88 M6 Brakes start to lock up. Also need rear Muffler

[RSheiman]

1) My brakes start to stick only after the car has run for a while. The PS lines from the fluid reservoir are new and I just got rid of all the rubber lines and exchanged for SS brake lines and I still have the same issue. They start off fine but after about 1/2 hour of driving, they start to stick and the brake pedal starts to get very firm.

2) Rear muffler has first layer gone, still works fine but I know I will need a new one. Cat has been changed so just the muffler. Bert, I know Billy Boat makes one but I want to keep the same sound. Any ideas appreciated.

[Bert Poliakoff]

The insides of the master cylinder, I forget which one, will swell after a bit and is known to cause a proble, possibly a fiber washer or seal IIRC. I think that would be a master cylinder "sticking" issue". a fellow named "Brucie" wrote a large how to, about this issue many moons ago on Big Coupe. You may want to go there and see if you can find it. Bruce was an engineer and a master of 6series issues.

[GazM3]

Yes most likey a failed master cylinder that swells with heat. I replaced mine with an e32 750il which has a 28mm bore rather than 25mm so the brake pedal feels slighly firmier. Had an e23 do the same so it must be common

[RSheiman]

I was thinking the same. Is yours an M6 or 635? I ask since I would lean toward the e32 MC. I have not looked but I suspect the price is a lot less than the M6.

Bert, yes, have seen many of his posts.

Thank you both. Let you know.

[Bert Poliakoff]

I am using a stock master cylinder in my 81 euro. While doing the restoration I replaced the mc , clutch master, slave and a full rebuild of the calipers front and rear. I started buying parts and trim 15 years ago when I first got the car and compared to prices now, they were free!!! I also did a careful cleaning of the proportioning device. I am not sure if the E28 based cars had that. My brake system couldn't be better Everything mechanically is rebuilt or new with the exception of the trans.

[RSheiman]

Well, I believe in closing the loop on issues that arise here so follow-up is that I replaced the master cylinder and all is well, problem solved. I have the old original and may take on a rebuild if I can find the right kit.

[sixerguy]

Did you end up getting a new exhaust?

I just today ordered a SuperSprint cat-back. It seems the e24/e28 product line has been discontinued so I figured I'd better put in an order before the option disappears. The price on the unit seems to have almost doubled in the last 2 years, but they may have upgraded from T409 to T304 - the TurnerMotorSport description page states that its T304 in one place and T409 in another... We'll see.

When I have my stock cat-back off the car I'm considering trying to fabricate a new clamshell for the rear mufffler and either welding or clamping it over the existing unit. Either that or just chucking it...definitely one of those.

[conditioner]

I have had the Billy Boat for many years. Just a tad too loud for me but I would have to wait longer for the Supersprint which was my first choice. The build quality is very good and still looks 'new ' to this day. One of the hangers did break off a few years back and I had to have it re-welded. If I had to do it again today I'd opt for the Supersprint assuming the wait time is not months. Compared to stock, the unit weighs like 20-25 lbs less. I wouldn't mind to get the Supersprint headers if there's a good sale.

[RSheiman]

I am very interested in the SS system but I have found the website confusing as there are multiple options for an American market M6/S38 from 1988. Can somebody confirm the part number for the muffler only? I do not need a cat, I replaced that already. Thanks.

[e24mpwr]

I had a dragging/sticky caliper. I had it rebuilt and it has been fine since.

[sixerguy]

The Supersprint website has a lot of different listings for an M6 car, but I could only find 4 US resellers - the two of those I remember are bimmerparts (or something like that) and Turnermotorsport (or ecstuning - same company different branding). Anyway, I bought from TMS and when you drill down they really only have 1 option to choose. So if you are going based on what can actually be bought in the US I think there's only the one option. In theory my order will ship today...fingers crossed it actually does and isn't canceled or something as an NLA.

SS breaks the rear section down into two part numbers, the resonator and the muffler. BMW seems to also have broken the rear section into two part numbers for some e24's, though for 86 US cars they just show one a single assembly for the entire cat-back. Anyway, you can source just the resonator or just the muffler, or the whole cat-back, and by cat-back I mean everything from the back of the cat to the back of the car.

Can anyone comment on what kind of gains an aftermarket exhaust manifold (headers) would actually offer?

