83 300TD Rear Caliper Advice - PeachParts Mercedes-Benz Forum

jdgrand · #1 05-21-2020, 11:33 PM

I'm replacing the discs, parking brake shoes (down to bare metal!), and hopefully rebuilding the calipers on my '83 300TD (173K).

It's my understanding (from Forum and FSM) that the wagon calipers have a larger piston (42mm) compared to the sedan (38mm). After I pulled them I measured the pistons in my calipers (ATE) and both both have 38mm pistons. I assume they are not original but I have no way of knowing -- I have only had the car 7 years. The piston seals did say ATE so they must be fairly old.

I was planning on rebuilding the calipers if they were in good enough shape -- and that appears to be the case. But since they are not the (supposed) stock size I am wondering if that's the best option. They have been stopping the car well enough for my 7 years of ownership.

I could rebuild these calipers (least expensive option).
I could buy rebuilt wagon calipers (more expensive but harder to find).
I could buy new wagon calipers (most expensive: almost $500 for both!!).

Suggestions?

Sugar Bear · #2 05-22-2020, 01:22 AM

If you go rebuilds confirm that they are 42mm. I wouldn't be surprised to find 38mm. 38mm would probably be ok but I'd try to find 42mm rebuilds...but that's just me. Have you checked for aftermarket upgraded calipers?

Good luck!!!

Diesel911 · #3 05-22-2020, 01:52 AM

My thought about rebuilding calipers is you won't know if you can rebuild them till you look inside to see how badly the bores and pistons are.

The 38 verses 42 mm piston is going to be a personal choice.

I tend to go with what is cheapest and most available. That means if the braking has been fine with 38mm pistons and the calipers for them are in good enough condition to rebuild I would rebuild them (making them the cheapest choice and the kits are likely more available).

Keeping the 38mm ones also means if you were off someplace on a trip and had a caliper failure the local parts store is more likely to have the 38mm ones then the ones for the wagon and you could replace the single bad caliper.

t walgamuth · #4 05-22-2020, 09:11 AM

I think it will be very difficult to find the 42 mm. Most important is to make sure both are the same size.

Sugar Bear · #5 05-22-2020, 09:49 AM

Good point about both being the same... whichever route you go confirm before installing that they are the same size pistons side-to-side. About 38 v 42 mm yes as said it's a personal choice.

Imagine trying to diagnose that brake pull!!! Different size pistons in calipers that look the same.

Good luck!!!

JHZR2 · #6 05-22-2020, 10:19 AM

Are the rotors or pads different on the TD? I would suspect that the upsized rear pistons were to increase bias towards the rear, more clamping force, in case there was more load or a trailer back there.

Personally, Id much prefer the TD calipers since they are correct, but if they are hard to find, then the answer might be 38 if youre not planning to haul heavy loads or trailer with it.

The same size side to side is key. Also, good/new brake hoses and fluid are important.

vwnate1 · #7 05-22-2020, 10:56 AM

I'd make a point of finding the correct calipers and not let go of the old ones until the job is finished to your satisfaction .

The T's are heavy cars and need all the braking help they can get .

t walgamuth · #8 05-22-2020, 11:32 AM

Exactly. Increasing the diameter gave a significant increase in braking power for the extra 2 to 300# of the wagon. When my Mrs was driving my wagon back in the day I could not keep front rotors on it. She does not coast up to the stops like I do. An early 126 front ventilated rotor conversion would have been a good choice.

jdgrand · #9 05-22-2020, 09:14 PM

Curiouser and curiouser...

My friend and fellow 123 owner in town had a set of rear brake calipers that he pulled off his 84 300TD before he scrapped it. He gave them to me this afternoon and guess what?
They also had 38mm pistons! I suspect that is was common practice (or a common mistake) to substitute sedan calipers when replacing them on wagons.
I'd prefer to go with the stock 42mm calipers but as t walgamuth noted they are hard to find. Pelican is out of stock for rebuilt units as is my local NAPA store. Rock Auto has a Centric rebuild for $45 plus $40 core deposit. I don't have the correct core and their warranty is only 90 days/3,000 miles which doesn't exactly inspire confidence. New ones seem to be available for $235 each which is beyond my budget.
So, I'm leaning toward rebuilding the best pair of 38mm out of the two I now have.

Diesel911 · #10 05-22-2020, 10:10 PM

Quote:

Originally Posted by jdgrand

Curiouser and curiouser...

My friend and fellow 123 owner in town had a set of rear brake calipers that he pulled off his 84 300TD before he scrapped it. He gave them to me this afternoon and guess what?
They also had 38mm pistons! I suspect that is was common practice (or a common mistake) to substitute sedan calipers when replacing them on wagons.
I'd prefer to go with the stock 42mm calipers but as t walgamuth noted they are hard to find. Pelican is out of stock for rebuilt units as is my local NAPA store. Rock Auto has a Centric rebuild for $45 plus $40 core deposit. I don't have the correct core and their warranty is only 90 days/3,000 miles which doesn't exactly inspire confidence. New ones seem to be available for $235 each which is beyond my budget.
So, I'm leaning toward rebuilding the best pair of 38mm out of the two I now have.

Centric sells rebuild kits (I have front and back ATE's) that have a new O-ring if you split the calipers. Not going to get into the argument if you should or should not split the calipers. Most rebuild kits don't have the O-ring.

JHZR2 · #11 05-22-2020, 10:56 PM

Frenkit offers full kits on eBay (generally shipped from Europe) that include pistons.

jdgrand · #12 05-23-2020, 08:14 PM

Thanks everyone for your advice.

I found the Centric kit at Rock Auto but pistons seem to be out of stock. Found eBay kits with pistons from UK and Lithuania.

Does anyone know the required torque for reassembling split calipers?

Diesel911 · #13 05-26-2020, 12:53 AM

Quote:

Originally Posted by jdgrand

Thanks everyone for your advice.

I found the Centric kit at Rock Auto but pistons seem to be out of stock. Found eBay kits with pistons from UK and Lithuania.

Does anyone know the required torque for reassembling split calipers?

When I did mine the bolts are M10x1.5 and the heads are marked 11.9 on the bolt head. (I found one metric torque chart that had M10x1.5 and 11.9 grade bolts but were Allen heads and I used that torque)My posts were from 2010 and no leaks between the calipers since then.
http://www.peachparts.com/shopforum/diesel-discussion/271499-caliper-problem-87sdl.html

I think I discussed it in one of the repair threads but it was not my thread. likely in the Repair links.
Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

Splitting the brake calipers (here is one of the threads)
http://www.peachparts.com/shopforum/diesel-discussion/273570-splitting-brake-calipers.html

.