TR2/3/3A 9 VS 10 Inch Rear Brakes

[CJD]

I've been working on the front brakes. When I ordered a set of rivet on brake linings for the front, they showed up as the smaller 9 inch linings...obviously NOT for the 10 inch front brakes. Thank you ...again...Ebay for accurate advertising!?!

Anyway, while I'm waiting for that seller to respond to the fact he sent the wrongly advertised front linings, I began to wonder whether the 9 inch linings would fit the REAR brakes. The result...I'm pretty confused right now.

It seems the TR2 started manufacture with 9 inch brakes on the rear axle. My wire rear hubs do have 9 inch drums. But, at TS5448 or so the rear drums went to 10 inch. My car is TS5248...and it came to me with 10 inch drums. I figure there is a chance that rears wear "upgraded" to the newer drums, but I find this highly unlikely, since nothing on the car so far gives me the feeling the PO's were into performance mods, and changing the backplates and all is such a pain.

I just wondered what everyone's thoughts are on the rear drums. Is it possible the car came with the 10 inch drums 200 numbers ahead of the official changeover? Even if it did, would it be advisable to return to the "more correct" 9 inchers, in case the car ever goes to a car show? And, is there any significant functional reason to go with one size over the other?

Thanks in advance for any thoughts you guys have...

 

[Don Elliott]

My 1958 TR3A (TS 27489 LO) came with 10" drums on the rear. I always thought that both front and rear drums on the TR2 and early smallmouth TR3s had 10" drums from the factory. When they changed the front brakes to disk brakes, they left the rear drums at 10". This may have been because they didn't know what would happen with 9" drums till they were tested properly. It may have been because they has thousands of 10" drums still in stock.

With the front disk brakes so efficient, S-T switched to 9" drums at some point in TR3A production and they work well. I also heard that so may cars (not only TRs) were using 9" drums that the price of the bare casting was so much cheaper, this would be another way to reduce production costs.

 

[TR3driver]

I always thought that both front and rear drums on the TR2 and early smallmouth TR3s had 10" drums from the factory.

Nope, they started out using 9" rear brakes, then changed as John said. It would be interesting to know if he also has the later hubs, since the hubs were improved shortly after the change to 10" brakes. (There appears to be a different seal involved as well.)

It seems like I have read somewhere that the change to 10" was to better balance the brakes front/rear, but I can't find the reference offhand. Another possibility is that the 9" were more prone to overheat, but I can't believe that was much of an issue with drum brakes on the front. The factory bulletin just says the later parts can be fitted to earlier cars (but not at factory expense), without giving any reason why you would want to (except that it made the shoes & drums common between front & rear).

When they changed the front brakes to disk brakes, they left the rear drums at 10". This may have been because they didn't know what would happen with 9" drums till they were tested properly. It may have been because they has thousands of 10" drums still in stock.

Or it may have just been what they felt gave the best overall front/rear balance. They adjusted the balance quite a few times over the years (by changing the cylinder bore), before finally going back to 9" rear drums; supposedly because they never could quite get the 10" to stop locking up before the fronts in certain conditions. But the only time I've found them to lock early is when hitting the brakes fairly hard in a hard turn.

 

[mgedit]

Do not know the history of change overs over the production runs, but my early 56 has 10 inch drums all round. Cheers, Mike

 

[TomMull]

It seems the TR2 started manufacture with 9 inch brakes on the rear axle. My wire rear hubs do have 9 inch drums. But, at TS5448 or so the rear drums went to 10 inch. My car is TS5248...and it came to me with 10 inch drums. I figure there is a chance that rears wear "upgraded" to the newer drums, but I find this highly unlikely, since nothing on the car so far gives me the feeling the PO's were into performance mods, and changing the backplates and all is such a pain.

I just wondered what everyone's thoughts are on the rear drums. Is it possible the car came with the 10 inch drums 200 numbers ahead of the official changeover? Even if it did, would it be advisable to return to the "more correct" 9 inchers, in case the car ever goes to a car show? And, is there any significant functional reason to go with one size over the other?

Thanks in advance for any thoughts you guys have...

My guess would be that the rear axle assembly on your car was changed at some point. Complete assemblies were readily available and relatively easy to swap. Repairs to the differential were much more difficult.
I think the judges might pick it up but in my opinion, there would be little difference in performance. Tom

 

[sp53]

Not sure on the real early stuff, but the ones I have seen all have the TS number stamped right on top of the casting. The 10 inch brake would provide more braking surface, be heaver, and cost more, and should work more efficiently. I did have the 10 inch lock up and stay locked once when I almost totaled out, very scary, but I stopped with rubber on the road. I like the 10 because they are beefier in a world where everything is getting cheesier. But don’t the front brakes do most the work.

