| len47merc | -- 08-28-2014 @ 4:53 AM |
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'47 Merc - New bias-ply tires re-checked for balance, radial and lateral run-out confirmed as well within tolerance, completely new suspension all around and low-mileage, long-idled lever-arm/Houdailles reworked and fundamentally new, 3.78 rear, springs are balanced/car rides and sits level. Plans are to drive the car at 60 mph MAX only when necessary with touring intent to maintain 55 by the speedo. Problem - the right rear ONLY begins an annoying, minor wheel hop on smooth asphalt as you approach 60 mph and worsens as you increase speed. A one-time test to 75 mph yielded no problems with any wheel other than the right rear. Side-to-side and front-to-back tire swaps have been tried but the right rear continues to be problematic. Shocks have been adjusted to be stronger but even with the right rear shock approaching max setting, the right rear only, regardless of which tire/wheel is on it, begins this hop above 55 (confirmed by feel as well as son viewing from behind in a separate vehicle). It was much worse before the shock rebuild and has improved significantly (both fronts and the left rear are rock solid now) since shock rebuild. I'd blow it off if it began to hop at 70 mph as when cruising at the planned 55 a 15 mph buffer would exist, but given it begins to be felt at about 56-57 it needs to be addressed. The right rear shock was sent back to the rebuilder and was gone through a second time without seeing any change in performance. This has to be something simple and fundamental that is being overlooked. I'm stumped. Greatly appreciate your knowledge and advice on this. Steve
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| cliftford | -- 08-28-2014 @ 6:29 AM |
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Try pulling RR hub and inspect bearing, hub bearing surface, and housing. I would almost bet that's where your problem is. Gene.
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| TomO | -- 08-28-2014 @ 6:50 AM |
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Pay special attention to the bottom bearing surface of the axle housing. Look for signs of wear and pitting. Check the bearings as well. Repack with StaLube drum brake bearing grease. Next, I would try replacing the drum. Tom
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| len47merc | -- 08-28-2014 @ 8:40 AM |
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Thanks cliftford and TomO. Upon receipt of the car last year the second order of business (after first dropping the fuel tank) was to strip the gunked-up, clogged-up brake system in its entirety and replace it all. The bearings were cleaned at that time but unfortunately I only performed a cursory inspection of the bearings for smoothness before repacking them. I ran my finger around all the axle and hub bearing surfaces for feel and felt nothing out of order at the time but in retrospect should have been more rigorous with the inspection. I bet you both are on the mark here - perhaps (hopefully) the bearing is just worn adequately enough to be the catalyst for the wheel hop without showing itself as 'loose' when testing with the wheel raised. Since I'm pulling the drum/hub again, in thinking about both your comments I plan to install a new bearing to eliminate this as a root cause regardless of what I find. TomO - what's your thinking/reasoning about replacing the drum as a potential next step? Sincere thanks again to you both - Steve This message was edited by len47merc on 8-28-14 @ 8:41 AM
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| carcrazy | -- 08-28-2014 @ 8:58 AM |
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Your right rear brake drum may be out of balance. Not sure if you can have it balanced individually. If you can find a tire shop that balances tires and wheels on the car you can have them spin balance the right rear tire and wheel on the car. Any weight they add to the wheel will serve to balance the tire, wheel, and brake drum assembly. The downside to doing this is that you will have to mark this wheel and the brake drum so that the pair are indexed to each other. This will allow you to install the wheel in the same location to maintain balance of the assembly.
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| cliftford | -- 08-28-2014 @ 10:51 AM |
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If you can't find someone to balance the RR wheel and drum on the car, and if all else fails, try swapping the rear drums, and see if the vibration shows up on the left side. If so I would say that the drum is at fault. Gene.
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| len47merc | -- 08-28-2014 @ 11:14 AM |
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Carcrazy & TomO - it's been so long since I dealt with pre-'70 brake drums that the more I thought about both your comments the more likely I think it is that the drum is the culprit. TomO - I should have recalled this with your comment alone but after carcrazy weighed in it finally clicked. In my previous reply I unintentionally omitted that during the brake system restoration all 4 drums were turned and at that time I did not recall the need for balancing them, even after noting the balancing weights tacked on to the exteriors. Back in the day I had a '68 International Travelall that routinely required having the tires balanced on the vehicle for just this reason - drums and hubs were no longer balanced after turning the drums. I called the old local facility that I used at the time and was surprised to find they are still in business and still had and use their on-car wheel balancer, although only one 'senior' guy knows how to use it. Before I pull the hub off I plan on driving the car over to them next week and giving the on-car balancing a go first. Still plan to clean, check and repack the bearing (or new one) again, especially if the on-car balancing does not address the problem. Since I can get no play at all in the elevated wheel anywhere in its rotation think the on-car balancing makes sense as a first step. TomO - found your brake bearing grease locally. Heavier and more viscous that what I have been using. Thanks for the recommendation. Thanks again to all three of you. Will update with bearing and balancing findings and results next week. Steve This message was edited by len47merc on 8-28-14 @ 3:56 PM
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| supereal | -- 08-29-2014 @ 8:02 PM |
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It is more likely that one of the tires is seriously out of balance or out of round. When I put a new set of Coker tires on my '47, it had a serious wheel tramp beginning about 40 mph. We added higher pressure to each tire until the problem lessened. We tried moving the tires on the rim with no luck. There was not enough run out to see on the car, so we believe there was a structural problem, probably, when the tires were made. Coker replaced them, and it cured it. I can now run at highway speeds with no hop or vibration. I've seen some really worn rear axle housings that didn't cause vibration.