[conditioner]

The BB came in as muffler and resonator and you can get either or both. I had both so it's a cat-back. I doubt the headers would offer much gains except a decent reduction in weight so for the entire exhaust you could lose probably 50lbs+/-. Other than Supersprint headers I don't know anyone else reputable and if someone can confirm if it has the same 2 or 3 bolt/nut fitting to match the cats or the bypass pipe.

[sixerguy]

The one I bought has 3 hole flanges to mate to the stock cat. That's pretty clear in the description and install notes on the Supersprint and reseller sites.

A bunch of companies had aftermarket headers back in the day. Racing Dynamics, Dinan, maybe Zender??, probably Alpina come to mind. I think Ireland Engineering has a product too. I can't speak to the quality on any of them, though I've heard the Racing Dynamics ones are lusted after. I get the potential weight savings - is it possible a subtle redesign would offer any performance benifit?

[RSheiman]

What will you do, replace the SS flange with a 2 bolt flange or the converter to 3 bolt and how do you plan on going about this? Inquiring minds want to know.........Tx

[conditioner]

I believe the BB exhaust has 2-bolt flange that connects to one end of my cats. I don't know what the other end looks like but I'll look. Headers would make my system complete and nice engine compartment.

[RSheiman]

I am interested in the Supersprint set up. Both you and Bert P. have hinted toward the BB set up being a bit loud. I am looking more for the OEM sound. Sean bought the SS setup which is for the euro cars but fits the US version if the flanges are modified.

[sixerguy]

Rob - my 635 has a 3 bolt flange on the stock cat so no modifications should be necessary to use the SS cat-back. I'm guessing you are inquiring about an M6 setup? I had anoother look on the SS site and they show a resonator section that does have a 2 bolt flange part# 781303- https://www.supersprint.com/en-us/bm....aspx?ID=31842

TMS shows a different looking setup on their site for an M6 that has a different style resonator - its also much less expensive than the 635 setup I just bought, though it may be NLA - https://www.turnermotorsport.com/p-3...-back-exhaust/

[RSheiman]

Thanks Sean , I think I just have to call them.

Is the IE setup for the 635 NLA? I purchased one from someone years ago that is sitting in my attic when my 635 needs a replacement. I replaced the 635 about 9 years ago with a Bosal set-up when they were still available but few left. That has held up and has an OEM sound.

[sixerguy]

I contacted IE and they say they are still taking orders, however I could not get their website to accept a CC on 3 different browsers. I've also heard reports of droning on the IE. If for some reason I dislike the SS I'll give them another try and maybe call in the order.
-Drew

[RSheiman]

IE customer service is not what it was........

[GazM3]

if you still haven't replaced it a good trick to confirm whether you have a shitty master cylinder is carry an esky with a bag of ice If the brakes start to lock on in stop / start traffic, turn the car off and carefully drip some of the iced water directly on the MC and if it releases well there is the issue

[Bert Poliakoff]

Here is a sound bite on a cat free BB system:

https://youtu.be/H1YqFrU6P3Q?si=g7X1fTHN3AVSzNai

[sixerguy]

Rob did you go with with an e32 master cylinder or stick with stock? I ask becuase I'm wondering if the larger MC can have any effect on steering weight/feel.

Also the SS mufler arrived today. Its T304, a somewhat unexpected delight since the marketing in some places say T409 and others T304. Its in two sections but immediately feels much lighter than the stock muffler/resonator. I'm planning on getting it mounted on the e28 this weekend - once I resolve the e24's transmission issue I'll transfer it over and stick something more basic on the e28. I'm hoping for good things in terms of exhaust note, but we'll see.!

[RSheiman]

I went with a stock MC which solved the issue.

My M6 is in storage so I cannot look at the exhaust but it is stock so I believe I cannot use the Supersprint set up. The TMS site is funny saying just basically cut the 3 bolt flange off your new $1700 setup and weld on a two bolt flange or cut the 2 bolt off your system and replace with a 3 bolt setup.

Bert : you have no resonator????? or do you have those 2 cherrybombs that the BB set-up shows? I ask because your set-up sounds loud, like really loud.

Drew: good for you T304. Let us know how it sounds and if you feel any extra power from the E28.

[Bert Poliakoff]

2 Cherry bombs, I love it's sound. My old hot rod days. When I pull into a cars and coffee it turns a lot oh heads. Between the cam and exhaust, it turns many heads. It is quite a different sound and rumble they are hearing from a BMW