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'82 750 nighthawk suspension questions???

Bmb2492

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So I have a nighthawk and see very little on here about these. It has sit for 29 years and I got it running. But I'm looking for rear shocks and maybe a different front suspension. Does anyone know the rear shock specs and will parts interchange between this model and the s/f/k bikes?
 

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Yeah, DOHC 750's generally and Nighthawks specifically, haven't gained the popularity for restoration/resto modding as the SOHC models - hence reproduction items mostly don't exist. One avenue is to find the p/n online at a site like Partzilla and then use that to search Ebay, etc., for used stuff - or even buy new items that are still available (fork seals, bushings).

On the shocks, they appear similar to SOHC with an eye top mount and clevis bottom - you'll need to measure the eye-to-eye length to maybe source replacements.

IDK if SOHC handlebar switches will work (imagine some differences) if modified, but there are many sources for reproduction switches for those models: CB750 Supply and others

 
The parts diagram sure looks very similar to the stock shocks from my bike. I bet they're very similar and would interchange, but this can't be confirmed without measuring them in person.
I'm assuming parts compatibility then with the 79-82 DOHC bikes, which I've got some experience with. Did a lot of parts research for my own 1980 CB750K.

For the front suspension, you can:
  • re-spring with either straight-rate springs of the correct rate for you from Race Tech or Sonic Springs, or Progressive dual-rate springs
  • Modify and tune preload on your fork springs by installing preload spacers, or fork caps with threaded plugs that allow for on-the-fly preload adjustment
  • Tune the damping speed with the stock damper rods by changing fork oil weight and oil level
  • replace the damper rod operation with cartridge emulators, which range from $60 from CB750Supply to $200 for RaceTech and make the forks behave like modern emulsion shocks
  • Swap the front end, and the corresponding parts to make it work. Modern upside-down forks will always require a triple tree swap but older sportbike front ends with 35mm or 37mm upper tubes are a fairly easy swap, depending on which diameter your bike is. A 37mm tree swap from another similar-vintage CB750 would likely be trivial if yours is a 35mm.
My own bike isn't a super sporty rebuild, so I went with Progressive springs, about 20mm of preload, and an ATF/10w fork oil mix with an oil level around 150mm.

For the rear suspension, there are shock options for a wide range of budgets:
  • Vintage CB750, CB750 Supply, Randakks Cycle Shack, and others all carry plenty of no-name non-adjustable shocks that are cheaper than $100. Some folks review them well, others don't. They're better than a pair of original 40-year-old shocks with no oil left, but your experience may vary and quality control is an issue.
  • If you are willing to rebuild shocks you can get the $200 or cheaper TEC, RFY, or no-name Chinesium shocks and go through them yourself. I have heard that this is a fairly good option if you have more time and mechanical aptitude than money. Some of them even have what appears to be adjustable rebound damping.
  • Next step up is Ikon Basix shocks. They are about $300 and have non-adjustable damping and 3-position preload. If you buy them straight from Ikon they will set them up with the right valving and spring rates for your weight.
  • $500 gets you Ikon Dial-A-Ride shocks with adjustable rebound damping, or Hagons with the same features if you're willing to order from Europe.
  • If you want the best you can get, Ohlins will set you back $800-900, and Race Tech can make you custom shocks to fit your bike that can be even more.
My bike has Ikon Basix because they match what it came with from the factory in terms of performance and adjustability.
 
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I ordered the rear shocks for my bike from vintagecb750 and they look and feel great. Now comes the fun part.. my front suspension is killed. I sit on the bike and there is maybe 2" left of the fork tubes. I haven't done a set of forks since my dirt bike years ago. Would re-springing be the best option? I mean the bike has 4,487 miles on it, would sitting for 20 years do that much damage or could it be that 40 years has done away with what oil was in the tubes??
 

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From what I've heard, most of these bikes had under-sprung front forks from the factory. That's why the Progressive springs are a common mod.

Because you have no idea whether that fork oil has ever been changed, or when it was last changed, I would highly recommend opening up those forks and re-springing them while you're at it. At the very least you should change out that oil -- oil technology has come a long way since this thing was made.
They're old-school damper rod forks so there really is not much going on in there, and there are plenty of tutorials on Youtube or in the shop manual that you should definitely own. Might even be less complicated than the dirt bike you did fork maintenance on.

Personally, whenever I acquire another vintage machine, I assume none of the correct maintenance has been done unless I have receipts or records to prove it was. Since you know for sure this has been sitting 20 years...it'll need a lot to be safe and reliable.

There are quite a few things that almost nobody ever does on these bikes that can be deadly if not attended to; probably the biggest one is inspecting, greasing, and re-tightening the steering head bearings.
If you're doing fork maintenance, you should absolutely get to the steering head bearings because you're already doing most of the steps to get there.

On my own 1980, the original Honda factory grease was still there, and it was so dried out that it was literally cracking into pieces. :eek:
 
What's up with the lines running to the top of the forks? I've never seen a setup like that? Air assist or something?
 
Now that feature I'm not so familiar with, but if they're Schrader-port air lines they're definitely air-assist forks. I've heard conflicting opinions about them and finding the right pressure for you will involve some experimentation. You should definitely give them some service regardless, though.
 
So I have a nighthawk and see very little on here about these. It has sit for 29 years and I got it running. But I'm looking for rear shocks and maybe a different front suspension. Does anyone know the rear shock specs and will parts interchange between this model and the s/f/k bikes?
Does your front forks have the air input at the top?
You can modify the dampening with various weights of oil mixed in.
 
They are air assist forks, I have the same bike, same story! Add air to the right amount of sag. Definitely swap out your oil and exhaust all options with various viscosities to adjust damping. Level of the oil will help as well. There also is an adjustment on bottom of left fork too. Nighthawk parts for 82-83 are impossible to find, try to rebuild repair everything you can. I’m have parts restored by Randy’s restoration and carbs done by Mike Nixon. The SC could turn out to be a sought after bike as the market expands to the DOHC’s. Good Luck! Stay in touch as I will as well.
Tom S
 
Not highjack your thread, but I just posted a question about this same bike. I am wondering what engine I can swap in here as the current one is bad. I'd really appreciate it if someone could chime in on my thread. Thank you
 
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