I picked up a project bike today - Trek 3700. It needs some parts so I’ve already been looking into what parts will fit. I.e. The freewheel is a Shimano TZ37 but the TZ500 (more readily available) will fit.

So my question is: Is there a source that shows what parts interchange within a manufacturer’s line.

The manufacturer of the bike, the freewheel, the rear derailleur or the hub?

Which is another way of saying "no". Too many players involved.

Shimano has provided consumers and dealers with compatibility charts for decades. The challenge is finding them as they are usually considered "tech" and not an operating manual stuff. At one time I had their tech doc website page saved but that was way long ago. Andy

But that they aren't going to tell you if the derailleur, which might not even be a Shimano product, will tolerate the change in gearing.

Duh...why would they? Why help their competitor?

What you seem to ask for was sort of provided by the Sutherland Manual back in the 1970s-1990s. But this type of data center requires a lot of energy. Human, financial and social. As the industry became more global and the pace of change quickened further the ability for a central source of data to be even just behind current became harder and harder to accomplish. Who will pay for a third party to do all the testing and compatibility testing? Most any manufacturer won't want to support their competitor's product and accept any potential liability that could be claimed. Manufacturer will keep their instructions/compatibilities between their own products. (The major exception to this I know of is SRAM's Grip Shift line has had Shimano specific/compatible gear indexing, but those two companies have some court history between them...) Andy

The point I was making is that the OP was asking for something that would guide him in replacing parts on his Trek bike, and a chart by just a single supplier of the many parts the bike is equipped with isn't going to help him much.

Duh?

Whatever bolts on, of course. Most **** on a bike, ain't really preprietary.

Andy, this is the most useful information. A quick google search turned up a Shimano webpage with compatibility, specifications and more going all the way back to 2004. Thank you

A bit of experience will go a long way.
The older stuff is pretty cross compatible within a few limitations.
British threaded Bottom Brackets are very "generic" in the US. Different cranks will use different spindle lengths.
Shimano REAR shifting/DER's are compatible up through 9 speed.
FRONT, however, is different between "road" & "mountain".

It'll start to fall in place once you start swapping a few parts.

I don't know of anything within the bike manufactures line that shows such. However within the same component makers line there is.

For Shimano it's at https://si.shimano.com/en/#/

Under the technical documents, there is a compatibility chart. And for things that are within several years of each other, you can sometimes see what Shimano says about their compatibility. But if you are looking at a decades old part you have to go back in the archives and trace forward through the various versions to get to the new component to attempt to see if it will or should work. Quite tedious if you have to go through several version changes. And many times you still won't get a answer.

For your FW, it's likely to fit the hub. But what you need to know is the RD specifications to make certain it'll handle the tooth counts on the low sprocket... the one with the most teeth and the high sprocket, the one with the fewest teeth. As well as total capacity and max front difference. And for that you need to look at the specifications charts under the Technical documents tab. And remember they all have archives for the older stuff. Spec's can also be found in the SI's and UM's... sometimes.

I have a 3700, but I got it as a bare frame so I can't comment on components. All freewheels (except some odd French/Swiss/Italian vintage bikes - these have different threads for several components) have a common thread mounting to the hub. Most 1990-on freewheels from any manufacturer are interchangeable as long as they're the same number of speeds, and the Shimano spline pattern for freewheel tools is fairly standard across many manufacturers. Note this is freewheels only, not freehubs/cassettes. The type of derailleur determines what the largest sprocket can be, and the size difference of front chainwheels. Changing the freewheel for a larger one can require increasing the length of the chain, fitting a new freewheel can require fitting a new chain as the old one may not mesh properly. Fitting smaller chainrings can require shortening the chain. There are a couple of different square taper crank axle standards, and a range of axle lengths depending on the frame and the cranks. Newer 2-piece cranks have the axle attached to the drive side crank, these use a variety of different bottom brackets, which gets complicated with newer higher-end bikes, but the 3700 is "entry level" so sticks to the older standards. All modern pedals are 9/16" thread apart from some BMX and child's bikes which are 1/2". That's a brief summary of a small part of freewheel and related stuff.