 

[TR3driver]

But don’t the front brakes do most the work.

Most, yes. That's why the later front disc/rear drum setup makes sense; the front brakes generate more heat than the rears do.

But "most" is not "all", so rear wheel braking is important as well, when you are trying to stop in a hurry. So is front/rear balance (since these cars have no ABS). You get the most braking effect when the tires are just starting to slip, but not fully broken loose, so ideally you want both front and rear brakes to reach that point at the same time. Once the brakes lock up, you get a lot less braking effort (plus of course losing all directional control, which may lead to a spin if the rears lock first).

But I've driven both (my previous TR3A had a later axle with 9" brakes, current TR3 has original 10" rear brakes) and the difference isn't much. Right at the limit, with the stock size cylinders, the 3A tended to lock the front wheels first, which was not my idea of safe. Bad memories of a Volvo station wagon turning left in front of me, and thinking "If you don't get your foot off the brake, you're going to die". Amazing how hard it is to override that instinct to stomp the brake pedal! (Obviously I did, and drove around him) But I went to 3/4" cylinders in the rear, and different tires up front, and it got a lot better.

Personally, I wouldn't even bother putting the front drum brakes back together, unless you are building a show car that will never be driven in traffic. I owned a 56 with front drums for several years, and they just never felt safe to me. Always wanted to pull to one side or the other, but not necessarily the same way each time. Tried fiddling with them several times, new shoes, drums turned and so on. The front discs were a huge improvement, IMO. The only hard part of retrofitting front disc brakes from a later TR3/A is finding someone to make the adapter hoses for you. Otherwise, the parts bolt up.

 

[2long]

My TR2 has the 9 inch rear drums. They work fine. I recently had to do a "panic stop" as a driver pulled a fast left turn right in front of me. First time that has happened in the TR, which I drive very defensively as it is a death trap in an accident. The car locked all 4 wheels at the same time and tracked straight. I was able to release pressure and regain traction and had a pretty good stopping distance from about 35 - 40 mph. As long as the brakes are adjusted properly and not fouled with axle grease, they work well. TRs went to 10 inchers at the rear to address brake fade, but went back to 9 inch due to grabbing. I address brake fade with wire wheels and Alfins. No problem there. The front drums are also fine. Remember, there was lots of high speed testing and rally work with the 9 inch rears and 10 inch drums at the front.

Dan

 

[TR3driver]

Remember, there was lots of high speed testing and rally work with the 9 inch rears and 10 inch drums at the front.

Which likely had a lot to do with the TR3 becoming one of the first production sports cars with front disc brakes

 

[CJD]

Thanks to all for the input...a lot of very good information!

Tom, I think you likely hit the nail on the head with my discrepancy. I bet the whole axle got changed at some point and the 10 inchers came with it. I'll clean both axles to see if there are any clues...but it sounds like 9 inch rears are the "correct" choice. I'll likely install those, but save the 10 inchers to go with a disc front upgrade at some future point. I know what you're saying, Randall...drum front brakes never seem to track straight. Your description brought back memories of those old "first cars" from the '60's and how bad the drums were. Most of all they go away in the rain!

Anyway, thanks again to all!

 

[HerronScott]

YouR description brought back memories of those old "first cars" from the '60's and how bad the drums were. Most of all they go away in the rain!

Anyway, thanks again to all!

I was amazed when I found that my parent's 1969 Olds Toronado (big heavy car at 4500 lbs with 455) had drum brakes front and rear! Front discs were an option but they bought this special order off the lot for a good price and that was one option it didn't have.

Scott

 

[sp53]

I think those old Oldsmobile’s had front wheel drive starting right about then also?

 

[HerronScott]

I think those old Oldsmobile’s had front wheel drive starting right about then also?

Right! The Toronado came out in 1966 and I think was Olds first FWD vehicle. Used a chain drive in the transmission and torsion bars for the front suspension both of which I found interesting. Loved the flat rear floor on family vacations since I got to sleep stretched out on the floor.

Scott

 

[TR3driver]

Only the Toronado was FWD though, the other Olds models stayed RWD. The X-body Omega in 1980 was the next FWD Olds, and I think they were all FWD by 85 or 86.

 

[carpecursusII]

John, my Tr2 ts3445 has a rear axle of TS 3678 so it is possible to have a 200 number overlap. The number is stamped on the top of the rear flange where the cover bolts up.

 

[CJD]

Thanks, I'll check both when I get the crud off. I've been moving toward the 9" brakes, though, after a couple Ebay purchases...and I went ahead and had the 9" drums turned. There is no end to the fun I have when the sales people ask for the type car the drums are off, and then ACTUALLY try to look it up for limits!!