so calling it .875" nominal is reasonable as a specified dimension with a tolerance band even if I have no idea what sort of tolerance band that Standard Motors found acceptable for those parts.

All of which raises the question of where did this .890" dimension for the bore in the arm come from? Was this a measure from another set of arms? Published technical information? An over the phone verbal from TRF? Bottom line is now I am confused on this since that .890" doesn't match my expectation of a manufacturing dimension for that bore in the old inch/pound world when and where these cars were built. It's just not a "nice" number like they taught people to use in engineering school nor does it agree with factory parts that I measured within the hour which did meet what I would expect as a "nice" number.

 

[Ribbs]

Thanks for the measurement Tybalt, your average value of .875" is the same measurement I got on the new TRF supplied arm. The .890" measurement was from the O.D. of the bushing that's supposed to fit in that hole. So strangely, the old A arm straight off my car (with 50,000 miles on it) measured .895" - maybe the additional 0.020" came from wear? Regardless, trying to force a .890" 'peg' into a .875" 'hole' doesn't sound right...

 

[Tybalt]

To be honest with you, I do not like the idea of opening up the bore in the arms. That would leave you with a set of arms that fall outside of what seems to be the OE specification leading to problems for you down the road or if made someone else's problem, making you one of those DPOs.

I'm really at a loss for an definitive explanation for this. I recall the nylon bearing/bushing being an slight interference fit into arm and the sleeve into the nylon bearing/bushing also being an interference fit but I do not recall either being what I would consider a struggle. Is it possible that the nylon bits are out of spec or that what is being produced is made with a greater plus side of the tolerance band for the OD? Short of sitting down with a pile of those nylon bits and measuring them, I have no answer. Maybe contact your source of the trunnion joint rebuild kit and see what they have to say about the situation but before contacting them get OD and ID measurements of the replacement nylon bits and those distance pieces/sleeves as well as the old ones if you still happen to have them.

Then there is always the "bigger hammer" approach. Have you considered using a vice to fit both nylon bits into the arm and then using the vice to press the distance piece/sleeve into the nylon bits? To make a smooth face for the vice jaws, take a paint stirrer from the hardware store, cut it to length of the vice jaws and hold in place with some tape to provide a smooth bearing surface during the pressing operation.

 

[Ribbs]

Yep, did try the vise approach, which eventually got the bushings in and fully seated. But by then, the inner hole on the bushing had been reduced so much that the crush sleeve tube only gouged out the interior of the bushing when forced in with the vise.

 

[Tybalt]

As long as there is still some nylon bearing surface and the bolt that goes through the two arms (fully bushed and sleeved) and trunnion, I'd say that you have this licked. I would suggest some sort of grease or anti-seize on that bolt. It will make life much easier in the event you find your self needing to remove in the future.

 

[Dazza 2500M]

I came upon this thread today after I encountered problems fitting the same CQSK200S suspension lower bushing kit on my TVR 2500M lower control arms. Although my car is not a TR-6, TVR used the TR6 trunion, vertical link, hub etc for the front wheels. I can't recall which supply house provided me the CQSK200S kit, the parts were ordered in 2021. I'll need to dig to find the receipts. The package is labeled "TR 4A 5 6 Sus. Lower Kit (2 Req) Made in England".

Comparison to the nylon bushings I am replacing (parts that have been in the car prior to 1980)

Color OD ID
Old Bushing White 0.884" 0.711"
CQSK200S Black 0.903" 0.683"

Not only that, the supplied bushing sleeves don't even fit over the supplied lower bolt
Supplied bolt is 0.566" diameter, the bushing sleeves are 0.560"

Being that I bought the kit in 2021, it sounds as if there were some incorrectly dimensioned replacement parts out there