If you don't already own one, Buy a Digital metric/American Caliper...

the 3700 uses a 1 1/8" steerer fork...
the BB is a BSA standard threaded unit... yes, a shimano HT2 BB and cranks will fit.
the rear hub is 135mm O.L.D. and standard 9.5 or 10mm axle size fits... you can install up to a 10sp. cassette if your rear hub is an 8-9-10 FREEHUB design...
the front wheel is a standard 100 O.L.D.x9mm axle size....
Rear Derailleur mounts are standardized, thank goodness.. BUT, the Der. HANGERS are somewhat specific, and must be an EXACT match of shape and hardware.
front Der. is a std. Clamp mount, BUT you'll want that digiCaliper i mentioned earlier to Confirm seat tube CLAMP SIZE before ordering a ft. der.
you'll want to also Measure the Seat Post if you want to get another one... and verify the Seat Tube ID too.. people have a bad habit of putting the Wrong Seat Post size into bikes...
the Brakes are standard V-Brakes... the fork might have disc mounts on it, if so, swapping on a disc hubbed wheel will allow installation of disc caliper.

There is a proprietary disc caliper mount on my 2004(?) frame, it needs an adapter to go from the frame to an IS mount, it appears to be a standard item available from Trek.

UPDATE:
I chatted with a rep from Trek and she/he (name was Lo) walked me through quite a bit of parts interchangeability. Said, as others here have, that just the application is enough to find a suitable replacement. i.e. For the front derailleur just the function will work - Front Derailleur 3 Speed - is enough to find a replacement.
I'm learning......
I also watched a video on YT by Seth from Berm Peak which cleared up a lot mere.

That's not enough - you need clamp diameter or direct-mount type, top or bottom cable pull, also top bottom or side swing, no.of speeds because 12 speed chains are narrower than 7 speed chains, and newer derailleurs also have different pull ratios, so road and mtb parts aren't 'interchangeable. And some older SRAM stuff is Shimano compatible while some isn't. There's probably obvious stuff I've missed too.

UPDATE: It appears that the previous owner already has done some parts upgrades. i.e. The bike came with a RST 191 front fork and now has a Sr Suntour M2025. Only a step or two above the original, but rebuild kits are more readily available.

instead of rebuilding that fork.. look for one of these..
Ebay search: Rock Shox Reba SL - Dual Air - 26" Wheel - Disc Brake - 120mm Travel
80, 100, or 120,mm travel, 26" wheel size, and a straight steerer in 1 1/8" size will fit... the SR fork you mentioned is not a good fork, but will work for a while, i'm sure.

A RockShox Judy Air is a good upgrade too.
the first thing you'll notice after installing one of the forks i mentioned is the Weight Reduction.. then, the Real damping they provide....

The Sheldon Brown website may also be a good resource. Perhaps not in tables of interchange capability, but more along the lines of, "Here's how to determine what capacity rear derailleur you need", and then you can look up specs for given RDs to find what you need. They have more info than most about rear cog spacing and doing adaptations to meet your needs. Chainline is critical, and they have articles on how to measure and calculate at the cogs, and at the chainrings. Bottom bracket spindle tapers has an especially good section on compatibility, as well as shell threading standards. There or elsewhere if you search, there will be some place that has tables and specs on various other bottom bracket bearing types, both threaded and press fit, there are many standards now.

Not at the level of completeness you seem to be looking for, especially for a 22 year-old low-priced MTB. Any 7-speed freewheel will work on a Trek 3700, as long as the largest cog doesn't exceed the upper limit of the rear derailleur. I believe this is a medium cage unit with an upper limit of 30 teeth. You can look up the model on Shimano.com. Basically, as long as you look for parts that work with Shimano 3x7 with long-pull linear pull brakes, you'll do fine. This is very common spec.