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| len47merc | -- 08-30-2014 @ 5:46 AM |
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Thanks supereal - as noted in the first post above these new bias-ply tires have been checked during balancing, rechecked during trouble-shooting and validated for lateral and radial run out under pressure all around and are well within spec. Rotating the tires side-to-side and front-to-back does not affect wheel hop on the right rear beginning at ~57 mph. Am taking the car next week to have the right rear wheel/hub/drum balanced on the car by an old-schooler with the equipment to do it. Will update then. Steve
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| supereal | -- 08-31-2014 @ 4:21 PM |
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Balancing on a machine usually detects only tires that are seriously affected. If the problem is in the carcass, such as the belts below the tread, it isn't always possible to find. This was the problem with my Coker tires. It isn't always known that an out of round or out of balance tire will affect the vehicle on either the front or back position. As you mention the tires are new, it seems obvious the problem is tires, if the "hopping" didn't occur with the old tires. A very small amount of radial deviation, not the tires, but the measurement between the hub and the tread, can produce the speed related vibration, as will a small out of balance . We see this when we balance flywheels and drive shafts at our machine shop.
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| len47merc | -- 09-01-2014 @ 5:48 AM |
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Agree with your logic supereal and appreciate your peeling the layers off the onion here. To clarify further, both this set of tires and the previous set, which were new as well, begin/began hopping at ~57 mph on the right rear only, even after swapping right-to-left and front-to-back. So now I've two sets of new tires exhibiting the same behavior on the same right rear location regardless of which of 6-8 tires were put on the right rear. (Btw - Coker replaced the first set under warranty for a completely unrelated issue) My search for a brake drum & hub balancer have not yielded a source so as noted earlier the plan is to have the entire wheel/hub/drum balanced on the car later this week. Hoping for a positive result with this effort. Thanks again supereal and to you all for your knowledge and support here. Steve
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| supereal | -- 09-01-2014 @ 2:19 PM |
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Thanks for the update. I suppose it is possible that the right rear axle end is slightly bent. I'd pull the drum and hub and give the end of the keyway a close look, and check it with a dial indicator. Generally, if the axle has been stressed, there will be a crack in that area. My '47 will run at 70 and above in overdrive, but I seldom exceed 50-60 on the highway unless necessary. I used to get wheel tramp with my old tires, as they flat spotted even after sitting overnight. The new Coker bias plies did away with the problem.
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| len47merc | -- 09-01-2014 @ 4:55 PM |
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Thanks supereal - will give this and the other recommendations all thorough examinations if the on-car balancing of the wheel/hub/drum does not address the issue. I have both a dial indicator and an original hub puller so this should be relatively easy if these next steps prove necessary. Update later this week. Steve
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| len47merc | -- 09-04-2014 @ 11:46 AM |
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UPDATE - Well, looks like a combination of issues at play here. First of all though, the rear bearings and axle/hub chases were checked and mic'd and found to be true, without pitting and within acceptable tolerance. Also, the axle was validated as not being cracked and/or bent. The bearings, bearing surfaces and axle were all checked with a micrometer and dial indicator. Thanks Gene and supereal for your thoughts here - I should've been more robust earlier in the restoration and it was good to take the time to validate this (glad no issue was found as well). So here we go. Tom & carcrazy, balancing the wheel on the car solved ~75% of the problem, so apparently when I had the drums turned this resulted in an out-of-balance condition on the right rear only (all drums are the originals). The right rear tire by itself was balanced, but back on the car and spun up to 70-80 mph produced a more than noticeable vibration. After balancing on the car it is very smooth now. Thanks Tom & carcrazy. Secondly, when installing the tires originally the installer verified the lateral and radial run-out as within spec. Both tires now on the front ARE within spec, but both now on the rear are outside of the spec limits per Coker. Disappointed in the original installer after finding this out and depending upon their information so am moving back to my old-schooler for the future on these bias-plys. Supereal - you pegged this aspect - thanks. Rotated all tires front-to-back and back-to-front and now the rear axle, with tires/wheels now balanced on the vehicle, is rock solid/dead still at 55-60 mph and even up to a short burst to 75 mph, so the on-car balancing combined with round(er) tires solved it. Now for the tires with radial run-out out-of-spec... Coker is standing behind their product and are sending me two new tires based on the out-of-spec condition for both. Very frustrating to say the least. Thanks to you all for your great advice and support. Steve
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| TomO | -- 09-05-2014 @ 6:42 AM |
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Glad you solved your problem. Tom
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| len47merc | -- 09-05-2014 @ 7:53 AM |
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You all deserve the credit - glad we all solved my problem. Steve
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| cliftford | -- 09-05-2014 @ 8:18 AM |
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Glad you solved yout problem. All of this proves two things. 1. Two{or 3 or 4] heads are better than one. 2. On line diagnosing is far from an excact science. It is more like a trial and error process. Good luck, Gene
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| supereal | -- 09-05-2014 @ 2:23 PM |
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Glad you solved it, Steve. When I had problems with Coker tires, they tried to tell me it was my fault as I didn't know how to install them. The shop that installed them has been in business since 1930, and really know their stuff. After I unloaded on Coker, they did replace the two faulty tires, and all was well. I know they are a good company, but no one should have to arm wrestle with a surly phone rep. I wonder if Corky Coker knows about this problem?
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